NXP Semiconductors 56800E Reference Manual

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NXP Semiconductors 56800E Reference Manual Manual pdf 41 page image

Auxiliary CircuitsOnline UPS Theory and Description, Rev. 0Freescale Semiconductor 1-25PreliminaryThe value of the resistors required to sense every signal are calculated in order to guarantee fullswing, minimizing analog and quantization noise at the ADCs.The reference level of the ADC is used to shift the AC input signal to swing from 0 to VRH (i.e.,0 volts in the input signal are mapped to VRH /2). If the output of the operational amplifier tendsto go out of limits for any reason, the diodes protect the ADC inputs.1.10.3 Voltage Reference SupplyThe voltage reference, V RH, is generated by the circuit shown in Figure 1-29. This circuit acts asa buffer to the reference voltage VREFH from the controller. This circuit also generates twoauxiliary voltage outputs:• V A equal to one diode voltage Vγ• V B with value VRH-VγThese voltages will be used to limit the values of voltage applied to A/D modules inside thecontroller.Figure 1-29. Voltage Reference Generator