BQ24075: Charging Issue

Hello,

Is there any load on OUT?

Morning Raheem, thanks for the response.

There is a load on OUT. I have tried reducing the load, but get the same results. My circuit, however, does not allow me to have No Load on OUT unless I cut some tracks.

How low can you reduce the load to?

Is the load more than the 500mA input current limit?

Hi Raheem

The load is far lower than 500mA. Normal operation is 20-25mA and low power mode is less than 5mA

to confirm, what is the battery voltage when you observe this behavior?

Morning Raheem

I have tried at various voltages from 3.5V for a flat battery and 4.1V for a charged battery.

Please see scope captures

1. Capture1 - Inrush current test

2. Capture 2 - charge starts after 25ms of the inrush Current Test

3. Capture  - charge lasts for 30ms

Hi Raheem

I have also tried the following:-

1. removed capacitors C1, C2 and C7 to ensure that the inrush current was not exceeded.

2. increased R7 to 4k7 to reduce fast charge current

The issue still exists

Hello Warren,

Those capacitors should not cause issues. The inrush current behavior you noticed is expected. 

How many volts do you measure on TS pin?

Hi Raheem

I measure a small spike of 1.2V that coincides with the Inrush Current test, but then the voltage drops to around 1-2mV. See capture 4 below.

Hi Raheem

I have also tried the following:-

1. Removed the Temp sense wire from the battery to ensure this has no effect

2. Cut the track that supplies my system so there is no load on the out pin at all

3. Pulled EN1 low to limit the Inrush current to 100mA

4. Tried various resistor values on ISET and ILIM

None of the above seem to help. The chip still does not seem to charge the battery. I need to get this product to a customer to evaluate, but cannot until I get the battery charger working. Please can you assist?

Warren,

Can you report the DC voltage you measure on every pin.

Sure Raheem, please find below with USB disconnected and then connected:-

Voltage at pin 16 starts 25mV and reduces to 4mV using a multimeter, but as we know from the scope captures above, we know this is about 2.2V for the Inrush Test

Hello,

I still see the same issues with TS pin, ILIM pin and ISET pin.

ISET pin will be proportional to the charge current. With VBAT at 3.7V, ISET should be around 2.25V.

The main issues are still with TS and ILIM set to 0V. The device will not charge when that happens.

Next thing we can try is using the silicon on an EVM board. Are you able to try that? 

I will like to separate the issue between the PCB and silicon

Hi Raheem

I unfortunately do not have an EVM. I have two of my boards and two different batteries, and the issue is on both. I am concerned about the silicon, as the marking is different to the datasheet - see photo below and zoom into U1. One of my engineers used this IC on a previous project and it worked fine, so not sure why it isn't working because the layout is very similar.

Is there any way I can inject a voltage to force a charge?

Yes.

You can try forcing 0.7V on T

However, the current sourced to the ISET pin is proportional to the charge current so charging will not occur if the current source is not working.

Send me your address privately so i can ship you an EVM board

Morning Raheem'

When I force the TS pin to 0.7V it seems to work perfectly. The issue is evident on two different batteries both with NTC , so I am not sure why this is occurring.

I have sent a connection request to get your email address for my physical address.

regards

Warren

Hello Warren,

This is a good development. That means the issue is definitely TS then. WHat happens if you dont connect a thermistor and just have 10k resistor on the TS pin?

Hello Raheem

Tried a 10k between TS and gnd, but this doe not work.

Injecting 0.7V on TS still works fine.

Any ideas Raheem?

Hello Warren,

I was out of office for a few days. I think the main issue is the current source on the TS and ISET pins not functioning properly. I'll send you the EVM boards which should be there in a few days. Place the ICs on those boards and let me know if normal operation occurs.

No problem Raheem

Thanks for sending the boards - will revert ass soon as I receive them.