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BQ25619: large ripple at SYS when battery removed

Wiky Liao
Intellectual 1550 points
Part Number: BQ25619

Hi Team,

I am using BQ25619EVM and checking the SYS pin performance. I notice when battery is removed(keep JP7 inserted, so 10K NTC still on board), the SYS ripple will be large - about 200mV peak to peak, and LED_D5 blink quickly(about 10Hz). Please refer below waveform, CH1 is SYS pin voltage while CH2 is LED_D5 voltage. I try to disable PFM in REG01h bit_7, the ripple will be larger than enable. 

May I know why SYS ripple seems large here? When battery is connected everything looks good and the SYS ripple will less than 20mV.

Best Regards.

Wiky Liao