RT8288ZSP データシートの表示（PDF） - Richtek Technology
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RT8288ZSP Datasheet PDF : 14 Pages
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RT8288
VIN
Chip Enable
REN
100k
Q1
1 VIN
BOOT 4
CIN
RT8288
5 EN
SW 2, 3
CBOOT
L
7
VCC
CC
FB 6
RT
GND 8, 9 (Exposed Pad)
VOUT
R1
COUT
R2
Figure 3. Enable Control Circuit for Logic Control with Low Voltage
VIN
REN
100k
1 VIN
BOOT 4
CBOOT
CIN
RT8288
5 EN
SW 2, 3
L
VOUT
REN2
CC
7
VCC
FB 6
RT
GND 8, 9 (Exposed Pad)
R1
COUT
R2
Figure 4. The Resistors can be Selected to Set IC Lockout Threshold
Under Output Voltage Protection-Hiccup Mode
For the IC, Hiccup Mode of Under Voltage Protection (UVP)
is provided. When the FB voltage drops below half of the
feedback reference voltage, VFB, the UVP function will be
triggered and the IC will shut down for a period of time and
then recover automatically. The Hiccup Mode of UVP can
reduce input current in short-circuit conditions.
Inductor Selection
For a given input and output voltage, the inductor value
and operating frequency determine the ripple current. The
ripple current ΔIL increases with higher VIN and decreases
with higher inductance.
ΔIL
=
⎡
⎢⎣
VOUT
f ×L
⎤
⎥⎦
×
⎡⎢⎣1−
VOUT
VIN
⎤
⎥⎦
Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output voltage
ripple. Highest efficiency operation is achieved by reducing
ripple current at low frequency, but it requires a large
inductor to attain this goal.
For the ripple current selection, the value of ΔIL = 0.24
(IMAX) will be a reasonable starting point. The largest ripple
current occurs at the highest VIN. To guarantee that the
ripple current stays below a specified maximum, the
inductor value should be chosen according to the following
equation :
L
=
⎡
⎢⎣
f
×
VOUT
ΔIL(MAX)
⎤
⎥⎦
×
⎡⎢⎣1−
VOUT
VIN(MAX)
⎤
⎥⎦
The inductor's current rating (caused a 40°C temperature
rising from 25°C ambient) should be greater than the
maximum load current and its saturation current should
be greater than the short circuit peak current limit. Please
see Table 2 for the inductor selection reference and it is
highly recommended to keep inductor value as close as
possible to the recommended inductor values for each
VOUT as shown in Table 1.
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
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
www.richtek.com
10
is a registered trademark of Richtek Technology Corporation.
DS8288-03 June 2012
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