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LMH6550: LMH6550 overheating

NP
Prodigy 150 points
Part Number: LMH6550


Hi,

I currently have the following circuit set-up (see pic). The amplifier is overheating during operation (with no signal at output) and I've checked all pins (non-floating except pin 7, which based on the datasheet can be left floating - EN pin) including power. I also tried enabling it to high but it was still overheating. The supply is also clean (scoped). The differential input signal is a 500kHz sine, 1Vpp.

Would anyone have a rough idea what the reason is?

  • 0
    TI__Genius 15975 points
    Hi,

    The input signal should not be directly connected to the LMH6550 input pins as you have shown above. The input signal Sig+ & Sig- should be instead connected through a series resistor to the LMH6550 input pins which sets the gain of the circuit. Please refer to Figure 21 in the datasheet for typical schematic operation of the LMH6550.

    Best Regards,
    Rohit
  • 0 in reply to Rohit Bhat
    Prodigy 150 points

    Hi Rohit,

    You're correct - thank you.  I do have the  resistors in series with the signal. I clipped the picture a bit early and it didn't show up in the picture. I'm going to take a look at the drive current to the input pins, possibly might be the culprit.

    Regards,

  • 0 in reply to NP
    TI__Genius 15975 points
    Hi,

    Would it be possible for you to attach a full schematic of your circuit? If the LMH6550 is being overheated, then there is a possibility that the part is oscillating. Have you tried to remove the feedback caps - C21 and C51 - to make sure the circuit stabilizes and does not get overheated?

    Best Regards,
    Rohit