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  Some customer need to config different I2C bus for their PMIC in DDR test period. There is a simple method can complete this, that is NXP DDR Config Tool. The tool download link is below: https://www.nxp.com/design/development-boards/i-mx-evaluation-and-development-boards/config-tools-for-i-mx-applications-processors:CONFIG-TOOLS-IMX I'm going to use the i.MX 93 EVK board here as a demonstration. On i.MX 93 EVK board, the default PMIC I2C Bus is I2C2, I will show you how to change I2C2 to I2C1, the other i2c bus is same.  Step 1 : Rework the board and make sure the PMIC is connected to I2C1. Remove R714 R715, connnect I2C1_SCL(C20) to U701 pin 41  and I2C1_SDA(C21) tp U701 pin 42. Step 2 : Setup I2C1 PinMux: Config Tool UI:   Advance -> IOMUX config   Command:           Address                Size               Value memory   set     0x443c0170            32                   0x10 memory   set     0x443c0174            32                   0x10 memory   set     0x443c0320            32                   0x40000b9e memory   set     0x443c0324            32                   0x40000b9e Step 3 : Set PMIC VDDQ as 1.1 V Config Tool UI:   Advance -> Custom PMIC initialization enabled   #  PMIC commands        Value 0         pmic_cfg             0x0025       /*I2C bus 1,  PMIC address 0x25 */ (0 for I2C1, 1 for I2C2, 2 for I2C3, 3 for I2c4 …) 1         pmic_set             0x0C29       /* BUCKxOUT_DVS0/1, preset_buck1=0.8V, preset_buck2=0.7V, preset_buck3=0.8V PCA9451_BUCK123_DVS, 0x29 */ 2         pmic_set             0x1118      /*  BUCK1OUT_DVS0=0.9V   PCA9451_BUCK1OUT_DVS0, 0x18 */ 3         pmic_set             0x1718      /*  BUCK3OUT_DVS0=0.9V   PCA9451_BUCK3OUT_DVS0, 0x18 */ 4         pmic_set             0x1428      /*  Set VDDQ to 1.1V  PCA9451_BUCK2OUT_DVS0, 0x28  */ PS : About pmic register, The first two bytes are the register address and the next two bytes are the register setting. Step 4 : Run the DDR "Firmware init test" and see the test result. The success log is as follows: DEBUG memtool.comm.serial_channel ==================hardware_init======================= DEBUG memtool.comm.serial_channel DEBUG memtool.comm.serial_channel Power up ddr... DEBUG memtool.comm.serial_channel DEBUG memtool.comm.serial_channel DDRMIX power on done... DEBUG memtool.comm.serial_channel DEBUG memtool.comm.serial_channel DDRPHY coldreset... DEBUG memtool.comm.serial_channel DEBUG memtool.comm.serial_channel DEBUG memtool.comm.serial_channel DEBUG memtool.comm.serial_channel ********Found PMIC PCA945X********** DEBUG memtool.comm.serial_channel DEBUG memtool.comm.serial_channel Set VDDQ to 1.1V for LPDDR4 DEBUG memtool.comm.serial_channel DEBUG memtool.comm.serial_channel ==================hardware_init exit==================    
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Overview Measuring the power consumed an i.MX application processor can be a challenging undertaking. This document describes several boards designed to instrument i.MX application boards for current measurements. While this system does not offer many digits of accuracy, it can be used to quantify power consumed by application use cases as well as while in low power modes. The system can be used to instrument up to four power supply rails and measure current in two ranges. Range switching on the sensor boards is controlled via software running on the Kinetis K20 at the heard of the profiler board. Measured data is sent to a host computer over a virtual serial link over USB. Power for the profiler system is obtained from the USB connection although a external 5V supply may be used. Dual-Range Current Sensors INA250 + INA21x Sensor Circuit Description: The INA250 + INA21x Sensor board can measure two ranges using the INA250 and INA21x current sense amplifiers. The high range is measured with an INA250, which has an integrated 0.002 Ohm shunt, and is available in four output gains. The low range is measured with shunt R1 and the INA21x sense amp. The low range shunt is taken out of the circuit (by shorting it) with two paralleled, very low-Rds(on) FETs, Q1 and Q1. VCC_SENSE powers the two sense amplifiers. VCC_FET supplies the gate voltage on Q1 and Q2. The DMN1019 device has a Vgs max of 8V. The sources of both FETs are tied to the i.MX side of the current sense loop, so the gate voltage Q1 and Q2 see is VCC_FET-(rail voltage). The signal /LOW_EN controls the state of both Q1 and Q2. The sense amplifier outputs (HIGH_OUT1 and LOW_OUT1) and rail voltage (V_RAIL_MEASURE) are sent down the ribbon cable (X2) to the profiler board for measurement. When not used for a wire loop for a Hall-effect current probe, resistor R3 should be shorted with a solder bridge, a piece of wire, or a 0.001 Ohm resistor. Schematic: Board Layout: The two large vias by the current sense connection points are provided for use with a 0.1" header and jumper to short the low range shunt, allowing normal operation of the target board when the profiler is not powered. It should be noted a jumper will not be as effective for relatively large currents. BOM: Part   Device C1,C2  0.1uF 0805 Q1,Q2  DMN1019USN-13 SOT23 R1     2 1% 0805 (resize to change low range) R2     10k 0805 R3     Solder bridge/wire loop (see schematic) U1     INA250 TSSOP16 (choose gain, A3 [0.8V/A] or A4 [2.0V/A]) U2     INA21X SC70 (choose desired gain) X2     WM6769CT/0527460871 (bottom contacts) Dual INA21x Sensor Circuit Description: The Dual INA21x Sensor board can measure two ranges using two INA21x current sense amplifiers and two different shunts. The high range shunt (R1) is always in place. The low range shunt is taken out of the circuit (by shorting it) with two paralleled, very low-Rds(on) FETs, Q1 and Q1. VCC_SENSE powers the two sense amplifiers. VCC_FET supplies the gate voltage on Q1 and Q2. The DMN1019 device has a Vgs max of 8V. The sources of both FETs are tied to the i.MX side of the current sense loop, so the gate voltage Q1 and Q2 see is VCC_FET-(rail voltage). The signal /LOW_EN controls the state of both Q1 and Q2. The sense amplifier outputs (HIGH_OUT1 and LOW_OUT1) and rail voltage (V_RAIL_MEASURE) are sent down the ribbon cable (X2) to the profiler board for measurement. Schematic: Board Layout: The two large vias by the current sense connection points are provided for use with a 0.1" header and jumper to short the low range shunt, allowing normal operation of the target board when the profiler is not powered. It should be