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Floating Ground Transistors

Hi, I've seen this floating ground transistor configuration in many of the power monitoring IC reference designs, and am having trouble understanding what it does. Some places it shows up are the datasheets of LTC2992, LTC2946, & LTC2947. I am guessing it's some kind of regulator circuit, but the other HW engineers at my job aren't sure either. If someone could clarify what the circled portion of the circuit is doing that would be very much appreciated.

  • Q1 is used as diode. M3 is const current source for Z1, Q1. This components are voltage regulator 5,7V.  Q2 works as emitter folower. Power stage of voltage regulator is created from controlled current source M1 and Q3. If the voltage between VDD and GND pins drops, the current through Q2 and R6 as well as base Q3 increases. Decreasing the resistance between the collector and emitter Q3 will cause the UGS transistor M1 to increase, the Drain current will increase and the voltage drop between VDD and GND pins will equalize.

  • Thanks for the prompt reply and helpful explanation.