OPA549: OPA549 application questions

Hi Kailyn,

for 8A output current the supply voltage must be 5V higher than the output voltage. This results in a heat dissipation of 5V x 8A = 40W within the OPA549! The thermal resistance from junction to case is 1.4°C/W. So, even with a ideal heat sink the junction would heat up by 1.4K/W x 40W = 56K. With an ambient temperature of 40°C this would mean a junction temperature of 96°C, an ideal heat sink assumed! With a real world heat sink of 1K/W, which would be huge, the junction would heat up even more, by additional 40K to 136°C. This is well beyond what would be recommended for a high reliable application. So, you would need an additional fan cooling for the heat sink.

If your output voltage is below 4V, then the heat dissipation will be even higher, because more voltage would drop across the OPA549...

Kai

Hi Kailyn,

Kai is absolutely correct regarding the power dissipation concerns of the OPA549 in the described application. And there are concerns about a circuit approach involving one master op amp, and a number of slaves to get the total current up to 50 Amperes. We did some work a few years ago for TI Design that attempted to use multiple slaves in conjunction with a master. The thermal management of multiple power op amps running at higher current turned out to be quite the issue. There were other smaller problems that were proving lengthy to resolve and the TI Design was eventually abandoned.

There are high-power transistors and MOSFETs that would be better candidates for handling 50 amperes of current. A power op amp could be used to drive the discrete transistors. A circuit of this nature would have to be designed from the ground up.

Regards, Thomas
Precision Amplifiers Applications Engineering

Kailyn

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Thanks