BQ25890H: Disconnection of a DCP is not detected by the BQ25890H.

-Patrick-

Part Number: BQ25890H
Other Parts Discussed in Thread: BQ25890

Dear All,

Our charger, build around a BQ258990H, exhibits a strange phenomenon. Charging the battery functions as desired.
But if we disconnect the power adapter (DCP) during the constant current mode the BQ25890H doesn't detect this and acts as if the battery is still being charged (STAT pin stays low).
What stands out is that VBUS is kept at 4.47V even at a light 100 ohm load. The VBUS voltage is even higher than the current battery voltage (4.08V).

OTG behavior with that note that OTG is disabled!

What I expect is that VBUS drops to 0V and the STAT pin becomes inactive (charging indicator LED turns off). Neither is true.

Hardware setting OTG pin grounded.
Software setting OTG disabled

Register values after disconnecting the DCP:

00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14
7F 01 1D 1A 3E 12 5E 89 00 44 73 76 00 12 00 00 00 98 00 08 1F

Explanation of a few register values:

(REG0B) VBUS_STAT = 011 -> DCP adapter connected
(REG0B) CHRG_STAT = 10 -> Fast charging
(REG0C)           = 00 -> no faults

Measured voltages:

VBUS voltage before disconnecting:    5.03V
Battery voltage before disconnecting: 4.09V
VBUS voltage after disconnecting:     4.47V
Battery voltage after disconnecting: 4.08V

Anyone have an idea what is caused this Chicken and Egg phenomenon?

Best regards,
Patrick

over 4 years ago

0 Ning T over 4 years ago

TI__Guru 57811 points

Patrick,

Does the SW pin switching after the power adaptor at VBUS is disconnected?

Thanks,

Ning.

0 -Patrick- over 4 years ago in reply to Ning T

Intellectual 360 points

Hello Ning,

Yes, the pin switches at a frequency of about 740kHz after disconnecting the DCP.

It seems that this phenomenon only occurs when during the "constact-current-phase" however this has not been extensively tested yet, so subject to change.

Best regards,

Patrick

0 Ning T over 4 years ago in reply to -Patrick-

TI__Guru 57811 points

Patrick,

Could you please change the VINDPM setting to 3.9V (i.e. REG0D=8D) and try again?

Thanks,

Ning

0 -Patrick- over 4 years ago in reply to Ning T

Intellectual 360 points

Hello Ning,

I tried again with REG0D=8D setting, but the behavior remains.

Best regards,

Patrick

0 Ning T over 4 years ago in reply to -Patrick-

TI__Guru 57811 points

Patrick,

Is there BTST resistor in series with BTST cap? How much are BTST resistor and BTST cap?

Thanks,

Ning.

0 -Patrick- over 4 years ago in reply to Ning T

Intellectual 360 points

Hello Ning,

Yes there is a resistor in series with the BTST cap.

R = 2 Ω

C = 47nF

Best regards,

Patrick

0 Ning T over 4 years ago in reply to -Patrick-

TI__Guru 57811 points

Patrick,

If the BTST resistor of 2ohm is removed, will the behavior occur?

Thanks,

Ning.

0 -Patrick- over 4 years ago in reply to Ning T

Intellectual 360 points

Hello Ning,

The behavior occurs even if the 2Ω resistor is removed (short-circuited).

Further testing revealed that the problem only occurs when the battery voltage (BAT pin of the BQ25890H) is in the range of 4.00 ~ 4.15 V.

Best regards,

Patrick

0 Ning T over 4 years ago in reply to -Patrick-

TI__Guru 57811 points

Patrick,

Please add 10kohm from VBUS to GND. It helps sometimes.

Thanks,

Ning.

0 -Patrick- over 4 years ago in reply to Ning T

Intellectual 360 points

Hello Ning,

We already tried your suggestion.

4kΩ is already in the design, even if I connect 270Ω between VBUS and GND the problem remains.

Best regards,

Patrick

0 Ning T over 4 years ago in reply to -Patrick-

TI__Guru 57811 points

Patrick,

The quality of CBTST is important. Please try similar BTST cap on the BQ25890 EVM - GRM155R71E473KA88D (CAP, CERM, 0.047uF, 25V, ±10%, X7R).

Thanks,

Ning.

0 -Patrick- over 4 years ago in reply to Ning T

Intellectual 360 points

Hello Ning,

Thanks to your help I finally found the cause of the problem. Both Cbtst and Cdsel were populated with an incorrect value. Apologies for this.

Best regards,

Patrick

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BQ25890H: Disconnection of a DCP is not detected by the BQ25890H.