TLV9301: Using amplifier to implement tracking for split rail supply

John Griffith

Part Number: TLV9301
Other Parts Discussed in Thread: TLV9351, LM10, LM10QML

Hello,

I have a customer that is looking to implement ±15V rails that track each other at power up and power down from a 24V rail. I wanted to check if an inverting amplifier could be used to invert the output of the negative voltage rail to feed into the tracking pin of the positive voltage buck converter.

I am thinking that you could have a wide voltage general purpose amp that had V+ tied to +24V and V- tied to the output of the negative voltage rail. At start up the amp would see +24V (+24V and 0V) and the input of the inverting amp would be fed 0V of the output of the negative voltage supply. As the negative rail powers up the input to the op amp will track the negative rail and the output will rise from zero (gain of -1V/V). This would require the amp to handle a minimum of >39V from V+ to V- (24V - -15V) and the input pin to handle inputs down to V-. Looking online this gives me 4 options:

TLV9301
TLV9351
LM10
LM10QML (Hi Rel)

Am I missing anything? Any concerns with this design idea?

Thanks,

John

over 3 years ago

0 kai klaas69 over 3 years ago

Guru 140200 points

Hi John,

can you show a schematic?

Kai

0 John Griffith over 3 years ago in reply to kai klaas69

TI__Mastermind 21441 points

Hi Kai,

I don't have a schematic as I am still trying to understand if this will work and if select the correct devices. But this is a "block diagram" of what I am thinking:

The resistors would be equal to each other so the gain is -1V/V.

Thanks,

John

0 Ron Michallick over 3 years ago in reply to John Griffith

TI__Guru*** 142736 points

Hello John,

I rewired your op amp negative power supply so you won't need such a high voltage op amp.

If U3 can keep up with U2 power up waveform (-15V) then it could work.

0 John Griffith over 3 years ago in reply to Ron Michallick

TI__Mastermind 21441 points

Hi Ron,

Sorry, I might be missing something. But if the amp does not have a negative rail, how will it "sense" a negative voltage on the input to invert it to the output? The output of U2 will go from 0V at start up to -15V at steady state. I need the output of the amp to go from 0V to +15V. I was thinking that I need a negative voltage rail to do this...

John

0 Ron Michallick over 3 years ago in reply to John Griffith

TI__Guru*** 142736 points

John,

That is the thing that make op amps so great. The (op amp) input is not negative; it is 0V. The op amp output voltage goes positive to reach the operating point where the two input voltages (IN+, IN-) are the same.

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TLV9301: Using amplifier to implement tracking for split rail supply