Hi,
  I need to design a protect circuit for a node, which has 2kOhm resistor connected to output of a -2v to 5.5v opamp output. I only have 3v devices to design this -2v to 5.5v protection, and I can't pull this node down.
   Anyone has some good idea.

Judy

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

Hi,
 
  Thanks for the reply, the gain is from -30db to 4dB, so most part it is attenuator.
   What do you mean with resistor divider, for which part, right now the gain is set by selecting different tap in a resistor ladder.
   the protection is for switch S1, S2 in the tap, I need to put some fancy voltage on the gate, so it won't exceed the 3.6v stress. I wonder what is the best way to protect them from the -2 to 5.5v.

Judy

Hello,
        Will some CDM structures help ?? as in the ones used for standard ESD Protection.

--Mayank