LM2611: LM2611- negative power supply regulator design

Aakash Dey

Part Number: LM2611
Other Parts Discussed in Thread: LM5157

Hi,

One of our MCU module need 12V and -5V for its operation. We are providing 12V to the MCU module from external Power Supply (SMPS). For -5V power supply, we are using LM2611 whose input is the 12V (SMPS supply). Below is the schematic for LM2611 for your reference.

While we are switching on the power supply (SMPS), we found that the MCU module is powering up by-5V first and then it is getting the 12V (delay of 3.7mS). Below is the graph for your reference. Here, Blue line is 12V voltage rail of the MCU module and red line is the -5V rail of the MCU module.

Can you please suggest some methods/modification in the schematic so that the MCU module get 12V and -5V at the same time interval.

Thanks.

over 2 years ago

0 Harry Hofner over 2 years ago

TI__Mastermind 19715 points

Hello Aakash,

Thanks for reaching out tu us via e2e.

It is not possible to slow down the ramp of the output voltage of the LM2611.
But you can use the Shutdown (SHDN) pin of the LM2611 to keep it disabled at the beginning and turn it on at a later time (when the supply reaches 12V).
SHDN below 0.5V means "OFF", SHDN between 1.5V and input voltage means "ON".
You may experiment with an external RC network or maybe with a Zener diode which would subtract 10V from the 12V supply, so that the SHDN pin will exceed 1.5V when the supply reaches 11.5V.

Best regards
Harry

0 Aakash Dey over 1 year ago in reply to Harry Hofner

Intellectual 300 points

Hi Harry,

Thanks for your feedback. As suggested, I have tried to provide the delay using RC network. But, I am facing some issue with the delay circuit. I have posted the same in the below forum link.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1304811/lm2611-lm2611-delay-in-start-up-via-shut-down-pin-using-rc-network

Could you please help me to resolve the issue.

0 Niklas Schwarz over 1 year ago in reply to Aakash Dey

TI__Mastermind 31850 points

Hi Aakash,

Harry and me are in the same team, so we are both able to see the two thread.
Thanks for opening the new thread and also thanks for addressing this thread again, so I have additional background on the application.

If both rails need to start up simultaneously, another approach would be using a flyback topology with two output rails.
This way both 12V and -5V rail are guaranteed to ramp up at the same time.
A suitable component for this would be LM5157.

As you already progressed with the current design, we can also work on debugging the delay on LM2611.
For this, feel free to post your update over in the other thread.

Thanks and best regards,
Niklas

0 Aakash Dey over 1 year ago in reply to Niklas Schwarz

Intellectual 300 points

Hi Harry and Niklas,

Thanks for your suggestions. As of now, I would like to work on LM2611 testing. I will update you on the test results on the another thread.

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LM2611: LM2611- negative power supply regulator design