BQ24725A: never starts charging sequence

Hey Olivier,

Can you take the following scope capture?

With the cells unconnected:

Ch.1 - VCC pin voltage, trigger on the rising edge of this channel, offset by 15V and scale to 1V/div

Ch.2 - SRN pin voltage, with same scale and offset and reference point as Ch.1 (this will let us see the differential voltage between VCC and SRN)

Ch.3 - Input current

Ch.4 - ACDRV

With the cell connected:

Same setup from above. Take a second waveform replacing Ch.4 showing the battery current.

Regards,

Joel H

Hi, Joel 

Here are some scope captures for you to help identify the problem 

Pic1 loaded 15 ohm
CH1 VCC
CH2 SRN
CH3 Current input R19
CH4 Current input R19

Pic2 Loaded 15 ohm
CH1 VCC
CH2 ACDRV
CH3 Current input R19
CH4 Current input R19

Pic3 unloaded
CH1 VCC
CH2 SRN
CH3 Current input R19
CH4 Current input R19

Pic4 unloaded
CH1 VCC
CH2 ACDRV
CH3 Current input R19
CH4 Current input R19

Pic5 unloaded with Batteries
CH1 VCC
CH2 SRN
CH3 Current input R19
CH4 Current input R19

Pic6 Loaded 15 ohm with Batteries
CH1 VCC
CH2 SRN
CH3 Current input R19
CH4 Current input R19

Pic7 unloaded with Batteries
CH1 VCC
CH2 ACDRV
CH3 Current input R19
CH4 Current input R19

Pic8 Loaded 15 ohm with Batteries
CH1 VCC
CH2 ACDRV
CH3 Current input R19
CH4 Current input R19

Pic9 unloaded with Batteries
CH1 VCC
CH2 ACDRV
CH3 Current Battery R27
CH4 Current Battery R27

Pic10 Loaded 15 ohm with Batteries
CH1 VCC
CH2 ACDRV
CH3 Current Battery R27
CH4 Current Battery R27

Thank you for your help 

Olivier

I need to review these waveforms Olivier, 

But just to confirm, I see the input current channels are measured in Volts, instead of Amps. Can you verify the scale and unit of measure?

Regards,

Joel H

We don't have a current probe on our scope so we took the voltage on each sides of R19 for the input current and R27 for the charge/battery

As for the actual 19V Source, the current was set to 1Amp but never produced more than 0.01Amp when it was connected

Thanks

Olivier

Hi Joel here the results we have 

Here are the same 10 graphs from the previous post without C17 and C18

Pic1 loaded 15 ohm
CH1 VCC
CH2 SRN
CH3 Current input R19
CH4 Current input R19

Pic2 Loaded 15 ohm
CH1 VCC
CH2 ACDRV
CH3 Current input R19
CH4 Current input R19

Pic3 unloaded
CH1 VCC
CH2 SRN
CH3 Current input R19
CH4 Current input R19

Pic4 unloaded
CH1 VCC
CH2 ACDRV
CH3 Current input R19
CH4 Current input R19

Pic5 unloaded with Batteries
CH1 VCC
CH2 SRN
CH3 Current input R19
CH4 Current input R19

Pic6 Loaded 15 ohm with Batteries
CH1 VCC
CH2 SRN
CH3 Current input R19
CH4 Current input R19

Pic7 unloaded with Batteries
CH1 VCC
CH2 ACDRV
CH3 Current input R19
CH4 Current input R19

Pic8 Loaded 15 ohm with Batteries
CH1 VCC
CH2 ACDRV
CH3 Current input R19
CH4 Current input R19

Pic9 unloaded with Batteries
CH1 VCC
CH2 ACDRV
CH3 Current Battery R27
CH4 Current Battery R27

Pic10 Loaded 15 ohm with Batteries
CH1 VCC
CH2 ACDRV
CH3 Current Battery R27
CH4 Current Battery R27

We then did the test by changing C16 to 1uF because we didn't have a 0.47uF in hand 

Pic1 loaded 15 ohm
CH1 VCC
CH2 SRN
CH3 Current input R19
CH4 Current input R19

Pic2 Loaded 15 ohm
CH1 VCC
CH2 ACDRV
CH3 Current input R19
CH4 Current input R19

Pic3 unloaded
CH1 VCC
CH2 SRN
CH3 Current input R19
CH4 Current input R19

Pic4 unloaded
CH1 VCC
CH2 ACDRV
CH3 Current input R19
CH4 Current input R19

Pic5 unloaded with Batteries
CH1 VCC
CH2 SRN
CH3 Current input R19
CH4 Current input R19

