Front End; Simplified Block Diagram Of Front End In Ucd3138 - Texas Instruments UCD3138 Technical Reference Manual

There are 3 Front-End modules available in UCD3138 (Front End 0, 1, 2). Here is a simplified block
diagram of the Front End showing an accurate representation of the block's overall functionality:
Figure 3-1. Simplified Block Diagram of Front End in UCD3138
(Front End 2 recommended for Peak Current Mode Control)
The input to the Front End is a differential signal on 2 input pins (EANx, EAPx, x=0, 1, 2) of the UCD3138
device. A differential amplifier resolves this to a single ended signal, representing the difference between
the two pins. Typically this signal represents voltage or current in the power supply, or some other value to
be regulated via a feedback loop to be measured.
This signal is fed into another differential amplifier. The other input to this differential amplifier comes from
a Digital to Analog Converter (DAC) which has an effective range of 0 to 1.6V. This DAC output typically
represents a target for a regulated value (reference).
There is a gain programmable differential amplifier which outputs the difference between the DAC output
and the Front End input. This analog signal typically represents the error between the regulated value and
the target value. This signal is turned into a digital value by the Error Analog to Digital Converter (EADC).
This digital value is typically fed to the input of one or more filters, although it can be used in other ways.
Other blocks in the UCD3138 Front End aid implementing typical power supply functions. The Successive
Approximation Control turns the Front End from a high speed, limited range error ADC to a 1.6V range,
slower, successive approximation ADC.
The Ramp Control ramps the EADC DAC value up or down at a programmable rate for simple soft start
and soft stop functionality. The Ramp engine can also be used for other ramps as well.
The Pre-Bias Control adds pre-bias handling support.
SNIU028A – February 2016 – Revised April 2016
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Copyright © 2016, Texas Instruments Incorporated
SNIU028A – February 2016 – Revised April 2016

Front End

Chapter 3
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Front End