LTM4608 LINER [Linear Technology], LTM4608 Datasheet - Page 19

• Manufacturer Part Number: LTM4608
• Description: Low VIN, 8A DC/DC ?ModuleTM with Tracking, Margining, and Frequency Synchronization
• Manufacturer: LINER [Linear Technology]

Output Margining
For a convenient system stress test on the LTM4608’s
output, the user can program the LTM4608’s output to
±5%, ±10% or ±15% of its normal operational voltage.
The margin pin with a voltage divider is driven with a small
three-state gate as shown in Figure 18, for the three margin
states (high, low, no margin). When the MGN pin is low, it
forces negative margining in which the output voltage is
below the regulation point. When MGN is high, the output
voltage is forced to above the regulation point. The amount
of output voltage margining is determined by the BSEL
pin. When BSEL is low, it is 5%. When BSEL is high, it is
10%. When BSEL is fl oating, it is 15%. When margining
is active, the internal output overvoltage and undervoltage
comparators are disabled and PGOOD remains high. Mar-
gining is disabled by tying the MGN pin to V
Thermal Considerations and Output Current Derating
The power loss curves in Figures 7 and 8 can be used
in coordination with the load current derating curves in
Figures 9 to 16 for calculating an approximate θ
module with various heat sinking methods. Thermal models
are derived from several temperature measurements at
the bench, and thermal modeling analysis. Thermal Ap-
plication Note 103 provides a detailed explanation of the
analysis for the thermal models and the derating curves.
Tables 4 and 5 provide a summary of the equivalent θ
for the noted conditions. These equivalent θ
are correlated to the measured values and improve with
air fl ow. The junction temperature is maintained at 125°C
or below for the derating curves.
Safety Considerations
The LTM4608 modules do not provide isolation from V
V
with a rating twice the maximum input current needs to be
provided to protect each unit from catastrophic failure.
Layout Checklist/Example
The high integration of LTM4608 makes the PCB board
layout very simple and easy. However, to optimize its
APPLICATIONS INFORMATION
OUT
. There is no internal fuse. If required, a slow blow fuse
JA
OUT
parameters
.
JA
for the
IN
JA
to
electrical and thermal performance, some layout con-
siderations are still necessary.
• Use large PCB copper areas for high current path,
• Place high frequency ceramic input and output capaci-
• Place a dedicated power ground layer underneath the
• To minimize the via conduction loss and reduce module
• Do not put vias directly on the pads, unless they are
• Use a separated SGND ground copper area for com-
Figure 17 gives a good example of the recommended
layout.
including V
PCB conduction loss and thermal stress.
tors next to the V
high frequency noise.
unit.
thermal stress, use multiple vias for interconnection
between top layer and other power layers.
capped.
ponents connected to signal pins. Connect the SGND
to GND underneath the unit.
C
GND
IN
C
V
IN
IN
Figure 17. Recommended PCB Layout
IN
, GND and V
IN
, GND and V
OUT
GND
. It helps to minimize the
OUT
LTM4608
pins to minimize
V
C
C
C
GND
4608 F17
OUT
19
OUT
OUT
OUT
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