noted a jumper will not be as effective for relatively large currents. BOM: Part   Device C1,C2  0.1uF 0805 Q1,Q2  DMN1019USN-13 SOT23 R1     0.002 1% 0805 (resize to change high range) R2     0.05 1% 0805 (resize to change low range) R3     10k 0805 U1,U2  INA21X SC70 (choose desired gain) X2     WM6769CT/0527460871  (bottom contacts) Four-Channel Power Profiler Circuit Description: The Four-Channel Power Profiler board has at its heart a Kinetis K20 on a Teensy3.2 board. The ADCs of the K20 measure all the current sense amplifier's outputs, the voltage of each instrumented rail. There is provision for measuring temperature using up to three thermistors. GPIO provide control each sensor board's current range, and optionally, a hardware wake-up signal for the instrumented target board. Up to four dual-range sensor boards can be connected (either sensor board mentioned above). A micro-SD card socket is included for storing measured data (the SD card functionality has been tested but not implemented for use with measurements). Measured data is sent to the host computer over a virtual serial port using the Teensy's USB. Charge pump U1 boosts the 5V supply to 12V. The output is regulated down to 8V on VCC_FET via regulator U2. R2 and C5 provide filtering for the 3.3V supply from the Teensy that feeds the sensor boards through VCC_SENSE. FETs Q1 through Q4 provide voltage level translation which protect the Teensy's GPIO pins from the 8V that's placed on the gates of the shorting FETs on the sensor boards. Regulator IC2 provides power for the micro-SD socket, since the 3.3V regulator on the Teensy does not provide enough capacity. Since there are not "smarts" on the sensor boards, the Teensy has no way of knowing what kind of sensor board is connected or what shunt values and sense amplifier gains are in use. As currently implemented, current and voltage calculations are hard coded in the Teensy application code. Schematic: Board Layout: BOM: Part    Device C1,C2   0.22uF 0805 C3-C7   1uF 0805 C10,C12 1uF 0805 C11     0.1uF 0805 IC2     MCP1825ST-3302 SOT223 Q1-Q4   DMN1019USN SOT23 R2-R4   20k 1% 0805 R5-R8   10k 0805 R9      Ferrite bead 0805 S1-S4   WM6769CT/0527460871 (bottom contacts) U$1     101-00660-68-6-1-ND MICROSD U1      MAX662CPASO8 SO08 U2      78L08SMD SO08 Use mating Molex cables: 8in: 0150200087 or 10in: 0151660091 Using the Power Profiler Obtaining Sensor and Profiler Boards: Bare boards may be ordered directly from OSH Park using these links: INA250 + INA21x Sensor board (order with 2oz copper option selected) Dual INA21x Sensor board (order with 2oz copper option selected) Power Profiler board The sensor boards should be ordered with the 2oz copper option selected to reduce the trace resistance of the target board's current path. No special option is needed for the profiler board. Teensy3.2 boards may be ordered from OSH Park as well, and at a slightly lower price than the manufacturer (PJRC) sells them. Choosing Current Ranges: To choose the value of a shunt resistor, use the following equation: Rsh = Vfs / (Ifs * gain) where: Rsh is the shunt resistance Vfs is the full scale sense amplifier output voltage (3.3V here) Ifs is the full scale current to be measured gain is the gain of the sense amp to be used For example, to measure a 66mA full scale current with a sense amp of gain 1000, Rsh = 3.3V / (0.066A * 1000) = 0.050 Ohms. For sleep/leakage current, say 1mA full scale: Rsh = 3.3V / (0.001 * 1000) = 3.3 Ohms. The pads on both sensor boards for the shunt resistors have been laid out for 0805 SMT resistors. Precision resistors should be used, 1% or better. The highest power dissipation resistor available should be used to minimize resistance change from the shunt resistor heating up; 0805 resistors are typically available with 1/8, 1/4, 1/2 and 1 Watt dissipation. Building and Testing: These boards were designed to be assembled by hand in small quantities. The most difficult components to solder are the ribbon connectors and the SC70 packaged sense amplifiers. A fine tip soldering iron and a microscope are required. Solder wick is helpful for removing solder bridges from between pins (typically the ribbon connector and the sense amplifiers).  Early versions of the profiler board were assembled with header pins soldered to the Teensy and mating female recepticles soldered to the profiler board. Later versions (like in the example below) were assembled with male header pins between the Teensy and the profiler board.  To test the boards after assembly, check for the presence of 8V on the pull-up resistors R5-R8 when a USB cable is plugged into the Teensy. Program the Teensy with suitable application code. Connect the sensor boards to the profiler. Connect all the sensor boards together in series, positive of one to negative of the next and connect to a calibrated current source. (The image below shows an early prototype of the profiler with the sensor boards connected in series. Current is forced through them via the Kelvin contact clips.) Open a terminal window on the host computer. Force known currents and toggle the ranges of each sensor to verify that each sensor operates correctly in both ranges. To check that the profiler measures rail voltage correctly, disconnect the current source and apply the positive side of a voltage source to either side of the sensors still connected in series and connect the ground of the voltage source to a ground point on the profiler. The rail voltage measured by each sensor should match the supplied voltage (0 to 3.3V max). Accuracy/Calibration: After building in excess of 20 sensor boards and 6 profiler boards and checking their measurements against a Keysight B2902 SMU forcing known currents, the profiler system is fairly accurate. Measurements are good down to about 2% of any range's full scale; lower than that gets into the input offset range of the sense amplifier. Individual readings within 1% of that range's full scale when compared against forced current values. No calibration or tuning has been necessary. Measured values should only be considered good to at most 3 significant figures. Limitations: The maximum current through any sensor should be limited to a maximum of 4A. The current limit when using the low range needs to avoid exceeding the power dissipation of the low range shunt resistor. Particularly, the dissipation in the low range shunt resistor can cause resistance changes that would affect measurement accuracy. The voltage of any instrumented