RT8286 데이터 시트보기 (PDF) - Richtek Technology
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RT8286 Datasheet PDF : 14 Pages
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RT8286
Table 2. Suggested Inductors for Typical
Application Circuit
Component Supplier Series Dimensions (mm)
TDK
VLF10045 10 x 9.7 x 4.5
TDK
SLF12565 12.5 x 12.5 x 6.5
TAIYO YUDEN NR8040
8x8x4
Input and Output Capacitors Selection
The input capacitance, CIN, is needed to filter the
trapezoidal current at the source of the high side MOSFET.
To prevent large ripple current, a low ESR input capacitor
sized for the maximum RMS current should be used. The
RMS current is given by :
IRMS
=
IOUT(MAX)
VOUT
VIN
VIN
VOUT
−1
This formula has a maximum at VIN = 2VOUT, where IRMS =
IOUT / 2. This simple worst case condition is commonly
used for design because even significant deviations do
not offer much relief.
Choose a capacitor rated at a higher temperature than
required. Several capacitors may also be paralleled to
meet size or height requirements in the design.
For the input capacitor, one 22μF low ESR ceramic
capacitors are recommended. For the recommended
capacitor, please refer to Table 3 for more detail.
Location
CIN
CIN
COUT
COUT
COUT
COUT
Table 3. Suggested Capacitors for CIN and COUT
Component Supplier
Part No.
Capacitance (μF)
MURATA
GRM32ER71C226M
22
TDK
C3225X5R1C226M
22
MURATA
GRM31CR60J476M
47
TDK
C3225X5R0J476M
47
MURATA
GRM32ER71C226M
22
TDK
C3225X5R1C226M
22
Case Size
1210
1210
1206
1210
1210
1210
The selection of COUT is determined by the required ESR
to minimize voltage ripple.
Moreover, the amount of bulk capacitance is also a key
for COUT selection to ensure that the control loop is stable.
Loop stability can be checked by viewing the load transient
response.
The output ripple, ΔVOUT, is determined by :
ΔVOUT
≤
ΔIL
⎡⎢⎣ESR +
1
8fCOUT
⎤
⎥⎦
Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at input and
output. When a ceramic capacitor is used at the input
and the power is supplied by a wall adapter through long
wires, a load step at the output can induce ringing at the
input, VIN. At best, this ringing can couple to the output
and be mistaken as loop instability. At worst, a sudden
inrush of current through the long wires can potentially
cause a voltage spike at VIN large enough to damage the
part.
Thermal Shutdown
Thermal shutdown is implemented to prevent the chip from
operating at excessively high temperatures. When the
junction temperature is higher than 150°C, the whole chip
is shutdown. The chip is automatically re-enable when
the junction temperature cools down by approximately
30 degrees.
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS8286-02 June 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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