TPSM861252: Maximum capacitive load for USB host function

Matt Nowick

Part Number: TPSM861252
Other Parts Discussed in Thread: TPSM863252

Tool/software:

The datasheet for the TPSM86125x lists the maximum load Cout as 100uF (Table 8-2). We would like to use a TPSM861252 to supply 5V for a USB host. This requires a 120uF capacitor on the 5V. The plan is to place a 20uF cap close to the power supply. Then there will be a load switch with approximately 20mohms on resistance followed by the 120uF cap. The connected USB device may add up to an additional 10uF. So the total Cout could be 150uF. Are there additional measures we should take to allow the power supply to drive higher capacitive loads? Is the TPSM861252 suitable for this application? Thanks in advance for the feedback.

19 days ago

0 Lucia Gao 19 days ago

TI__Mastermind 20340 points

Dear Sir,

Thanks for reaching out. Could you pls share me your schematic? Thanks!

BRs

Lucia

0 Matt Nowick 16 days ago in reply to Lucia Gao

Prodigy 10 points

Sorry, schematics are not ready yet. The circuit is simple, however. The question is about loop stability when the TPSM861252 drives a capacitive load, and is additional compensation needed?

0 Lucia Gao 16 days ago in reply to Matt Nowick

TI__Mastermind 20340 points

Hi Matt,

Yes, pls carefully check the loop stability based on your application. We have an app note discuss about DCAP loop stability and the effect of Cout.

Stability Analysis and Design of D-CAP2 and D-CAP3 Converter – Part 1

Thank you!

BRs

Lucia

0 Matt Nowick 5 days ago in reply to Lucia Gao

Prodigy 10 points

Thank you for the app note. Enclosed is the schematic if you can provide any specific guidance. One option would be to change the 22pF compensation cap (C145). I did add in a small series resistance (0.1ohm) before the 100uF cap to help add in more stability. This could be changed to a ferrite, inductor, or different value of resistance if needed. Is a simulation model available for the TPSM861252? I didn't see one.

0 Lucia Gao 3 days ago in reply to Matt Nowick

TI__Mastermind 20340 points

Hi Matt,

Thanks for your feedback. I will check the schematic. Thanks!

BRs

Lucia

0 Lucia Gao 3 days ago in reply to Lucia Gao

TI__Mastermind 20340 points

Hi Matt,

You can try with TPSM863252 simulation model. It's available in ti.com and can be applied to TPSM861252.

Thank you!

BRs

Lucia

Power management

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TPSM861252: Maximum capacitive load for USB host function