Problem with initial power-up of BQ297xx

Jonathan Guy1

Other Parts Discussed in Thread: CSD85302L

I'm using a BQ29733 battery protection circuit in a standard configuration (with a CSD85302L MOSFET). However when battery power is first applied, the BQ29733 only sometimes turns on the external MOSFETs. Most times when power is applied the COUT pin is high, but the DOUT pin remains low. Occasionally power-up will complete after multiple cycles.

Any suggestions on what the issue might be?

For test purposes, adding 10k resistor across the Source pins of the MOSFET somehow provides bias for the device to activate correctly every time.

over 8 years ago

0 Vish Nadarajah over 8 years ago

TI__Expert 6085 points

its all about quick TURN off. Seems to have too much GS capacitance of the FET. recommend to deplete Gate to Source with 2M-5M resistor.

0 Jonathan Guy1 over 8 years ago in reply to Vish Nadarajah

Prodigy 90 points

Thanks for the quick response. Can you explain how increasing resistance across Gate-Source helps with start-up and turn-on of the DOUT MOSFET? I currently have even lower value (1M ohm between GS).

0 Vish Nadarajah over 8 years ago

TI__Expert 6085 points

do you see the problem, if V- and VSS pin are shorted when the BAT is connected for the firs time. Seems the part is in NOT in the NORMAL mode and not RESET>.

0 Jonathan Guy1 over 8 years ago in reply to Vish Nadarajah

Prodigy 90 points

Hi Vish,
If I have a temporary connection from V- to VSS (i.e. From Source to Source of the MOSFET) then the part powers up just fine. The short can then be removed. Also, a 10k resistor has the same effect. We have also installed a BQ29733 on the TI eval board (instead if bq29700DSE) and we see the same behavior.

I know that the BQ29733 variant is new. Presumably the BQ29733 sample parts have been programmed/trimmed correctly?

The waveform on BAT seems to match the datasheet (trc = 33us). Are there are other signals I can validate?

0 Vish Nadarajah over 8 years ago in reply to Jonathan Guy1

TI__Expert 6085 points

Hi Jonathan,
there is an CAUTION endorsement on pp 17 of the d/s of an another option for the part to reset properly....between the version, its the trim that's different. so what you are noting functionally will be across all devices. Only the config parameters will change as in pp 3 of the d/s.

0 Jonathan Guy1 over 8 years ago in reply to Jonathan Guy1

Prodigy 90 points

I completely missed that. Thanks.

0 Jonathan Guy1 over 8 years ago in reply to Jonathan Guy1

Prodigy 90 points

Also. It would be really useful to have that warning in the evaluation board documentation: www.ti.com/.../sluuaz3.pdf

0 Vish Nadarajah over 8 years ago in reply to Jonathan Guy1

TI__Expert 6085 points

Jonathan, I will definitely agree with you too and have made note to the core team. Assured it will be on the next revision.

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Problem with initial power-up of BQ297xx