Handbook
November 2011 / 59-UMC0071 / Issue 01
Mercury iTC
Page 75
FUNCTIONAL DESCRIPTION
Original Instructions
The power for the linear amplifier is provided by a pulse-width modulator converter,
controlled by U24. The output of this converter is filtered and passed to the linear
amplifier via a current monitor. This current signal is passed back to U24, and also
drives an overcurrent trip circuit. If the measured current is too high, the current trip
circuit latches on and disables the linear amplifier. The linear amplifier is also disabled if
regular pulses are not received from the microcontroller (referred to as the “dead man’s
handle” feature).
4.6.2.2 Calibrating the heater circuit
The ADC performs an internal self-calibration routine when the user requests a
calibration. This calibrates each gain range (1, 8, 16, 32, 64, 128) on each input pair, at
full-scale only. It is only necessary to perform this calibration using a positive excitation
voltage. The ADC is operated in chop mode, which eliminates any offsets in the ADC.
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