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PCM1792 - I/V-Stage-OP burns my fingers.
i´f build a DAC with PCM1792, OPA4134 (I/V-Stage) an LT1028 (unbalancer). It works and sound´s good.
My problem: The OPA4134 in the I/V-Stage heats up and after a few seconds it burns my finger. The Stage is build like the schematic in the datasheet with R 750 Ohm and C 2200p. On BPZ i have -4.4V over the resistors and at the output-lines. The OPA4134 drives in this state 4x 5.8mA.
Is the heating ok and i have to cool them down or is here a failure in my schematic?
The current of the OPA4134 is 60mA on the -15V and 12mA on the +15V Rail.
Each amp of the OPA4134 drives 12mA on BPZ.
Thats IMHO all seems to be OK, i wonder about the heating of the i/v-Stage......
The temperature can definitely get warm on these devices, but how warm depends on the operating point of the output. For example if V+ is sourcing 12mA and and the V- is sinking 60mA, and the output is at 0V, then the total dissapation is (12mA*15V)+(60mA*15V)=1.08 Watts. Now looking at the thermal resistance of the part (on the bottom of page 2 of the datasheet) it is 110C/W from the die junction to ambient temperature.
This means that the temperature will rise from the ambient by 1.08W*110C/W=119C. Just enough to burn your fingers.
If the output is less than 0V, then less of the power is dissipated by the package and more is dissipated by the load.
Joseph Wu and Marek Lis
Are you really trying to drive 12mA per op-amp? It's a lot to be sourcing (or sinking if it's coming from V- supply).
You really should try to reduce the current especially if the temperature is getting close to the 150C limit.
thank you for your reply.
The schematic is nearly in the datasheet from the pcm1792 page 35:
So i wonder about the current and the temperatur.
Now i have fixed heatsinks on the op-amps (13K/W) and the tempertur is at ~50°C. Tomorrow we will install the DAC in our test car, the i will try to reduce the current.
Just to make sure, I'll just contact you directly.
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