Capacitive load driver

How it calculates

Local loaded open-loop model: Aloaded = A0(s)[1+s Riso CL]/[1+s(Ro+Riso)CL]

Dual-feedback components: CF = max[1/(2*pi*RF fblend), 3 Riso CL/RF]; RG = RF/(NGdc-1)

Exact passive feedback network: YCF(V--VO) + (V--Vload)/RF + V-/RG = 0

Loop gain: T(s) = A0(s) * V-/Vinternal

Assumptions

• Generic amplifier: dominant pole, entered second pole and constant open-loop output resistance. The dual-feedback passive network is solved by nodal analysis including RF/CF loading. At DC, RF senses the load; at high frequency, CF senses the amplifier pin. For gains above unity, high-frequency noise gain tends to one, so the amplifier must be unity-gain stable.
• The CF choice puts RF CF at least three times Riso CL and below the requested transition frequency. The resistor search finds the first target-margin crossing on a logarithmic grid and refines it; it is a bounded numerical design suggestion, not a guarantee for a real device. The chosen Riso remains the plotted operating point. DC error neglects finite AOL and offset.

Worked example

These are the calculator's default inputs. Change any input above to recalculate.

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