Pic6 Loaded 15 ohm with Batteries
CH1 VCC
CH2 SRN
CH3 Current input R19
CH4 Current input R19

Pic7 unloaded with Batteries
CH1 VCC
CH2 ACDRV
CH3 Current input R19
CH4 Current input R19

Pic8 Loaded 15 ohm with Batteries
CH1 VCC
CH2 ACDRV
CH3 Current input R19
CH4 Current input R19

Pic9 unloaded with Batteries
CH1 VCC
CH2 ACDRV
CH3 Current Battery R27
CH4 Current Battery R27

Pic10 Loaded 15 ohm with Batteries
CH1 VCC
CH2 ACDRV
CH3 Current Battery R27
CH4 Current Battery R27

We concluded the higher value at C16 was not helping the circuit and ACDRV was not able to drive with the 1uF cap 

We also did a bit more searching on our own and we noticed something strange behavior at HIDRIVE 

Once the input is turned on, the ACDRV works properly and the BATDRIVE goes down to let the Charger take control, but after 1-2 seconds the ACDRV goes back down 

We probed the HIGH and LOW drive to see and theses are the results

CH1  VDD

CH2 ACDRV

CH3 HIDRV

CH4 LODRV

We are not sure if this is normal and we can see that ACDRV starts to drop. We can`t see it in the picture but it drops to zero right after.

We think the behavior we are seeing throughout theses tests is the 8.4.18 Inductor Short, MOSFET Short Protection because it describes exactly the response from the IC

Hope all this informations is helpful

Thanks 

Olivier 

Hey Olivier,

I was looking at the first set of waveforms and I am noticing that the VCC voltage seems to droop about 1V or so (5V/div scale), which means that VIN is also drooping with the same magnitude.

You also mentioned you are using 19V input with 1A current limit. However, your load on pictures 3/4 and 6/8 are with a 15-Ohm load, which means the input current would be roughly 1.3A of peak current. Even though the DC current you saw was only 0.01A, you like did not see the peak current. It is very difficult to measure using the R19 capture you have taken because the differential voltage we are looking for between CH.3 and CH.4 is on the order of 10mV, and we are seeing a 5V/div scale.

We can try several things:

1) Confirm that the unloaded cases starts up. From pictures 1/2 and 5/7 of the original set of waveforms, you mention the system is unloaded, yet I still see the same characteristic glitch on VCC, which would assume the voltage is still drooping, perhaps from inrush current.

2) Increase the input power rating, both voltage and current. So use something like 20V w/3A current limit.

3) Either depopulate R28 (66.5kOhm) or increase its value to the same as R24 (430kOhm).

From the second set of waveforms, it seems that either removing the delay elements make the issue worse with an increased current spike, and increase the 0.1uF delay element by 10x slows the response too much which may trigger some other logic. 

I cannot explain the HIDRV waveform yet, but let's take a look at my actions for (1), (2), and (3) above. I would also suggest capturing the ACDET voltage (instead of the input or battery currents as they are not providing too much information right now). If you capture the ACDET voltage, please put a 2.4V offset, and set to 100-200mV/div vertical scale to capture any dip on ACDET. 

Regards,

Joel H

We didn't have to time to look into it recently but we are planning on investigating on the 2019/11/20.

We should be able to give you an update by the end of that day.

Olivier 

We tried to increased the current and voltage to 20V/3A and nothing seemed to change from the charging perspective.

With our unloaded setup this is what we see,

We also checked the ACDET and without the modification mentioned at step 3  here are the results 

After theses tests we don't think it is related to ACDET or the inrush current because the ACOK is acting correctly and no drop was seen on ACDET.

We also tried to change the resistance at the ACDET to a 430kOhm, we don't understand why because the datasheet specifies that When the ACDET pin voltage is higher than 3.15V, it is considered as adapter over voltage. ACOK will be pulled low, and charge will be disabled. ACFET will be turned off to disconnect the high voltage adapter to system during ACOVP. BATFET will be turned on if turns on conditions are valid. See the System Power Selection section for details. We did try it and as expected the voltage at ACDET was around 9V and ACOK went down. 

Thank you for your help