LM75B sensor mode transition failure

Hi, I'm using NXP LM75B temprature sensor based on nRF SDK's example code.

I would like to save power on this sensor.

I have prepared the code as follows:

/* Mode for LM75B. */
#define LM75B_MODE_NORMAL   0U
#define LM75B_MODE_SHUTDOWN 1U // Add

/**
 * @brief Function for setting sleep mode on LM75B temperature sensor.
 */
void LM75B_sdn_mode(void)
{
    ret_code_t err_code;

    /* Writing to LM75B_REG_CONF "1" set temperature sensor in SHUTDOWN mode. */
    uint8_t reg[2] = {LM75B_REG_CONF, LM75B_MODE_SHUTDOWN};
    err_code = nrf_drv_twi_tx(&m_twi, LM75B_ADDR, reg, sizeof(reg), false);
    APP_ERROR_CHECK(err_code);
    while (m_xfer_done == false);

    /* Writing to pointer byte. */
    reg[0] = LM75B_REG_TEMP;
    m_xfer_done = false;
    err_code = nrf_drv_twi_tx(&m_twi, LM75B_ADDR, reg, 1, false);
    APP_ERROR_CHECK(err_code);
    while (m_xfer_done == false);
}

Following main() is work fine:

/**@brief Function for application main entry.
 */
int main(void)
{	
    uint32_t err_code;
    LmHandlerErrorStatus_t lm_Error_code;
	
    // Initialize logs.
    log_init();
    NRF_LOG_INFO("LoRaWan end-device started.");
	
    // Initialize clocks & power
    nrf_drv_clock_init();
    nrf_drv_clock_lfclk_request(NULL);
    nrf_pwr_mgmt_init();

    // Enable nRF52 DCDC
    NRF_POWER->DCDCEN = 1;

    // Initialize Scheduler and timer
    timers_init();

    // Initialize NVM
    NvmDataMgmtInit();
  		
    // Initialize TWI
    twi_init();

    // Initialize LM75B
    LM75B_set_mode();
    nrf_delay_ms(200);

    // Initialize LoRa chip.
    err_code = lora_hardware_init();
    APP_ERROR_CHECK(err_code);

    // Initialize transmission periodicity variable
    TxPeriodicity = APP_TX_DUTYCYCLE + randr(-APP_TX_DUTYCYCLE_RND, APP_TX_DUTYCYCLE_RND);
	
    // Initialize LoRaWan
    lm_Error_code = LmHandlerInit(&LmHandlerCallbacks, &LmHandlerParams);
    APP_ERROR_CHECK_BOOL(lm_Error_code == LORAMAC_HANDLER_SUCCESS);

    // Set system maximum tolerated rx error in milliseconds
    LmHandlerSetSystemMaxRxError(20);

    // The LoRa-Alliance Compliance protocol package should always be initialized and activated.
    LmHandlerPackageRegister(PACKAGE_ID_COMPLIANCE, &LmhpComplianceParams);

    // Start Join procedure
    LmHandlerJoin();

    StartTxProcess(LORAMAC_HANDLER_TX_ON_TIMER);
		
    // Enter main loop.
    for (;;)
    {
        // Process the LoRaMac events
        LmHandlerProcess();

        // Process application uplinks management
        UplinkProcess();

        // Process events managed by the scheduler
        app_sched_execute();

        if (IsMacProcessPending == 1)
        {
            // Clear flag and prevent MCU to go into low power modes.
            IsMacProcessPending = 0;
        }
        else
        {
            if (NRF_LOG_PROCESS() == false)
            {
                nrf_pwr_mgmt_run();
            }	
        }
    }
}

And the following code is also work fine (This is only a function test. No sensor is used.):

    // Initialize LM75B
//    LM75B_set_mode();
//    nrf_delay_ms(200);
    LM75B_sdn_mode();
    nrf_delay_ms(200);

But the following code stops with some error. (Normal mode -> Shutdown mode transition test.):

    // Initialize LM75B
    LM75B_set_mode();
    nrf_delay_ms(200);
    LM75B_sdn_mode();
    nrf_delay_ms(200);

I don't think the problem is caused by AD conversion timing since I put in 200mSec weighting.

I believe I am making a basic oversight. Do you know what the problem is?

thanks,

tyro