LM2735XMFSLASHNOPB datasheet(37/59 Pages) TI

37 / 59 page

LM2735, LM2735-Q1

www.ti.com

SNVS485G – JUNE 2007 – REVISED AUGUST 2015

9 Power Supply Recommendations

The LM2735 device is designed to operate from an input voltage supply range from 2.7 V to 5.5 V. This input

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

where input supply is located farther away (more than a few inches) from the device, additional bulk capacitance

may be required in addition to the ceramic bypass capacitors.

10 Layout

10.1 Layout Guidelines

When planning layout, there are a few things to consider when trying to achieve a clean, regulated output. The

most important consideration when completing a boost converter layout is the close coupling of the GND

connections of the COUT capacitor and the LM2735 PGND pin. The GND ends should be close to one another

and be connected to the GND plane with at least two through-holes. There should be a continuous ground plane

on the bottom layer of a two-layer board except under the switching node island. The FB pin is a high impedance

node and care should be taken to make the FB trace short to avoid noise pickup and inaccurate regulation. The

feedback resistors should be placed as close as possible to the IC, with the AGND of R1 placed as close as

possible to the GND (pin 5 for the WSON) of the IC. The VOUT trace to R2 should be routed away from the

inductor and any other traces that are switching. High AC currents flow through the VIN, SW and VOUT traces, so

they should be as short and wide as possible. However, making the traces wide increases radiated noise, so the

designer must make this trade-off. Radiated noise can be decreased by choosing a shielded inductor. The

remaining components should also be placed as close as possible to the IC. See Application Note AN-1229

SIMPLE SWITCHER® PCB Layout Guidelines (SNVA054) for further considerations and the LM2735 demo

board as an example of a 4-layer layout.

Below is an example of a good thermal and electrical PCB design. This is very similar to our LM2735

demonstration boards that are obtainable through the TI website. The demonstration board consists of a 2-layer

PCB with a common input and output voltage application. Most of the routing is on the top layer, with the bottom

layer consisting of a large ground plane. The placement of the external components satisfies the electrical

considerations, and the thermal performance has been improved by adding thermal vias and a top layer Dog-

Bone.

10.1.1 WSON Package

The LM2735 packaged in the 6–pin WSON:

Figure 42. Internal WSON Connection

For certain high power applications, the PCB land may be modified to a dog bone shape (see Figure 43).

Increasing the size of ground plane, and adding thermal vias can reduce the RθJA for the application.

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LM2735XMF/NOPB Datasheet(PDF) 37 Page - Texas Instruments