BQ2057W: Charge Circuit not matching charge profile in datasheet.

Parker Henzel

Part Number: BQ2057W
Other Parts Discussed in Thread: BQ24005,

Or testing has shown a massive inrush of current when charging our batteries from cutoff voltages. This is not what the data sheet says should happen (Diagram 2). What are some possible causes of this/solutions? I am at a loss for how to fix it.

This circuit (Diagram 1) is taken directly from the data sheet. There is no thermistor hooked up to the pin instead it just has the voltage divider to keep the device on. Our goal is to use a 9.1V input to charge a 2s battery pack to 8.4V at a rate of ~400mA (~.5C).

Testing done with this Battery Pack: https://www.batteryspace.com/polymer-li-ion-battery-7-4v-750mah-5-55wh-5a-rate-rechargeable-battery.aspx

Testing was also done with (https://www.batteryspace.com/lithium-14500-battery-7-4v-800mah-5-92wh-0-8a-rate---un38-3-passed.aspx

Test Procedure:

1) The battery was discharged to cutoff via a 10 Ohm Resistor.

2) The battery was given a 5 minute rest.

3) The battery was put on the charger and voltages and currents were recorded for the duration of charging shown in Diagram 3.

Diagram 1

Diagram 2

Diagram 3

over 4 years ago

0 Parker Henzel over 4 years ago

Prodigy 80 points

Battery Charge.xlsx

0 Anthony P Pham over 4 years ago in reply to Parker Henzel

TI__Mastermind 23410 points

Hi Parker,

Are you able to test the charger with batteries at a lower voltage such as 6V? What happens if you increase the Rsns resistor?

0 Parker Henzel over 4 years ago in reply to Anthony P Pham

Prodigy 80 points

Hey Anthony,

I increased the resistor to a 1 Ohm and performed the following tests located in the excel spreadsheet attached.

The testing procedure was the same, but I did not charge them to capacity.Battery Charge Testing 2.xlsx

0 Anthony P Pham over 4 years ago in reply to Parker Henzel

TI__Mastermind 23410 points

Hi Parker,

Alright, are you able to measure the voltage on the CC pin? This would indicate whether or not the device knows current is not at the regulation point.

It is also recommended to use the BQ24005 in place of the BQ2057W as it is an older device with the BQ24005 reducing the number of parts needed for configuration.

0 Parker Henzel over 4 years ago in reply to Anthony P Pham

Prodigy 80 points

Hi Anthony,

I just measured the CC pin voltage and found that it measures 8.2V when the battery is dead.

I will look into the BQ24005.

0 Anthony P Pham over 4 years ago in reply to Parker Henzel

TI__Mastermind 23410 points

Hi Parker,

Glad to hear.

If you're still interested in the BQ2057W, can you measure the voltage when you are seeing the incorrect current? This will be a better indication as to whether or not the gate voltage on the FET is too high and letting too much current instead of being regulated by the device.

0 Parker Henzel over 4 years ago in reply to Anthony P Pham

Prodigy 80 points

Hi Anthony,

We are still interested in BQ2057W for now. 8.2V was the voltage on the CC pin when the current was at 1.6A. The voltage on the CC pin seems to always be 8.2V.

Thanks,

Parker

0 Anthony P Pham over 4 years ago in reply to Parker Henzel

TI__Mastermind 23410 points

Hi Parker,

Understandable. I will look into this and reply to you soon.

0 Parker Henzel over 4 years ago in reply to Anthony P Pham

Prodigy 80 points

It seems that our pfet was broken the whole time. Thanks for your time. We are changing the Pfet out with one that actually meets our specifications.

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BQ2057W: Charge Circuit not matching charge profile in datasheet.