ADP1974

Data Sheet

Rev. 0 | Page 16 of 19

Programming the Dead Time

To adjust the dead time on the synchronous DH and DL







3.76

28.51

ns

V







DEAD

DT

DT

t

I

V

(11)

DT

DT

DT

I

V

R



(12)

where:





3.76

28.51

ns

kΩ



DT

t

R

(13)

0

25

50

75

100

125

150

175

0

100

200

300

400

500

600

700

PROGRAMMING THE MAXIMUM DUTY CYCLE

The ADP1974 is designed with a 97% (typical) maximum

internal duty cycle. By connecting a resistor from DMAX to

ground, the maximum duty cycle can be programmed at any

value from 0% to 97%, by using the following equation:



5

.

10

5

.

21

%









FREQ

DMAX

FREQ

MAX

R

R

V

D

(14)

where:

maximum duty cycle.

The DMAX current source is equivalent to the programmed

current of the FREQ pin:

FREQ

FREQ

FREQ

DMAX

R

V

I

I





(15)

FREQ pin.

DUTY CYCLE (%)

0

50

100

150

200

250

300

350

400

450

020

60

80

100

40

The maximum duty cycle of the ADP1974 is 97% (typical). If

the resistor on DMAX sets a maximum duty cycle larger than

97%, the ADP1974 defaults to its internal maximum. If the 97%

internal maximum duty cycle is sufficient for the application, tie

the DMAX pin to VREG or leave it floating.

ground plane must be 47 pF or greater.

ADJUSTING THE SOFT START PERIOD

The ADP1974 has a programmable soft start feature that

prevents output voltage overshoot during startup. Refer to

Figure 22 for a soft start diagram. To calculate the delay time

SS

SS

REG

C

I

t



 0.52

(16)

where:

The output voltage rising ramp is then proportional to the ramp

on SS and the input voltage of the ADP1974.

SS

SS

RAMP

C

I

t



 4

(V/s)

)

s

(

RAMP

IN

OUT

t

V

Time

V

RAMP_RATE



