HOT!! That Chip burned my finger

Recently, I solve a problem which make a DA converter very very hot boiler. But thanks god, it works very well.. so other guys just ignore that problem, errr, I want to fix it.

First, I need to check which pin is convert current to pass the chip then work as a resistor heater to heat up the chip. And I find that it is pin 8 – A Reference Voltage Pin which is a input pin to give the DA convert a reference. It can absorb more than 100mA current from a 5V precise voltage source.

So problem is pretty easy. The 5V precisely Voltage source must be in some overvoltage conditon somehow.  So I attach a prober to the 5V ref source, then here is the problem. When system starts, the Voltage can be up to nearly 15V for about 25ms, so it cause the chip to be breakdown.

Reference Voltage Generated from here

And Voltage from DAVREF is here

So. Pretty easy solution to fix it up. Just remove the MJD127. Voltage never go beyond 5V,

So From this issue, I learned that never trust the circuit which already been tested and verfied by other people, you need to doubt while it is obviously wrong.

About Chenxiang Hsu

A Geek, An engineer, a programmer, and a Model Maker.