BQ24090: BQ24090 not getting 500mA at 5V.

Hello
This could be caused by a couple of things a good post to start with is the below FAQ.
e2e.ti.com/.../763227

You are configured for 1A charge current -- R-ISET= 540 ohms and ISET2 = Low (ISET)

Thanks for your reply.

1. TS pin voltage needs to be in the normal range. At low temp half charge will reduce current TS between 790mV and 1230mV.    I measured TS pin and it is 490mV. 

2. ISET2 pin, Float will limit current to 100mA. ISET2 is configured to LOW.

3. Input voltage low, need 700mV to 1000mV drop across the device for full output current. My input voltage is 5V.

4. Internal thermal limit, if the die temp reaches 125C output current is reduced to control thermal rise. The IC is not hot.

Any other suggestions? With my configurations, I should be able to get 1A at 5V right?

Can you send layout for review?
PDF if possible.

Please find above PCB layout. D1 is diode and F1 is fuse. I have removed both of these and shorted them to ensure correct VIN. It would be great if you could suggest any way to improve this. Thank you very much.

Do not see any problem with the layout.

Voltage drop on D1 and F1 could be a problem, if the voltage at IN is 5V or more you are OK.
V-DO (In-Out) is spec at 520mV max -- BUT this is with a drop in output current from 1A to 500mA.

Another thing to check that will give a clue to what the unit is doing is voltage at ISET pin with unit in CC mode. Voltage should be 1.5V with ISET2 low, the 1A output configuration. With ISET2 high and input current limit to 500mA voltage will be 700mV.

ISET is a sample of the output current ratio is about 1:360, for 1A out the ISET current is 2.77mA.

- Voltage drop on D1 and F1 could be a problem, if the voltage at IN is 5V or more you are OK. 

I have removed D1 and F1.

- V-DO (In-Out) is spec at 520mV max -- BUT this is with a drop in output current from 1A to 500mA. 

Measured VIN = 4.32V 

Measure VOUT = 3.89V

VDO = 0.43V

- Another thing to check that will give a clue to what the unit is doing is voltage at ISET pin with unit in CC mode.

Measured Voltage at ISET pin =400mV.

It seems like my ISET voltage isn't right. 

If I increased my bench top power supply to around 5.7V, then I will be able to get charging current of 500mA and the voltage of ISET pin is 720 mV.

Hi
"- V-DO (In-Out) is spec at 520mV max -- BUT this is with a drop in output current from 1A to 500mA. "

"Measured VIN = 4.32V "

"Measure VOUT = 3.89V"

If voltage at the IC IN pin is dropping to 4.32V it will be a problem and limit how much current you can get out of the device.

Hi,

As I have removed the D1 & F1, IC IN pin was actually connected directly to the power supply and the power supply was set to 5V. I am not sure why there is a voltage dropped to 4.32V when charging the battery.

Is that a normal behaviour?

Regards,

Boon

Hi
No you should not see this much voltage drop between input and IN pin of the device.
Couple of things to try:
1.) Take a look at the Gnd return, may have some losses there
2.) Check for loss in connectors
3.) Try mapping the voltage drop, starts at power supply as 5V the drops as it goes to IC IN pin.

The layout looks good do not expect this much drop.