52840 usb power supply power consumption is large

[Август]

Hello，

I am testing nrf52840 low power module on usb power supply, but it's current is about 22ua not 7ua.

hardware design

software design

int main(void)
{
    nrf_delay_ms(100);
    NRF_POWER->DCDCEN = 1;
    APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
    NRF_LOG_DEFAULT_BACKENDS_INIT();
    clock_init();
    NRF_LOG_INFO("lowpower test.");
    m_flag = true;
    while (true) {
        NRF_LOG_PROCESS();
        if (m_flag) {
            nrf_delay_ms(100);

            for (uint8_t index = 0; index < 32; index++) {
                NRF_GPIO->PIN_CNF[index] =
                    (GPIO_PIN_CNF_SENSE_Disabled << GPIO_PIN_CNF_SENSE_Pos) |
                    (GPIO_PIN_CNF_DRIVE_S0S1 << GPIO_PIN_CNF_DRIVE_Pos) |
                    (GPIO_PIN_CNF_PULL_Disabled << GPIO_PIN_CNF_PULL_Pos) |
                    (GPIO_PIN_CNF_INPUT_Disconnect << GPIO_PIN_CNF_INPUT_Pos) |
                    (GPIO_PIN_CNF_DIR_Input << GPIO_PIN_CNF_DIR_Pos);
            }

            NRF_TIMER2->TASKS_SHUTDOWN = 1;
            NRF_TIMER1->TASKS_SHUTDOWN = 1;
            NRF_TIMER0->TASKS_SHUTDOWN = 1;
            NRF_RTC0->TASKS_STOP       = 1;
            NRF_RTC1->TASKS_STOP       = 1;
            NRF_RADIO->TASKS_STOP      = 1;
            NRF_CLOCK->TASKS_HFCLKSTOP = 1;
            NRF_CLOCK->TASKS_LFCLKSTOP = 1;
            __WFE();
            __WFE();
            __WFI();
            __WFI();
            __WFI();
        }
    }
}

Can you give me some advice? Thanks.

[Vidar Berg]

Hello,

Can you please confirm if you have the NRF_LOG_BACKEND_UART_ENABLED setting disabled in your sdk_config header? The UART block will have an impact on the idle curren if not.

Best regards,

Vidar

[Август]

Hello,

Thank you for your response,the NRF_LOG_BACKEND_UART_ENABLED setting disabled in my sdk_config header.

I think the key point is not here.

When I onley use VDDH power on it's about 3.735ua, VDD power on it's about 3.428ua.

[Vidar Berg]

Hello,

Thanks for confirming, I just wanted to rule the UART first.  From your schematics it looks like VBUS is connected directly to VDD, or is (edit: R0) R1 not mounted on your board?

[Август]

I'm sorry for making you confused.

When we use VDDH for power supply, we will remove resistor R2 and leave R1, if we use USB for power supply, we will remove resistor R1 and leave R2.

[Vidar Berg]

No worries, thanks for the clarification. I also meant R1 when I said R0. In any case, I see now that you are measuring the current going into VDDH while the specification is stating the current for VDD. In other words, the 7 ua typ. rating will not apply to your configuration where you have the VBUS supply on VDDH and VDD as an external supply output.

But is power consumption really that critical when you get all the power from the USB?

[Август]

Thanks

Our USB-powered devices are also low power consumption, so we need to calculate the precise usage time.

So how much current is consumed in the low power consumption mode of usb power supply?

[Vidar Berg]

Sorry, but we have not specified a typical current draw for VDDH in this scenario. I think it's best you base your estimates on the measurements you have done.

[Август]

Thank you.