LM5009A as inverting output

Martin Christoffersen

Other Parts Discussed in Thread: LM5009A, TINA-TI

Hi.

I am trying to use the LM5009A for an inverting power supply. Input is 18-56V, output is 15V. Current 10 - 100mA.

When I turn on the input power, the output is -15V, for some time (1hour), after this the output voltage rises to -19V, and I am unable to regulate the output using the FB resistors.

I have tried to simulate in TINA-TI simulation program. File is attached.

6758.LM5009 as inverting output.TSC

Since the simulation does not work when GND is used as output, I have set the input voltage relative to the output, to simulate an inverting output.

The simulation does not show problems.

Is there something special about the LM5009A that should be considered when using it as a inverting supply ?

over 12 years ago

0 JohnTucker over 12 years ago

TI__Guru**** 191445 points

Can you post your schematic?

0 Vijay86929 over 12 years ago in reply to JohnTucker

TI__Genius 11490 points

Your actual hardware schematic will be useful.

0 Martin Christoffersen over 12 years ago in reply to Vijay86929

Prodigy 70 points

Hi.

Here is a printout of the schematics. I have now measured the actual current draw with an external -15V supply to 20mA.

0 JohnTucker over 12 years ago in reply to Martin Christoffersen

TI__Guru**** 191445 points

I cannot comment directly on LM5009A, but for many converters it is necessary to add 10 uF from Vin to the IC GND which is now your negative output.

0 Vijay86929 over 12 years ago in reply to JohnTucker

TI__Genius 11490 points

The circuit looks ok, other than the bypass capacitor that John mentioned. The inverting converter has switching current flow from both input and output capacitors so good layout is essential for proper operation. Can you send some waveforms (SW, IL) for normal and abnormal operaion?

Thanks and regards,

Vijay

0 Martin Christoffersen over 12 years ago in reply to Vijay86929

Prodigy 70 points

Thank you for the input. I will try to move the bypass caps to the -15VA supply instead of GND.

I will send waveforms when I have a system running again. I am currently out of stock with the LM5009A.

Best regards Martin.

0 JohnTucker over 12 years ago in reply to Martin Christoffersen

TI__Guru**** 191445 points

Don't move the bypass caps. Just add an additional cap from Vin to the minus output (IC GND).

0 Martin Christoffersen over 12 years ago in reply to Martin Christoffersen

Prodigy 70 points

It seams the converter now is stable after I have added the decoupling to the -15VA.

Thank you all for the input.

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LM5009A as inverting output