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Recommended Source Resistance vs Capacitive Load for OPA820

Karen
Intellectual 940 points
Other Parts Discussed in Thread: OPA820

Looking at the OPA820 datasheet in regards to the “RECOMMENDED RS vs CAPACITIVE LOAD” graph on page 12, can you tell me if I need to have a resistance greater than what the line specifies or the same as the value indicated. For example, at 100pF should I have 20W or 50W?

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    TI__Intellectual 940 points

    To achieve the desired peaking you will need at least the value indicated on the graph.  So at 100pF capacitive load, you will need at least 20ohm to achieve 0dB peaking.  If the value for the series resistance used is higher than that in the plot, you will achieve more stability at the cost of limiting the bandwidth. For example, since the bandwidth is limited by the RC load; for 20W and 100pF, you will have 79.5MHz bandwidth.  For 50W and 100pF, you will have only 31.8MHz.