AN-1280| Application Note

LM2731/LM2733 Evaluation Board

LM2731/LM2733 Evaluation Board
The LM2731 and LM2733 are high frequency switching boost regulators which offer small size and high power conversion efficiency. The "X" version of the part operates at 1.6MHz switching frequency and the "Y" version at 600kHz. The primary difference between the LM2731 and LM2733 is that the LM2731 has a higher current internal switch FET (with lower breakdown voltage), while the LM2733 has a higher voltage FET which handles less current. The LM2733 targets applications with higher output voltages, while the

National Semiconductor Application Note 1280 April 2003

LM2731 is intended for applications requiring higher load currents at lower output voltages. This application note will describe the evaluation board supplied to demonstrate the operation of these parts and give information on its usage.

Basic Application Circuit
The basic application circuit shown below provides the component designators used on the evaluation board.

20069101

Eval Board Basic Applicatrion Circuit

20069102

Eval Board Component Layout

Component Values
The initial build of evaluation boards were built up in 12V and 24V output versions using different components at selected locations (see Note 1 below). The components which are common to all boards are: 1. PCB 2. R1, resistor 51k, 5% 3. R3, resistor 13.3k, 1% 4. C1, capacitor, 2.2 uF, ceramic, Taiyo-Yuden #EMK316BJ225ML 5. D1, diode, MBR0530 6. L1, inductor:10 uH (Sumida #CR43-100)

The components which are application specific are: 1. C2, output capacitor: a 4.7 uF cap is installed on the board for LM2733 (X and Y) and the LM2731X devices. A 10 uF output capacitor is used for the LM2731Y devices. 2. R2, resistor which sets output voltage. See section on adjusting the output voltage for details. 3. C3, feed forward capacitor. Dependent on R2, see section on feedforward compensation.
Note 1: (addendum 02/06/03) An additional build of eval boards for 3.3V to 5V applications using the LM2731 were made on this date. See Demo Board section for details.

AN-1280

2003 National Semiconductor Corporation

AN200691

www.national.com