AMC1300: Tolerance for low input Z

Jonathan Navor

Part Number: AMC1300

Hi Team,

Good day!

Cuold you please help if there is a tolerance for the very low input Z of 20kR?

Another question is if you hold one input (let's say VinN to dc voltage on the isolated high side) what will be the output on the non-isolated side?

Best regards,

Jonathan

over 2 years ago

0 Alexander Smith over 2 years ago

TI__Guru 51351 points

Hi Jonathan,

Please see this FAQ post: https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1023946/faq-does-ti-provide-guidance-on-input-resistance-variation-due-to-manufacturing-process-temperature-drift-and-lifetime-for-isolated-converters

For your second question, it will depend on the state of VinP, since AMC1300 is a single-channel differential in, differential out isolated amplifier. It's common to tie VinN to the high side ground and the measurement resistor to allow VinP to swing +/-250mV with respect to VinN and the high side ground. This ensures that the input signal remains within the common-mode voltage input range of the device.

We also have a voltage sensing excel calculator: https://www.ti.com/lit/zip/sbar013 and current sensing excel calculator: https://www.ti.com/lit/zip/sbar020 that may help your customer with their device selection.

Can you tell me a little more about the application? What voltage or current signals are being sensed?

0 kai klaas69 over 2 years ago

Guru 140200 points

Hi Jonathan,

the 20k differential input resistance of AMC1300 is not very low because the AMC1300 is optimized for current measurement using shunt resistors. The simplified schematic on the front page of datasheet demonstrates that the best performance can be achieved when the shunt resistance is smaller than the input offset voltage divided by the input bias current which is

0.01mV / 30µA = 0.33R

With a higher shunt resistance the input bias current of 30µA would cause a voltage drop exceeding the typical input offset voltage of 0.01mV.

The typical 20k differential input resistance of AMC1300 is 61,000 times higher than the above shunt resistance and plays almost no role, even not when considering some manufacturing tolerances.

Kai

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AMC1300: Tolerance for low input Z