LP2985A: Pin funciton of LP2985A-50DBVR

Jimmy WANG

Genius 3205 points

Part Number: LP2985A

Hi team,

My customer used to LT1761ES5-5. I suggest LP2985A for the test. But the Bypass pin is different from LT1761ES5-5.

LT1761 has Cap pull to Vo. but LP2985A cap pull to GND.

So does TI have the same function device? or just suggest removing the cap? thanks

over 1 year ago

0 Kyle Van Renterghem over 1 year ago

TI__Genius 13345 points

Hi Jimmy,

Yes if LP2985A can be used in existing LT1761 applications by removing the Bypass capacitor.

Often times to Noise Reduction pins used to decrease noise and increase low frequency PSRR require a capacitor from the pin to GND like the LP2985A. Looking at the schematic and the PSRR/Trainsient plots of the LT1761, it appears that their BYPASS pin is what is often referred to as a feedforward capacitor in more modern LDOs.

You can see our app note on the Pros and Cons of Feedforward Capacitors with Linear Regulators for more information.

0 Jimmy WANG over 1 year ago in reply to Kyle Van Renterghem

Genius 3205 points

Hi Kyle.

Yes. I know feedforward cap function. But now different with ADI solution.

Hard to talk customers into removing the cap.

0 Kyle Van Renterghem over 1 year ago in reply to Jimmy WANG

TI__Genius 13345 points

Hey Jimmy,

I'm traveling so I'm not able to check if there is any drop in replacements. The chances are not good since this is a non-standard pinout but I'm going to have the team look into it in more detail and follow up.

0 Aaron Paxton over 1 year ago in reply to Kyle Van Renterghem

TI__Expert 5145 points

Hey Jimmy,

How about TPS7A2450DBVR? The input voltage is a little lower than LT1761 (16V vs. 20V) but pin 4 is an NC instead of a BYP pin. Connection a capacitor between OUT and NC will not adversely affect performance. Let me know if you have any questions.

~ Aaron

Power management

Power management forum

LP2985A: Pin funciton of LP2985A-50DBVR