rail cannot be greater than 3.3V, the maximum input voltage of the K20's ADC inputs. Minimum resistance the sensor introduces is in high range is about 0.012 to 0.015 Ohms with a 0.002 Ohm shunt. At least 0.005 Ohms comes from the two shorting FETs on the sensor board. The rest comes from the traces on the board as well as the interconnect wires. The bottom line is: the sensor board has to be mounted as closely as possible to the current sense point on the target board. The maximum resistance the sensor introduces depends on the low range shunt. With a 0.020 Ohm low range shunt, the resistance is about 0.025 to 0.030 Ohms. With a 0.050 Ohm low range shunt, the resistance is about 0.065 to 0.075 Ohms. The sensor board needs to be rigidly mounted to prevent ripping up the current sense points on the target board. This can be a challenge when many rails are instrumented. Instrumenting Target Board: When instrumenting a target board, the on-board current sense resistor should be removed. The sensor board should be attached to the target board placed as close as possible to the sense resistor pads. Connection wires to the sensor board should be as short as possible to minimize series resistance. Great care should be taken to prevent movement of the sensor boards that could in turn lift the sense resistor pads off the target board. Foam double sticky tape should be used over clear areas of the target board to avoid dislodging components when the tape is removed. In the photos below, seven power supplies are instrumented on an interposer card. In this example, the sensor boards were affixed to perf board held in place by the headers. Because of the physical constraints of the target board and its power supply card, mounting the sensor boards directly to the interposer was not possible. Four sensors were mounted on one side and three on the other. Notches were cut in the perf board for the sensor's connection wires on the opposite side. Two profiler boards are required for simultaneous use. (Two were also required because the 0.1" headers and jumpers were not installed on the sensor boards to passively short the low-range shunts; all the sensor boards need to be powered to actively short the low-range shunts.)  The positive input of the sensor board (the center of the three connection points) goes to the regulator side of the current sense resistor. The negative input (either of the two outside connections) goes to the i.MX side of the sense resistor. [NOTE: In this example, the power profiler boards have not been fully populated: the thermistor-related components and the micro-SD card socket. The sensor boards were fully populated with the exception of the passive shorting jumper.] Here is another example of a board with six instrumented rails. The sensors in this case are mounted directly on the target board. In this example, the 12V rail is instrumented, which required modding to add a voltage divider to V_RAIL_LOWSIDE on that sensor board.  And here's yet another example of an instrumented i.MX6Q SDB (which still has wires on it from measuring it the old way...). Although it's difficult to see in this photo, all of the sensor boards have a jumper across the low range shunt which permits normal operation of the board without the profiler board attached to provide power to the shorting FETs. Profiler Application Code for Kinetis/Teensy: Below is sample application code for the Teensy for use with four INA250 + INA21x sensor boards populated with the INA250A3 (0.8V/A gain) for the high range and 0.05 Ohm shunts and INA212 (gain 1000). The current range of each channel can be independently changed. This code is also attached below as a file. Data is sent to the host computer over a USB virtual serial port. To reflash/update Teensy code, follow the instructions from PJRC. Download Windows virtual com port driver. /* MIT License (https://spdx.org/licenses/MIT.html) Copyright 2017 NXP Teensy Power Profiler v.2 (revised main board with individual Hi/Lo GPIO, fixed voltage levels, and on-board uSD card socket. Very basic code for the Teensy Power Profiler that sets up the ADCs and controls the GPIO with very basic, single-character serial commands... This version for all INA250A3 on high range, and 0.05Ohms+INA212 (1000 gain) on low range. */ // These constants won't change.  They're used to give names to the pins used: const int LoHiEn1 = 0; const int LoHiEn2 = 1; const int LoHiEn3 = 2; const int LoHiEn4 = 3; const int WakeUp = 5; const int Lo_1 = A0; const int Vrail_1 = A1; const int Hi_1 = A2; const int Lo_2 = A3; const int Vrail_2 = A4;  const int Hi_2 = A5; const int Lo_3 = A6; const int Vrail_3 = A7; const int Hi_3 = A8; const int Lo_4 = A9; const int Vrail_4 = A11; const int Hi_4 = A10; const int Therm1 = A14; #include <math.h> // thermistor temperature calculation stuff... int sensorValue = 0;        // value read from the pot float sensorValuef = 0.0; int B = 4334; // B25/100 value for thermistor NXRT15WF104FA1B040 // other stuff... int delayintvl = 20; int incomingByte; float vrefL = 3.3; float vrefH = 3.3; float vrefV = 3.3; bool one=true;   bool dispone=true; bool two=true;   bool disptwo=true; bool three=true; bool dispthree=true; bool four=true;  bool dispfour=true; int i,j; int num=100; float v1, v2, v3, v4, i1, i2, i3, i4; float il1, il2, il3, il4; void setup() {   // initialize serial communications at 115200 bps:   Serial.begin(115200);   // set analog resolution to 12 bits... (we want more than the 8 default bits...)   analogReadResolution(12);   // set up low/high range wakeup GPIO signals...   pinMode(LoHiEn1, OUTPUT); digitalWrite(LoHiEn1, HIGH);   pinMode(LoHiEn2, OUTPUT); digitalWrite(LoHiEn2, HIGH);   pinMode(LoHiEn3, OUTPUT); digitalWrite(LoHiEn3, HIGH);   pinMode(LoHiEn4, OUTPUT); digitalWrite(LoHiEn4, HIGH);   pinMode(WakeUp, OUTPUT); digitalWrite(WakeUp, HIGH); } void loop() {   // average voltages and currents...   v1=0; v2=0; v3=0; v4=0;   i1=0; i2=0; i3=0; i4=0;   il1=0; il2=0; il3=0; il4=0;   for (i=0; i<num; i++){     v1 = v1+ analogRead(Vrail_1)/4095.*vrefV;     i1 = i1+ analogRead(Hi_1)/4095.*vrefH/0.8*1000;     il1 = il1+ analogRead(Lo_1)/4095.*vrefH/0.05;     v2 = v2+ analogRead(Vrail_2)/4095.*vrefV;     i2 = i2+ analogRead(Hi_2)/4095.*vrefH/0.8*1000;     il2 = il2+ analogRead(Lo_2)/4095.*vrefH/0.05;     v3 = v3+ analogRead(Vrail_3)/4095.*vrefV;     i3 = i3+ analogRead(Hi_3)/4095.*vrefH/0.8*1000;     il3 = il3+ analogRead(Lo_3)/4095.*vrefH/0.05;     v4 = v4+ analogRead(Vrail_4)/4095.