Emulator Target Voltage

Problem

  • A: target voltage with current-measurement is unstable (oscillation for low voltage / low load)

  • B: voltage buffer feedback is excluding the switch afterward

Setup

  • BB powered by bench-supply

  • Target voltage drained by keithley source meter (current mode)

  • target voltage is monitored by scope with probe in AC-Mode to analyze Noise

NOTE: part of the oscillation is probably also partly caused by the measurement setup ⇾ heisenbug

Measurements for unstable Voltage

  • VTarget = 0.5 V shows 10mVpp oscillation ~ 260 kHz

  • VTarget = 1.0 V is stable

  • other documentation is lost

  • problem is fixed

Measurements for voltage drop

  • source current ⇾ TargetA Voltage

    • 0 uA; 2.9983 V

    • 1 mA; 2.9987 V

    • 5 mA; 3.0001 V

    • 10 mA; 3.0024 V

    • 20 mA; 3.0065 V

    • 30 mA; 3.0106 V

    • 40 mA; 3.0148 V

  • drain current ⇾ TargetA Voltage

    • 0 mA; 2.9983 V

    • 1 mA; 2.9979 V

    • 10 mA; 2.9942 V

    • 20 mA; 2.9901 V

    • 30 mA; 2.9860 V

    • 40 mA; 2.9818 V

    • 50 mA; 2.9732 V

Analysis of voltage drop

  • side node: shepherd is able to drain power

  • drain-experiment shows voltage drop of 25.1 mV for 50 mA ⇾ 502 mOhm Internal Resistance after OpAmp

  • switch-datasheet claims 500 mOhm Rds_on ⇾ very close to measurement including traces

  • influence of switch ⇾ 50mA @ 3V equals 60 Ohm ⇾ 500 mOhm are 0.83 % of that

Conclusion

  • A: oscillation can be fixed by bigger shunt-resistance

  • B: voltage drop can be fixed by including switch into feedback loop ⇾ needs additional switch