BQ51050B: Charging small 40mAh LiPo Battery

Hello

The BQ51050B will not work well at low charge current, accuracy is low a low current.  This will be true for both fast charge current (43mA) and termination current.

Recommend charging at about 100mA and termination at 30mA..

Thanks for the quick answer Bill.

Our battery manufacturer is suggesting we should charge at 0.5C so the problem is exacerbated by having a charge current of just 20mA..

Further to this, I have noticed two other comments in the forum that hopefully you can help clarify.

1. The rating of capacitors connected to CLAMP1, CLAMP2, BOOT1 & BOOT2 we are currently using on our solution are at 6.3V, the rest are rated at 25V. Will this severely affect the performance/stability of the RX circuit?

2. With reference to :https://e2e.ti.com/support/power-management/f/196/t/654439?tisearch=e2e-sitesearch&keymatch=bq51050%20jeita , we are trying to charge a LiPo battery with an charging temperature upper limit of 45 degC. Would you expect an issue with compatibility/performance? Our TS/CTRL line is pulled to GND through a 10k resistor, so there is no NTC circuit.

Thanks for your help.

Thanks again for your help Bill.

With regard to:

1. The rating of capacitors connected to CLAMP1, CLAMP2, BOOT1 & BOOT2 we are currently using on our solution are at 6.3V, the rest are rated at 25V. Will this severely affect the performance/stability of the RX circuit?  -- Bill J - recommend increasing voltage rating to 25V on the capacitors.

What could be the expected behaviour of using 6.3V rated capacitors on CLAMP1, CLAMP2, BOOT1 & BOOT2?

Also, as mentioned in the first post, we are experiencing an issue charging batteries at 40mA using the BQ51050B unit. Below is a trace of the output (pin 4 BAT) when connected to our 40maH LiPo battery - is this what you would expect?

Hello

1. The rating of capacitors connected to CLAMP1, CLAMP2, BOOT1 & BOOT2 we are currently using on our solution are at 6.3V, the rest are rated at 25V. Will this severely affect the performance/stability of the RX circuit?  -- Bill J - recommend increasing voltage rating to 25V on the capacitors.

What could be the expected behaviour of using 6.3V rated capacitors on CLAMP1, CLAMP2, BOOT1 & BOOT2?  --- Bill J Nov 24-- This will depend on how the capacitor acts in an overvoltage condition.  If we say it will decrease in capacitor value the BOOT circuit will be under powered, COMM will not be effective communicating with TX, CLAMP will not reduce voltage during overload condition.

Also, as mentioned in the first post, we are experiencing an issue charging batteries at 40mA using the BQ51050B unit. Below is a trace of the output (pin 4 BAT) when connected to our 40maH LiPo battery - is this what you would expect?  Bill J Nov 24 -- The BQ51050B is designed to charge 1A, it will not scale down well and charge / termination accuracy is poor at 40mA.  Take a look at reference design TIDA-00318 for lower charge currents.

The scope capture does not look right.  Can you send a scope capture of RECT pin.

Hi Bill,

Please disregard the trace in the previous post.

The output (BAT) from a faulty unit looks like the first image.

The output of RECT from a faulty unit looks like the second image.

Thanks

Hello

the RECT in last post does not look correct.  Voltage is over 8V for then drops to 6V.  The on time does not look correct this is 25mS time base. 

could you double check.  Should look more like attached.

3247.bqTESLA FAQ--Start up.pdf

And this would look similar on a BQ51050B system?

Thanks