*vrefV;     i4 = i4+ analogRead(Hi_4)/4095.*vrefH/0.8*1000;     il4 = il4+ analogRead(Lo_4)/4095.*vrefH/0.05;   }   v1 = v1/num; v2 = v2/num; v3 = v3/num; v4 = v4/num;   i1 = i1/num; i2 = i2/num; i3 = i3/num; i4 = i4/num;   il1 = il1/num; il2 = il2/num; il3 = il3/num; il4 = il4/num;   // print the results to the serial monitor:   if (dispone) {   Serial.print(" RAIL1 (V)= ");  Serial.print(v1);  //Serial.print("\r\n");   if (!one) {Serial.print("    L1 (mA)= ");  Serial.print(il1, 1);}  //Serial.print("\r\n");   if (1==1) {Serial.print("    H1 (mA)= ");  Serial.print(i1, 1); }   Serial.print("\r\n");   }   if (disptwo) {   Serial.print(" RAIL2 (V)= ");  Serial.print(v2);  //Serial.print("\r\n");   if (!two) {Serial.print("    L2 (mA)= ");  Serial.print(il2, 1);}  //Serial.print("\r\n");   if (1==1) {Serial.print("    H2 (mA)= ");  Serial.print(i2, 1);}    Serial.print("\r\n");   }   if (dispthree) {   Serial.print(" RAIL3 (V)= ");  Serial.print(v3);  //Serial.print("\r\n");   if (!three) {Serial.print("    L3 (mA)= ");  Serial.print(il3, 1);}  //Serial.print("\r\n");   if (1==1) {Serial.print("    H3 (mA)= ");  Serial.print(i3, 1);}    Serial.print("\r\n");   }   if (dispfour) {   Serial.print(" RAIL4 (V)= ");  Serial.print(v4);  //Serial.print("\r\n");   if (!four) {Serial.print("    L4 (mA)= ");  Serial.print(il4, 1);}  //Serial.print("\r\n");   if (1==1) {Serial.print("    H4 (mA)= ");  Serial.print(i4, 1);}    Serial.print("\r\n");   }   Serial.print("\r\n");   Serial.print("\r\n");   while (Serial.available()) {  // while there are characters in the buffer, grab them all...     incomingByte = Serial.read();  // will not be -1     Serial.print("Incoming byte: "); Serial.print(incomingByte);     // Serial.print("    Delay interval:"); Serial.print(delayintvl);  Serial.print("\r\n");     if (incomingByte == 'h' || incomingByte == 'H'){       Serial.print("\r\n\r\nHelp:\r\n\r\n");       Serial.print("  +/= delay interval +/- 10mS\r\n");       Serial.print("  /- delay interval 20msec/1sec\r\n");       Serial.print("  l/L all rails low/high range in unison\r\n");       Serial.print("  q/w/e/r toggle display of rail 1/2/3/4\r\n");       Serial.print("  1/2/3/4 high range of rail 1/2/3/4\r\n");       Serial.print("  !/@/#/$ low range of rail 1/2/3/4\r\n");       Serial.print("  h print this help...\r\n");       Serial.print("\r\n");       delay(2000);       }     // change delay interval...     if (incomingByte == '+') delayintvl = delayintvl + 10;     if (incomingByte == '=') delayintvl = delayintvl - 10;     if (incomingByte == '_') delayintvl = 20;     if (incomingByte == '-') delayintvl = 1000;     if (delayintvl<1) delayintvl = 20;     // toggle low/high range of all rails in unison...     if (incomingByte == 'L') {       digitalWrite(LoHiEn1, LOW);       digitalWrite(LoHiEn2, LOW);       digitalWrite(LoHiEn3, LOW);       digitalWrite(LoHiEn4, LOW);       one = true; two = true; three = true; four = true;     }     if (incomingByte == 'l') {       digitalWrite(LoHiEn1, HIGH);       digitalWrite(LoHiEn2, HIGH);       digitalWrite(LoHiEn3, HIGH);       digitalWrite(LoHiEn4, HIGH);       one = false; two = false; three = false; four = false;     }     // still unimplemented, but for wakeup of target board...     if (incomingByte == 'w') digitalWrite(WakeUp, LOW);     if (incomingByte == 'W') digitalWrite(WakeUp, HIGH);     // toggle display of rail...     if (incomingByte == 'q') dispone = !dispone;     if (incomingByte == 'w') disptwo = !disptwo;     if (incomingByte == 'e') dispthree = !dispthree;     if (incomingByte == 'r') dispfour = !dispfour;     // change between high/low range..     if (incomingByte == '1') { digitalWrite(LoHiEn1, LOW);  one = true; }     if (incomingByte == '!') { digitalWrite(LoHiEn1, HIGH); one = false;}     if (incomingByte == '2') { digitalWrite(LoHiEn2, LOW);  two = true;}     if (incomingByte == '@') { digitalWrite(LoHiEn2, HIGH); two = false;}     if (incomingByte == '3') { digitalWrite(LoHiEn3, LOW);  three = true;}     if (incomingByte == '#') { digitalWrite(LoHiEn3, HIGH); three = false;}     if (incomingByte == '4') { digitalWrite(LoHiEn4, LOW);  four = true;}     if (incomingByte == '$') { digitalWrite(LoHiEn4, HIGH); four = false;}     }   // wait delayintvl mS after the last reading:   delay(delayintvl); }‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍ Future Work and Improvements Work on a "smart" sensor with a local Kinetis device (KL02Z or KL05Z) on the sensor board itself that has three separate sense amplifiers (one run/high current and two low) has begun. There are several advantages to having a microcontroller on each sensor board: All instrumented rails can be measured simultaneously The sampling rate can be increase over current generation's round robin Measured data is sent over I2C or UART, allowing arbitrary number of rails to be instrumented Each sensor board can provide all its shunt and gain info Sensor board can be used in isolation, i.e., without a master profiler board A GUI interface for the serial data output by the profiler would be really nice... Addditional Information For more information on current measurements in general, see this tutorial series: A Current Sensing Tutorial--Part 1: Fundamentals | EE Times  A Current Sensing Tutorial-Part II: Devices | EE Times  A Current Sensing Tutorial--Part III: Accuracy | EE Times  A Current Sensing Tutorial-Part IV: Layout and Troubleshooting Guidelines | EE Times 
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NOTE: Always de-power the target board and the aggregator when plugging or unplugging smart sensors from the aggregator. NOTE: See this link to instrument a board with a Smart Sensor. This page documents the triple-range "smart" current sensor that's part of a larger system for profiling power on application boards. The smart sensor features a Kinetis KL05Z with three current sense amplifiers. It allows measurement currents in three ranges. Four assembly options allow measurement of rail voltages 0-3.3V (two overall current ranges), 0-6.6V, and 12V. It connects to an aggregator, which powers, controls and aggregates data from a number of smart sensor boards. One of the biggest improvements over the older dual-range measurement system is that the on-sensor microcontroller allows near-simultaneous measurement of all instrumented rails on a board. The dual range profiler can only make one measurement at a time.  