LTC3614_15 Datasheet, PDF (21/30 Pages) Linear Technology – 4A, 4MHz Monolithic Synchronous Step-Down DC/DC Converter

LTC3614
Applications Information
To implement the coincident tracking behavior in Fig-
ure 6a, 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 to be the same as that of the
slave channel’s feedback divider (Figure 7a). In this track-
ing mode, the master channel’s output must be set higher
than slave channel’s output. To implement the ratiometric
tracking behavior in Figure 6b, different resistor divider
values must be used as specified in Figure 7b.
V_OUT2
V_OUT1
R4
V_FB2
R2
LTC3614
R4 R3
V_FB1
V_IN
R2 R2 _LTC3614
TRACK/SS2
R4 ≤ R3
TRACK/SS1
LTC3614 CHANNEL 2
SLAVE
LTC3614 CHANNEL 1
MASTER
3614 F07a
Figure 7a. Setup for Coincident Tracking
V_OUT2
V_OUT1
R1
V_FB2
R2
LTC3614
TRACK/SS2
LTC3614 CHANNEL 2
SLAVE
R5 R3 R1/R2 < R5/R6
V_FB1
R6 R4 _LTC3614
TRACK/SS1
V_IN
LTC3614 CHANNEL 1
MASTER
3614 F07b
Figure 7b. Setup for Ratiometric Tracking
For coincident start-up, the voltage value at the TRACK/SS
pin for the slave channel needs to reach the final reference
value after the internal soft-start time (around 1ms). The
master start-up time needs to be adjusted with an external
capacitor and resistor to ensure this.
External Reference Input (DDR Mode)
If the DDR pin is tied to SV_IN (DDR mode), the run state is
entered when V_TRACK/SS exceeds 0.3V and tracking down
behavior is possible if the V_TRACK/SS voltage is below 0.6V.
This allows TRACK/SS to be used as an external reference
between 0.3V and 0.6V if desired. During the run state in
DDR mode, the power good window moves in relation
to the actual TRACK/SS pin voltage if the voltage value
is between 0.3V and 0.6V. Note: if TRACK/SS voltage is
0.6V, either the tracking circuit or the internal reference
can be used.
During up/down tracking the output current foldback is
disabled and the PGOOD pin is always pulled down (see
Figure 9).
For more information www.linear.com/LTC3614
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