LTM4604 LINER [Linear Technology], LTM4604 Datasheet - Page 11

• Manufacturer Part Number: LTM4604
• Description: Low Voltage, 4A DC/DC ?ModuleTM with Tracking
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Ratio metric modes of tracking can be achieved by selecting
different resistor values to change the output tracking ratio.
The master output must be greater than the slave output
for the tracking to work. Linear Technology Tracker Cad26
can be used to implement different tracking scenarios. The
Master and Slave data inputs can be used to implement
the correct resistor values for coincident or ratio tracking.
The master and slave regulators require load current for
tracking 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 ±7.5% window around the regulation point.
COMP Pin
The pin is the external compensation pin. The module
has already been internally compensated for all output
voltages. Table 4 is provided for most application require-
ments. A spice model will be provided for other control
loop optimizations.
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
Figure 4. 1.2V Power Loss
1
LOAD CURRENT (A)
2
3
5V TO 1.2V
POWER LOSS
3.3V TO 1.2V
POWER LOSS
4
4604 F04
5
Parallel Operation
The LTM4604 device is an inherently current mode con-
trolled device. Parallel modules will have very good current
sharing. This will balance the thermals on the design.
Figure 16 shows a schematic of the parallel design. The
voltage feedback changes with the variable N as more
modules are paralleled. The equation:
N is the number of paralleled modules.
Thermal Considerations and Output Current Derating
The power loss curves in Figures 4 and 5 can be used
in coordination with the load derating curves in Figures
6 through 13 for calculating an approximate θ
module with and without heat sinking methods with vari-
ous airfl ow conditions. Thermal models are derived from
several temperature measurements at the bench, and are
correlated with thermal analysis software. Tables 2 and
3 provide a summary of the equivalent θ
conditions. These equivalent θ
to the measured values and improve with air fl ow. The
maximum junction temperature is monitored while the
derating curves are derived.
V
OUT
=
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0 8
0
.
0
V
•
Figure 5. 2.5V Power Loss
4 99
1
.
N
LOAD CURRENT (A)
R
k
FB
+
2
R
FB
JA
3
parameters are correlated
5V TO 2.5V
POWER LOSS
3.3V TO 2.5V
POWER LOSS
4
LTM4604
4604 F05
JA
5
for the noted
JA
11
for the
4604f