BQ25792: How to measure IBAT?

Hi Carey,

When ADC enabled by REG2E bit 7 and IBAT enabled in REG15 bit 5, the ADC should be reporting IBAT.  Are the other ADC values working?

Regards,

Jeff

All the other ADC values are OK.  Here are all the registers. Do you see where my error is? Thanks.

Read Charger
00 0000000000101010/00101010 002Ah = 13000 mV Minimal System Voltage
01 0000010011101100/00000100 04ECh = 12600 mV Charge Voltage Limit
03 0000000001100100/00000000 0064h = 1000 mA Charge Current Limit
05 0000000011011100/11011100 00DCh = 22000 mV Input Voltage Limit
06 0000000010001110/00000000 008Eh = 1420 mA Input Current Limit
09 00000101 05h
0F 10100010 A2h
10 00000000 00h
11 01000000 40h
12 00000000 00h
13 01000001 41h
14 00010110 16h
16 11000000 C0h
19 0000000010001110/00000000 008Eh = 1420 mA ICO Current Limit
1B 01001111 4Fh
1C 01101010 6Ah
1D 00000001 01h
1E 01010000 50h
1F 00000000 00h
2E 10001000 88h
31 0000000000001110/00000000 000Eh = 14 mA IBUS ADC
33 0000000000000000/00000000 0000h = 0 mA IBAT ADC
35 0100000110101010/01000001 41AAh = 16810 mV VBUS ADC
37 0100000110001000/01000001 4188h = 16776 mV VAC1 ADC
39 0100000110001000/01000001 4188h = 16776 mV VAC2 ADC
3B 0011000010101001/00110000 30A9h = 12457 mV VBAT ADC
3D 0011000011001001/00110000 30C9h = 12489 mV VSYS ADC
3F 0000001001001111/00000010 024Fh = 59 % TS ADC
41 0000000000101011/00000000 002Bh = 21 deg-C TDIE ADC
43 0000000000000000/00000000 0000h = 0 mV D+ ADC
45 0000000000000000/00000000 0000h = 0 mV D- ADC
47 00000000 00h
48 00001000 08h

Hi Jeff,

Can you explain HiZ mode?

Thanks,

Carey

Also, what does Minimal System Voltage mean? Will the charger ensure the output voltage is at least that value?

Hi Jeff,

Thank you for those answers.

I'm having a very hard time getting the charger to work as I think it should. I'm using the EVM and playing with the different values and settings. When I have it "running" correctly, after a time it stops charging the battery even though the battery is running down.

Is there a written process for using the charger chip other than the description of how it works (which must be way over my head)? I think I understand all the settings but the charger is still failing to work like I think it should.

Thanks,

Carey

Thanks Jeff. I've already been using that doc but I'll give it another go.

Hi Jeff,

OK. The procedure convinced me that the EVM works. Now, how can I get specific help for my specific application?

Thanks,

Carey

Hi Carey,

Are you still having issues with the ADC reporting IBAT?

Regards,
Jeff

Well, I read your explanation and, if I understand correctly, you can't read battery discharge current except when there is no Vin input power. But, in that situation, the EVM doesn't work, so I'll just give up on that. (Quite frankly, I'm about the give up on this device.)

I still have the problem where the EVM is not charging the battery even though the input voltage is 18VDC. What check block do I need to check to get the Vin to charge the battery?

Yes, the data showing VINPM etc was taken on my application when I knew a little less than I do now.

Currently, I'm using the EVM, input Voltage is set to 18.0V, VINDPM was set using the Auto button and it's 16.1V. I'm getting only 4 mA out of the power supply at Vin. The Power supply is set for 1A current limit. The battery is discharging and no current is coming out of the power supply.

HI Carey,

REF0x0F is reporting 1s configuration but the battery voltage is close to 4S regulation point.  If the charger thinks that the cell config is for 1S but the attached battery is 4S, the charger is in battery OVP and has shut down the converter.

Regards,
Jeff

I don't see any incorrect settings.

HI Carey,

Can you send the status and fault register screen as well as the current ADC screen?

Regards,
Jeff

Hi Carey,

I don't see any thing wrong with the settings.  Is the /CE pin on the EVM shorted to ground with the shunt on JP17?

Regards,

Jeff 

Yes, JP17 is installed. I rechecked all the shunts and they match the Users Guide.

Is there a specific connection sequence I need to use to connect the battery, Vin and Load?

HI Carey,

The IC was designed expecting that the battery is installed first and is never hot plugged (i.e. battery installed while power is applied).  Even if power is applied first, the IC may reply faults but should recover once the battery is installed.  

Can you send the chip configuration page from the GUI as shown below?

  Regards,

Jeff

Hi Jeff,

I've had to take my test set apart for a couple of days (end of month & quarter shipments) but as soon as I put it back together I'll send a screen shot of the configuration screen (and the other screens since it will be a new power-up for the board).

Thanks for your help and your patience.

Carey

Hi Jeff,

Well, we discovered two of the BQ25792 were dead; one in the EVM and the other in our application. The 5V regulator in each appears to have died. We replaced the chips and they seem to be working. The question is how we killed them. Could the problem be caused by connecting and disconnecting the battery while Vin was present?

Thanks,

Hi Carey,

I would not expect that to happen but BQ25792 was designed with no expectation of battery hotplug. Are you 100% certain that you did not plug in the battery backwards because that will definitely damage the device. If there was significant ringing at hotplug of a 4S battery that is fully charged due to long, highly inductive leads, there might be a possibility of damage but I couldn't not expect it to damage REGN.  Did you happen to keep those 2 units?  If so, can you submit them as returns for failure analysis?

Regards,

Jeff  

Hi Jeff,

I don't know if we kept those parts but I'll try to find them. I'm sure I didn't reverse polarity two different setups.

Also, can you clarify for me the meaning of VINDPM. It is called Input_Voltage_Limit and described as Absolute VINDPM Threshold. Is this an upper or lower limit? What happens when this limit is reached?

Thank you,

Carey

We have the failed parts. Where do we send them?