CS3001_08 Datasheet, PDF (9/16 Pages) Cirrus Logic – Precision Low-voltage Amplifier; DC to 2 kHz

CS3001
CS3002
3.2 Open-loop Gain and Stability Compensation
3.2.1 Discussion
The CS3001 and CS3002 achieve ultra-high open
loop gain. Figure 16 illustrates the amplifier in a
non-inverting gain configuration. The open loop
gain and phase plots indicate that the amplifier is
stable for closed-loop gains less than 50 V/V and
R1 ≤ 100 Ohms. For a gain of 50, the phase margin
is between 40° and 60° depending upon the loading
conditions. As shown in Figure 17, on page 12, the
operational amplifier has an input capacitance at
the + and – signal inputs of typically 50 pF. This
capacitance adds an additional pole in the loop gain
transfer function at a frequency of f = 1/(2πR*C_in)
where R is the parallel combination of R1 and R2
(R1 || R2). A higher value for R produces a pole at
a lower frequency, thus reducing the phase margin.
R1 is recommended to be less than or equal to 100
ohms, which results in a pole at 30 MHz or higher.
If a higher value of R1 is desired, a compensation
capacitor (C2) should be added in parallel with R2.
C2 should be chosen such that R2*C2 ≥ R1*C_in.
R_S
V in
Vo
R2
R1
Figure 16. Non-inverting Gain Configuration
DS490F8
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