LM27313, LM27313-Q1

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SNVS487E – DECEMBER 2006 – REVISED JANUARY 2015

9 Power Supply Recommendations

The LM27313 is designed to operate from an input voltage supply range from 2.7 V to 14 V. This input supply

should be able to withstand the maximum input current and maintain a voltage above 2.7 V. In cases where input

supply is located farther away (more than a few inches) from LM27313, additional bulk capacitance may be

required in addition to the ceramic bypass capacitors.

10 Layout

10.1 Layout Guidelines

High-frequency switching regulators require very careful layout of components in order to get stable operation

and low noise. All components must be as close as possible to the LM27313 device. It is recommended that a 4-

layer PCB be used so that internal ground planes are available.

Some additional guidelines to be observed:

1. Keep the path between L1, D1, and C2 extremely short. Parasitic trace inductance in series with D1 and C2

will increase noise and ringing.

2. The feedback components R1, R2 and CF must be kept close to the FB pin of the LM27313 to prevent noise

injection on the high impedance FB pin.

3. If internal ground planes are available (recommended) use vias to connect directly to the LM27313 ground at

device pin 2, as well as the negative sides of capacitors C1 and C2.

10.2 Layout Example

Figure 22. Recommended PCB Component Layout

10.3 Thermal Considerations

At higher duty cycles, the increased ON time of the FET means the maximum output current will be determined

by power dissipation within the LM27313 FET switch. The switch power dissipation from ON-state conduction is

calculated by:

PSW = DC x IIND(AVG)

2 x R

DS(ON)

(18)

There will be some switching losses as well, so some derating needs to be applied when calculating IC power

dissipation.

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Product Folder Links: LM27313 LM27313-Q1