9

SCD5031 Rev B

Pr

el

im

in

ary

Dead Time

The amount of dead time determines the maximum duty cycle that can be achieved. The Dead Time and the frequency of

operation will determine the duty cycle.

Selecting Rset and Cset

To select values for Rset and Cset perform the following steps to insure the smallest Dead Time..

1) Determine what frequency is required for your design.

2) Use Figure 4 to select a capacitor value for Cset that will provide the highest duty cycle (shortest Dead Time) at

the frequency required.

3) Calculate the value of Rset using the formula:

Note small values of Rset increase power consumption for the PWM5031 and small values of Cset may make PCB and

stray capacitance a source of error.

Dead Time

5280 C

set

12pF

+

()

=

Duty Cycle

1

Dead Time

1 F

osc

⁄

-----------------------------

⎝⎠

⎛⎞

–

=

R

set

1

.84

F

osc

×

C

set

×

-----------------------------------------

=

10K

100K

Duty Cycle

1M

%

86

100

98

96

94

92

90

88

47pF

100pF

200pF

20pF

10pF

390pF

Frequency Hz

FIGURE 4 – Duty Cycle vs Frequency