BQ24005: Using a comparator to turn on charger is hit or miss

Tom Panian

Part Number: BQ24005

I am using a comparator to sense the presence of a pull down resistor (499ohms) in the battery pack. The EN pin on the BQ24005 is held low by the comparator until the pack is plugged in. Every time I plug in the pack (which also has NTC thermistor set for 10K at room temp) the charger will flash the STAT1 LED for just an instant. Other times it will charge but the charge current is only 75mA with a 0.1ohm sense R.

VCHARG is 9V in this case. BTYPE is the connection to the 499ohm pull down resistor in the pack.

over 5 years ago

0 Nick Brylski over 5 years ago

TI__Mastermind 19195 points

Hi Tom,

Can you try inserting the image again? Use these icons should work.

Thanks,

0 Tom Panian over 5 years ago

Intellectual 295 points

I tried a simple cut and paste using MS Snipping Tool.. guess that doesn't work!

0 Nick Brylski over 5 years ago in reply to Tom Panian

TI__Mastermind 19195 points

Tom,

What is the voltage on EN pin reading when pack is connected? Threshold to turn device on is 2.25 volts.

Is charger operating correctly when EN manually held high?

Best,

0 Tom Panian over 5 years ago in reply to Nick Brylski

Intellectual 295 points

Hello Nick.

The voltage on the EN pin is within 200mV of the VCHARG voltage. In this case, VCHARG is 8.9V, so VEN is 8.8V. I have tried removing the comparator and pulling EN high with just R10. I have used both 10K and 5K pullup values and the behavior of U1 is exactly the same as when the comparator is controlling the EN voltage.

0 Nick Brylski over 5 years ago in reply to Tom Panian

TI__Mastermind 19195 points

Tom,

What is voltage on APG/THM pin? If outside hot/cold thresholds charge is disabled.

Best,

0 Tom Panian over 5 years ago in reply to Tom Panian

Intellectual 295 points

Nick,

There is a switching power supply and an e-fuse sitting in front of the charger site. The output of this front-end passes through a safety fuse to the charger. When I looked at it on the scope, it was quite noisy. I pulled the fuse and applied 9VDC directly to the input of the BQ24005, everything operated normally.

Thanks for your help. At least I know where to look for the cause.

-Tom

0 Nick Brylski over 5 years ago in reply to Tom Panian

TI__Mastermind 19195 points

Thanks for letting us know. Any more issues feel free to start a new thread.

Best,

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BQ24005: Using a comparator to turn on charger is hit or miss