D24V6F12 buck converter SHDN problem

Support Voltage regulators
1

We are using the D24V6F12 buck regulator and have problems with SHDN function.

Basically we are seeing that after first enable cycle (low - high - low), the SHDN does not work again until the output has fallen below ~2.5V

Its like there is a reset that needs to happen on Vout before it will “listen” to enable again.

The attached analog analyzer output shows the problem. It shows:

  1. Initial enable with VOUT reacting as expected (VOUT is scaled to 1/5 for measurement)
  2. Next enable is ignored - VOUT just keeps discharging
  3. We do a manual discharge of the output
  4. Enable works again as expected

Is this as designed? Or can it be avoided so SHDN always turns device on?

pololu
pololu1775×236 16.1 KB

2

Hi.

I tried to reproduce your issue and was not able to. Could you post more details about your setup? How are you controlling the EN pin? Is anything else connected to it? Could you post pictures of the setup that show all connections? What text is written on the 6-pin IC circled in the picture below?

reg04
reg04800×786 104 KB

-Claire

3

Hi Claire, We have large capacitors on the output, and removing them solves the problem - voltage then drops. It just seems like the device does not work if the load “keeps voltage high” after turnoff, meaning it effectively becomes a supply… I’m going to try adding a diode next…

4

Added a schottky diode between out of regulator and our supercaps that we are charging with the regulator solved the issue. Thanks, Jacob.

5

I’m glad you were able to find a solution! Thanks for letting us know.

-Claire