RT9266 RICHTEK [Richtek Technology Corporation], RT9266 Datasheet - Page 12

• Manufacturer Part Number: RT9266
• Description: Tiny Package, High Efficiency, Step-up DC/DC Converter
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9266
Application Information
Output Voltage Setting
Referring to Typical Application Circuits, the output voltage
of the switching regulator (V
(1).
Feedback Loop Design
Referring to Typical Application Circuits. The selection of
R1 and R2 based on the trade-off between quiescent
current consumption and interference immunity is stated
below:
l
l
l
l
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
sensitive to any interference, which require careful layout
and avoid any interference, e.g. probing to FB pin.
www.richtek.com
12
Follow Equation (1)
Higher R reduces the quiescent current (Path current
= 1.25V/R2), however resistors beyond 5M
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 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
M , and 10nF~0.1 F for feedback resistors of tens to
hundreds k .
Q
+
_
V
Prober Parasitics
OUT
“
high impedance feedback loops
= ( 1+
R2
R1
OUT
) 1.25V
) can be set with Equation
V
OUT
R1
R2
FB Pin
are not
”
are
(1)
Layout Guide
l
l
l
l
l
Board Layout Example (2-Layer Board)
(Refer to Typical Application Circuits Figure 2 for the board)
A full GND plane without gap break.
V
for the 1 F MLCC capacitor between Pin5 and Pin3.
V
inductor, when V
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.
DD
IN
to GND noise bypass Add a capacitor close to L1
to GND noise bypass Short and wide connection
IN
- Bottom Layer -
is not an idea voltage source.
- Top Layer -
DS9266-12 May 2007