bq25504: minimum time between VBAT_OK asserted high and VBAT_OK asserted low

lloyd konneker

Other Parts Discussed in Thread: BQ25504, BQ25570

Can the bq 25504 assert VBAT_OK low sooner than 64msec after the bq25504 asserts VBAT_OK high?

Reading the datasheet, it seems like the programming resistors are sampled every 64 msec but it is not clear how often the bq25504 checks voltage on pin VBAT and updates VBAT_OK level.

I'm using VBAT_OK to switch a MOSFET switching a large current load, and it seems like the load drains my small storage to below VBAT_OK_PROG (the low threshold) and worse, below VSTOR_CHGEN of 1.8V before VBAT_OK is asserted low.

I will try a larger storage and limiting the current of the load so that the time constant is above 64msec.

over 10 years ago

0 lloyd konneker over 10 years ago

Expert 1790 points

Nevermind. More info on the internal circuitry is at a presentation by TI employee on "Powering the Internet of Things" and the BQ25570.

http://www.hotchips.org/wp-content/uploads/hc_archives/hc26/HC26-10-tutorial-epub/HC26.10-tutorial2-IoT-epub/HC26.10.215-Powering-Ramadass-TI-YR_hotchips_2014_tutorial.pdf

That circuit seems to indicate that VBAT_OK is only updated every polling period, 64msec.

So I increased my storage to 4.4mF. The BQ switches it to a 100mA load when it reaches 2.8V. Apparently it falls to about 2.1V but only after one polling period and since this is below VBAT_OK_PROG of 2.4V, the BQ25504 seems to drive VBAT_OK low, switching out the load. And keeping the BQ in main charging mode.

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bq25504: minimum time between VBAT_OK asserted high and VBAT_OK asserted low