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OPA2822 Output Capacitance

Mark Guastaferro
Genius 11645 points
Other Parts Discussed in Thread: THS5661A, OPA2822

Customer is looking at using the OPA2822 configured as a current divider between a current output DAC (THS5661A) and their analog ASIC. Their ASIC input is an amplifier and is very sensitive to capacitance on the input.  They want to know what the output capacitance of the OPA2822 (including package) would be. DAC can be clocked as high as 48 MHz.

 Op amp circuit:

 

ASIC input (output load for op amp circuit)

  • 0
    TI__Genius 13935 points

    We don't have that specification on the datasheet, but if you look at the closed loop output impedance chart on page 8 of the datasheet it shows the output impedance goes up with frequency.  This means that the output is primarily inductive.  If the capacitance were large it would show up on this chart. 

    Your first schematic shows a 2k resistor betweenthe amplifier outputand the input, this should isolate the amplifer output capacitance very well.  The non inverting input is conected on the other side of the resistor, so it's 1pF of capacitance and the PCB trace will probably be the main capactiance seen by the ASIC.