IRU3137CS IRF [International Rectifier], IRU3137CS Datasheet - Page 6

• Manufacturer Part Number: IRU3137CS
• Description: 8-PIN SYNCHRONOUS PWM CONTROLLER
• Manufacturer: IRF [International Rectifier]

IRU3137
the output start-up time is the time period when soft-
start capacitor voltage increases from 1V to 2V. The start-
up time will be dependent on the size of the external
soft-start capacitor. The start-up time can be estimated
by:
For a given start up time, the soft-start capacitor can be
estimated as:
MOSFET Drivers
The driver capabilities of both high and low side drivers
are optimized to maintain fast switching transitions. They
are sized to drive a MOSFET that can deliver up to 20A
output current.
The low side MOSFET driver is supplied directly by V
while the high side driver is supplied by V
An internal dead time control is implemented to prevent
cross-conduction and allows the use of several kinds of
MOSFETs.
6
20 A T
C
SS
≅ 20 A T
START
/C
START
SS
= 2V-1V
/1V
C
.
www.irf.com
CC
Short-Circuit Protection
The outputs are protected against the short-circuit. The
IRU3137 protects the circuit for shorted output by sens-
ing the output voltage (through the external resistor di-
vider). The IRU3137 turns off both drivers, when the out-
put voltage drops below 0.4V.
The IRU3137 also protects the output from over-voltaging
when the control FET is shorted. This is done by turning
on the sync FET with the maximum duty cycle.
Under-Voltage Lockout
The under-voltage lockout circuit assures that the
MOSFET driver outputs remain in the off state whenever
the supply voltage drops below set parameters. Lockout
occurs if Vc and Vcc fall below 3.5V and 4.25V respec-
tively. Normal operation resumes once Vc and Vcc rise
above the set values.
Shutdown
The converter can be shutdown by pulling the soft-start
pin below 2.8V. This can be easily done by using an
external small signal transistor. During shutdown both
MOSFET drivers turn off.
Rev. 1.0
06/22/04