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Part Number: OPA2170
Can OPA2170 short-circuit output current limits be adjusted to custom levels during test process at TI?
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In reply to Paul Goedeke:
HI Paul. This is for analog output on precision scientific instrumentation. The opamp is driven by DAC60004 to generate 0-5V or 0-10V signal.
I need a single supply(4-35V) opamp with low input offset(on the order of 1-2mV for worse case, but lower is better), whose input includes GND, and whose output can swing within a few millivolts of ground.
I'm interested in short-circuit limits because the output of this opamp circuit is customer facing and be connected to GND or 32V. If the short-circuit current limit is low enough and the thermal resistance of the package is low enough, then the op-amp won't overheat. From my testing it seems that short-circuit current limit on sinking current is especially important.
OPA2170 short-circuit sinking current is 20mA or less.
If output is connected to 32V, and sinking 20mA, then 150 ohms used for RISO compensation dissipates 60mW and has 3V drop across it.
OPA2170 dissipates(32V-3V)*20mA = 580mW. In a WSON package 580mW*71.5C/W = 41.47C temperature rise, which is respectable.
If the circuit-circuit sinking current limit were lower, it'd be better because the OPA2170 would dissipate less heat.
In reply to Dave Knight:
Regards,Ronald MichallickLinear Applications
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In reply to Ron Michallick:
Dave, Oh yes, the D1 diode. I didn't scroll up high enough the see that diode this morning. VCC and VOUT will increase in current limit as you have seen. Power dissipated is IOUT * VOUT so lowering VOUT and IOUT will be helpful. One other plan is to make output try to go high if output is greater than VCC. That would greatly reduce current. Do you have your circuit in Ti-Tina that you can upload?
8688.opa2170 analog output.TSC
This modified circuit should provide full sink current until op amp V+ pin starts to rise, at that point the output is suppose to go high so the output will not fight the external voltage anymore and op amps' V+ will rise with just a little current to run the PNP transistor.
However, that doesn't model well. It won't solve if voltage starts at 32V but will solve for voltage ramping to 32V (DC transfer function). Also current doesn't drop and op amp's ground current flows in the wrong direction most of the time.
I will need to build this to prove it out.
8688.opa2170 analog output(with high voltage input reversal).TSC
So the worst case should be external voltage close to 12V and low current above that.
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