There is no better way to welcome in springtime than with NPI! The LPC553x family has just be released and I thought it would be a great time to introduce some of the important new features that make it special. Like other parts in the LPC5500 series, the LPC553x is built on the same 40nm technology using the Cortex®-M33 CPU core. When the LPC5500 series was first released, I wrote quite a bit about its differentiating features. Many of these features apply to the LPC553x family.
One of the neat features in the LPC55S6x was the PowerQuad DSP coprocessor and I wrote some articles highlighting some of the use cases:
- https://community.nxp.com/community/general-purpose-mcus/lpc/blog/2020/06/15/lpc55s69-powerquad-part...
- https://community.nxp.com/community/general-purpose-mcus/lpc/blog/2020/07/05/lpc55s69-powerquad-part...
- https://community.nxp.com/community/general-purpose-mcus/lpc/blog/2020/07/21/lpc55s69-powerquad-part...
This article will focus on the LPC553x, which does not include the secure features. The “S” version which has specialized security features will be released later this year. The LPC553x core platform that includes one Cortex®-M33 CPU and the PowerQuad DSP coprocessor.
Figure 1. LPC553X Core Platform
The LPC553x family builds upon the LPC5500 series foundation by adding peripherals that make it highly suitable for motor control, industrial IO, robotics, and sensing.
High Performance Analog Integration
Hooking up to the external world usually means that our MCUs must learn to “speak” analog. A high-performance analog system was added to the LPC553x family to enable more integrated, lower external component count designs.
Figure 2. LPC553X Analog Subsystem
16-bit Analog to Digital Converters
To support advanced sensing, motor control and robotics applications, the new ADC in the LPC553x can support up to 4 simultaneous conversions. This can be important when sampling voltage & current channel pairs for precise energy computations. It can also be very important in certain control applications.
Figure 3: LPC55S3x 16-Bit ADC Block Diagram
Some other highlights of the new ADC IP:
- 2MSa/sec in 16-bit mode or 3.2MSa/Sec in 12-bit mode
- Both differential and single ended input options
- Flexible triggering options with up to 16 sources w/ priority
- 16 entry FIFOs with configurable watermark and overflow detection
- Gain/linearity offset calibration logic
- Polled, DMA or interrupt operation
- Hardware Averager for Oversampling
3x Opamps
Anytime you have a powerful ADC in a system, opamps are often nearby on the PCB. The LPC553x has three built-in configurable opamps to help reduce the need for external parts when tying external signals into the ADC.
Figure 4. LPC553x Opamp Block Diagram
The built-in opamp is a rail to rail in/out device with 110dB open loop voltage gain, a 2v/mS (3MHz GBW) in low noise mode, and a 5.5v/mS (15MHz GBW) in high-speed mode. It supports both single ended and differential configurations with programmable gains. The output can be wired into the built-in high-speed analog comparators and/or the 16-bit ADC. A programmable reference can be fed into the opamp with the internal DAC being one of the options. One of the primary use cases of the opamp block is to directly measure current via a shunt resistor . This new feature supports many of the motor control and robotics use cases.
Application note AN13508 provides more information about how to use the opamp in the most common configurations.
https://www.nxp.com/docs/en/application-note/AN13508.pdf
4x High Speed Comparator (HSCMP)
In many analog power control designs, it is also common to find analog comparators. The LPC553x has four high speed analog comparators (HSCMP) built in which can reduce or eliminate the need for external components.
Figure 5. HSCMP Block Diagram
The internal comparators support rail to rail operation and contain a programmable 8-bit DAC to use for a programmable setpoint. The higher precision12-bit DAC can also be connected to the comparator inputs if additional setpoint resolution is required.
A common use case for a high-speed comparator in a power control system is over-current protection. To ensure fast response, it is common to see a high-speed comparator used to gate PWM control signals to quickly disable output power transistors. In my own designs, I will add external circuitry to implement this behavior. By combining some of the analog features in the LPC553x, it is possible to implement fast over current protection with minimal external electronics and no software delay.
