Datasheet
LTC3416
10
3416fa
APPLICATIO S I FOR ATIO
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coincidentally or ratiometrically track another output volt-
age as shown in Figure 3.
If the voltage on the TRACK pin is less than 0.8V, voltage
tracking is enabled. During voltage tracking, the output
voltage regulates to the tracking voltage through a resistor
divider network. The output voltage during tracking can be
calculated with the following equation:
VV
R
R
OUT TRACK
=+
⎛
⎝
⎜
⎞
⎠
⎟
1
2
1
, V
TRACK
< 0.8V
Voltage tracking can be accomplished by sensing a frac-
tion of the output voltage from another regulator. This is
typically done by using a resistor divider to attenuate the
output voltage that is being tracked. Setting this attenua-
tion factor equal to the reciprocal of the gain factor
provided by the feedback resistors will force the regulator
outputs to be equal to each other during tracking. If
tracking is not desired, connect the TRACK pin to SV
IN
.
To implement the coincident tracking shown in Figure 3a,
connect an extra resistor divider to the output of V
OUT2
and
connect its midpoint to the TRACK pin of the LTC3416 as
shown in Figure 4. The ratio of this divider should be
selected the same as that of V
OUT1
’s resistor divider. To
implement the ratiometric sequencing in Figure 3b, the
extra resistor divider’s ratio should be set so that the
TRACK pin voltage exceeds 1.05V by the end of the start-
up period. The LTC3416 utilizes a method in which the
TRACK pin’s control over the output voltage is gradually
released as the TRACK pin voltage approaches 0.8V. With
this technique, some overdrive will be required on the
TRACK pin to ensure that the tracking function is com-
pletely disabled at the end of the start-up period.
For coincident tracking, the following condition should be
satisfied to ensure that tracking is disabled at the end of
start-up.
V
OUT2
≥ 1.32 V
OUT1
For ratiometric tracking, the following equation can be
used to calculate the resistor values:
RR
V
V
VV
OUT
TRACK
TRACK
43 1
105
2
=
⎛
⎝
⎜
⎞
⎠
⎟
≥
–
.
TIME
(3a) Coincident Tracking
V
OUT2
V
OUT1
OUTPUT VOLTAGE
TIME
3416 F03
(3b) Ratiometric Sequencing
V
OUT2
V
OUT1
OUTPUT VOLTAGE
Figure 3. Two Different Modes of Output Voltage Sequencing
Figure 4. Setup for Tracking and Ratiometric Sequencing
R4 R2
R3 R1
TO
V
FB(MASTER)
PIN
TO
TRACK
PIN
V
OUT2
3416 F04