LTC3633 LINER [Linear Technology], LTC3633 Datasheet - Page 17

• Manufacturer Part Number: LTC3633
• Description: Dual Channel 3A, 15V Monolithic Synchronous Step-Down Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
MODE/SYNC Operation
The MODE/SYNC pin is a multipurpose pin allowing both
mode selection and operating frequency synchronization.
Floating this pin or connecting it to INTV
Mode operation for superior effi ciency at low load currents
at the expense of slightly higher output voltage ripple. When
the MODE/SYNC pin is tied to ground, forced continuous
mode operation is selected, creating the lowest fi xed output
ripple at the expense of light load effi ciency.
The LTC3633 will detect the presence of the external clock
signal on the MODE/SYNC pin and synchronize the internal
oscillator to the phase and frequency of the incoming
clock. The presence of an external clock will place both
regulators into forced continuous mode operation.
Output Voltage Tracking and Soft-Start
The LTC3633 allows the user to control the output voltage
ramp rate by means of the TRACKSS pin. From 0 to 0.6V, the
TRACKSS voltage will override the internal 0.6V reference
input to the error amplifi er, thus regulating the feedback
voltage to that of the TRACKSS pin. When TRACKSS is
above 0.6V, tracking is disabled and the feedback voltage
will regulate to the internal reference voltage.
(4a) Coincident Tracking
TIME
Figure 4. Two Different Modes of Output Voltage Tracking
CC
3633 F04a
V
V
enables Burst
OUT1
OUT2
The voltage at the TRACKSS pin may be driven from an
external source, or alternatively, the user may leverage
the internal 1.4μA pull-up current source to implement
a soft-start function by connecting an external capacitor
(C
between output rise time and TRACKSS capacitance is
given by:
A default internal soft-start ramp forces a minimum soft-
start time of 400μs by overriding the TRACKSS pin input
during this time period. Hence, capacitance values less
than approximately 1000pF will not signifi cantly affect
soft-start behavior.
When driving the TRACKSS pin from another source, each
channel’s output can be set up to either coincidentally or
ratiometrically track another supply’s output, as shown in
Figure 4. In the following discussions, V
LTC3633 output 1 as a master channel and V
to output 2 as a slave channel. In practice, either channel
can be used as the master.
To implement the coincident tracking in Figure 4a, con-
nect an additional resistive divider to V
its midpoint to the TRACKSS pin of the slave channel.
SS
t
SS
) from the TRACKSS pin to ground. The relationship
= 430000Ω • C
(4b) Ratiometric Tracking
SS
TIME
OUT1
LTC3633
OUT1
3633 F04b
V
V
OUT1
OUT2
and connect
refers to the
OUT2
17
refers
3633f