These are intended to be used with a microncontroller board to act as a trigger and data aggregator. This aggregator could also be used to reprogram the sensors.  The series resistance added by the smart sensor when in run mode (highest current range) is under 11 milliOhms as measured with 4-point probes and a Keysight B2902B SMU.  A "power oscilloscope" can be made by triggering measurements at regular intervals and presenting the results graphically.... Schematic: Board Layout, Top: Board Layout, Bottom: Here's a photo of two with a nickel is included to show scale. The board measures about 0.5 by 1.3 inches. Connections: The smart sensor header connections are: 5V: powers the 3.3V regulator, which in turn powers everything else on the sensor board 12V: all the gates of all the switching FETs are pulled pulled up to 12V GND: ground connection SCL/TX: I2C clock line  SDA/RX: I2C data line  SWD_CLK:  line for triggering smart sensors to make measurements RESET_B:  line for resetting the smart sensor board SWD_IO: select line for the smart sensor Theory of operation: Three shunts and current sense amplifiers are used to measure current in three ranges. One shunt/sense amp pair has a 0.002Ω shunt integrated into the IC package (U1, INA250). The other two sense amps (U2 and U3, INA212) require an external shunt.  FETs Q1, Q2,  and Q3 are used to switch the two lower range shunt/sense amp pairs in and out of circuit. In normal run operation (highest current range), Q1 (FDMC012N03, with Rds(on) under 1.5mΩ) is turned on, which shorts leaves only U1 in circuit. FETs Q4, Q5 and Q6 translate the voltages to 3.3V so that GPIO on U4 (MCU KL05Z) can control them.  Rail voltage measurement is facilitated via resistors R3, R4, and R12 and Q7. Not all of these are populated in every assembly option. For measuring rail voltages 0-3.3V, R12 is populated. To measure 0-6.6V, R3, R4,and Q7 are populated. When turned on Q7 enables the voltage divider. All of the assembly option population info can be found in the schematic (attached). Regulator U5 (AP2210N) provides the 3.3V supply for all of the components on the board. This 1% tolerance regulator is used to provide a good reference for the ADC in U4.  Microcontroller U4 detects the assembly population option of the board via resistors R9, R10, and R11 so that the same application code can be used across all variations of the sensor boards. GPIO control the FETs and four ADC channels are used to measure the sense amplifier outputs and the rail voltage. Having a microcontroller on the sensor board allows the user to do extra credit things like count coulombs as well as allowing all similarly instrumented rails to measure at the same time via trigger line SWD_CLK. Data communication can be via I2C or UART, since these two pins can do both.  But if multiple sensor boards are to be used with an aggregator, communication needs to be over I2C. Application Code: The latest application code for the KL05Z on the smart sensor resides here: https://os.mbed.com/users/r14793/code/30847-SMRTSNSR-KL05Z/. The latest binary is attached below. In order to re-flash a smart sensor, the modification detailed in the aggregator page needs to be made. Once the modification is completed, leave the aggregator unpowered while pluging the SWD debugger into J5 and the smart sensor to be programmed into JP15. Very old UART-based application code for the KL05Z, built in the on-line MBED compiler (note that it requires the modified mbed library for internal oscillator). This code was used while testing the first smart sensor prototypes. It has since been abandoned. It's published here in the event that a user wants to use a single sensor plugged into JP15 with UART breakout connector J6. /****************************************************************************** * * MIT License (https://spdx.org/licenses/MIT.html) * Copyright 2017-2018 NXP * * MBED code for KL05Z-based "smart" current sensor board, basic testing * of functions via UART (connected via FRDM board and OpenSDA USB virtual * COM port). * * Eventual goal is to have each smart sensor communicate over I2C to an * aggregator board (FRDM board with a custom shield), allowing 1-10 power * supply rails to be instrumented. Extra credit effort is to support * sensors and aggregator with sigrok... * * Because there is no crystal on the board, need to edit source mbed-dev library * to use internal oscillator with pound-define: * change to "#define CLOCK_SETUP 0" in file: * mbed-dev/targets/TARGET_Freescale/TARGET_KLXX/TARGET_KL05Z/device/system_MKL05Z4.c * ******************************************************************************/ #include "mbed.h" // These will be GPIO for programming I2C address... // not yet implemented, using as test pins... DigitalOut addr0(PTA3); DigitalOut addr1(PTA4); DigitalOut addr2(PTA5); DigitalOut addr3(PTA6); // configure pins for measurements... // analog inputs from sense amps and rail voltage divider... AnalogIn HIGH_ADC(PTB10); AnalogIn VRAIL_ADC(PTB11); AnalogIn LOW1_ADC(PTA9); AnalogIn LOW2_ADC(PTA8); // outputs which control switching FETs... DigitalOut VRAIL_MEAS(PTA7); // turns on Q7, connecting voltage divider DigitalOut LOW_ENABLE(PTB0); // turns on Q4, turning off Q1, enabling low measurement DigitalOut LOW1(PTB2); // turns on Q5, turning off Q2, disconnecting shunt R1 DigitalOut LOW2(PTB1); // turns on Q6, turning off Q3, disconnecting shunt R2 // input used for triggering measurement... // will eventually need to be set up as an interrupt so it minimizes delay before measurement InterruptIn trigger(PTA0); // use as a trigger to make measurement... // PTB3/4 can be used as UART or I2C... // For easier development with one smart sensor, we are using UART here... Serial uart(PTB3, PTB4); // tx, rx long int count=0; int n=25; // global number of averages for each measurement int i, temp; bool repeat=true; // flag indicating whether measurements should repeat or not const float vref = 3.3; // set vref for use in calculations... float delay=0.25; // default delay between measurement bool gui = false; // flag for controlling human vs machine readable output bool statistics = false;// flag for outputting min and max along with average (GUI mode only) void enableHighRange(){ LOW_ENABLE = 0; // short both low current shunts, close Q1 wait_us(5); // delay for FET to settle... (make before break) LOW1 = 0; LOW2 = 0; // connect both shunts to make lower series resistance VRAIL_MEAS = 0; // disconnect rail voltage divider wait_us(250); // wait for B2902A settling... } void enableLow1Range(){ LOW1 = 0; LOW2 = 1; // disconnect LOW2 shunt so LOW1 can measure wait_us(5); // delay for FET to settle... (make before break) LOW_ENABLE = 1; // unshort low current shunts, open Q1 VRAIL_MEAS = 0; // disconnect rail voltage divider wait_us(250); // wait for B2902A settling... } void enableLow2Range(){ LOW1 = 1; LOW2 = 0; // disconnect LOW1 shunt so LOW2 can measure wait_us(5); // delay for FET to settle... (make before break) LOW_ENABLE = 1; // unshort low current shunts, open Q1 VRAIL_MEAS = 0; // disconnect rail voltage divider wait_us(500); // wait for B2902A settling... } void enableRailV(){ VRAIL_MEAS = 1; // turn on Q7, to enable R3-R4 voltage divider wait_us(125); // wait for divider to settle... // Compensation cap can be used to make // voltage at ADC a "square wave" but it is // rail voltage and FET dependent. Cap will // need tuning if this wait time is to be // removed/reduced. // // So, as it turns out, this settling time and // compensation capacitance are voltage dependent // because of the depletion region changes in the // FET. Reminiscent of grad school and DLTS. // Gotta love device physics... } void disableRailV(){ VRAIL_MEAS = 0; // turn off Q7, disabling R3-R4 voltage divider } // this function measures current, autoranging as necessary // to get the best measurement... void measureAuto(){ Timer t; float itemp; float tempI=0; float imin = 1.0; // used to keep track of the minimum... float imax = 0; // used to keep track of the maximum... t.start(); // use timer to see how long things take... enableHighRange(); // this should already be the case, but do it anyway... for (i = 0; i < n; i++){ itemp = HIGH_ADC; // read HIGH range sense amp output if (statistics && itemp>imax) imax = itemp; // update max if necessary if (statistics && itemp<imin) imin = itemp; // update min if necessary tempI += itemp; // add current sample to running sum } tempI = tempI/n *vref/0.8; // compute average we just took... if (gui) uart.printf("=> %5.3f ", tempI); if (statistics && gui) uart.printf("[%5.3f/%5.3f] ", imin*vref/0.8, imax*vref/0.8); // if current is below this threshold, use LOW1 to measure... if (tempI < 0.060) { if (!gui) uart.printf("... too Low: %f A, switching to low1 ==>\r\n", tempI); tempI=0; enableLow1Range(); // change FETs to enable LOW1 measurement... imin = 1.0; imax = 0; for (i = 0; i < n; i++){ itemp = LOW1_ADC; // read LOW1 sense amp output if (statistics && itemp>imax) imax = itemp; // update max if necessary if (statistics && itemp<imin) imin = itemp; // update min if necessary tempI += itemp; // add current sample to running sum } tempI = tempI/n *vref/0.05/1000; // compute average we just took... if (gui) uart.printf("%6.4f ", tempI); if (statistics && gui) uart.printf("[%6.4f/%6.4f] ", imin*vref/0.05/1000, imax*vref/0.05/1000); // if current is below this threshold, use LOW2 to measure... if (tempI < 0.0009){ if (!gui) uart.printf("... too Low: %f A, switching to low2 ==>\r\n", tempI); tempI=0; enableLow2Range(); // change FETs to enable LOW1 measurement... imin = 1.0; imax = 0; for (i = 0; i < n; i++){ itemp = LOW2_ADC; // read LOW2 sense amp output if (statistics && itemp>imax) imax = itemp; // update max if necessary if (statistics && itemp<imin) imin = itemp; // update min if necessary tempI += itemp; // add current sample to running sum } tempI = tempI/n *vref/2/1000; // compute average we just took... if (gui) uart.printf("%8.6f ", tempI); if (statistics && gui) uart.printf("[%8.6f/%8.6f] ", imin*vref/2/1000, imax*vref/2/1000); } } t.stop(); // stop the timer to see how long it took do do this... enableHighRange(); if (!gui) uart.printf("\r\nCurrent = %f A Current Measure Time = %f sec\r\n", tempI, t.read()); } // the autoranging should really be done with functions that return values, as should the // functions below... This would make for shorter and more elegant code, but the author // is a bit of a pasta programmer... void measureHigh(){ float highI=0; enableHighRange(); for (i = 0; i < n; i++){ highI += HIGH_ADC; } highI = highI/n; uart.printf("HIghI = %f A\r\n", vref*highI/0.8); } void measureLow1(){ float low1I=0; enableLow1Range(); for (i = 0; i < n; i++){ low1I += LOW1_ADC; } enableHighRange(); low1I = low1I/n; uart.printf("low1I = %f A\r\n", vref*low1I/0.05/1000); } void measureLow2(){ float low2I=0; enableLow2Range(); for (i = 0; i < n; i++){ low2I += LOW2_ADC; } enableHighRange(); low2I = low2I/n; uart.printf("low2I = %f A\r\n", vref*low2I/2/1000); } // measure the rail voltage, default being with // a divide by 2 resistor divider // It has to be switched out when not in use or it will // add to the measured current, at least in the low ranges... void measureRailV(){ float railv=0; float mult = vref*2; // since divide by 2, we can measure up to 6.6V... float vmin = 5; float vmax = 0; float vtemp; enableRailV(); // switch FETs so divider is connected... for (i = 0; i < n; i++){ vtemp = VRAIL_ADC; // read voltage at divider output... if (statistics && vtemp>vmax) vmax = vtemp; // update max if necessary if (statistics && vtemp<vmin) vmin = vtemp; // update min if necessary railv += vtemp; // add current sample to running sum } disableRailV(); // now disconnect the voltage divider railv = railv/n; // compute average (note this is in normalized ADC [0..1]) // Convert to voltage by multiplying by "mult" if (!gui) uart.printf("RailV = %5.3f V ", mult*railv); if (gui) uart.printf("%5.3f ", mult*railv); if (statistics && gui) uart.printf("[%5.3f/%5.3f] ", mult*vmin, mult*vmax); uart.printf("\r\n"); } // not sure how useful this function is... void measureAll(){ measureHigh(); measureLow1(); measureLow2(); measureRailV(); } // test function to see if trigger pin is being hit... // intended for use later to do timed triggering of measurements... void triggerIn(){ uart.printf("You're triggering me! \r\n"); measureAll(); } // main... int main() { // set up basic conditions... Timer m; uart.baud(115200); enableHighRange(); // default state - only HIGH sense amp in circuit, no divider // signal that we're alive... uart.printf("Hello World!