LM2904-Q1: LM2904-Q1 Vcm

guozhu Lyu

Prodigy 100 points

Part Number: LM2904-Q1
Other Parts Discussed in Thread: LM2904LV, TLV9151-Q1

How to caculate the Vcm, in dual and single power supply cases?

What will happen if the Vcm over spec and why?

9 months ago

0 Clemens Ladisch 9 months ago

Guru 261240 points

The guaranteed minimum upper limit of the input common-mode voltage range always is 2 V below the positive supply rail.

When the input voltage goes higher, the electrical characteristics will degrade, or the amplifier no longer work correctly. See section 2.2 of the Application Design Guidelines for LM324 and LM358 Devices.

0 guozhu Lyu 9 months ago in reply to Clemens Ladisch

Prodigy 100 points

In below application, if V+=5V, V-=0, what the Vcm is?

And , is any risk to damage the OP?

0 Jerry Madalvanos 9 months ago in reply to guozhu Lyu

TI__Mastermind 25391 points

Hey Guozhu,

Is this a low or high side current sense?

Additionally, if you are looking at using a 5V supply, LM2904LV is created specifically for low-voltage (5.5V supply and below). It still has a similar common-mode limitation, but is resilient to phase reversal.

Best,
Jerry

0 guozhu Lyu 9 months ago in reply to Jerry Madalvanos

Prodigy 100 points

hello, Jerry;

Yes, it is a high side current sense circuit.

In our design, the power supply of the OP is range from 5 to 6.5V, so maybe LM2904LV is not the suitable one. And it has Vcm limitation too.

The phase reversal here means if the inputs below the Vcm limitation, the outoup will react VOH or VOL correctly, but if it's higher than the Vcm limitation, the output will reverse?

if LM2904BQPWRQ1 input higher than the Vcm, what will happen? and it will damage the OP or not?

0 Clemens Ladisch 9 months ago in reply to guozhu Lyu

Guru 261240 points

Phase reversal is a specific error mode that happens only for negative inputs. But when the inputs are above 3 V (for a 5 V supply), the amplifier will just not work correctly. (This does not damage it.)

To handle larger input voltages, you need an amplifer whose Vcm includes the positive rail, or with rail-to-rail inputs, like the TLV9151-Q1.

0 guozhu Lyu 9 months ago in reply to Clemens Ladisch

Prodigy 100 points

Got it, thanks.

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LM2904-Q1: LM2904-Q1 Vcm