LTC3709 Linear Technology, LTC3709 Datasheet - Page 18

• Manufacturer Part Number: LTC3709
• Description: No RSENSE Synchronous DC/DC Controller
• Manufacturer: Linear Technology

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LTC3709
APPLICATIO S I FOR ATIO
Output Voltage Tracking
The feedback voltage, V
voltage when the TRACK pin voltage is less than the
reference voltage, V
voltage is greater than V
servo to V
pin, ensure the final steady-state voltage on the TRACK pin
is greater than V
The LTC3709 allows the user to set up start-up sequenc-
ing among different supplies in either coincident tracking
or ratiometric tracking as shown in Figure 6. To implement
the coincident tracking, connect an extra resistor divider
to the output of supply 1. This resistor divider is selected
18
3.3V OR 5V
Figure 5. RUN/SS Pin Interfacing with Latchoff Defeated
REF
D1
. When selecting components for the TRACK
(5a)
V
REF
IN
R
U
SS
at the end of the tracking interval.
*
REF
RUN/SS
(6a) Coincident Tracking
FB
(0.6V). When the TRACK pin
U
REF
C
SS
, will follow the TRACK pin
, the feedback voltage will
TIME
Figure 6. Two Different Forms of Output Voltage Sequencing
W
*OPTIONAL TO OVERRIDE
OVERCURRENT LATCHOFF
V
CC
2N7002
R
D2*
SS
(5b)
*
RUN/SS
U
V
V
OUT1
OUT2
3709 F05
C
SS
to be the same as the divider across supply 2’s output. The
TRACK pin of supply 2 is connected to this extra resistor
divider. For the ratiometric tracking, simply connect the
TRACK pin of supply 2 to the V
shows this implementation. Note that in the coincident
tracking, output voltage of supply 1 has to be set higher
than output voltage of supply 2.
Note that since the shutdown trip point varies from part to
part, the “slave” part’s RUN/SS pin will need to be con-
nected to V
LTC3709s may shut down at different times.
If output sequencing is not needed, connect the TRACK
pins to V
Figure 7. Setup for Coincident and Ratiometric Tracking
CC
SUPPLY 1
CC
. Do Not Float these pins .
R3
R4
R3
R4
(6b) Ratiometric Tracking
V
. This eliminates the possibility that different
FB
= R5
= R1
R6
R2
V
RATIOMETRIC POWER UP
BETWEEN V
OUT2
R1
R2
COINCIDENTLY TRACKS V
TIME
R3
R4
OUT1
V
OUT1
AND V
FB
SUPPLY 2
TRACK
LTC3709
OUT2
pin of supply 1. Figure 7
3709 F06
V
FB
V
V
OUT1
OUT1
OUT2
R5
R6
3709 F07
V
OUT2
3709f