\r\n"); // configure the trigger interrupt... trigger.rise(&triggerIn); while (true) { count++; wait(delay); if (repeat){ // if repeat flag is set, keep making measurements... m.reset(); // reset and start timer... m.start(); measureAuto(); // measuring current using auto-ranging... measureRailV(); // measure rail voltage... m.stop(); // stop the timer. if (!gui) uart.printf(" Total Measure Time = %f sec", m.read()); if (!gui) uart.printf("\r\n\r\n"); } // see if there are any characters in the receive buffer... // this is how we change things on the fly... // Commands (single keystroke... it's easier) // t = one shot automeasure // v = measure volt // h = one shot high measure // k = one shot LOW1 measure // l = one shot LOW2 measure (letter l) // r = toggle repeat // R = turn off repeat // + = faster repeat rate // - = slower repeat rate // = = set repeat rate to 0.25 sec // g = use human readable text output // G = use compressed text format for GUI // s = turn statistics output off // S = turn statistics output on (only in GUI mode) // n = decrease number of averages for each measurement // N = increase number of averages for each measurement // // these were for testing FET switching... // 1 = LOW_ENABLE = 0 (the number 1) // 2 = LOW1 = 0 // 3 = LOW2 = 0 // 4 = VRAIL_MEAS = 0 // ! = LOW_ENABLE = 1 // @ = LOW1 = 1 // # = LOW2 = 1 // $ = VRAIL_MEAS = 1 if (uart.readable()){ temp = uart.getc(); if (temp==(int) 't') { if (!gui) uart.printf("Keyboard trigger: "); measureAuto(); measureRailV(); //measureAll(); } if (temp==(int) 'v') { uart.printf("Keyboard trigger: "); measureRailV(); } if (temp==(int) 'h') { uart.printf("Keyboard trigger: "); measureHigh(); } if (temp==(int) 'k') { uart.printf("Keyboard trigger: "); measureLow1(); } if (temp==(int) 'l') { uart.printf("Keyboard trigger: "); measureLow2(); } if (temp==(int) '1') { LOW_ENABLE = 0; uart.printf("Keyboard trigger: LowEnable = %d\r\n", 0); } if (temp==(int) '2') { LOW1 = 0; uart.printf("Keyboard trigger: LOW1 = %d\r\n", 0); } if (temp==(int) '3') { LOW2 = 0; uart.printf("Keyboard trigger: LOW2 = %d\r\n", 0); } if (temp==(int) '4') { VRAIL_MEAS = 0; uart.printf("Keyboard trigger: VRAILMEAS = %d\r\n", 0); } if (temp==(int) '!') { LOW_ENABLE = 1; uart.printf("Keyboard trigger: LowEnable = %d\r\n", 1); } if (temp==(int) '@') { LOW1 = 1; uart.printf("Keyboard trigger: LOW1 = %d\r\n", 1); } if (temp==(int) '#') { LOW2 = 1; uart.printf("Keyboard trigger: LOW2 = %d\r\n", 1); } if (temp==(int) '$') { VRAIL_MEAS = 1; uart.printf("Keyboard trigger: VRAILMEAS = %d\r\n", 1); } if (temp==(int) 'r') { repeat = !repeat; uart.printf("Keyboard trigger: repeat toggle: %s \r\n", repeat ? "true" : "false"); } if (temp==(int) 'R') repeat = false; if (temp==(int) '+') { delay -= 0.05; if (delay<0.05) delay = 0.05; } if (temp==(int) '-') { delay += 0.05; if (delay>1) delay = 1; } if (temp==(int) '=') delay = 0.25; if (temp==(int) 'g') gui = false; if (temp==(int) 'G') gui = true; if (temp==(int) 's') statistics = false; if (temp==(int) 'S') statistics = true; if (temp==(int) 'n') { n -= 25; if (n<25) n = 25; } if (temp==(int) 'N') { n += 25; if (n>1000) n = 1000; } if (temp==(int) 'N' || temp==(int) 'n') uart.printf("/r/n/r/n Averages = %d \r\n\r\b", n); } } 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Instrumenting A Board To instrument a board, the connection between the power supply and the target device needs to be broken, usually via a series resistor that's placed on the board. Sometimes the inductor needs to be lifted if no series resistor was included on the rail by the board's designer. In the ideal case, through-hole connections were also provided on the board for the connection of these off-board sensors. Here are three close-up photos that show several boards that have been instrumented: In all three cases, the sensors stand in place via the two outer current carrying wires. The middle and right used insulated wires where as the one on the left used bare wires. In all three cases, the sensor's + connection needs to go towards the power supply and the - connection goes to the target device. The outer wires here are 24-26 gauge. (The relatively heavy gauge wire is used to keep the series resistance of inserting a smart sensor to a minimum.) The ground connection is the middle hole of the smart sensor. In the left and middle photos, a 30 gauge wire connects to the middle hole ground connection on the  board. In the right photo, the ground wire was more conveniently added to a big cap just below the bottom of edge of the photo. Here are wider angle view photos of two of the boards above: The sensors on the left are free-standing since the current carrying wires are stiff enough to hold them upright. Care must be taken since too much flexing will cause a wire to break. Too much bending can also cause a short to the board (and that's why insulated wires were used on these boards). The board on the right has the sensors laying parallel to the board. They are not affixed to the board, but a wire is wrapped around the bundle of ribbon cables out of view past the right edge of the photo. For boards without the through hole connections, the smart sensors need to be immobilized to keep from pulling the SMT pads off the board. If there is room on the board or sides of connectors or large components, the sensors may be attached down with foam double-sticky tape (see photo below, sensor affixed on top i.MX7ULP): For boards where there are no convenient unpopulated areas or there are too many sensors, some other means needs to be devised to immoblize the smart sensors. In the left photo below, two inductors per sensor have been flipped and the two sensors inserted to instrument the two rails. The solder pads on the inductors would easily be broken off by any movement of the smart sensors, so a cage with clamps to hold the ribbon cables was 3D printed. On the back side, there is room for the aggregator to be zip tied to the bottom plate, so the instrumented board can be moved as a single unit with minimal flexing of the ribbon cables.
