BQ24190 Usys oscillating problem

Hello Rainer,

Rainer Mohrlok said:

At 6.9V Usys starts to oscillate.

Are you referring to when the input (VBUS) increases to 6.9V or the system (SYS). The operational voltage range for the SYS pin should be within the programmable MINSYS threshold to VBATREG (max typically 4.35V). 

Could you please provide the operation condtions during this behavior (charge current, battery voltage, system load current, VINDPM setting, etc.)?

How much capacitance do you have at VBUS, PMID, and SYS pins? 

Any waveform would also be helpful.

Thanks.

Hello Fernando,

it is VBUS!
If we increase VBUS to 6.9V charging stops and Usys begins to oscillate.
while reducing VBUS the situation persits.
Charge current setting is 2A
Input current setting is 1.5A
Battery is 50% (SOC)
Capacitance (all X5R)
VBUS: 1uF/25V
PMID: 10uF/16V
SYS: 4x10uF/16V
Inductor: 2.2uH

best regards
Rainer

Hello Rainer,

The PMID pin is the actual input to the converter stage; I recommend adding some extra capacitance to the PMID pin to ensure the converter gets a clear, decoupled input, start by adding another 10uF and see if the issue persists.

Do you have a 10uF at the BAT pin as well? Is this behavior on the EVM or a custom PCB? If the latter, do you have an EVM you can repeat your test on and verify the behavior?

Any waveform showing the BAT, SYS, VBUS, IBAT would be helpful.

Hello Fernando,

I am the project partner of Rainer and I made some waveforms of our problem. I already tried to increase the capacitance at the PMID PIN with additional 10µF at the PMID PIN before we decide to ask the Forum. It dosen’t change the behavior.

The waveforms showing the start of the charging process with a 5V 2,1A USB power supply. The behavior doesn’t change with my laboratory power supply. I ordered the EVM yesterday to reproduce the problem.

Best regards

Dirk

Hello Dirk,

Thank you for the waveforms. Is the battery being disconnected from the device after powering up the charger? This ripple is very similar to setups where the battery is missing and we are seeing the decoupling cap at BAT being charged to VBATREG and discharged over and over.

Could you please share your setup settings, both register and system settings?

Do you have a system load present during the time of the test? If so, is the behavior the same without it?

Please keep us informed of the results of the EVM tests.

Hello Fernando,

i already tryed to bridge our protection circuit, because the overcurrent protection is very close to 2A. It dident help. But i will have a look on it again.

Update:

I think we have 2 problems:

1.The overcurrent protection is set too low.
2.The BQ24190 need more then 5V input Voltage to charge with stable 2A.

After I reduced the max charge current to 1,7A everythink is fine. With more then 1,7A the charge current start to ripple. If I increase the supply voltage a little bit, the charge current is ok again.

Whats your experiance with charge currents >=2A@5V supply Voltage?

I

best regards

Dirk

Hello,

this are the register settings

Reg 0:   00110101

Reg 1:   00010111

Reg 2:   default

Reg 3:   default

Reg 4:   11010110

Reg 5:   10001110

Reg 6:   default

Reg 7:   default

Best regards

Rainer

Hello Fernando,


i already tryed to bridge our protection circuit, because the overcurrent protection is very close to 2A. It dident help. But i will have a look on it again.

Update:

I think we have 2 problems:

1.The overcurrent protection is set too low.
2.The BQ24190 need more then 5V input Voltage to charge with stable 2A.

After I reduced the max charge current to 1,7A everythink is fine. With more then 1,7A the charge current start to ripple. If I increase the supply voltage a little bit, the charge current is ok again.

Whats your experiance with charge currents >=2A@5V supply Voltage?

I

best regards

Dirk

Hello Dirk,

From the settings you provided, your input current limit is set to 1.5A. This means your 5V/2A supply is only providing 7.5W, which is not sufficient for a 4.2V battery, 2A charging. At low voltages it should be fine, but as the battery voltage rises, the device will enter input current limit. Seems the input current limit loop is unstable which is usually resolved by adding extra capacitance at VBUS, PMID and ensure a proper PCB layout.

If the overcurrent protection is close to 2A that also may be causing the protection circuit to trip over and over again, causing the ripple we observed. Is the protection threshold adjustable on the protection circuit?