OPA549: continuous output current

Jerry Chen

Part Number: OPA549

Hi team,

I found in datasheet that, when supply voltage is 5V beyond output voltage, OPA549 can output continuous 8A current. However, I just measured below maxim current (Io). Beyond these current, output voltage (Vo) will drop. V+ and V- are the supply voltage, I+ and I- are the measured current of supply. RL is load and Vin is the input of OPA549.

Is this because of the thermal protection? Is there any other thing that I could have a check?

Thanks.

over 4 years ago

0 kai klaas69 over 4 years ago

Guru 140200 points

Hi Jerry,

for the last entry in your table the OPA549 has to dissipate:

(10V - 4.54V) x 6.47A = 35.3W

This is quite a lot. Higher output currents are only available with a proper heatsink providing a theta of better than 1.4°C/W:

(1.4°C/W + 1.4°C/W) x 35.3W = 99°C = (125°C - 26°C)

where 125°C is the recommended maximum junction temperature of OPA549 over long periods, 26°C is the temperature of ambient and 1.4°C/W is the junction to case thermal resistance of OPA549.

So yes, without such a heatsink the built-in thermal protection of OPA549 which provides a very helpful SOA protection (safe operating area) will prevent higher output currents.

All this is very nicely discussed in the datasheet, by the way :-)

Kai