Author Topic: AD8099 Power Supply Confusion  (Read 317 times)

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Offline MuriTheMythTopic starter

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AD8099 Power Supply Confusion
« on: May 22, 2024, 07:08:26 am »
Hello folks, I hope you are well!

I'm kinda confused by the statement of AD8099 datasheet. I'm planning to use ±5V supply, does the current values stated refers to current for each rail or combined?

Also, should I design the -5V rail against the "short circuit current" or "quiescent current"? AD8099 is the only one drawing -5V and the output is fed into two TLV3601 comparators.

Thanks for your time! I've included a clip of referenced datasheet in attachment.

Sincerely,
Muri
 

Offline mikerj

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Re: AD8099 Power Supply Confusion
« Reply #1 on: May 22, 2024, 07:34:40 am »
Hello folks, I hope you are well!

I'm kinda confused by the statement of AD8099 datasheet. I'm planning to use ±5V supply, does the current values stated refers to current for each rail or combined?

The quiescent current of an op-amp flows (conventionaly) from the +Vs to the -Vs pin.  Remember that an op-amp has no "knowledge" that it is connected to a split rail supply, it just sees a potential difference from +Vs to -Vs, so from a quiescent current point of view +-5v rails are the same as a 10v single rail.

Also, should I design the -5V rail against the "short circuit current" or "quiescent current"? AD8099 is the only one drawing -5V and the output is fed into two TLV3601 comparators.

Neither.  Short circuit current is an abnormal operating condition i.e. something has already gone wrong at that point.  If your -ve rail can't provide enough current to drive the rated short circuit current then it's not going to make anything worse, in fact it will reduce power dissipation in the op-amp.  Under normal operation you can expect some current to be going in or out of the op-amp output pin, depending on its load, and if the op-amp is amplifying an high frequency AC signal it's internal power consumption will also increase.  You design your supply rails to deliver the total current that the op-amp requires under normal working conditions plus some margin  (100% or more wouldn't be unreasonable for very low current rails).
 
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Offline aliarifat794

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Re: AD8099 Power Supply Confusion
« Reply #2 on: May 22, 2024, 11:01:46 am »
Design your -5V rail to handle the quiescent current primarily but also consider short circuit conditions for robustness.
Your -5V supply should have a margin above the quiescent current requirement and include protections for short-circuit conditions.
 
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Offline MuriTheMythTopic starter

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Re: AD8099 Power Supply Confusion
« Reply #3 on: May 22, 2024, 08:22:01 pm »
I'm wondering if this combination will work for the negative rail of AD8099. I already have a +6V rail to power drivers and LDOs on the board.

Thanks a lot guys for your advice!
 


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