PTH08T250W Prebias Startup Capability

Xuezhuan

Other Parts Discussed in Thread: PTH08T250W, PTH08T220W

Hi Expert,

In our design, 1.8V back feed to 3.3V, 1.8V is PTH08T220(12V to 1.8V), 3.3V is PTH08T250W(12V to 3.3V).

PTH08T250W datasheet describe the feature of Prebias Startup Capability at page31, I'm not sure if my understand is right: we can use this method to protect the POLA DC/DC

(1) disable Track function

(2) Input voltage must always be greater than output AND the backfeed voltage. In our design, 12V>3.3V&1.8V.

Should above two items be met at the same? Are our power design safte?

over 12 years ago

0 Tom Guerin over 12 years ago

TI__Mastermind 38230 points

Xuezhuan:

The prebias start-up with 1.8V(PTH08T220W) active prior to the 3..3V (PTH08T250W)actively enabled will function as you described.

The PTH08T250W 3.3V must be controlled by the open drain FET on its inhibit pin for prebias to function correctly.The autotrack pin must be disabled by direct connection to Vin for prebias to function correctly.

I attached a recommended delay circuit (about 20ms)which will assure 3.3V is functional with 1.8V prebias .

Tom

2013 PTH08T250withSVS TPS3808 G18.pdf

0 Xuezhuan over 12 years ago in reply to Tom Guerin

Prodigy 100 points

On our design the inhibit and track pins are controlled as you said, thank you, Tom.

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PTH08T250W Prebias Startup Capability