UC1903: UC1903

MANOJ R

Part Number: UC1903

I am using the following circuit with UC1903 IC to monitor a negative supply.

R1=11K, R2 = 56K. I am using WADJ = 1V for a +/-10% threshold limit. The IC is powered by +15V which is also potentially divided to 2.5V to monitor using SENSE 1 input. My circuit output is POWER OK pin with a pull up to 5V with a 10K resistor (a LOW indicates voltages monitored are NOT HEALTHY and a HIGH indicated monitored voltages are HEALTHY).

My assumption was, if i float the -Vs input, since there is a 11K across the inverter, Pin 5 will be virtual GND and output of the IC will be "NOT HEALTHY". But i am getting the output still as "HEALTHY". If connect a 5 Meg Ohm resistor from Pin 5 to GND, the output shows "HEALTHY" once in a while and "NOT HEALTHY" other times. Can you help me out with this problem? My circuitry is fixed and i do not have a provision in my layout to connect a resistor from Pin 5 to GND permanently.

1. Is this behaviour expected?

2. How to circumvent this issue and indicate a "NOT HEALTHY" output when i float the -Vs?

over 5 years ago

0 Kyle Rakos over 5 years ago

TI__Mastermind 20045 points

Hello Mano,

The image wasn't uploaded. Could you try again? What image format are you using?

Thanks,
Kyle

0 MANOJ R over 5 years ago in reply to Kyle Rakos

Prodigy 125 points

I used .png format. Anyways, the schematic I am referring to is identical to Fig. 6 in Page 8 of the UC1903 datasheet in the link below

0 Kyle Rakos over 5 years ago in reply to MANOJ R

TI__Mastermind 20045 points

Hello Mano,

Thanks for clarifying. I tend to agree with your analysis. I would expect the output to indicate "not healthy" when floating -Vs.

Let me ask you a couple questions to see if we can figure out how this is happening. When you say float -Vs, are you fully disconnecting the power supply or something else? I would like to know the use case for this operation to figure out if it's not truly "floating". Also are you able to upload your full schematic? Maybe I'll see something else that could be the cause of the issue.

Thanks,
Kyle

0 Kyle Rakos over 5 years ago in reply to Kyle Rakos

TI__Mastermind 20045 points

Hello Mano,

Just checking to see if you've had a chance to look at these questions.

Thanks,
Kyle

0 Kyle Rakos over 5 years ago in reply to Kyle Rakos

TI__Mastermind 20045 points

Hello Mano,

I will assume you were able to figure out the problem since I haven't heard back. If you still need further assistance feel free to follow-up here or ask a related question if this thread has closed.

Thanks,
Kyle

0 MANOJ R over 5 years ago in reply to Kyle Rakos

Prodigy 125 points

I am completely disconnecting the power supply. No i am still having the problem. can you message me your email id so that i can mail you the circuit? This is really important.

0 MANOJ R over 5 years ago in reply to Kyle Rakos

Prodigy 125 points

Nope. I am still having the same problem

0 Kyle Rakos over 5 years ago in reply to MANOJ R

TI__Mastermind 20045 points

Hello Mano,

It looks like you uploaded your circuit at e2e.ti.com/.../705657. I will continue providing support in that thread and will mark this one closed.

Thanks,
Kyle

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UC1903: UC1903