RT9263 datasheet(7/10 Pages) RICHTEK

7 / 10 page

Preliminary

RT9263

DS9263-00 November 2001

www.richtek-ic.com.tw

Application Note

Output Voltage Setting

Referring to application circuits Fig.1 to Fig.4, the

output voltage of the switching regulator (VOUT1) can

be set with Eq.1.

Feedback Loop Design

Referring to application circuits Fig.1 to Fig.4, 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

Ω 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.

• A proper value of feed forward capacitor parallel

with R1 on Fig.1 to Fig.4 can improve the noise

immunity of the feedback loops, especially in an

improper layout. An empirical suggestion is around

100pF ~ 1nF for feedback resistors of M

Ω, and

10nF ~ 0.1

µF for feedback resistors of tens to

hundreds K

Ω.

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 pins.

PRECAUTION 1: Improper probing to FB pin will

cause fluctuation at VOUT1. It may damage RT9263

and system chips because VOUT1 may drastically rise

to an over-rated level due to unexpected interference

or parasitics being added to FB pin.

PRECAUTION 2: Disconnecting R1 or short circuit

across R2 may also cause similar IC damage as

described in precaution 1.

PRECAUTION 3: When large R values were used in

feedback loops, any leakage in FB node may also

cause VOUT1 voltage fluctuation, and IC damage. To

be especially highlight here is when the air moisture

frozen and re-melt on the circuit board may cause

several

µA leakage between IC or component pins.

So, when large R values are used in feedback loops,

post coating, or some other moisture-preventing

processes are recommended.

Layout Guide

• A full GND plane without gap break.

• VOUT1 to GND noise bypass – Short and wide

connection for C2 to Pin2 and Pin5.

• VIN to GND noise bypass – Add a 100µF 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.

)

(

OUT

Eq.1

Prober Parasitics

FB Pin

VOUT1

RT9263 Datasheet(PDF) 7 Page - Richtek Technology Corporation

RT9263 Datasheet(HTML) 7 Page - Richtek Technology Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10

Datasheet Download

Link URL