BQ25606: Charging current doesn't go higher than 500 mA

user4725373

Part Number: BQ25606
Other Parts Discussed in Thread: TS5A3154

Hi,

We have a BQ25606 on our design used to charged via USB a 1Ah Li-ion 1 cell battery.

We put a 536 Ohms resistor on ILIM, which should set the maximum input current to 1A. However, The maximum I get is 500mA, whether it is on my PC's USB port or on a Samsung S9 charger, which can output 2A.

The ICHG resistor is 680 Ohms.

How long does the detection take? We put D+/D- on a multiplexer because we use the USB lines for communication, and we didn't want the manipulations that the charger does to affect the communication. Right now, we let the charger 500ms to detect the type of input. I have tried with 1.5s, but the results were the same (i.e. 500mA input limit).

What can I look at to get a 1A charging current?

Thank you,

Fred

over 6 years ago

0 Hong Mao over 6 years ago

TI__Expert 5590 points

Hi Fred:

Can you short D+/D- and check the charge current and them float D+/D- and check the charge current? If D+/D- is short, the input current limit is set at 2.4A; If D+/D- is floating, the input current limit is 478/536. If you can achieve 1A charge current then it is D+/D- detection issue. I do not suggest you use multiplexer. Instead, connect D+/D- directly. The detection time is 500mA to 2s, after detection, the input impedance is high and then communication can start.

0 user4725373 over 6 years ago in reply to Hong Mao

Expert 1645 points

Hi Hong,

Thank you for the answer. I tried both, but I wasn't able to get a current higher than 500mA. I don't have the 1Ah battery right now, so what I'm using are two 550mAh batteries in parallel. Would that influence the charging current?

Thanks,

Fred

0 user4725373 over 6 years ago in reply to user4725373

Expert 1645 points

I just tested with a power supply limited to 1.1A and the batteries can sink it no problem. Do you have other leads that I can investigate?

0 user4725373 over 6 years ago in reply to Hong Mao

Expert 1645 points

Hi Hong,

What other issues could there be besides bad detection?

0 Hong Mao over 6 years ago in reply to user4725373

TI__Expert 5590 points

One possibility is the battery has high impedance and the 1A current cannot be pushed in. Can you check the BAT pin voltage when your battery is charged at 500mA. Second, discharge your battery to lower voltage level and charge again.

0 user4725373 over 6 years ago in reply to Hong Mao

Expert 1645 points

I already did those tests before posting here. An almost empty battery still synced only 500mA

0 Hong Mao over 6 years ago in reply to user4725373

TI__Expert 5590 points

Please help do this:
-Double check ILIM resistance
-Double check ICHG resistance
-Short D+/D-
-VBUS = 5.2V
-Check the BAT pin voltage when battery is charging at 500mA

0 user4725373 over 6 years ago in reply to Hong Mao

Expert 1645 points

Hi Hong,

I forgot that Vbus was going through a mux that had a 1 Ohm impedance (TS5A3154), thus dropping largely Vbus when it was charging.

I bypassed the mux and I can now charge at 700mA. It's still not 1A, but I'll try with an empty battery (currently discharging), and then I'll try again shorting/opening D+/D-.

I will keep you updated,

Fred

0 Hong Mao over 6 years ago in reply to user4725373

TI__Expert 5590 points

Thanks for let me know. If the voltage at BAT pin has reached the charge voltage but charge current is still low then this could be battery issue.

0 user4725373 over 6 years ago in reply to Hong Mao

Expert 1645 points

Hi Hong,

I'm charging with a battery at ~60% and I still charging at 700mA. I observed that Vbus is at 4.38V. When I disconnect the battery, Vbus goes up to 4.88V with the Samsung Galaxy S9 charger, and 5.23V when using the USB port on my computer.

Is this normal?

0 Hong Mao over 6 years ago in reply to user4725373

TI__Expert 5590 points

Your cable is too long, we need 4.6V voltage at VBUS of the IC to charge at higher current.

0 user4725373 over 6 years ago in reply to Hong Mao

Expert 1645 points

Thank you, that was it. Good to know!

0 Hong Mao over 6 years ago in reply to user4725373

TI__Expert 5590 points

Glad to help. Please click the issue is resolved to close the case.

0 user4725373 over 6 years ago in reply to Hong Mao

Expert 1645 points

Correct me if I'm wrong, but I accepted your previous answer as the solution (cable was too long). Is there another step I have to do?

0 Hong Mao over 6 years ago in reply to user4725373

TI__Expert 5590 points

If the voltage at VBUS is not high enough, the charger operates at VINDPM mode and the charge current have to be regulated down. What is VBUS voltage at VBUS pin?

0 user4725373 over 6 years ago in reply to Hong Mao

Expert 1645 points

Hong, your previous answers fixed my issue. It was indeed a VBUS that was too low because it was going through a TS5A3154, coupled with a USB cable that was too long.

Thanks for your help

0 Hong Mao over 6 years ago in reply to user4725373

TI__Expert 5590 points

Never mind, I thought there is a button you can confirm the problem is solved. Thanks.

0 user4725373 over 6 years ago in reply to Hong Mao

Expert 1645 points

Hi Hong,

I was wondering, you said in your first answer that the detection time is 500 ms to 2 seconds. Where is this in the datasheet? I see that it takes 30 ms to detect a bad adapter, but not the overall detection time. Would this be specified in the USB Battery Charging Specification 1.2 (BC1.2)?

Thanks,

Fred

0 Hong Mao over 6 years ago in reply to user4725373

TI__Expert 5590 points

Hi Fred:

D+/D- detection is different from 30ms poor adapter detection. The detection time depends on inserted USB port as well. 500ms is typical.

0 user4725373 over 6 years ago in reply to Hong Mao

Expert 1645 points

Ok, thank you

0 Hong Mao over 6 years ago

TI__Expert 5590 points

Hi Fred:

Is your charge current exact 500mA or around 500mA? Typically, D+/D- takes about 500ms to detect, it could take longer up to 2 sec. Can you try to short D+/D- and check the charge current? After D+/D- short, if the charger current is 1A or close to 1A, then we can tell this is D+/D- detection issue. Otherwise, I would think this is probably battery impedance issue or cable impedance issue. Let's suspect cable impedance first, do you have long cable before VBUS, can you measure the voltage at VBUS pin, if the voltage is around 4.3V, then it is in VINDPM mode and charge current will be reduced. If the voltage is above 4.5V, then we can suspect the battery impedance is too high. When the charger is charging at 500mA, what is the voltage at BAT pin? For fast charge, the battery voltage should be lower than charge voltage in fast charge mode. What is the actual battery voltage before charge starts? You may lower the battery voltage to avoid CV charge. Following the above debug steps, you should be able to find the issue.

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BQ25606: Charging current doesn't go higher than 500 mA