LTC3615 LINER [Linear Technology], LTC3615 Datasheet - Page 22

• Manufacturer Part Number: LTC3615
• Description: Dual 4MHz, 3A Synchronous Step-Down DC/DC Converter
• Manufacturer: LINER [Linear Technology]

LTC3615
applicaTions inForMaTion
Output Voltage Tracking Input
If SRLIM is low, once V
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
the down-tracking state and the V
the TRACK/SS voltage. If V
the switching frequency is reduced by 4x to ensure that
the minimum duty cycle limit does not prevent the out-
put from following the TRACK/SS pin. The run state will
resume if the V
is referenced to the internal reference.

TRACK/SS
Figure 10. Set for Coincidentally
Tracking (R3 = R5, R4 = R6)
R3
R4
V
V
again drops below 0.6V, the LTC3615 enters
OUT1
OUT2
Figure 8. Coincident Start-Up Tracking
R1
R2
R5
R6
TRACK/SS
FB1
TRACK/SS2
FB2
LTC3615
TRACK/SS
3615 F10
again exceeds 0.6V and the V
TIME
TRACK/SS
reaches or exceeds 0.6V
OUT
reaches 0.1V value
3615 F08
is referenced to
V
V
Figure 11. Alternative Set-Up for Coincident
Start-Up Tracking (R1 = R3, R2 = R3 = R5)
OUT1
OUT2
V
V
OUT1
OUT2
OUT
R1
R2
R3
R4
R5
FB1
TRACK/SS2
FB2
LTC3615
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
3615 F11
FB
Figure 9. Ratiometric Start-Up Tracking
pin (Figure 12).
TIME
V
V
OUT1
OUT2
Figure 12. Set-Up for
Ratiometric Tracking
R1
R2
R3
R4
3615 F09
FB1
TRACK/SS2
FB2
V
V
LTC3615
OUT1
OUT2
3615 F12
3615f