HT45FM03B datasheet(41/83 Pages) HOLTEK

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HT45FM03B

Rev. 1.10

May 7, 2010

PWM Dead Time Function

Each PWM output normally drives a pair of push-pull

power transistors for load driving. The danger here is

that for short periods of time, both both output transis-

tors may be on simultaneously resulting in virtual short

circuit conditions across the power supply. To prevent

this happening a dead time function is included which

ensures that there is a period of time when both output

transistors are off when the PWM output changes state.

The dead time can have a value of 1/fD, 2/fD, 3/fD, 4/fD,

5/fD, 6/fD, 7/fD or 8/fD where fD is fSYS/1, fSYS/2, fSYS/4 or

fSYS/8. The PWM dead time is determined using the

PWMDT2, PWMDT1 and PWMDT0 bits in the PWMC0

ter select the value for fD.

The dead time is a function of the system clock fre-

quency, the DTPSn bits and the PWMDTn bits. By pro-

gramming suitable values for these bits a wide range of

dead times can be chosen. The following equation

shows how the dead time can be calculated. The deci-

mal equivalent of the binary bit value should be substi-

tuted to calculate the value.

Dead Time value= (1/fD)

´((PWMDT2~PWMDT0)+1)

where fD is determined by the DTPSn bits.

For example:

· f

SYS=12MHz

· DTPS1, DTPS0= 11, i.e. f

D=fSYS/8

· PWMDT2~PWMDT0 = 101 (decimal 5)

¼ gives a dead time of 4ms.

A c t i v e

I n a c t i v e

P W M x H

P W M x L

P W M x H

P W M x L

( P W M w i t h o u t D e a d T i m e )

( P W M w i t h D e a d T i m e )

D e a d T i m e

Note:

The PWM and Complementary PWM Outputs include Dead Time ( Both PWMLEV and PWMCLEV= 0)

PWM Dead Time Timing

HT45FM03B Datasheet(PDF) 41 Page - Holtek Semiconductor Inc

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