TPS799: schematic check

Brian Antheunisse

Expert 5195 points

Part Number: TPS799

Hi guys,

Can you review my customer's schematic real quick?

Thanks,

Brian

over 6 years ago

0 Jason Song over 6 years ago

TI__Mastermind 23361 points

Hi Brian,

I have checked the input, output cap and the values for the resistor dividers and they are okay. Can you help me to understand what they are trying to achieve with F18, D81, C211 and L24? What is F18?

Regards,
Jason Song

0 Brian Antheunisse over 5 years ago in reply to Jason Song

TI__Expert 5195 points

the purpose of these components is to protect the LDO supply and reduce EMC since this node is on a connector that powers external devices. F18 is a PTC, BelFuse 0ZCJ0035AF2E to protect against short circuits or an accidental connection to a different potential, such as 12V.

0 Jason Song over 5 years ago in reply to Brian Antheunisse

TI__Mastermind 23361 points

Hi Brian,

The D81 is a transient suppressor for overshot voltage on Vout. Like I mentioned in my previous post, the LDO portion is good. The added protection circuit seems to make sense as well but I am not very family with their application requirement. Just looking at the schematic, the circuitry they have there should work.

Regards,
Jason Song

0 kai klaas69 over 5 years ago in reply to Brian Antheunisse

Guru 140200 points

Hi Brian,

you should probably add a protection diode form output of regulator to its input.

I find C211 and L24 not very useful. C211 is unusually small. If the purpose of C211 is to protect the fuse against ESD, you should take 100n.

Kai

0 Jason Song over 5 years ago in reply to kai klaas69

TI__Mastermind 23361 points

Hi Brian,

If you see the voltage ringing due to the added inductor has the risk to bring Vout higher than Vin+0.3, you can consider adding a forward biased diode from Vout to Vin of the regulator to protect the device from reverse current like Kai suggested.

Regards,
Jason Song

0 Brian Antheunisse over 5 years ago in reply to Jason Song

TI__Expert 5195 points

Jason,

They would like to implement the diode.

Would RB521S30T1G be a good choice?

Thanks,

Brian

0 Jason Song over 5 years ago in reply to Brian Antheunisse

TI__Mastermind 23361 points

Hi Brian,

RB521S30T1G has a turn on voltage of 0.5V and forward biased DC current of 200mA. Ideally you would want to have a turn on voltage less than 0.3V because the absolutely max for Vout is Vin+0.3V.

Regards,
Jason Song

Power management

Power management forum

TPS799: schematic check