Datasheet
LT3692
19
3692fa
For more information www.linear.com/3692
applicaTions inForMaTion
If the synchronization signal powers up in an undetermined
state (V
OL
, V
OH
, Hi-Z), connect the synchronization clock
to the LT3692 as shown in Figure 9. The circuit as shown
will isolate the synchronization signal when the output
voltage is below 90% of the regulated output. The LT3692
will start up with a switching frequency determined by the
resistor from the RT/SYNC pin to ground.
If the synchronization signal powers up in a low impedance
state (V
OL
), connect a resistor between the RT/SYNC pin
and the synchronizing clock. The equivalent resistance
seen from the RT/SYNC pin to ground will set the start-
up frequency.
If the synchronization signal powers up in a high imped
-
ance state (Hi-Z), connect a resistor from the RT/SYNC
pin to ground. The equivalent resistance seen from the
R
T/SYNC pin to ground will set the start-up frequency
.
Reducing Input Ripple Voltage
Synchronizing the switches to the rising and falling edges
of the synchronization signal provides the unique ability to
reduce input ripple currents in systems where V
IN1
and V
IN2
are connected to the same supply. Decreasing the input
current ripple reduces the required input capacitance. For
example, the input ripple voltage shown in Figure 12 for
a typical antiphase dual 14.4V to 8.5V and 14.4V to 3.3V
regulator is decreased from a peak of 472mV to 160mV
as shown in Figure 13 by driving the LT3692 with a 71%
duty cycle synchronization signal.
Figure 9. Synchronous Signal Powered from Regulator’s Output
Figure 10. Timing Diagram RT/SYNC = 1MHz, Duty Cycle = 50%
Figure 11. Timing Diagram RT/SYNC = 1MHz, Duty Cycle > 50%
Figure 12. Dual 14.4V/8.5V, 14.4V/3.3V with 180° Phase
Figure 13. Dual 14.4V/8.5V, 14.4V/3.3V with 256° Phase
t
P
t
P
t
P
t
P
/2
t
P
/2
t
P
t
P
/2
t
DCLKOSW2
t
DRTSYNC
t
DCLKOSW1
SW1
SW2
CLKOUT
RT/SYNC
3692 F10
t
P
t
DCLKOSW2
t
DCLKOSW1
SW1
SW2
CLKOUT
RT/SYNC
t
DRTSYNCH
t
DRTSYNCH
3692 F11
t
P
t
PON
t
PON
t
P
t
P
LT3692 SYNCHRONIZATION
CIRCUITRY
V
OUT1
RT/SYNC
3692 F09
V
CC
CLK
PG1
SW1
SW2
RT/SYNC
3692 F12
INPUT
RIPPLE V
SW1
SW2
RT/SYNC
INPUT
RIPPLE V
3692 F13