Datasheet

LTC3615/LTC3615-1
22
3615fb
For more information www.linear.com/LTC3615
Output Voltage Tracking Input
If SRLIM is low, once V
TRACK/SS
reaches or exceeds 0.6V
the run state is entered, and the MODE selection, power
good and current foldback circuits are enabled.
In the run state, the TRACK/SS pin can be used to track
down/up the output voltage of another supply. If the V
TRACK/
SS
again drops below 0.6V, the LTC3615 enters the down-
tracking state and the V
OUT
is referenced to the TRACK/
SS voltage. If V
TRACK/SS
reaches 0.1V value the switching
frequency is reduced by 4x to ensure that the minimum
duty cycle limit does not prevent the output from following
the TRACK/SS pin. The run state will resume if the V
TRACK/
SS
again exceeds 0.6V and the V
OUT
is referenced to the
internal reference.
Through the TRACK/SS pin, the output voltage can be set
up to either coincidental or ratiometric tracking, as shown
in Figures 8 and 9.
To implement the coincidental tracking waveform in
Figure 8, connect an
extra resistive divider to the output
of the master channel and connect its midpoint to the
TRACK/SS pin for the slave channel. The ratio of this
divider should be selected the same
as that of the slave
channel’s feedback divider (Figure 10).
In this tracking mode, the master channel’s output must
be set higher than slave channel’s output. To implement
the ratiometric start-up in Figure 9, no extra divider is
needed; simply connect the TRACK/SS pin to the other
channel’s V
FB
pin (Figure 12).
applicaTions inForMaTion
Figure 8. Coincident Start-Up Tracking Figure 9. Ratiometric Start-Up Tracking
Figure 10. Set for Coincidentally
Tracking (R3 = R5, R4 = R6)
Figure 11. Alternative Set-Up for Coincident
Start-Up Tracking (R1 = R3, R2 = R3 = R5)
Figure 12. Set-Up for
Ratiometric Tracking
TIME
V
OUT1
V
OUT2
OUTPUT VOLTAGE
3615 F08
TIME
3615 F09
V
OUT1
V
OUT2
OUTPUT VOLTAGE
R3
R4
R1
R2
V
OUT1
FB1
LTC3615
TRACK/SS2
FB2
R5
R6
V
OUT2
3615 F10
R2
R1
R3
V
OUT1
FB1
LTC3615
TRACK/SS2
FB2
R4
R5
V
OUT2
3615 F11
R1
R2
V
OUT1
FB1
LTC3615
TRACK/SS2
FB2
R3
R4
V
OUT2
3615 F12
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