LPCOMP doesn't sense the pulse count correctly

[Pavan kumar]

Hii every one, We are working on a project where we are using a temperature sensor LMT01, its giving a pulse output the pulse out is from 220mV to 600m. So I'm using lpcomp to count the number of pulses. my config is like this

> Blockquote/**
 * @brief Initialize LPCOMP driver.
 */

static void lpcomp_init(void)
{
    uint32_t                err_code;

    nrf_drv_lpcomp_config_t config;

    config.hal.reference = NRF_LPCOMP_REF_SUPPLY_1_8;
    config.hal.detection = NRF_LPCOMP_DETECT_UP;
    config.input = TEMP_VN_PIN;

    // initialize LPCOMP driver, from this point LPCOMP will be active and provided
    // event handler will be executed when defined action is detected
    err_code = nrf_drv_lpcomp_init(&config, lpcomp_event_handler);
    APP_ERROR_CHECK(err_code);
    nrf_drv_lpcomp_enable();
}
my power supply is 3.3V as I think refrence will be 3.3/8 = 0.4125
 and incremented the pulse count in event handler

void lpcomp_event_handler(nrf_lpcomp_event_t event)
{
	if(event ==  NRF_LPCOMP_EVENT_UP)
    {
		m_temp_pulse_count++;
}
}

in the span of 50ms the temp sensor giving more than a thousand pulses but lpcomp showing the output as 17. I want someone to help in this regards

Thanks in advance

[Hung Bui]

Hi Pavan, Which chip are you testing with ?

How big is the pulse, if it's shorter than 15us, the LPCOMP won't detect the pulse. As you wrote the reference is 0.4125V , but the pulses are from 0.220V to 0.6V, are you planing to monitor only pulse higher than 0.4125V ?

[Pavan kumar]

Thanks for your reply Hung

I'm using nrf51822 chip, the temperature sensor will give a pulse of frequency 88kHz ie, the pulse is 11.36us may be that causing the issue, is there any way to detect high frequency signals.

[Hung Bui]

@Pavan: You can think of using the nRF52, the LPCOMP only needs 5us to detect. And you have more option for VREF.

[Pavan kumar]

ooh that's well, I wanna ask you one more question like is there any possibility to increase the sensitivity of lpcomp, I mean like by using external crystal or any other. Thanks

[Hung Bui]

No, it's not possible.