LM393: LM393B issue

Jimmy Lai

Part Number: LM393

Dear Team,

Our customer have an OPA(LM393BIDR) issue as below, please help to check if the design is ok.

When DCIN_27V_1 greater than "V+", the pin1 will output "Hi-Z".

When DCIN_27V_1 less than "V+, " the pin1 will output "0".

But we found that some PCBs behave abnormally

Channel 1 : Pin1 (3.205~3.245V)

Channel 2: Pin2 (2.449~2.482V)

Channel 3: Pin3 (2.365~2.43V)

Many Thanks,

Jimmy

0 Paul Grohe over 2 years ago

Hello Jimmy,

The input range of the LM393B is Vcc-2V, or 1.3V max on a 3.3V supply. They are violating the input range on both inputs.

For the "B" device, the output should go high when both inputs are taken out of range.

They will need to adjust the resistor values to keep the input voltages below 1.3V.

If they cannot change the circuit, they can try the LM393LV, which has R-R inputs and can accept input voltages up to VCC.

0 Jimmy Lai over 2 years ago in reply to Paul Grohe

Hi Paul,

We appreciated your great support!

The voltage rails can be modified and I changed the resistance as below,

V+ voltage rail is about 0.918V~0.963V

V- voltage rail is about 1.028V

Can you help me check if this circuit is ok?

Many Thanks,

Jimmy

0 Paul Grohe over 2 years ago in reply to Jimmy Lai

Hi Jimmy,

Much better. As long as the input voltages to the comparator are <1.3V, it should work fine.

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