RT9266PE Ver la hoja de datos (PDF) - Richtek Technology
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RT9266PE Datasheet PDF : 14 Pages
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RT9266
Application Information
Output Voltage Setting
Referring to Typical Application Circuits, the output voltage
of the switching regulator (VOUT) can be set with Equation
(1).
R1
VOUT = ( 1+ ) × 1.25V
(1)
R2
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 Follow Equation (1)
l Higher R reduces the quiescent current (Path current
= 1.25V/R2), however resistors beyond 5MΩ are not
recommended.
l Lower R gives better noise immunity, and is less
sensitive to interference, layout parasitics, FB node
leakage, and improper probing to FB pins.
VOUT
Prober Parasitics
_
Q
+
R1
FB Pin
R2
l 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.
Layout Guide
l A full GND plane without gap break.
l VDD to GND noise bypass − Short and wide connection
for the 1µF MLCC capacitor between Pin5 and Pin3.
l VIN to GND noise bypass − Add a capacitor close to L1
inductor, when VIN is not an idea voltage source.
l Minimized FB node copper area and keep far away
from noise sources.
l Minimized parasitic capacitance connecting to LX and
EXT nodes, which may cause additional switching loss.
Board Layout Example (2-Layer Board)
(Refer to Typical Application Circuits Figure 2 for the board)
- Top Layer -
www.richtek.com
12
- Bottom Layer -
DS9266-12 May 2007
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