BQ25750: STAT1 is on, but no switching

rick ash

Part Number: BQ25750

Tool/software:

Hello,

I am trying to build a stand alone (no I2C) charger only (no back regulation to system). I have shorted ACN and ACP together and tied to VAC, as I do not need current limit on the input. SYS is also tied to VAC and they are tied to 19V input voltage. The full battery is 58V. Currently the battery is at 50V. When I power up STAT1 goes on, which means it is charging, but there is no switching action. I checked and REGN has 5V, both low-side FETs are on and boost cap has zero volt on it. I suspect SYS pin should perhaps be tied to the battery top, but not sure and can't find the information in the datasheet. The FB measures around 1.3V, which is less than the 1.536V, so it should try and provide charge, but nothing is happening. Please let me know what might be causing this. Thanks

1 month ago

0 Ethan Galloway 1 month ago

TI__Mastermind 30785 points

Hello Rick,

Can you send me a clearer image of your schematic? I'm having trouble reading the schematic.

Do you have the BATFETs installed in the circuit?

Also, we have an FAQ on the BQ25750 power path that may help. We also have a general FAQ as well.

Best Regards,
Ethan Galloway

0 rick ash 1 month ago in reply to Ethan Galloway

Prodigy 60 points

bq25750.pdfHi Ethan, I replied to your email, but to be sure, here is the schematic again. Hope we can reach a resolutions soon. Thanks

0 rick ash 1 month ago in reply to rick ash

Prodigy 60 points

Hi Ethan,

Update to this issue, realized that the boost diodes are not integrated in the device and were missing. Added the boost diodes and it is now switching. The new issue is that it seems to be working open-loop and is not regulating. On power up, we reach ~63V on the battery, where the regulation should be around 58V. I have verified the feedback resistors and they are correct. Please share your thoughts. Thanks

0 Ethan Galloway 1 month ago in reply to rick ash

TI__Mastermind 30785 points

Hello Rick,

Thanks for the new information. I don't I've received an email from you. I'm not sure what you mean by this.

I'm looking at your schematic and I think you need more capacitance. We recommend at least 80µF on the input and the output of the converter. Also, the SRN and SRP resistors should be 10Ω.

Also, have you checked the schematic against the schematic and layout checklist? We also have a general FAQ page that may help.

Best Regards,
Ethan Galloway

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BQ25750: STAT1 is on, but no switching