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# LT1763 wrong output voltage in low temperature

Hey.

We make design with the LT1763 to output 5V with 250mA.

We enter the the card to oven to check the functionality in high and low temperature.

In this test we measured the voltage in two places

1) In the card with A/D (accurate measured)

2) With resistor to act has load. it not accurate because we measured between the legs of the resistor. so the ground was not absolute zero.

we start the with 85 degree for 4 hours and the card output 5V.

after the 4 hours we start to cool to -40 degree .

when we start to coll down the output voltage decrease to 4.7V.

we check the feedback resistor and they capable to be in -55 to 150 degree

according the datasheet the LT1763 work from -40 to 125.

we put thermocouple on the LT1762 when it worked and the temperature was -20 to 92.

what can cause this problem?

I add the schematics of the design and the data from the test.

The data of the output voltage is not accurate and showed we have 4.6V , when i read from the A/D the voltage was 4.7V.

The data start when we cool the oven , the card was in 85 degree for 4 hours

• The time in the graph is seconds

• Hi Ariel,

I don't think that it is the LT1763 that's causing this wrong output voltage at low temp.
Since it states in the datasheet that it is guaranteed at full -40degC to 125degC operating junction temp range.

What I'm thinking that affects this are some external factors other than the chip such as:

Layout: this can greatly affect the output of your design as it may cause some ripple on Vout.
If you can check your output voltage using an oscilloscope maybe you can see the actual behavior of your Vout properly.
Maybe you are only measuring the average value of the output and cannot clearly see if there are any ripple present.
A waveform measurement can help in figuring this out.

Capacitor on your output. Capacitor have a temperature coefficient that varies with different types. There are some with temperature coefficient varies greatly with a low/negative temperature. This change in capacitance can also caused instability with your output that can probably be the reason for the wrong Vout.

This are just some things you can consider and check to figure out the wrong output from your design.

regards,
Ash