AMC1311: AMC1311 Output Stage

Varunesh Kumar

Intellectual 980 points

Part Number: AMC1311
Other Parts Discussed in Thread: XTR111,

Hello

I am Designing an Isolated 0-20 mA corresponding to a 0-2V Isolated signal .

I am planning to use AMC1311 Isolator in conjunction with XTR111 ( and an External P Ch MOSFET NTP2955 )

to generate a 20 mA O/P proportional to 0-2V Input to AMC1311 .

Can I use the OUTP & OUTN with a 2 uS Filter to directly connect to Vin & Set of XTR111 ;

or do I need an additional Op Amp in between as a Diff Amp .

Basic proposed Ckt is as follows :

over 6 years ago

0 Alexander Smith over 6 years ago

TI__Guru 56572 points

Hi Varunesh,

Thanks for your post!

As your circuit is currently set up, you essentially have VOUTN connected to GND through a 1k resistor and VOUTP has a 1kOhm +1nF RC filter before being connected to VIN of the XTR111.

The best thing to do would be to use an additional opamp to do a differential to single-ended conversion. Otherwise, I would recommend increasing the size of the resistor to 10k between VOUTN and GND. This will reduce the power dissipated across the resistor.

Please see these posts for more details:
e2e.ti.com/.../790912
e2e.ti.com/.../793206

0 Varunesh Kumar over 6 years ago in reply to Alexander Smith

Intellectual 980 points

Hi Alex

Thanks for your reply .

I've one additional Q ; if you will .

I am okay with 2 X 10K from VOUTP & VOUTN .

My Q is for an Input Voltage of 0 V ; will the O/P swing to zero ;

or is there a minimum Output Voltage for a zero V In ?

Thanks and regards

Varun

0 Alexander Smith over 6 years ago in reply to Varunesh Kumar

TI__Guru 56572 points

Hi Varun,

Happy to help!

Please see Figure 22. Output Voltage vs Input Voltage in the datasheet.

At 0 volt input, both output's will be outputting the common-mode voltage of ~1.44V.

0 kai klaas69 over 6 years ago

Guru 140200 points

Hi Varunesh,

as Alexander already mentioned the AMC1311 has a true differential output and it's really recommended to connect a differential amplifier to the output. Keep in mind that the common mode rejection of input to output noise and EMI can be heavily degraded when using your asymmetrical topology.

Kai

0 Varunesh Kumar over 6 years ago in reply to Alexander Smith

Intellectual 980 points

Hi Alex

Thanks for your reply ; which has answered my Q .

I think the Differential Amp shall be necessary ; which I'll incorporate .

Thanks and with best regards

Varun

0 Varunesh Kumar over 6 years ago in reply to kai klaas69

Intellectual 980 points

Hi Kai
Thanks for your reply too ; which I saw later ;
after Alex's reply ; which answered my Q .
Thanks and with best regards
Varun

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AMC1311: AMC1311 Output Stage