Datasheet

LTM4622
13
Rev. G
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APPLICATIONS INFORMATION
tracked up and down with another regulator. Figure4 and
Figure5 show an example waveform and schematic of a
Ratiometric tracking where the slave regulator’s output
slew rate is proportional to the master’s.
Since the slave regulator’s TRACK/SS is connected to
the master’s output through a R
TR(TOP)
/R
TR(BOT)
resistor
The R
FB(SL)
is the feedback resistor and the R
TR(TOP)
/
R
TR(BOT)
is the resistor divider on the TRACK/SS pin of
the slave regulator, as shown in Figure5.
Following the upper equation, the master’s output slew
rate (MR) and the slave’s output slew rate (SR) in Volts/
Time is determined by:
MR
SR
=
R
FB(SL)
R
FB(SL)
+ 60.4k
R
TR(BOT)
R
TR(TOP)
+ R
TR(BOT)
For example, V
OUT(MA)
= 1.5V, MR = 1.4V/1ms and
V
OUT(SL)
= 1.2V, SR = 1.2V/1ms. From the equation, we
could solve out that R
TR(TOP)
=60.4k and R
TR(BOT)
= 40.2k
is a good combination for the Ratiometric tracking.
The TRACK pins will have the 1.5µA 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 values 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.
Figure5. Example Schematic of Ratiometric
Output Voltage Tracking
Figure6. Output Coincident Tracking Waveform
TIME
MASTER OUTPUT
SLAVE OUTPUT
OUTPUT VOLTAGE
4622 F06
divider and its voltage used to regulate the slave output
voltage when TRACK/SS voltage is below 0.6V, the slave
output voltage and the master output voltage should sat-
isfy the following equation during the start-up.
V
OUT(SL)
•
R
FB(SL)
R
FB(SL)
+ 60.4k
=
V
OUT(MA)
•
R
TR(BOT)
R
TR(TOP)
+ R
TR(BOT)
Figure4. Output Ratiometric Tracking Waveform
TIME
SLAVE OUTPUT
MASTER OUTPUT
OUTPUT VOLTAGE
4622 F04
0.1µF
40.2k
60.4k
V
OUT1
40.2k
4622 F05
10µF
25V
V
IN
4V TO 20V
V
OUT1
1.5V, 2.5A
47µF
4V
V
OUT1
V
OUT2
1.2V, 2.5A
47µF
4V
V
OUT2
FB1
COMP1
COMP2
GND
LTM4622
PGOOD1 PGOOD2
V
IN2
V
IN1
RUN1
RUN2
INTV
CC
SYNC/MODE
TRACK/SS1
TRACK/SS2
FREQ
60.4k
FB2
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