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BQ25570 faster Cold Start

Michael Liesenberg85
Mastermind 7560 points
Other Parts Discussed in Thread: BQ25570

Hi,

How can I make the cold start faster?

On VStor i have only two capacitor 10u and the 100n. My MCU is connected directly to the battery and also monitors its voltage so if gets UV it shut down completely.

The Coldstart is tajen too lobg, if i take the 10uf out will it ve faster?

  • 0
    TI__Guru**** 166996 points

    Just to confirm, if you plug in a partially charged battery at BAT (>VBAT_OK  threshold), you should not enter cold start.

    Any load connected to VSTOR (recommended) or BAT should be isolated from the VSTOR or BAT pins by a relatively low Rdson PFET (source connected to IC).  The gate of PFET can be driven by an inverted VBAT_OK output.  You can inverted with the VBAT_OK with a low cost NFET and pull resistor. 

     

  • 0 in reply to Jeff F
    Mastermind 7560 points

    Hi Jeff,

    on the BAT pin i have a full charged LiOn battery connected, no loads on VSTOR except those two capacitors.

    My MCU is connected to the battery and doesnt draw too much current at start up <1mA

    So cold start shouldnt happen right?

    How much time does the BQ25570 needs so it can receive a signal from load control pin and switch the buck converter on?

    Which PFET and NFET would you recommend for the circuit?

  • 0 in reply to Michael Liesenberg85
    TI__Guru**** 166996 points
    Datasheet section 7.4.3 explains about attaching a charged battery to VBAT in order to avoid cold start. VBAT and VSTOR voltages must be < 200mV when the battery is attached. There is a 45ms deglitch during which the VSTOR capacitor must charge to greater than VBAT_OK or the internal PFET between VBAT and VSTOR will close and the only connection between VSTOR and VBAT is the diode allowing current flow from VBAT to VSTOR. If you will never be changing the battery with the system running and the replacement battery will always be partially charged and the system will never fully deplete the battery, you should not enter cold start.

    There is no time limit on when the buck converter can be turned on.

    NFET can be a cheap 2N7000. PFET should be something with a bit lower Rdson, Si2301.