Datasheet

LTM4644/LTM4644-1
14
Rev. F
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APPLICATIONS INFORMATION
4644 F05
V
IN1
SV
IN1
RUN1
INTV
CC1
MODE1
V
OUT1
FB1 COMP1 TRACK/SS1 PGOOD1
CH1
C
SS
0.1µF
R
FB1
13.3k
V
IN
4V TO 14V
R
TR(TOP)2
60.4k
3.3V/4A
2.5V/4A 1.8V/4A 1.2V/4A
V
IN2
SV
IN2
RUN2
INTV
CC2
MODE2
V
OUT2
FB2 COMP2 TRACK/SS2 PGOOD2
CH2
R
FB(SL)2
19.1k
V
IN3
SV
IN3
RUN3
INTV
CC3
MODE3
V
OUT3
FB3 COMP3 TRACK/SS3 PGOOD3
CH3
R
FB(SL)3
30.1k
V
IN4
SV
IN4
RUN4
INTV
CC4
MODE4
V
OUT4
FB4 COMP4 TRACK/SS4 PGOOD4
CH4
LTM4644
R
FB(SL)4
60.4k
R
TR(BOT)2
13.3k
R
TR(TOP)3
60.4k
R
TR(BOT)3
13.3k
R
TR(TOP)4
60.4k
R
TR(BOT)4
13.3k
60.4k 60.4k 60.4k 60.4k
4644 F04
TIME
OUTPUT VOLTAGE
V
OUT4
= 1.2V
V
OUT3
= 1.8V
V
OUT2
= 2.5V
V
OUT1
= 3.3V
Figure 4. Output Ratiometric Tracking Waveform
Figure 5. Output Ratiometric Tracking Schematic
For example, V
OUT(MA)
= 3.3V, MR = 3.3V/24ms and V
OUT(SL)
= 1.2V, SR = 1.2V/24ms as V
OUT1
and V
OUT4
shown in
Figure 5. From the
equation, we could solve out that
R
TR4(TOP)
= 60.4k and R
TR4(BOT)
= 13.3k is a good com-
bination. Follow
the same equation, we can get the same
R
TR(TOP)
/R
TR(BOT)
resistor divider value for V
OUT2
and
V
OUT3
.
The TRACK pins will have the 2.5µA current source on
when a resistive divider is used to implement tracking on
that specific channel. This will impose an offset on the
TRACK pin input. Smaller value resistors with the same
ratios as the resistor values calculated from the above
equation can be used. For example, where the 60.4k is
used then a 6.04k can be used to reduce the TRACK pin
offset to a negligible value.
The coincident output tracking can be recognized as a
special ratiometric output tracking which the master’s
output slew rate (MR) is the same as the slave’s output
slew rate (SR), as waveform shown in Figure 6.
From the equation we could easily find
out that
, in the
coincident tracking, the slave regulator’s TRACK/SS pin
resistor divider is always the same as its output voltage
divider.
R
FB(SL)
R
FB(SL)
+ 60.4k
=
R
TR(BOT)
R
TR(TOP)
+R
TR(BOT)
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