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BQ24780S: Maxumum duty cycle

PAN-M
Mastermind 8375 points

Part Number: BQ24780S

Dear all.

How much of maximum duty cycle of bq24780S at 8.4V charge voltage?
How much minimum input voltage is necessary?

Regards,
PAN-M

  • 0
    TI__Guru 56650 points
    bq24780S allows the top FETs turn-on time longer than one full switching cycle. So, the minimum input voltage is limited by the sleep comparator (VCC to SRN comparator) and the voltage drop in VCC series diode. If assume VCC series schottky diode forward drop is 0.4V, sleep comparator threshold is 360mV rising threshold and 140mV falling threshold. The input voltage should be 8.4V+0.4V+0.36V=9.16V during the start up. After start up, the minimum input voltage should be higher than 8.4V+0.4V+0.14V=8.94V

    The duty cycle is about 8.4/8.94= 94%. With 800kHz switching frequency, the HIDRV off time is about 75ns in every switching cycle.
  • 0 in reply to Wang5577
    Mastermind 8375 points

    Thank you for a detailed answer.
    PAN-M