LM124A: Voltage drop when used as a voltage follower

jeong seungheon

Part Number: LM124A
Other Parts Discussed in Thread: ADC128S102, , OPA4991-EP, TLV2374-EP, TLV9004, , OPA4991, OPA4H199-SEP

Tool/software:

hello.
I implemented OPAMP LM124A as a voltage follower and designed to monitor each power source through ADC128S102, a SAR 12bit ADC, and deliver it to MCU via SPI communication. When I completed the actual fabrication and measured 5VD, I found that there is a voltage drop of about 1.5V from the OPAMP output to the ADC input. (3.985V, 3.834V) I am sending you an excerpt of the circuit diagram as shown below.
Do you think there is anything that could cause the voltage drop?
Also, we would like to know how we can minimize the voltage drop in the circuit design.
The PCB is designed to be 0.181mm.

I would appreciate your response.

Best Regards,

Seungheon Jeong

2 months ago

0 Clemens Ladisch 2 months ago

Guru 296680 points

The LM124A does not have rail-to-rail I/Os; it requires a 2 V headroom to the positive rail and thus does not work in some low-voltage applications.

There is no suitable replacement in the CFP package.
If you need temperatures below −40 °C, use the TLV2374-EP or OPA4991-EP. Otherwise, use the TLV9004 (the X2QFN package has the smallest height).

0 Art Kay 2 months ago

TI__Mastermind 23588 points

Jeong,

I agree with Clemens comment. Let us know if you have additional questions.

best regards, Art

0 jeong seungheon 2 months ago in reply to Clemens Ladisch

Prodigy 10 points

Thank you for your response. However, we selected LM124AQML-SP first because we need it for our satellite project, and we are using LM124AWB as a commercial grade part. Is there any alternative part or circuit change that can be done?

I need to minimize losses to monitor each power source.

And which is 0.15V instead of 1.5V. I stand corrected.

0 Clemens Ladisch 2 months ago in reply to jeong seungheon

Guru 296680 points

The space-grade variant of the OPA4991 is the OPA4H199-SEP.

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LM124A: Voltage drop when used as a voltage follower