UCD3138128APFCR datasheet(25/83 Pages) TI1

25 / 83 page

Error ADC

(Front End)

Filter

Digital

PWM

EAP

EAN

DPWMA

DPWMB

UCD3138128A

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SLUSC99 – JULY 2016

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9.3.2 Peripherals

9.3.2.1

Digital Power Peripherals (DPPs)

At the core of the UCD3138xA controller are three DDPs. Each DPP can be configured to drive from one to eight

DPWM outputs. Each DPP consists of:

•

Differential input error ADC (EADC) with sophisticated controls

•

Hardware accelerated digital 2-pole/2-zero PID based compensator

•

Digital PWM module with support for a variety of topologies

These can be connected in many different combinations, with multiple filters and DPWMs. They are capable of

supporting functions like input voltage feed forward, current mode control, and constant current/constant power,

and so on. The simplest configuration is shown in Figure 10.

Figure 10. Multiple Filters and DPWMs

9.3.2.1.1

Front End

Figure 11 shows the block diagram of the front end module. It consists of a differential amplifier, an adjustable

gain error amplifier, a high speed flash analog to digital converter (EADC), digital averaging filters and a precision

high resolution set point DAC reference. The programmable gain amplifier in concert with the EADC and the

adjustable digital gain on the EADC output work together to provide 9 bits of range with 6 bits of resolution on the

EADC output. The output of the Front End module is a 9-bit sign extended result with a gain of 1 LSB / mV.

Depending on the value of AFE selected, the resolution of this output could be either 1, 2, 4 or 8 LSBs. In

addition each EADC has the ability to automatically select the AFE value such that the minimum resolution is

maintained that still allows the voltage to fit within the range of the measurement. The EADC control logic

receives the sample request from the DPWM module for initiating an EADC conversion. EADC control circuitry

captures the EADC-9-bit-code and strobes the digital compensator for processing of the representative error. The

set point DAC has 10 bits with an additional 4 bits of dithering resulting in an effective resolution of 14 bits. This

DAC can be driven from a variety of sources to facilitate things like soft start, nested loops, and so on. Some

additional features include the ability to change the polarity of the error measurement and an absolute value

mode which automatically adds the DAC value to the error.

It is possible to operate the controller in a peak current mode control configuration; an EADC is recommended for

implementing peak current mode control. In this mode, topologies like a phase shifted full bridge converter can

be controlled to maintain transformer flux balance. The internal DAC can be ramped at a synchronously

controlled slew rate to achieve a programmable slope compensation. This eliminates the sub-harmonic oscillation

as well as improves input voltage feed-forward performance. A0 is a unity gain buffer used to isolate the peak

current mode comparator. The offset of this buffer is specified in Electrical Characteristics.

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