UCD3138A64 datasheet(25/80 Pages) TI

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UCD3138128, UCD3138A64

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SLUSBZ8A – JUNE 2014 – REVISED SEPTEMBER 2014

9.3.2.1.4

High Resolution DPWM

Unlike conventional PWM controllers where the frequency of the clock dictates the maximum resolution of PWM

edges, the UCD3138x DPWM can generate waveforms with resolutions as small as 250 ps. This is 16 times the

resolution of the clock driving the DPWM module.

This is achieved by providing the DPWM mechanism with 16 phase shifted clock signals of 250 MHz each.

9.3.2.1.5

Over Sampling

The DPWM module has the capability to trigger an over sampling event by initiating the EADC to sample the

error voltage. The default “00” configuration has the DPWM trigger the EADC once based on the sample trigger

Thus the time the over sample happens is at the divide by 2, 4, or 8 time set in the sampling register. The “01”

setting triggers 2X over sampling, the “10” setting triggers 4X over sampling, and the “11” triggers over sampling

at 8X.

9.3.2.1.6

DPWM Interrupt Generation

The DPWM has the capability to generate a CPU interrupt based on the PWM frequency programmed in the

period register. The interrupt can be scaled by a divider ratio of up to 255 for developing a slower interrupt

service execution loop. This interrupt can be fed to the ADC circuitry for providing an ADC12 trigger for sequence

synchronization. Table 2 outlines the divide ratios that can be programmed.

9.3.2.1.7

DPWM Interrupt Scaling/Range

Table 2. DPWM Interrupt Divide Ratio

NUMBER OF 32

INTERRUPT

SWITCHING PERIOD

MHZ

DIVIDE

FRAMES (assume

PROCESSOR

SETTING

COUNT

COUNT (HEX)

1MHz loop)

CYCLES

128

256

512

1024

1536

2048

2560

3072

127

128

4096

159

160

5120

191

192

6144

223

224

7168

255

256

8192

9.3.3 Automatic Mode Switching

Automatic Mode switching enables the DPWM module to switch between modes automatically, with no firmware

intervention. This is useful to increase efficiency and power range. The following paragraphs describe phase-

shifted full bridge and LLC examples.

9.3.3.1 Phase Shifted Full Bridge Example

In phase shifted full bridge topologies, efficiency can be increased by using pulse width modulation, rather than

phase shift, at light load. This is shown below:

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