Datasheet

LTM4603/LTM4603-1
19
4603fb
and are improved with air flow. The case temperature is
maintained at 100°C or below for the derating curves.
This allows for 4W maximum power dissipation in the
total module with top and bottom heat sinking, and 2W
power dissipation through the top of the module with an
approximate θ
JC
between 6°C/W to 9°C/W. This equates
to a total of 124°C at the junction of the device.
Safety Considerations
The LTM4603 modules do not provide isolation from V
IN
to V
OUT
. There is no internal fuse. If required, a slow blow
fuse 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 LTM4603 makes the PCB board
layout very simple and easy. However, to optimize its electri-
cal and thermal performance, some layout considerations
are still necessary.
• Use large PCB copper areas for high current path, in-
cluding V
IN
, PGND and V
OUT
. It helps to minimize the
PCB conduction loss and thermal stress.
• Place high frequency ceramic input and output capaci-
tors next to the V
IN
, PGND and V
OUT
pins to minimize
high frequency noise.
• Place a dedicated power ground layer underneath the
unit.
• To minimize the via conduction loss and reduce module
thermal stress, use multiple vias for interconnection
between top layer and other power layers.
• Do not put vias directly on pads.
• If vias are placed onto the pads, the the vias must be
capped.
• Interstitial via placement can also be used if necessary.
• Use a separated SGND ground copper area for com-
ponents connected to signal pins. Connect the SGND
to PGND underneath the unit.
Figure 15 gives a good example of the recommended layout.
Frequency Adjustment
The LTM4603 is designed to typically operate at 1MHz
across most input conditions. The f
SET
pin is typically
left open. The switching frequency has been optimized
for maintaining constant output ripple noise over most
operating ranges. The 1MHz switching frequency and
the 400ns minimum off time can limit operation at higher
duty cycles like 5V
IN
to 3.3V
OUT
, and produce excessive
inductor ripple currents for lower duty cycle applications
such as 20V
IN
to 5V
OUT
. The 5V
OUT
and 3.3V
OUT
drop
out curves are modified by adding an external resistor on
the f
SET
pin to allow for lower input voltage operation, or
higher input voltage operation.
SIGNAL
GND
V
OUT
V
IN
GND
C
OUT
C
IN
C
IN
C
OUT
4603 F15
Figure 15. Recommended Layout
applications inForMation