Figure 6. Using the Op-amp and HSCMP for Overcurrent Shutdown
AN13540 has more details on the HSCMP and the overcurrent shutdown use-case.
https://www.nxp.com/docs/en/nxp/application-notes/AN13540.pdf
With some creativity, the LPC55S3x analog functions can be orchestrated to support a wide variety of power electronics and control functions. The integration of these analog features can help simplify design, reduce BOM line items and reduce area used on the PCB.
3x 12-Bit DAC
I often find that having a programmable DAC is very useful in my designs. Sometimes I will use a DAC to control a DC-DC converter (programmable output) or for miscellaneous setpoints. Most microcontrollers do not have DACs built-in and I must add another component to the BOM The LPC55S3x has three 12-bit 1MSa/sec DACs included in the device package. This is a very helpful feature as it could be used for programmable setpoints, waveform synthesis, medium quality audio, and control signal generation.
Figure 7. LPC55S3x DAC (x3)
The DAC in the LPC55S3x can be updated via software or hardware triggers. There is a 256 entry FIFO which can be combined with DMA for high speed, continuous updates.
Motor/Power Electronics Control Logic
The analog subsystem provides flexible components to implement the sensing side of a motor/control/power application. Located in the digital fabric of the LPC55S3x is a flexible motor control subsystem to that can be configured to control a variety of power electronics circuit configurations.
Figure 8. Motor Control Subsystem
The key feature of the motor control subsystem is the Qty 2 FlexPWM units that provide up to a total of 24 PWM outputs which can support two 3-phase motors.
Figure 9. Flex PWM
There are also 2 channels of quadrature decoder logic for position/velocity feedback from a motor/actuator.
Figure 10. Quadrature Encoder Interface (QEI) Peripheral
The AOI (AND/OR/Invert) combinatorial logic block is used for implementing custom logic/gating which can reduce need for external logic ICs.
Figure 10: Simplified AOI Block Diagram.
An important aspect of the AOI unit is that its input and outputs are connected to internal crossbars/multiplexers. A plethora of internal signals can be routed through the AOI unit enabling a great deal of flexibility and customization of behaviors between internal peripherals.
Industrial Communications
Connectivity is a big part of any design. The LPC553x supports many different communications interfaces but I want to point out two that may be particularly useful for industrial control and robotics applications. I had previously written an article on implementing Industrial Modbus communications with the LPC55S06 baseline MCU. The combination of the UART and MRT timer applies to the LPC553x as well. Modbus is a legacy protocol that has seen widespread adaption in the automation industry.
One differentiating feature in the LPC553x is the CAN Flex Data (FD) controller. CAN bus has been widely adopted in the automotive, robotics and industrial realms since the 1980’s. It is a proven technology that is the backbone for highly ruggedized networks of sensors and controllers. However, CAN is limited to a max data rate of 1Mb/s with a maximum of 8 data bytes. CAN-FD increases this to a maximum of 64 bytes per message.
An interesting aspect of CAN-FD is that it can co-exist on the same bus as classic CAN controllers. The arbitration phase of the CAN-FD is very similar except that there are flags to indicate that the data phase will be clocked 8x faster. CAN-FD controllers will understand the increased data rate and a legacy CAN device will simply throw the packet away as a CRC fail. It is a simple, yet effective way to send more data bytes in the existing frame while coexisting with traditional CAN devices. NXP has been leading the way with new microcontrollers implementing CAN-FD capability. You can learn more about CAN-FD here:
https://www.can-cia.org/can-knowledge/can/can-fd/
Summary
It is difficult to capture all the new features in LPC553x in one article, but I hope I got you interested the analog subsystem. Combined with industrial communications interfaces, FlexPWM, and the PowerQuad DSP peripheral the LPC553x is quite an interesting device. In future articles, I will dive into some of the other digital peripherals new to the LPC553x including the FlexSPI (for adding RAM/Flash over QSPI or Octal SPI) and the I3C controller. I will also be demonstrating some of the new features using the LPC55S36 EVK.
Stop by the family product page and checkout the documentation. There is plenty of application notes and reference material to get you started.