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LTM4603/LTM4603-1

4603f

APPLICATIO S I FOR ATIO

Safety Considerations

The LTM4603 modules do not provide isolation from VIN to

VOUT. 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 VIN, PGND and VOUT. It helps to minimize the

PCB conduction loss and thermal stress.

• Place high frequency ceramic input and output capaci-

tors next to the VIN, PGND and VOUT 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 fSET pin is typically left

open or decoupled with an optional 1000pF capacitor. 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 to

3.3V, and produce excessive inductor ripple currents for

lower duty cycle applications like 20V to 5V. The 5V and

3.3V drop out curves are modiﬁed by adding an external

resistor on the fSET pin to allow for lower input voltage

operation, or higher input voltage operation.

SIGNAL

GND

VOUT

VIN

GND

COUT

CIN

COUT

4603 F15

Figure 15. Recommended Layout

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