ST92185B datasheet(159/178 Pages) STMICROELECTRONICS

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ST92185B - VOLTAGE SYNTHESIS TUNING CONVERTER (VS)

VOLTAGE SYNTHESIS (Cont’d)

BRM Generation

The BRM bits allow the addition of a pulse to wid-

en a standard PWM pulse for specific PWM cy-

cles. This has the effect of “fine-tuning” the PWM

Duty cycle (without modifying the base duty cycle),

thus, with the external filtering, providing additional

fine voltage steps.

The incremental pulses (with duration of TINTCLK/

4) are added to the beginning of the original PWM

pulse and thus cause the PWM high time to be ex-

tended by this time with a corresponding reduction

in the low time. The PWM intervals which are add-

ed to are specified in the lower 7 bits of the tuning

word and are encoded as shown in the following

table.

Table 29. 7-Bit BRM Pulse Addition Positions

The BRM values shown may be combined togeth-

er to provide a summation of the incremental pulse

intervals specified.

The pulse increment corresponds to the PWM res-

olution.

Figure 101. Simplified Filtered Voltage Output Schematic with BRM added

Fine Tuning

No. of Pulses added at the

following Cycles

0000001

0000010

32, 96

0000100

16, 48, 80, 112

0001000

8, 24,... 104, 120

0010000

4, 12,... 116, 124

0100000

2, 6,... 122, 126

1000000

1, 3,... 125, 127

VDD

PWMOUT

VDD

OUTPUT

VOLTAGE

BRM = 1

BRM = 0

INTCLK/4

BRM

EXTENDED PULSE

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