Author Topic: High Side Current Monitor NCS213RSQT2G  (Read 913 times)

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Offline maurosmartinsTopic starter

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High Side Current Monitor NCS213RSQT2G
« on: December 07, 2019, 11:12:01 pm »
Hello all,

on a small power supply I'm working, I've added an On Semiconductor NCS213RSQT2G high side current monitor as follows:
885970-0

if I set the power supply to 12V and draw 100mA the NCS corretly outputs 0.5V (0.1Ohms * 0.1Amps * 50V/V = 0.5V)

nevertheless if I set the power supply to a different (lower voltage) and draw the same 100mA the output should still be 0.5V but it isn't and I don't understand why.

I'm supplying the NCS with more or less 15V and the Vref is tied to 0V.

can anyone help to shed light over this issue?

looking forward your reply,
Best regards, Mauro.
« Last Edit: December 07, 2019, 11:18:55 pm by maurosmartins »
 

Offline MadScientist

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Re: High Side Current Monitor NCS213RSQT2G
« Reply #1 on: December 08, 2019, 05:10:16 pm »
Have you measured the voktage across the sense resistor
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Offline maurosmartinsTopic starter

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Re: High Side Current Monitor NCS213RSQT2G
« Reply #2 on: December 08, 2019, 07:38:20 pm »
Hello MadScientist,

thank you for your reply.

Yes, I've measured the voltage across the resistor and it is fine the same 10mV for 100mA.

Best regards, Mauro.

 

Offline Yansi

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Re: High Side Current Monitor NCS213RSQT2G
« Reply #3 on: December 08, 2019, 07:50:42 pm »
As far as I can tell, I do not see a single compensation RC network, nor even a damping resistor in the output of the opamp.

So, quite a good bet is it is oscillating and providing you a false reading.

Have you poked the design with an osmelloscope? Verified the stability? At LEAST  done a stepped load test?
 

Offline maurosmartinsTopic starter

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Re: High Side Current Monitor NCS213RSQT2G
« Reply #4 on: December 08, 2019, 08:05:11 pm »
Hello Yansi,

that might be the case, maybe the opamp is oscillating. But I don't know where the RC network / damping resistor should be.

can you please provide some guidelines?

Have you poked the design with an osmelloscope? Verified the stability? At LEAST  done a stepped load test?

I have not, I hadn't reached there yet and possibly was looking at wrong causes. I'll do as you say and check the step response.

Mauro.
 


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