BQ25792: Device not charging

Hello Jeff,

Customer didn’t connect the SYS because thinking that it only just serves to deliver power to the system.

"Since I will not use this and power the system from the battery, where should i connect the sys pin after the capacitors rail? I don’t really follow how the SYS is vital for the charger to function?

ok so if I connect the capacitors to SYS and connect the termistors and connect the pull-up to the CE pin. The charger should work autonomously??

What about the D+ and D- pins?"

Thank you,
Archie A.

Hello Jeff,

Thank you for your guidance. This helps a lot. We still have follow up.

So I have connected the 10u capacitor to a SYS pin and i have connected the wire from CE pin straight to the ground. I have overwritten the ts ignore bit to HIGH. However, the charger still doesnt charge..

The values from status registers are:
REG1B_Charger_Status_0 (0x1B): 0b00001011
REG1C_Charger_Status_1 (0x1C): 0b00001010
REG1D_Charger_Status_2 (0x1D): 0b00000001
REG1E_Charger_Status_3 (0x1E): 0b11000000
REG1F_Charger_Status_4 (0x1F): 0b00000000

I have VBUS with PD 15V a 3A as input source and 2s lithium-ion battery connected.

Please do you have any idea whats wrong?

Regards,
Archie A.

Hi Archie,

The charge status is NOT charging which usually only occurs if /CE =/= GND or EN_Charge bit =/=1.  Can you send REG0x0F and REG0x20-0x21?    Is REGN pin providing ~5V?  What voltage does you measure at SYS pin?

Regards,

Jeff

Hello Jeff,

The REGN is providing 0V and on the SYS is 6.82V, which equals the voltage of the battery.
I am sending the values of registers below, I have added the 0F and 20-21 registers...

REG1B_Charger_Status_0 (0x1B): 0b00101011
REG1C_Charger_Status_1 (0x1C): 0b00001010
REG1D_Charger_Status_2 (0x1D): 0b00000001
REG1E_Charger_Status_3 (0x1E): 0b11000000
REG1F_Charger_Status_4 (0x1F): 0b00000000
REG20_FAULT_Status_0 (0x20): 0b00000000
REG21_FAULT_Status_1 (0x21): 0b00000000
REG0F_Charger_Control_0 (0xF): 0b10100110

Thank you.

73,
Archie A.

Hi Archie,

The charger is in HiZ mode because EN_HIZ bit =1.  It only auto sets EN_HIZ bit =1 under fault conditions like:

1. VSYS<2V when VBUS is applied - this is not your condition based on your measurement at SYS pin above.

2. Multiple inductor peak spikes >7.5A - do you have large, fast transients on SYS?  Is your inductor's ISAT spec too low for your application? ISAT needs to be at least 3.3A*1.25

Regards,

Jeff

Hello Jeff,

We are not currently able to measure transient on SYS, since we don't have oscilloscope, but will be, later this week.
ISAT of inductor should be 13.32A.

We have this inductor:

https://cz.mouser.com/ProductDetail/TDK/SPM6530T-1R0M-HZ?qs=lYGu3FyN48fb3MC9WsFhMQ%3D%3D

Thank you for your support.

73,
Archie A.

Hi Archie,

Ok.  Keep me posted.

Regards,

Jeff

Hello Jeff,

I have an update. I didn't measure any fast transients on SYS. Its straight line.

Let me know if there's needed to check.

Regards,
Archie A.

Hi Archie,

Can you try adding more capacitance at SYS?  

Regards,

Jeff

Helo Jeff,

Customer responded:

I have measured the voltage on the gate on the SHIP N mosfet and I think it doesn’t work correctly since it switches very fast. I have attached two images taken from oscilloscope.

The Yellow line is gate, Green is voltage of the battery and the purple one is a math of these two signals.

Is this how it is supposed the work?

I had a battery connected with 6.82V and 15V on VBUS.

I have this MOSFET: PXN018-30QLJ

And I also noticed the 9.2V spike on the inductor when I connect the VBUS in.

I didn’t connect any more capacitors to SYS.
And I also don’t have the SYS pin connected to a system load, since i don’t want to use it.

Regards,
Archie A.

Hi Archie,

In battery only mode, the 10Mohm scope probe loads the SDRV pin, which runs at 50% duty, so the above waveform is expected.  Since you are applying VBUS and still see this, then there is a problem.  You can use a DMM set to 10Gohm impedance to measure the dc voltage of SDRV in any mode.  Can you remove all power from the charger and measure the resistance from SDRV pin to ground?

Regards,

Jeff

Hi Archie,

Also, can you measure the resistance to ground on SWx, SYS, PMID, VBUS and BAT?  I think one of the power pins has a short to GND.

Regards,

Jeff

Hello Jeff,

Thank you.

You are right. I can't measure resistance on PMID and SDRV. On VBUS, SYS, SWx and BAT I measure pretty high resistance.
So I have a short on PMID and SDRV?

Regards,
Archie A.

HI Archie,

SDRV to GND should be really high resistance (>10Mohm). PMID to GND should be moderately high (>10kohm)

Regards,

Jeff