About comparators in STM32G474.

[xiaoyu wang]

I am enquiring about comparators in STM32G474.

For COMP4, it says that the INP can be connected to PB0 and INM can be connected to DAC1_CH1. But when PB0=1.65V and PA4(which is the output of DAC1_CH1)=3.15V , the VALUE bit in COMP_CSR is 1, which should be 0. I measured in from nucleo board and they are exactly the values I expected. And VALUE bit remains 1 when I changed the DAC1_CH1 to other values.

It makes me wonder if there is an issue in the manual. It seems that DAC1 is not really connected to COMP4.

Thank you!

[mƎALLEm]

Hello ​@xiaoyu wang and welcome to the ST community,

Please attach your project you’ve used for this test.

[xiaoyu wang]

The code related to the COMP4 and DAC1 configuration is as follows:

/* overcurrent protection configuration

* current limiting, max 3A (3.5A max for inductor,3A max for ADC) */

//Enable DAC1 clock

RCC->AHB2ENR |= (uint32_t) 0x10000U;

//DAC_out=V_ref*DOR/4096=1.65(offset)+1.5(3A in reality,gain for IN240A1=20,3*(25e-3)*20=1.5)=3.15,V_ref=3.3V

DAC1->DHR12R1 = (uint32_t)(12902.0f/3.3f);

//DAC enable

DAC1->CR |= (uint32_t)0x1U;

for(volatile int i=0; i<10000; i++);

//COMP4 configuration

RCC->APB2ENR |= (uint32_t)0x1U;

/* Select DAC1 CH1 as negative input

* Non-inverting input selection (PB0 over-current protection) for positive input

* inverted output(make enable bit in gate driver work)

* Enable comparator */

COMP4->CSR = (uint32_t)0x8051U;

[waclawek.jan]

Measuring PA4 shows the expected voltage?

Read out and check/post the relevant COMP and GPIO registers’ content.

JW

[xiaoyu wang]

Yes, PA4 and PB0 all shows the expected voltage. And I checked PB14, which is COMP4_OUT, it is not the expected voltage.

[mƎALLEm]

Hello,

I’ve just created a project with CubeMx with the same config as yours:

COMP4_INP (PB0): input connected to an external power supply.

COMP4_INM: input from DAC1_CH1_OUT.

DAC1_CH1_OUT (PA4) is monitored with an oscilloscope as well as COMP4_INP (PB0).

The result is as the following:

When the voltage on COMP4_INP > DAC1_CH1_OUT: COMP_CSR.VALUE = 1

When the voltage on COMP4_INP < DAC1_CH1_OUT: COMP_CSR.VALUE = 0

→ There is no issue with the documentation nor with the HAL nor with the hardware.

It seems the issue is in your bare metal code.

I’ve attached a project for your reference that you can test to confirm my saying.

In the project, the on board green LED turns on when COMP_CSR.VALUE=1 and it turns off when COMP_CSR.VALUE=0.

In next time, I recommend to start with HAL/CubeMx then move on to the bare metal coding.

Please confirm if it worked for you.

Hope that helps.

[xiaoyu wang]

I got it. I missed a register configuration DAC1->MCR so the DAC is not connected to COMP4 but only connect to output pin PA4