BQ24125: Power-path management system not selecting the right source

Hi Jeff. 

I just changed Q3(Q11 in my board) by a new transistor. And rechecked its pinout and the board layout which is correct. The circuit is still not working. 

Take a look. 

Thank you.

Ubiratan

HI Ubiratan,

Can you use an oscilloscope to show me VIN, /PG, Q3gate and SYS when you attach VIN and then when you remove VIN?

Regards,

Jeff

Hi Jeff, please find below the requested waveforms. I am using a 12V pull-up connected to PG/. Originally I had a 3.3Vcc pull-up tied to PG/.

Waveforms for power on

1) Vin x PG/

2) Vin x Q3gate

3) Vin x Vsys

Waveforms for power off

1) Vin x PG/

2) Vin x Q3gate

x

3) Vin x Vsys

Thank you.

UBiratan

Hi Jeff, I also tested with PG/ tied to a 3v3 pull-up.

1) Vin x PG/ (power supply disconnected. Only batteries connected) Here we can see that the batteries voltage is present at the Vin pin.

2) Vin x Q3gate (power supply disconnected. Only batteries connected)

3) Vin x Vsys (power supply disconnected. Only batteries connected)

Waveforms for power on

1) Vin x PG/

2) Vin x Q3gate

For waveforms Vin x Vsys no clear transition was noticed, only a change in DC level. Considering this I saved one waveform before connecting power supply and one waveform after.

3) Vin x Vsys (before connecting power supply)

4) Vin x Vsys (after connecting power supply)

Waveforms for power off

No transition was noticed when disconnecting power supply.

Thank you.

Ubiratan

Hi Jeff, I removed the pull-up resistor and cut the track that was connecting that to the uC but it is still not working. 

I saved new waveforms. See.

Waveforms for power on

1) Vin x PG/ 

2) Vin x Q3gate

3) Vin x Vsys

Waveforms for power off

4) Vin x PG/ 

5) Vin x Q3gate

6) Vin x Vsys

After noticing PG/ pin if going on and off periodically I noticed that STAT1 is doing the same.

7) PG/ x STAT1

8) STAT1 x STAT2

When the power supply is feeding Vin a current is still flowing through battery with no control by BQ24125 and is only limited by my bench power supply current limit. 

Thank you.

Ubiratan

Hi Ubiratan,

Something is wrong.  The green pulses are lower now.  What is connected to /PG pin that is off the screen?  Did you remove the 4.7kohm resistor on /PG and connect a wire to the gate of Q4?  

Regards,

Jeff

Jeff,

I removed the R24 resistor and cut the copper track that was connecting this signal to the uC pin. 

Thank you.

Ubiratan

Hi Ubiratan,

Now that I see the whole schematic, you only needed to remove the 4.7kohm resistor.  No sure what is dragging down the pull up voltage as it should be VIN.  

Regards,

Jeff

Jeff,

If I remove the batteries and connect the power supply, STAT1 is always HIGH (OFF) and PG/ still goes ON and OFF. 

Before soldering Q9, Q10, Q11 and Q12 the charging process was working correctly.

Thanks.

Ubiratan

HI Ubiratan,

Where do you see the circuit below?

I have supported this part for a while and never had a customer use this.  The issue I see is that when /PG goes high, Q3 must turn off before Q1 and Q2 turn on.  Simply having 10kohm pull up for Q1 and Q2 and 20kohm pull up for Q3 likely will not ensure that happens. 

STAT1 high makes sense if there is no battery present.

/PG on and off is odd.  Do you have a way to measure current?

Regards,

Jeff

Hi Jeff. Yes I can measure current. 

What do you suggest to measure ?

Thanks.

Ubiratan

Hi Ubiratan,

Can you measure VIN, IIN, /PG and Q11 gate, triggered at VIN plug in?

Regards,

Jeff

Hi Jeff, I can only measure current using a multimeter. Do you need to see the IIN waveform, right ?

Hi Jeff, I performed some other tests. 

First I removed Q9 and soldered a jumper to connect its drain and source pads. 

After that I measured some voltages and currents with power supply OFF and ON.                           

Please note that VgQ10 presents some high pulses like PG/ pin in the previous waveforms. 

Thank you.

Ubiratan

HI Jeff.

I just replaced Q1, Q2 and Q3 and BQ for fresh parts. Now the PG/ pin is not going ON and OFF and when the power supply is disconnected the voltage at Vin = 0V. 

The problem that still persists is that when I connect the power supply a current flows through the battery without BQ control.

Thanks.

Ubiratan