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# LTC4364 Over voltage cut off not working

Category: Hardware
Product Number: LTC4364HMS-2#PBF

Hi Team,

We have designed LTC4364 for circuit for under and over voltage protection, this design the under voltage cut off functionality was working properly, but the Over voltage cut off  functionality Not.

We have set the over voltage cut off at 40V, anyone please answer why this feature not working.

Our Schematics attached below please review the same and share the feedback.

Regards,

Ajnas C

Parents
• If we are given a 42V directly, we get 0V output, but if we slowly increase the voltage from below the cutoff to above the cutoff voltage, the LTC4364 output does get input voltage. I don't understand why the LTC4364 doesn't cut the voltage when it exceeds the limit.

Initially when the voltage is higher than the limit, the output is 0V, and the voltage is slowly reduced, the limit goes below the cutoff voltage and the LTC4364's output shows high. When the voltage exceeds the limit, how will it be cut?

• If we are given a 42V directly, we get 0V output, but if we slowly increase the voltage from below the cutoff to above the cutoff voltage, the LTC4364 output does get input voltage. I don't understand why the LTC4364 doesn't cut the voltage when it exceeds the limit.

Initially when the voltage is higher than the limit, the output is 0V, and the voltage is slowly reduced, the limit goes below the cutoff voltage and the LTC4364's output shows high. When the voltage exceeds the limit, how will it be cut?

Children
• Hello Ajnas,

your observations are exactly the expected behaviour. The OV-Input keeps the FET off, if an overvoltage ist detected at startup (during the first 100µs). If the input voltage exceeds the limit later, the FET will not be switched off.

The datasheet says:

"At power-up, if the OV pin voltage is higher than its 1.25V
threshold before the
100μs internal power-on-reset expires,
.....

the HGATE pin will be held low until the OV pin volt-
age drops below its threshold.

.....

Once the HGATE pin begins pulling high, an input over-
voltage condition detected by OV will not turn off the pass

device.
"

So once the FET is turned on, it will not be turned off by an overvoltage detected at OV. In that case, the reaction to the overvoltage has to come over the FB-pin (which is not used in your circuit).

best regards

Achim

• Hi Team,

Is any IC available for the under and over voltage cut off, could you please suggest any  AEC-Q100 qualified IC with this specification?

• Hello Ajnas,

correct me if I'm wrong, but I think the LTC4364 has all the features you ask for.

best regards

Achim

• But the LTC4364's Over voltage cut off will only works initial power up, right?

When the voltage exceeds the limit in the continuous working state, the over voltage cut off circuit cuts the voltage at that time as well. Is there any IC suitable for this application?

• Hello Ajnas,

the LTC4364 will cut off the overvoltage also in continuous working state, if you connect the FB-pin accordingly (see e.g. fig. 1 of datasheet).

When the overvoltage happens in continuous working state, the cut off does not happen immediately. The LTC4364 will first try to regulate the output voltage to safe values so that the load does not see any overvoltage. But if this condition persists to long, the LTC364 will still cut off.

And you can control the time when the complete cut off occurs by the value of the timer capacitor.

best regards

Achim