MAX5974A MAXIM [Maxim Integrated Products], MAX5974A Datasheet - Page 17

• Manufacturer Part Number: MAX5974A
• Description: Active-Clamped, Spread-Spectrum, Current-Mode PWM Controllers
• Manufacturer: MAXIM [Maxim Integrated Products]

startup to provide a slow and smooth increase of the
duty cycle to its steady-state value. Calculate the value
of C
where I
ing soft-start and t
A resistor can also be added from the SS pin to GND to
clamp V
cycle to be less than 80% (see the Duty-Cycle Clamping
section).
The NDRV output drives an external n-channel MOSFET.
NDRV can source/sink in excess of 650mA/1000mA
peak current; therefore, select a MOSFET that yields
acceptable conduction and switching losses. The exter-
nal MOSFET used must be able to withstand the maxi-
mum clamp voltage.
Figure 3. Dead Time Between AUXDRV and NDRV
SS
SS-CH
as follows:
SS
< 2V and, hence, program the maximum duty
(10FA typ) is the current charging C
n-Channel MOSFET Gate Driver
BLANKING, t
DEAD TIME, t
SS
C
SS
is the programmed soft-start time.
AUXDRV
=
NDRV
I
BLK
DT
SS-CH
2V
Active-Clamped, Spread-Spectrum,
×
t
ss
Current-Mode PWM Controllers
SS
dur-
The AUXDRV output drives an external p-channel
MOSFET with the aid of a level shifter. The level shifter
consists of C
Application Circuits. When AUXDRV is high, C
recharged through D5. When AUXDRV is low, the gate
of the p-channel MOSFET is pulled below the source by
the voltage stored on C
Dead time between the main and AUX output edges
allow ZVS to occur, minimizing conduction losses and
improving efficiency. The dead time (t
both leading and trailing edges of the main and AUX out-
puts as shown in Figure 3. Connect a resistor between
DT and GND to set t
400ns:
AUX
p-Channel MOSFET Gate Driver
, R
R
AUX
DT
DT
, and D5 as shown in the Typical
AUX
=
to any value between 40ns and
10k
40ns
, turning on the pFET.
Ω
×
t
DT
DT
) is applied to
Dead Time
AUX
17
is