LTC3415 Datasheet, PDF (16/28 Pages) Linear Technology – 7A, PolyPhase Synchronous Step-Down Regulator

LTC3415
OPERATION
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+ ^RR21,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 floating. To implement
the coincident tracking shown in Figure 10a, connect an
extra resistive divider to the output of V_OUT2 and connect
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_

16
V_OUT2
TO
TRACK
PIN
R4 R2
TO
V_FB2(MASTER)
PIN
R3 R1
V_OUT2
TO
TRACK
PIN
R2
TO
V_FB2(MASTER)
PIN
R1
3415 F11
(11a) Coincident Tracking Setup
(11b) Ratiometric Setup
Figure 11. Setup for Tracking and Ratiometric Sequencing
V_OUT2
R5
R4
V_FB
LTC3415
R3
SGND
V_OUT1
R2
TRACK
V_FB
LTC3415
R1
SGND
3415 F12
Figure 12. Dual Voltage System with Tracking
3415fa