circuit_cook
Junior Member
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Posts: 25
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Hi,
Here is what I want to achieve, a classAB driving a 16Ohm load with variable gain setting from -30 db to 4dB by feedback resistance. there is a charge pump on chip, when it is enabled, the opamp power supply is (vdd=5.5 and vss=-2, ouput common mode is 0v), when it is disabled, the opamp power supply is (vdd=5.5 and vss=0, output common mode 1.5. All I have is 3.3v device, the output switch SW1 and SW2 is realized with cascode transistor, but how to protecte the switch S1, S2 etc. I can't pull A, B, C, D to 0, when it is open loop. Another question is there any limiation for this architecture, with pragrammable gain comined classAB, driving a 16Ohm load, the minimum feedback resistance is 2K in the lowest setting.
Judy
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