Datasheet

LM2733
SNVS209E –NOVEMBER 2002–REVISED APRIL 2013 www.ti.com
Figure 25. Recommended PCB Component Layout
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 U1 to prevent noise injection
on the FB pin trace.
3. If internal ground planes are available (recommended) use vias to connect directly to ground at pin 2 of U1,
as well as the negative sides of capacitors C1 and C2.
SETTING THE OUTPUT VOLTAGE
The output voltage is set using the external resistors R1 and R2 (see Figure 26). A value of approximately 13.3
kΩ is recommended for R2 to establish a divider current of approximately 92 µA. R1 is calculated using the
formula:
R1 = R2 X (V
OUT
/1.23 − 1) (2)
SWITCHING FREQUENCY
The LM2733 is provided with two switching frequencies: the “X” version is typically 1.6 MHz, while the “Y” version
is typically 600 kHz. The best frequency for a specific application must be determined based on the tradeoffs
involved:
Higher switching frequency means the inductors and capacitors can be made smaller and cheaper for a given
output voltage and current. The down side is that efficiency is slightly lower because the fixed switching losses
occur more frequently and become a larger percentage of total power loss. EMI is typically worse at higher
switching frequencies because more EMI energy will be seen in the higher frequency spectrum where most
circuits are more sensitive to such interference.
Figure 26. Basic Application Circuit
10 Submit Documentation Feedback Copyright © 2002–2013, Texas Instruments Incorporated
Product Folder Links: LM2733