Electronic – How to debug STM32L433 Current leakage

debugginglow-powerstm32

I have a circuit board with STM32L433 that has around 320uA of baseline current draw in STOP 2 mode. Only LSE with a 32kHz crystal is active.

The board has separate analog Vdda power which is disabled for the stop mode. (tied to ground). Before disabling Vdda, ADC, DAC and OPAMP are disabled and their pins put into an OD low mode.

The configuration was done using the STM32CubeMX software.

Any ideas how to debug this? I disconnected and measured pretty much every external peripheral to see what is drawing current, but it seems like the STM32L433 is the culprit.

I'm measuring current with an oscilloscope using a 2ohm resistor in series with the battery. The LDO could be responsible for 20uA of it, which still leaves 300uA unaccounted for.

EDIT:

~ 120uA of it was using STOP 0 instead of STOP 2. This was left over from some experimentation. Now I'm at 200uA.
I've also disconnected both the BMI160 and DRV2603 chips. And they aren't the problem.

EDIT2

I've soldered another board with just an STM32L433 and an LDO LP5907-3.0 and a couple of decoupling capacitors. SAME PROBLEM.

This is the minimal code I used to set the GPIOs

GPIO_InitTypeDef GPIO_InitStruct;

/* GPIO Ports Clock Enable */
__HAL_RCC_GPIOC_CLK_ENABLE()
;
__HAL_RCC_GPIOH_CLK_ENABLE()
;
__HAL_RCC_GPIOA_CLK_ENABLE()
;
__HAL_RCC_GPIOB_CLK_ENABLE()
;

GPIO_InitStruct.Pin = 0xFFFFFFFF;
GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
GPIO_InitStruct.Pull = GPIO_NOPULL;
HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
HAL_GPIO_WritePin(GPIOA, GPIO_InitStruct.Pin, GPIO_PIN_SET);

GPIO_InitStruct.Pin = 0xFFFFFFFF;
GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
GPIO_InitStruct.Pull = GPIO_NOPULL;
HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);
HAL_GPIO_WritePin(GPIOB, GPIO_InitStruct.Pin, GPIO_PIN_SET);

GPIO_InitStruct.Pin = 0xFFFFFFFF;
GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
GPIO_InitStruct.Pull = GPIO_NOPULL;
HAL_GPIO_Init(GPIOC, &GPIO_InitStruct);
HAL_GPIO_WritePin(GPIOC, GPIO_InitStruct.Pin, GPIO_PIN_SET);

GPIO_InitStruct.Pin = 0xFFFFFFFF;
GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
GPIO_InitStruct.Pull = GPIO_NOPULL;
HAL_GPIO_Init(GPIOH, &GPIO_InitStruct);
HAL_GPIO_WritePin(GPIOH, GPIO_InitStruct.Pin, GPIO_PIN_SET);

//BOOT0 PIN
GPIO_InitStruct.Pin = GPIO_PIN_3;
GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
GPIO_InitStruct.Pull = GPIO_NOPULL;
HAL_GPIO_Init(GPIOH, &GPIO_InitStruct);


HAL_PWREx_EnterSTOP2Mode(PWR_STOPENTRY_WFI);

EDIT3

USB DM pin floats when USB in is low power mode. This caused the seen 200uA current drow. Pulling this pin down externally removes the 200uA. Now i'm trying to find a way around this in firmware.

Best Answer

After spending much too much time on this here are the results.

When USB is put to a low power mode after suspend with 

void HAL_PCD_IRQHandler(PCD_HandleTypeDef *hpcd){
    .....
    hpcd->Instance->CNTR |= USB_CNTR_FSUSP;
    hpcd->Instance->CNTR |= USB_CNTR_LPMODE;
    ...

There is a remaining residual ~200uA caused by a floating USB DM pin.(Floating digital inputs draw power (Implications of Slow or Floating CMOS Inputs)

The solution is to use/enable the Battery Charge Detection circuit that's built into this chips.

Something like this:

PCD_HandleTypeDef *hpcd = (PCD_HandleTypeDef*)hUsbDeviceFS.pData;
USB_TypeDef *USBx = hpcd->Instance;

int stabilizationCounter = 0;

HAL_PCDEx_ActivateBCD(hpcd); 

//run on a 10ms Timer
if( USBx->BCDR & USB_BCDR_DCDET ){
    stabilizationCounter++;
    if( stabilizationCounter >= USBPC_STABILIZATION_TIME ){
        USBD_Start(&hUsbDeviceFS);
        //stop the timer
    }
}else{
    stabilizationCounter = 0;
}

Note: HAL does have a void HAL_PCDEx_BCD_VBUSDetect(PCD_HandleTypeDef *hpcd) function, but your are expected to call this yourself after VBus power is detected. Which means an extra pin used and in my case a big layout reshuffle. Some details on the ST's recommended circuit is here USB hardware and PCB guidelines using STM32 MCUs

Is still have some 40uA caused by the LDO (~10uA) and a reverse leakage current of a Schottky diode (~30uA) but that's at least documented.

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