BQ25120: SYSout voltage return to default value after a few sec of configuration via I2c

Part Number: BQ25120
Other Parts Discussed in Thread: BQ25121A

BQ25120 SYSout voltage return to default value after a few sec of configuration via I2c.

Observation: The SYSout voltage won't drop if we constantly read the system register(0x06) valuevia I2c

Configuration:

We pull up pin NCD pin all time high. Here is our code for register configuration.

/* Common addresses definition for pmic. */
/* BQ25120 power management IC TWI/I2C slaves address */
#define BQ25120_SLAVE_ADDR        0x6A
#define BQ25120_BTTN_REG          0x08
#define BQ25120_SYS_REG           0x06
#define BQ25120_LDO_REG           0x07
#define BQ25120_FAST_CHRG_REG     0x03
#define BQ25120_PRECHRG_REG       0x04
#define BQ25120_BATTV_CTRL_REG    0x05
#define BQ25120_ILIM_CTRL_REG     0x09

void pmic_init (void)
{
    ret_code_t err_code;

    /*BQ25120  register configuration*/
    uint8_t bttn_config[2]= {BQ25120_BTTN_REG, 0xFC};
    uint8_t sysv_config[2]= {BQ25120_SYS_REG, 0xF8};
    uint8_t ldo_config1[2]= {BQ25120_LDO_REG, 0x44};
    uint8_t ldo_config2[2]= {BQ25120_LDO_REG, 0xC4};
    uint8_t fast_chrg_config[2]= {BQ25120_FAST_CHRG_REG, 0x90};
    uint8_t prechrg_config[2]= {BQ25120_PRECHRG_REG, 0x8A};
    uint8_t batt_vol_config[2]= {BQ25120_BATTV_CTRL_REG, 0x78};
    uint8_t ilim_config[2]= {BQ25120_PRECHRG_REG, 0x22};

    /* configure BQ25120 register */
    /*Push-button Control Register, 1st wake up event at 600ms, 2nd wakeup event at 1.5s*/
    err_code = nrf_drv_twi_tx(&m_twi1, BQ25120_SLAVE_ADDR, bttn_config, sizeof(bttn_config), false);
    APP_ERROR_CHECK(err_code);
    /*SYS VOUT control Register, Range 1.8V~3.3V, SYS output at 3V*/
    err_code = nrf_drv_twi_tx(&m_twi1, BQ25120_SLAVE_ADDR, sysv_config, sizeof(sysv_config), false);
    APP_ERROR_CHECK(err_code);
    /*Load Switch and LDO control Register, Range 1.8V~3.3V, SYS output at 3V*/
    err_code = nrf_drv_twi_tx(&m_twi1, BQ25120_SLAVE_ADDR, ldo_config1, sizeof(ldo_config1), false);
    APP_ERROR_CHECK(err_code); 
    /*Load Switch and LDO control Register, Range 1.8V~3.3V, SYS output at 3V*/
    err_code = nrf_drv_twi_tx(&m_twi1, BQ25120_SLAVE_ADDR, ldo_config2, sizeof(ldo_config2), false);
    APP_ERROR_CHECK(err_code); 
    /*Fast Charging current control Register, Iset pin connects to 2.49kohm resistor for 80mA charging current*/
    err_code = nrf_drv_twi_tx(&m_twi1, BQ25120_SLAVE_ADDR, fast_chrg_config, sizeof(fast_chrg_config), false);
    APP_ERROR_CHECK(err_code); 
    /*Pre-charge current control Register, 10% pre-charge/termination current (8mA)*/
    err_code = nrf_drv_twi_tx(&m_twi1, BQ25120_SLAVE_ADDR, prechrg_config, sizeof(prechrg_config), false);
    APP_ERROR_CHECK(err_code); 
    /*Battery Voltage Control Register, Charging voltage 4.2V (default)*/
    err_code = nrf_drv_twi_tx(&m_twi1, BQ25120_SLAVE_ADDR, batt_vol_config, sizeof(batt_vol_config), false);
    APP_ERROR_CHECK(err_code); 
    /*Input current and voltage protection control Register, Input current 200mA, UVLO 3.0V*/
    err_code = nrf_drv_twi_tx(&m_twi1, BQ25120_SLAVE_ADDR, ilim_config, sizeof(ilim_config), false);
    APP_ERROR_CHECK(err_code); 
}