bq78350 PreDischarge

JeremyStreet-Thomas

Other Parts Discussed in Thread: BQ78350

Hi,

I am using a bq78350 with the bq7692000 AFE and have discovered in our system significant inrush currents. Our system will then trip based on an AOLD or ASCD fault, as it should. We are looking at introducing a pre-discharge path through a resistor to allow any bulk capacitance to charge up without having huge surge currents. Currently we are seeing surge currents of around 800A for about 250us and have set the limits to over 250A. (ASCD is 352A for 70us; AOLD is 264A for 80ms).

We will control the logic for the pre-discharge via a microcontroller but want to know how to reliably control the amount of time the pre-discharge will be on before the DSG FETs come on. I've noticed that to clear an error on the BMS by resetting takes *around* 4 seconds (before it is ready to communicate).

How can I reset an error on the BMS and turn on a pre-discharge FET with a microcontroller and be sure that XXXms later the main FETs will turn on?

Thanks in advance for the help,

Jeremy

over 9 years ago

0 JeremyStreet-Thomas over 9 years ago

Prodigy 200 points

Any ideas on how to know how long it takes before the FETs turn on after sending a reset command to a bq78350?

Thanks,
Jeremy

0 Onyx Ahiakwo over 9 years ago in reply to JeremyStreet-Thomas

TI__Guru* 76230 points

hi Jeremy.

There is an aold recovery time which is programmable by you which controls when the discharge fet comes back on as well as the charge fet if it is also set to be turned off. ps refer to the technical reference manual, pg 24 for further details. I hope this helps.

thanks

Onyx

0 JeremyStreet-Thomas over 9 years ago in reply to Onyx Ahiakwo

Prodigy 200 points

Hi Onyx,

Due to the application we don't want the autorecovery feature, but want to have an error user reset-able. This is handled by a microcontroller which clears the error by reseting the bq78350.

How can I control/know the time it takes for the bq78350 to turn FETs back on from a reset command sent?

Thanks for the suggestion,
Jeremy

0 Onyx Ahiakwo over 9 years ago in reply to JeremyStreet-Thomas

TI__Guru* 76230 points

Hi Jeremy,
The best way forward with this would to put a scope to the device and measure the exact timing after issuing the command. This is not something we have characterized

thanks
Onyx

0 JeremyStreet-Thomas over 9 years ago in reply to Onyx Ahiakwo

Prodigy 200 points

Hi Onyx,

I can definitely put a scope and measure but by some rough tests it seems to be around 4 seconds but doesn't have the same delay every time. Can you confirm if this delay will change or not?

Thanks for the help,
Jeremy

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bq78350 PreDischarge