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NOTE: Always de-power the target board and the aggregator when plugging or unplugging smart sensors from the aggregator. The aggregator portion of the i.MX Power Profiling System sits between the "smart" current sensor boards and the host computer. It provides power and signal connections to each connected sensor board. The communication is done over I2C, where three I2C bus extenders (PCA9518) effectively provide a dedicated bus to each I2C device, to better allow for cabling.  More information will follow... A photo, layout images and schematic attached below.   MBED source for the FRDM-KL25Z is available here: 30848-KL25Z-AGGREGATOR    Smart Sensor Connections At each smart sensor header JP0-JP13, these are the connections provided: 5V: powers the 3.3V regulator on each sensor board 12V: all the gates of all the switching FETs are pulled pulled up to 12V GND: ground connection SCL/TX0: I2C clock line  SDA/RX0: I2C data line  SWD_CLK:  global line for triggering smart sensors to make measurements RESET_B:  global line for resetting all smart sensor boards SWD_IO_n: individual select line for each smart sensor I2C Bus Connection Three I2C bus extenders (PCA9518) provide buffered connections between the FRDM board and all the connected smart sensors. The bus extenders were added to allow for longer cables between the aggregator and the smart sensor boards. Each bus extender has five ports and along with connections that allow extending the bus to more bus extenders. Gate Supply The aggregator contains a boost regulator that boost the 5V input from the FRDM board to 12V. The boosted voltage is fed to each of the smart sensor headers. It's used by the smart sensor board to pull up the gates of the switching FETs above any of the rails under test by at least 4.5V in order to benefit from a lower Rds(on). Caution must be exercised with some older FRDM boards since the 5V from the USB connection passes through diodes with a maximum current of 200mA.  The boost regulator and the load presented by the smart sensor boards may exceed the diode's limit and damage it. (Yes, it's happened... two older FRDM-KL25Z boards were used during development. One of them failed with the diode shorted (~0.05 Ohms), so everything kept working. The other failed with a  short of ~45 Ohms, so it kind of worked but not really...) Application Code for Aggregator  To date, application code has only been developed for the FRDM-KL25Z board. The latest application code resides at: https://os.mbed.com/users/r14793/code/30848-KL25Z-AGGREGATOR/, with the latest binary attached below. SWD Programming of Smart Sensors  Connectors J5 and JP15 are provided as an adapter for programming the smart sensor boards via SWD. JP15 provides power to the smart sensor board, since they have no direct 3.3V input for the KL05Z. An SWD programmer (or suitably modified FRDM-KL05Z board) connects to J5. Both connections use 10-pin 0.05"-spaced ribbon cables. Additionally, when a smart sensor is connected to JP15, J6 provides access to the UART pins of the smart sensor (the I2C pins on the smart sensor also mux out the UART of the KL05Z). No hardware changes are necessary at all; changing the code running on the smart sensor is all that's required. In fact, during the initial prototyping of the smart sensors, the serial UART connection was used instead of I2C. Modify Aggregator To Use SWD Dongle To Program Smart Sensor:  Add a wire as shown on the bottom side of the aggregator board as shown below. This ties 3.3V on the aggregator to the debug header, enabling the voltage level translators on the dongle to communicate with the KL05Z on the smart sensor board.  
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NOTE: Always de-power the target board and the aggregator when plugging or unplugging smart sensors from the aggregator. NOTE: See this link to instrument a board with a Smart Sensor. Overview The i.MX Power Profiler system consists of one to fourteen "smart" current sensors, an aggregator shield, and a Kinetis FRDM board (the FRDM-KL25 has been used in prototyping but the FRDM-K64F and FRDM-K66F should also be fully compatible). One of the biggest improvements of this system over its preceeding dual-range measurement system is that the microcontroller on each sensor board allows near-simultaneous measurement of all instrumented rails on a board. The dual range profiler has only a single MCU for all sensors, so only one measurement can be made at a time.  It is intended to be used to instrument one to fourteen rails of a target i.MX appliation board. Ideally, the target board will have been designed with a matching/mating power sense footprint for each rail to be measured.  Each smart sensor can sense current in three ranges with three current sense amplifiers. They are "smart" because each sensor board has a Kinetis KL05Z on it to control the switching FETs and to digitize the analog signals (the sense amplifier outputs and the target's power supply rail voltage). A 1% voltage regulator on each smart sensor provides a good voltage reference right next to the KL05Z to ensure better ADC accuracy. Each smart sensor board communicates via I2C. The aggregator shield has three I2C bus extenders (PCA9518) which essentially provide a dedicated I2C bus for each of the connected smart sensors. The FRDM board's I2C is also connected to one of the bus extenders ports. Individual GPIO lines are routed to each smart sensor's connected along with a ganged reset and trigger line for all of the connected smart sensors. A boost regulator generates almost 12V from the FRDM board's 5V supply, which is used for all the switching FETs on the smart sensor boards. The FRDM board's 5V rail is also routed to each smart sensor, which is regulated down to 3.3V locally on each connected smart sensor. Here is a photo of the very first prototypes after moving to 10-pin 0.05" spaced headers and ribbon cables instead of FFC: The smart sensor is intended to mate with through-hole current sense tap points on the target i.MX application board. Three holes spaced at 0.05" each. When not instrumented with sensor, a short needs to be placed across the outer two pins so that the board will function normally. The through hole connections provide physical protection to the target board, keeping traces from getting ripped off. The ground connection in the center provides a reference for meauring the rail voltage on the target board. A partial layout example of the implementation of the current sense footprint is below, where two 0805 shorting resistors in parallel are placed on each side of the holes. The top trace connects to the regulator output and the bottom to the load, usually an i.MX power supply rail. To include the current sense footprint into a board during the design phase, it should be configured as in the following partial schematic:  Every effort should be made to place the feedback on the i.MX side of the sense points so that the regulator compensates for the additional series resistance of the smart sensor, which effectively eliminates the additional series resistance the smart sensor adds. The Feedback should be before the smart sensor if the switching supply won't tolerate the additional series resistance (i.e., output becomes unstable).
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