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LTC3810
29
3810fc
Output Voltage Tracking
The LTC3810 allows the user to program how its output
ramps up by means of the TRACK/SS pin. Through this
pin, the output can be set up to either coincidentally or
ratiometrically track with another supply’s output, as shown
in Figure 15. In the following discussions, V
OUT1
refers
to the master LTC3810’s output and V
OUT2
refers to the
slave LTC3810’s output.
To implement the coincident tracking in Figure 15a, con-
nect an additional resistive divider to V
OUT1
and connect its
midpoint to the TRACK/SS pin of the slave IC. The ratio of
this divider should be selected the same as that of the slave
IC’s feedback divider shown in Figure 16. In this tracking
mode, V
OUT1
must be set higher than V
OUT2
. To implement
the ratiometric tracking, the ratio of the divider should be
exactly the same as the master IC’s feedback divider. Note
that the internal soft-start current will introduce a small
Figure 15. Two Different Modes of Output Voltage Tracking
Figure 16. Setup for Coincident and Ratiometric Tracking
Figure 17. Equivalent Input Circuit of Error Amplifi er
APPLICATIONS INFORMATION
TIME
(15a) Coincident Tracking
V
OUT1
V
OUT2
OUTPUT VOLTAGE
TIME
3810 F15
(15b) Ratiometric Tracking
V
OUT1
V
OUT2
OUTPUT VOLTAGE
R3 R1
R4 R2
R3
V
OUT2
R4
(16a) Coincident Tracking Setup
TO
V
FB1
PIN
TO
TRACK/SS2
PIN
TO
V
FB2
PIN
V
OUT1
R1
R2
R3
V
OUT2
R4
3810 F16
(16b) Ratiometric Tracking Setup
TO
V
FB1
PIN
TO
TRACK/SS2
PIN
TO
V
FB2
PIN
V
OUT1
–
+
II
D1
TRACK/SS2
0.8V
V
FB2
D2
D3
3810 F17
EA2
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