ltm4608a Linear Technology Corporation, ltm4608a Datasheet - Page 16

• Manufacturer Part Number: ltm4608a
• Description: Low Vin, 8a Dc/dc ?module With Tracking, Margining, And Frequency Synchronization
• Manufacturer: Linear Technology Corporation

LTM4608A
Ratiometric tracking can be achieved by a few simple
calculations and the slew rate value applied to the master’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:
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
is equal the 10k. R
where V
tor and V
top feedback resistor of the slave regulator in equal slew
rate or coincident tracking, then R
V
Figure 5.
In ratiometric tracking, a different slew rate maybe desired
for the slave regulator. R
slower than MR. Make sure that the slave supply slew rate
is chosen to be fast enough so that the slave output voltage
will reach it fi nal value before the master output.
16
APPLICATIONS INFORMATION
FB
R
MR
SR
= V
FB
4
Figure 7. 3.3V
• 10
TRACK
FB
=
TRACK
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
is the feedback voltage reference of the regula-
10
V
k R
0
FB
0
=
k
. Therefore R
+
is 0.596V. Since R
FB
R
0 596
V
FB4
3
FB
.
FB
IN
2
2
, 2.5V and 1.5V
LOAD CURRENT (A)
is derived from equation:
–
V
FB3
V
R
FB3
TRACK
4
can be solved for when SR is
FB
3
= 10k and R
3.3V
3.3V
FB4
FB3
OUT
6
IN
IN
is equal to R
1.5V
2.5V
is equal to the 10k
Power Loss
4608A F07
OUT
OUT
8
FB4
= 6.65k in
FB2
with
FB3
For example: MR = 3.3V/ms and SR = 1.5V/ms. Then
R
For applications that do not require tracking or sequencing,
simply tie the TRACK pin to SV
turn on/off. Connecting TRACK to SV
~100μs of internal soft-start during start-up. Load current
needs to be present during track down.
Power Good
The PGOOD pin is an open-drain pin that can be used to
monitor valid output voltage regulation. This pin monitors
a ±10% window around the regulation point. As shown
in Figure 20, the sequencing function can be realized in a
dual output application by controlling the RUN pins and the
PGOOD signals from each other. The 1.5V output begins
its soft starting after the PGOOD signal of 3.3V output
becomes high, and 3.3V output starts its shut down after
the PGOOD signal of 1.5V output becomes low. This can
be applied to systems that require voltage sequencing
between the core and sub-power supplies.
Slope Compensation
The module has already been internally compensated for
all output voltages. Table 3 is provided for most applica-
tion requirements. A spice model will be provided for other
control loop optimization. For single module operation,
connect I
pins together and then connect to SGND at one point. Tie
I
TH
FB3
pins together to share currents evenly for all phases.
= 22.1k. Solve for R
Figure 8. 5V
THM
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
0
pin to SGND. For parallel operation, tie I
IN
2
, 3.3V and 1.5V
LOAD CURRENT (A)
FB4
4
to equal to 4.87k.
IN
5V
5V
to let RUN control the
OUT
6
IN
IN
1.5V
3.3V
IN
Power Loss
4608A F08
OUT
OUT
also enables the
8
4608af
THM