LMP8480: Consultation of output range and other related specs

Hello Adrian,

Adrian Liu said:

1. The LMP8480 device is powered by 5V. Under normal conditions, Vadc is less than 5V. However, in some cases, an increase in current can cause the differential input I*Rsense*60 of the LMP8480 to exceed 5V. In this situation, will the output of Vadc be clamped at 5V max? Will there be overvoltage stress on the IN+/- pins? If so, how can this problem be resolved?

I will answer your question about output clamping at #3, below. The differential input ratings of the LMP8480 are ±85V as defined in the Absolute Maximum Ratings below:

So I would not expect any trouble from 5V across the input terminals.

Adrian Liu said:

2. The figure below shows the range of Vsense when VCC=16V. Will the range be the same when VCC=5V?

No, V_{SENSE (Max)} is simply the useful range of the amplifier before the output is clamped to the maximum output voltage for the value of VCC. In your case the maximum useful input range will be closer to 80mV.

Adrian Liu said:

3. The figure below shows the margin between Vout and VCC when VCC=4.5V and Vrsp=48V. Will the parameters be the same when VCC=5V?

Yes, the parameters are approximately the same irregardless of VCC level. please see section 8.3.10, Maximum Output Voltage, for more information:

Let me know if you have any more questions,

Levi DeVries

Adrian,

Adrian Liu said:

When the VRSP – VRSN > 80mV, the LMP8480's output will clamp at 5V, and won't damage the chip, right?

Technically the device is within the absolute maximum ratings for voltage under these conditions, however you must keep in mind that noise and transient signals can also create temporary voltage spikes on the pins that you must account for when designing this close to the absolute maximum ratings. Keep in mind that the voltages on the input pins with respect to the ground pin must also remain within -0.3-85V, so there are two different limits you will need to be careful of.

You should also keep in mind that the device is not guaranteed to operate normally in this region, the device is only guaranteed to survive. You must abide by the recommended operating conditions (below) for the values listed in the Electrical Characteristics to apply.

Adrian Liu said:

the LMP8480's output will clamp at 5V,

I wouldn't expect the output to exceed the supply voltage, but because you will be exceeding the recommended operating conditions, the output characteristics may exhibit unexpected behavior.

If you expect to exceed the recommended operating conditions or saturate the device, you should also keep in mind that the device will need to wait a recovery time before the device will operate normally again. For the LMP8480, the recovery time is 50µs from saturation, and the recovery time may be even longer if you exceed the recommended operating conditions.

Let me know if you have any more questions,

Levi DeVries

Adrian,

I'm sorry, I misread your question, I thought you had asked about 80V, not 80mV. What I typed above applies to 80V differential voltages, not 80mV differential input voltages.

What I said in my last paragraph about the recovery time still applies, but you don't need to worry about exceeding the recommended operating conditions:

Levi DV said:

If you expect to exceed the recommended operating conditions or saturate the device, you should also keep in mind that the device will need to wait a recovery time before the device will operate normally again. For the LMP8480, the recovery time is 50µs from saturation

Sorry for my confusion, let me know if you need any more clarification,

Levi DeVries