Datasheet
LTM4627
15
4627fc
For more information www.linear.com/LTM4627
its final value from the slave’s regulation point. Voltage
tracking is disabled when V
TRACK
is more than 0.6V. R
TA
in Figure 4 will be equal to the R
FB
for coincident tracking.
The TRACK/SS pin of the master can be controlled by an
external ramp or the soft-start function of that regulator
can be used to develop that master ramp. The LTM4627 can
be used as a master by setting the ramp rate on its track
pin using a soft-start capacitor. A 1.2µA current source
is used to charge the soft-start capacitor. The following
equation can be used:
t
SOFT-START
= 0.6V •
C
SS
1.2µA
Ratiometric tracking can be achieved by a few simple
calculations and the slew rate value applied to the master’s
TRACK/SS pin. As mentioned above, the TRACK/SS pin
has a control range from 0V to 0.6V. The master’s TRACK/
SS pin slew rate is directly equal to the master’
s output
slew rate in volts/time. The equation:
MR
SR
• 60.4k = R
TB
where MR is the master’s output slew rate and SR is the
slave’s output slew rate in volts/time. When coincident
tracking is desired, then MR and SR are equal, thus R
TB
is equal to 60.4k. R
TA
is derived from equation:
R
TA
=
0.6V
V
FB
60.4k
+
V
FB
R
FB
–
V
TRACK
R
TB
where V
FB
is the feedback voltage reference of the regula-
tor, and V
TRACK
is 0.6V. Since R
TB
is equal to the 60.4k
APPLICATIONS INFORMATION
Figure 4. Dual Outputs (1.5V and 1.2V) with Coincident Tracking
COMP
TRACK/SS
RUN
f
SET
MODE_PLLIN
PGOOD
V
OUT
V
OUT_LCL
DIFF_OUT
V
OSNS
+
V
OSNS
–
V
FB
LTM4627
V
IN
R2
10k
R
FB1
40.2k
R4
100k
C10
22µF
16V
C7
22µF
16V
82pF
C
SS
SOFT-START
CAPACITOR
470µF
6.3V
100µF
6.3V
V
OUT2
1.5V AT 15A
C8
C11
C9
22µF
16V
INTV
CC
EXTV
CC
V
IN
6V
TO 16V
SGND GND
+
COMP
TRACK/SS
RUN
f
SET
MODE_PLLIN
PGOOD
V
OUT
V
OUT_LCL
DIFF_OUT
V
OSNS
+
V
OSNS
–
V
FB
LTM4627
V
IN
R1
10k
R
FB
60.4k
R3
100k
C2
22µF
16V
C3
22µF
16V
82pF
470µF
6.3V
100µF
6.3V
V
OUT1
1.2V
15A
C4
C6
C1
22µF
16V
INTV
CC
EXTV
CC
4627 F04
SGND GND
+
R
TB
60.4k
R
TA
60.4k
MASTER RAMP
OR OUTPUT
V
IN
6V
TO 16V
150pF
150pF