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OPA564-Q1: The temperature of the OPA564-Q1 is too high

user6222316
Prodigy 90 points
Part Number: OPA564-Q1
Other Parts Discussed in Thread: OPA564

I use OPA564-Q1 as a constant current source to drive LD.

The schematic is as follows：

The OPA564-Q1 works fine，but when the OPA564-Q1 output voltage and current are -1.45V/680mA，The temperature of the OPA564-Q1 reached nearly 100 ℃。

The current output by the OPA564-Q1 changes from small to large, and the temperature increases linearly accordingly.

The package I use is PowerPAD on Bottom.During the OPA564-Q1 is working, I did’t add heat sink or fan.

I think the temperature is too high, what's the problem?

thanks！

  • 0
    Guru 140200 points

    Hi,

    you dissipate a lot of heat within the OPA564: (5V - 1.45V) x 680mA = 2.4W.

    To reduce this heat you can decrease the supply voltage or increase R40. And, of course, a heat sink could be used.

    By the way, are you sure that the OPA564 isn't oscillating? This can happen, if D1 has a large junction capacitance or if long cabling is involved. In this case you can increase R40 to 3R0. Place R40 directly at the output pin of OPAmp. And you can place a small cap in parallel to R24. Do you need such a fast OPAmp?

    Furthermore, D1 is in danger to be destroyed. If the output voltage is only a bit too high, the LED gets barbecued because R40 will not really limit the current. Also from this point of view R40 should be increased.

    Have you seen the Howland current pump in figure 51 of datasheet?

    Kai

  • 0
    TI__Guru* 93105 points

    Hello user6222316,

    Kai has provided a number of points that need to be examined in relation to your particular circuit to assure that the OPA564-Q1 isn't being set up for unnecessarily high power dissipation, or experiencing excessive heating due to oscillation. 

    Thermal management for high power op amps such as the OPA564-Q1 that use the bottom side thermal pad (PowerPAD) to transfer heat require careful forethought in their design. There is a good chance if the thermal design is insufficient that the device is getting hotter than expected.The thermal pad to which the OPA564-Q1 is attached needs to be able to conduct the heat from the op amp, and then radiate it into the surrounding ambient environment. It is very important that the PC board design abide by the information provided in the datasheet Figure 47, Thermal Resistance vs Circuit Board Copper Area, is observed in the design. It is easy to overlook this information and then the op amp ends up becoming too hot.

    We sometimes find with that a user is unable to correctly solder the OPA564-Q1 PowerPAD to the PC board pad. When this happens the thermal resistance is higher than it would be with a completely soldered thermal path. If you have some flexibility with your design you may find that the topside PowerPAD is easier to work with from a thermal standpoint. With some creative efforts a small heat sink can be arranged to contact the topside PowerPAD. That may make removing the heat from the OPA564-Q1 easier than trying to provide several square inches of PC board for thermal conduction and heat radiation.

    Regards, Thomas

    Precision Amplifiers Applications Engineering