Datasheet

LTC3835-1
15
38351fc
APPLICATIONS INFORMATION
Alternatively, the TRACK/SS pin can be used to track two
(or more) supplies during start-up, as shown qualitatively
in Figures 4a and 4b. To do this, a resistor divider should
be connected from the master supply (V
X
) to the TRACK/
SS pin of the slave supply (V
OUT
), as shown in Figure 5.
During start-up V
OUT
will track V
X
according to the ratio
set by the resistor divider:
V
V
R
R
RR
RR
X
OUT
A
TRACKA
TRACKA TRACKB
AB
=
+
+
•
For coincident tracking (V
OUT
= V
X
during start-up),
R
A
= R
TRACKA
R
B
= R
TRACKB
INTV
CC
Regulators
The LTC3835-1 features an internal P-channel low dropout
linear regulator (LDO) that supplies power at the INTV
CC
pin from the V
IN
supply pin. INTV
CC
powers the gate
drivers and much of the LTC3835-1’s internal circuitry.
The V
IN
LDO regulates the voltage at the INTV
CC
pin to
5.25V. It can supply a peak current of 50mA and must be
bypassed to ground with a minimum of 4.7μF tantalum,
10μF special polymer, or low ESR electrolytic capacitor.
A ceramic capacitor with a minimum value of 4.7μF can
also be used if a 1Ω resistor is added in series with the
capacitor. No matter what type of bulk capacitor is used, an
additional 1μF ceramic capacitor placed directly adjacent
to the INTV
CC
and PGND IC pins is highly recommended.
Good bypassing is needed to supply the high transient
currents required by the MOSFET gate drivers and to
prevent interaction between the channels.
TIME
(4a) Coincident Tracking
V
X
(MASTER)
V
OUT
(SLAVE)
OUTPUT VOLTAGE
3835-1 F04A
V
X
(MASTER)
V
OUT
(SLAVE)
TIME
3835-1 F04B
(4b) Ratiometric Tracking
OUTPUT VOLTAGE
Figure 4. Two Different Modes of Output Voltage Tracking
LTC3835-1
V
OUT
V
x
V
FB
TRACK/SS
38351 F05
RB
RA
R
TRACKA
R
TRACKB
Figure 5. Using the TRACK/SS Pin for Tracking