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Topic: Opamp selection to drive 50 Ohm impedance (Read 2214 times) previous topic - next topic


Feb 22, 2012, 04:40 pm Last Edit: Feb 22, 2012, 04:48 pm by mcleung Reason: 1
Hi Guys!

I'm trying to amplify a signal from a high impedance source (MCP4725, Sparkfun)
I need to find an buffer opamp that will be able to drive a 50 Ohm input impedance load.

Most opamps I've seen so far only drive a couple miliamps at most. To obtain the fullscale voltage range (0-5V), by Ohm's law V=IR I'd need something that is able to output 100mA. (Unless I am confused?)

If you guys could suggest opamps or workarounds I'd appreciate it!


The Analog Devices AD8531 is rated for 250mA output, is rail-to-rail input/output at 5V, and has a slew rate of 5V/us, 10 times higher than that of your DAC, so it should do the job. Input offset voltage is a bit high (25mV) but I'm not sure if that's an issue for your application. It's <$1 so not a bad place to start.

The Flexible MIDI Shield: MIDI IN/OUT, stacking headers, your choice of I/O pins

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