UCD3138ARMHT datasheet(61/83 Pages) TI

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2 B – QB2

( EDGEGEN )

2 A – QT 2

( EDGEGEN )

0 B – QSYN 2,4

1 B – QSYN 1,3

Current

Peak Level

3 A – QB1

( DPWM 1 C)

3 B – QT1

( DPWM 2 C)

Period Start

Period End

Chopping point

Y 1

UCD3138A

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SLUSC66B – MARCH 2015 – REVISED MAY 2015

Figure 7-7. Final 6 Gate Signals

Note how the falling edge of DPWM2AF aligns with the X1 edge, and how the rising edge of DPWM2BF

aligns with the X3 edge. The falling edges on DPWM2AF and DPWM3AF are caused by the peak

detection logic. This is fed through the Cycle By Cycle logic. The Cycle By Cycle logic also has a special

feature to control the rising edges of DPWM2BF (X1 and X3) and DPWM3BF (Y1 and Y3). It uses the

value of Event3 – Event2 to control the time between the edges. The same feature is used with DPWM0

and DPWM1 to control the X2 and Y2 signals. Using the other 2 DPWMs permits these signals to have a

different dead time.

The same setup can be used for voltage mode control. In this case, the Filter output sets the timing of the

falling edge on DPWMxAF.

All DPWMs are configured in Normal mode, with CBC enabled. If external slope compensation is used,

DPWM1A and DPWM1B are used to reset the external compensator at the beginning of each half cycle. If

no PCMC event occurs, the values of Events 2 and 3 determine the locations of the edges, just as in open

loop mode.

7.2.6

System Initialization for PCM

PCM (Peak Current Mode) is a specialized configuration for the UCD3138A which involves several

peripherals. This section describes how it works across the peripherals.

7.2.6.1

Use of Front Ends and Filters in PSFB

All three front ends are used in PSFB. The same signals are used in the same places for both PCMC and

voltage mode. The same hardware can be used for both control modes, with the mode determined by

which firmware is loaded into the device. FE0 and FE1 are used with their associated filters, but Filter 2 is

not used at all.

FE0 – Vout – voltage loop

FE1 – Iout – current loop

FE2 – Ipri – PCM

In PCMC mode, FE2 is used for PCMC, and the voltage loop is normally used to provide the start point for

the compensation ramp. If the CPCC firmware detects a need for constant current mode, it switches to the

current loop for the start point.

Application, Implementation, and Layout

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