rt9263ccx5 Richtek Technology Corporation, rt9263ccx5 Datasheet - Page 7

• Manufacturer Part Number: rt9263ccx5
• Description: High Efficiency Supply Current Step Dc/dc Converter
• Manufacturer: Richtek Technology Corporation

Application Note
Output Voltage Setting
Referring to application circuits Fig.1 to Fig.4, the
output voltage of the switching regulator (V
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
interference immunity is stated below:
• Follow Eq.1
• Higher R reduces the quiescent current (Path
• Lower R gives better noise immunity, and is less
• A proper value of feed forward capacitor parallel
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.
DS9263-00 November 2001
current = 1.25V/R2), however resistors beyond
5MΩ are not recommended.
sensitive to interference, layout parasitics, FB
node leakage, and improper probing to FB pins.
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 MΩ, and
10nF ~ 0.1µF for feedback resistors of tens to
hundreds KΩ.
V
OUT
quiescent
1
=
1 (
+
R
R
1
2
)
×
current
. 1
25
V
consumption
OUT1
) can
Eq.1
and
Preliminary
PRECAUTION 1: Improper probing to FB pin will
cause fluctuation at V
and system chips because V
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 V
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.
• V
• V
• Minimized FB node copper area and keep far
• Minimized parasitic capacitance connecting to LX
connection for C2 to Pin2 and Pin5.
close to L1 inductor, when VIN is not an idea
voltage source.
away from noise sources.
and EXT nodes, which may cause additional
switching loss.
OUT1
IN
to GND noise bypass – Add a 100µF capacitor
OUT1
to GND noise bypass – Short and wide
Q
+
Prober Parasitics
_
voltage fluctuation, and IC damage. To
OUT1
. It may damage RT9263
OUT1
V
www.richtek-ic.com.tw
OUT1
may drastically rise
R2
R1
RT9263
FB Pin
7