Cannot shut down LP2951 with microcontroller

Dat Chau

Other Parts Discussed in Thread: LP2951

Hi,

I am using the 3.3V version of LP2951. The input is 4.5V and the Shutdown pin is connected to a microcontroller, which runs off of a different 3.3V supply. When I switch the Shutdown pin to HIGH, the LP2951 output goes from 3.3V to 1.9V. It's supposed to be zero!

I replaced it with another LP2951 - same result. I then connected the Shutdown pin directly to the input 4.5V and that did shut it down. The Shutdown pin input is supposed to be logic compatible, so what's going on? Has anyone seen this before?

I've been using this chip in almost 200,000 devices, but always tied the Shutdown pin to the input. Appreciate any light you can shed on this.

over 12 years ago

0 Donald Jones over 12 years ago

TI__Mastermind 22610 points

Having the full LP2951 part number may be helpful.

LP2951 Shutdown (OFF) threshold is 2V. Being a bipolar design, the SHUTDOWN pin will typically draw 30uA to 50uA at the 2V level

When you switch the Shutdown pin to HIGH, what is the voltage measured at the Shutdown pin?

0 Dat Chau over 12 years ago in reply to Donald Jones

Prodigy 20 points

Thanks, Donald, for your reply!

The exact part number is LP2951-33DR. The voltage at the Shutdown pin when the uC switch to HIGH is 3.3V. The IO pin on the uC can source 20mA. I can turn it off if I tie the Shutdown pin directly to Input pin at 4.5V. I'm scratching my head...

0 Donald Jones over 12 years ago in reply to Dat Chau

TI__Mastermind 22610 points

I'm scratching my head as well.

Typical Shutdown threshold should be in the vicinity of 1.2V to 1.3V.

Power management

Power management forum

Cannot shut down LP2951 with microcontroller