Datasheet

LTC3415
16
3415fa
If the voltage on the TRACK pin is less than 0.57V, voltage
tracking is enabled. During voltage tracking, the output
voltage is regulated by the tracking voltage through a resis-
tive divider network. The output voltage during tracking
can be calculated with the following equation:
V
OUT
= V
TRACK
1+
R2
R1






,V
TRACK
< 0.57V
Voltage tracking can be accomplished by sensing a frac-
tion of the output voltage from another regulator. This is
typically done by using a resistive divider to attenuate the
output voltage that is being tracked. Setting this resistive
divider equal to the feedback resistive divider will force the
regulator outputs to be equal to each other during track-
ing. If tracking is not desired, connect the TRACK pin to
SV
IN.
Do not leave the TRACK pin fl oating. To implement
the coincident tracking shown in Figure 10a, connect an
extra resistive divider to the output of V
OUT2
and connect
OPERATION
its midpoint to the TRACK pin of the LTC3415 as shown
in Figure 11. The ratio of this divider should be selected
the same as that of V
OUT1
’s resistive divider. To implement
the ratiometric sequencing in Figure 10b, no extra resis-
tive divider is necessary. Simply connect the TRACK pin
to V
FB
of the master.
An alternative method of tracking is shown in Figure 12.
For the circuit of Figure 12, the following equations can
be used to determine the resistor values:
V
OUT1
= 0.596V 1+
R2
R1






V
OUT2
= 0.596V 1+
R4+ R5
R3






R4 = R3
V
OUT2
V
OUT1
–1






Figure 12. Dual Voltage System with Tracking
Figure 11. Setup for Tracking and Ratiometric Sequencing
(11a) Coincident Tracking Setup
(11b) Ratiometric Setup
R4 R2
R3 R1
TO
V
FB2(MASTER)
PIN
TO
TRACK
PIN
V
OUT2
R2
R1
3415 F11
TO
V
FB2(MASTER)
PIN
TO
TRACK
PIN
V
OUT2
LTC3415
SGND
R1
3415 F12
R2
V
FB
TRACK
V
OUT1
LTC3415
SGND
R3
R4
R5
V
FB
V
OUT2