Datasheet
LTM4616
16
4616ff
For more information www.linear.com/LTM4616
applications inForMation
coincident tracking. The LTM4616 uses an accurate 10k
resistor internally for the top feedback resistor. Figure 5
shows an example of coincident tracking:
Slave = 1+
10k
R
TA
⎛
⎝
⎜
⎞
⎠
⎟
• V
TRACK
V
TRACK
is the track ramp applied to the slave’s track pin.
V
TRACK
has a control range of 0V to 0.596V, or the internal
reference voltage. When the master’s output is divided
down with the same resistor values used to set the slave’s
output, then the slave will coincident track with the master
until it reaches its final value. The master will continue to its
final value from the slave’s regulation point. Voltage track
-
ing is disabled when V
TRACK
is more than 0.596V. R
TA
in
Figure 5 will be equal to R
FB
for coincident tracking.
The track pin of the master can be controlled by an external
ramp or by R
SR
and C
SR
in Figure 5 referenced to V
IN
.
The RC ramp time can be programmed using equation:
t = – ln 1–
0.596V
V
IN
⎛
⎝
⎜
⎞
⎠
⎟
• R
SR
• C
SR
⎛
⎝
⎜
⎞
⎠
⎟
Figure 5. Dual Outputs (3.3V and 1.5V) with Tracking
Ratiometric tracking can be achieved by a few simple
calculations and the slew rate value applied to the mas-
ter’s track
pin. As mentioned above, the TRACK pin has
a
control range from 0V to 0.596V. The master’s TRACK
pin slew rate is directly equal to the master’s output slew
rate in Volts/Time:
MR
SR
• 10k = 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 10k. R
TA
is derived from equation:
R
TA
=
0.596V
V
FB
10k
+
V
FB
R
FB
–
V
TRACK
R
TB
where V
FB
is the feedback voltage reference of the regula-
tor and V
TRACK
is 0.596V. Since R
TB
is equal to the 10k
top feedback resistor of the slave regulator in coincident
tracking, then R
TA
is equal to R
FB2
with V
FB
= V
TRACK
.
R
FB2
6.65k
10µF
100µF 100µF
50k
50k
SLAVE
1.5V/8A
V
IN1
SV
IN1
RUN1
PLLLPF1
MODE1
PHMODE1
TRACK1
V
IN2
SV
IN2
RUN2
PLLLPF2
MODE2
PHMODE2
TRACK2
V
OUT1
FB1
I
TH1
I
THM1
PGOOD1
BSEL1
MGN1
V
OUT2
FB2
I
TH2
I
THM2
PGOOD2
BSEL2
MGN2
SW1 CLKIN1 CLKOUT1 CLKIN2 CLKOUT2
SW2 SGND1 GND1 SGND2 GND2
CLKIN1
4616 F05
LTM4616
R
FB1
2.21k
10µF
PGOOD
BSEL
V
IN
4V TO 5.5V
MASTER
3.3V/7A
RUN
RUN
R
TB
10k
R
TA
6.65k
MASTER
3.3V
C
SR
R
SR
FOR TRACK1:
1. TIE TO VIN TO DISABLE TRACK WITH DEFAULT 100µs SOFT START
2. APPLY A CONTROL RAMP WITH R
SR
AND C
SR
TIED TO V
IN
WITH t = –(ln(1–0.596/V
IN
) • R
SR
• C
SR
))
3. APPLY AN EXTERNAL TRACKING RAMP DIRECTLY
100µF
V
IN