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i.MX Processors Knowledge Base

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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 0.002 Ω 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 1.5m Ω ) 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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