TPS25751: Charging and switch off not working after migrating from TPS25750

Bart,

Do you mean audibly noisy?

Can you share the old json used with the TPS25750 and the new json used with the TPS25751. There may be a difference there that will help us determine what has changed.

I'm also assigning this thread to the BQ25792 team so they can help narrow down why the inductor may be noisy.

Thanks and Regards,

Chris

Hi Bart,

I don't see any issues on the BQ schematic.  How are you placing the BQ device in ship mode?  Using the I2C pass through write of the TPS25751?  

Regarding the audible noise, it is likely the capacitors near the inductor that are noisy.  Ceramic capacitors have piezoelectric effect that makes them move with voltage ripple.  There are a few conditions where this can occur even with PFM OutOfAudio enabled:

1. Just before entering buck-boost with VBUS very close to VBAT voltage

2. transition between PFM to DCM to CCM at ISYS+IBAT~=250mA.  This can be prevented by disabling PFM.

Can you capture VBUS, VSYS, SW1 and VBAT on an oscope?  And/or do register dump of the status and fault registers, REG0x1B through REG0x27?

Regards,

Jeff

yes, audibly noisy.

Here are the json's from both eeprom configs

configs.zip

Yes, I use the I2C pass through to write to the BQ. I'll try to capture the registers and scope pictures

Christopher Lim1 , Jeff F  

Due to summer holiday I will be 3 weeks offline. Please let me know if you find something. I'll try it after my holiday.

Hi Christopher Lim1 ,

Do you have an update about this question?

Hi,

Jeff F said:

Can you capture VBUS, VSYS, SW1 and VBAT on an oscope?  And/or do register dump of the status and fault registers, REG0x1B through REG0x27?

Do you have these waveforms?

Best,
Michael

Yellow = Vbus, Pink = Vsys, Blue = SW1, Green = Vbat

Hi,

Can you zoom out to a wider time scale? The audible frequency range is <25 kHz. Also, I cannot see the typical switching action of the device. An additional time scale of the switching frequency would be helpful too.

Jeff F said:

1. Just before entering buck-boost with VBUS very close to VBAT voltage

Also, you might be running into this issue here.

Best,
Michael

the noise is solved, I think it was a bad soldering. When I connect the USB charger I can see the charger draws a current from the USB (0,5A for a battery which is 75% charged).

But I still cannot switch off Vsys. I enable the shipping fet during startup in the same way as I do with the TPS25750 (write 0x96 to REG14_Charger_Control_5 of the BQ25792). When I press the power button on my device, QON_N and a GPIO pin of my MCU is connected to GND. When the MCU detects this for 3 seconds, I send an 'enter shipping mode' command to the BQ25792 (write 0x44 to REG11_Charger_Control_2). On an old device with the TPS25750, this causes that Vsys is switched off after a couple of seconds. On my new device with the TPS25751, Vsys is not switched off

Hi Bart,

It is good to hear that the noise is gone. I have a couple of questions to debug the ship mode issue:

• Does reading back the registers reflect what you have written?
• How does the SDRV signal respond when you put the device in ship mode?
• Is there a load on your system that would pull down the voltage from the capacitors when entering ship mode?

Best regards,
Michael