iru3072 International Rectifier Corp., iru3072 Datasheet - Page 10

• Manufacturer Part Number: iru3072
• Description: 20-pin Synchronous Pwm Controller/ 3 Ldo Controller -
• Manufacturer: International Rectifier Corp.

IRU3072
(a). Shutdown and start up PWM output by controlling
soft start SS1. LDO output such as Vout2 will not be
affected.
(b). Shutdown and start up LDO output by controlling
soft-start SSLDO. PWM output V
One issue related to shutdown of PWM output by pull-
ing down the soft-start, there is a small negative voltage
shown in the output during the shutdown. It is because
the low side MOSFET driver is on when the soft-start
capacitor voltage is pulling down. The output inductor
resonates with output capacitor and load. This occurs
especially often when output current is small (light load
or no load condition). The operation waveforms are shown
as follows.
10
Figure 10 - Shutdown PWM or LDO by
controlling soft-start.
OUT1
will not be affected.
www.irf.com
Both PWM output and LDO output can be shutdown by
pulling the pin V
as follows.
IRU3072
Soft-Start
SS1
UVLO
U1
Figure 11 - Operation waveforms when PWM
V
Shutdown
SEN33
External
SS
VccLDO
Figure 12 - External shutdown by
converter is shutdown by pulling
OCSet
/ SDB
LDO
down the soft-start capacitor.
HDrv
Drv2
LDrv
Fb2
Vcc
Vc
SEN33
using pin V
/SDB down. One example is shown
R7
SEN33
4.7K
/SDB.
Q4
Q5
C6
L1
L2
Rev. 1.0
V
3/25/04
BUS
V
3.3V
C10
OUT1
=5V