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Original question:

BQ25150: LS/LDO output not working on power up from battery

BQ25150: BQ25150: LS/LDO output not working on power up from battery part II

user4052185
Prodigy 230 points
Part Number: BQ25150
Other Parts Discussed in Thread: TPS62802, BQ25155

Continuing discussion from " BQ25150: LS/LDO output not working on power up from battery part"

Here are the scope pics from BAT, PMID, /MR and LS/LDO lines. It seem using PMID for releasing FET makes /MR line high before digital wakes up keeping LS/LDO low. 

When PMID was driving earlier LDO that released FET did not have this issue, most probably due BQ25150 digital was completely powered up before /MR release?

  • 0
    TI__Genius 12485 points

    Hello,

    I think this is caused due to the device going into a low power mode before the LDOs have started up. When the battery is inserted, if the /MR pin was held low till the power up is complete do you still see this?

    LDO turning ON with VIN or /LP pin going high makes sense as the device is not in low power mode. 

    Regards,

    Gautham

  • 0 in reply to Gautham
    Prodigy 230 points

    "The LS/LDO outputs will remain in the state set by the EN_LS_LDO bit prior to entering Low Power Mode. " 

    At least in normal operation default register settings keep LDO active. Would it be so that in power up sequence if /MR pin is release too early, regiter settings are not valid?

    In previous deisgn, i did not have this issue. I used external regulator (TPS62802 supplied from PMID) to releas the FETs driving /MR line.

  • 0 in reply to user4052185
    TI__Genius 12485 points

    Hello,

    The register settings are loaded through OTP. however, when the /MR went high early it did not provide the LDO enough time to start up and went to low power mode.

    Is it possible to extend the /MR low duration and try the wake up from Shipmode on your side?

    Regards,

    Gautham

  • 0 in reply to Gautham
    Prodigy 230 points

    In this design, its acceptable compromise that BQ25150 is in low power mode during startup and woken up with /LP or VIN since LS/LDO is not used straight after power up.

    For future designs, possible solution could be resistor divider and/or RC delay in gate of N4400B. What is the required extend time, is it this LS/LDO delay from PMID (20ms) or something less?

  • +1 in reply to user4052185
    TI__Expert 5645 points

    Hello, 

    The 20ms delay from PMID should be good for giving the extra time for the LDO to fully power-up. Another alternative is to look into the BQ25155 which is a pin-2-pin and firmware compatible device, and is a newer device which has a faster startup.   

    Best regards, 

    Arelis Guerrero