AD8137 getting hot when power on

Hello,

I am using AD8137YRZ to convert single-ended input to differential output. After power on, the AD8137 is gatting hot. The AD8137 was oscillating. After removed the capacitor C620 and C621 on the feedback loop, the oscillating is gone. However, the AD8137 is still warm. The temperature of the part is at about 50C. Is it normal or anything wrong on my schematic? The input voltage is feed through R615. The input voltage is set to zero. The input has 10K resistor tied to ground (does not show in the figure below).

Thank you in advance for the help.

Lily

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  • Anna,

    Thank you very much for your quick response.

    The reason that caused the AD8137 getting hot is the PD (power down) pin, which has been connceted to the +5V. It causes the amplifier draws excessive current and induce oscillations. This actually has been mentioned in the datasheet. It is my fault when I did the schematic design. By keeping the PD pin floating, I have put back the capacitors, the amplifier is still stable. The reason of adding capacitor is try to add a low pass filter, since the frequency of the input signal is pretty low.

    I also use AD8137 as 16 bit ADC driver (AD7677), which I did not post the schematic here. The issue I have right now is the Vocm voltage. I am going to apply a 1.25 V voltage at Vocm. This 1.25 V is generated from 2.5V reference voltage (REF5025IDG4), and then is divided by two 10K resistors in serial to get 1.25V. If without connect 1.25V to AD8137, the circuit works correct. However, when connects 1.25V to Vocm pin, the voltage drops to 1.08V. The 2.5 V does not change. Do you know what causes this problem?

    The front stage of the schematic I posted is the analog switch. The input voltage source will be applied to the AD8137 only when the analog switch is on. I will try your comment 1 and read ANN-0990.

    Thank you so much for the help. And hopefully I will hear from you again or anybody who can help me on the Vocm issue.

    Thanks,

    Lily

Reply
  • Anna,

    Thank you very much for your quick response.

    The reason that caused the AD8137 getting hot is the PD (power down) pin, which has been connceted to the +5V. It causes the amplifier draws excessive current and induce oscillations. This actually has been mentioned in the datasheet. It is my fault when I did the schematic design. By keeping the PD pin floating, I have put back the capacitors, the amplifier is still stable. The reason of adding capacitor is try to add a low pass filter, since the frequency of the input signal is pretty low.

    I also use AD8137 as 16 bit ADC driver (AD7677), which I did not post the schematic here. The issue I have right now is the Vocm voltage. I am going to apply a 1.25 V voltage at Vocm. This 1.25 V is generated from 2.5V reference voltage (REF5025IDG4), and then is divided by two 10K resistors in serial to get 1.25V. If without connect 1.25V to AD8137, the circuit works correct. However, when connects 1.25V to Vocm pin, the voltage drops to 1.08V. The 2.5 V does not change. Do you know what causes this problem?

    The front stage of the schematic I posted is the analog switch. The input voltage source will be applied to the AD8137 only when the analog switch is on. I will try your comment 1 and read ANN-0990.

    Thank you so much for the help. And hopefully I will hear from you again or anybody who can help me on the Vocm issue.

    Thanks,

    Lily

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