RT9266CE 데이터 시트보기 (PDF) - Richtek Technology

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RT9266CE

Tiny Package, High Efficiency, Step-up DC/DC Converter

Richtek Technology 

RT9266

Preliminary

Application Note

Output Voltage Setting

Referring to application circuits, the output voltage of

the switching regulator (VOUT) can be set with Eq.1.

VOUT1 = (1+ R1) ×1.25V

R2

Eq.1

Feedback Loop Design

Referring to application circuits, The selection of R1

and R2 based on the trade-off between quiescent

current consumption and interference immunity is

stated below:

• Follow Eq.1

• Higher R reduces the quiescent current (Path

current = 1.25V/R2), however resistors beyond

5MΩ are not recommended.

• Lower R gives better noise immunity, and is less

sensitive to interference, layout parasitics, FB

node leakage, and improper probing to FB pins.

Layout Guide

• A full GND plane without gap break.

• VDD to GND noise bypass – Short and wide

connection for the 1µF MLCC capacitor between

Pin5 and Pin3.

• VIN to GND noise bypass – Add a capacitor close

to L1 inductor, when VIN is not an idea voltage

source.

• Minimized FB node copper area and keep far

away from noise sources.

• Minimized parasitic capacitance connecting to LX

and EXT nodes, which may cause additional

switching loss.

Board Layout Example (2-Layer Board)

(Refer to Application Circuit Fig. 2 for the board)

Prober Parasitics

_

Q

+

VOU T1

R1

FB Pin

R2

• A proper value of feed forward capacitor parallel

with R1 can improve the noise immunity of the

feedback loops, especially in an improper layout.

An empirical suggestion is around 0~33pF for

feedback resistors of MΩ, and 10nF~0.1µF for

feedback resistors of tens to hundreds KΩ.

For applications without standby or suspend modes,

lower values of R1 and R2 are preferred. For

applications concerning the current consumption in

standby or suspend modes, the higher values of R1

and R2 are needed. Such “high impedance feedback

loops” are sensitive to any interference, which require

careful layout and avoid any interference, e.g.

probing to FB pin.

- Top Layer –

- Bottom Layer -

www.richtek.com

10

DS9266-02 February 2003

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