RT8256 데이터 시트보기 (PDF) - Richtek Technology
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RT8256 Datasheet PDF : 12 Pages
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RT8256
Table 1. Recommended Component Selection
VOUT (V) R1 (kΩ) R2 (kΩ) RC (kΩ) CC (nF)
12
88.7
10
62
0.82
5
30
10
20
2.2
3.3
17
10
10
1.5
2.5
10.45
10
7.5
1.5
1.8
4.75
10
6
1.5
1.222
0
10
6
3.9
L1 (μH)
33
22
15
10
10
6.8
C OUT (μF)
22
22
22
22
22
22
Functional Pin Description
Pin No.
1
2
3
4
Pin Name
NC
BOOT
VIN
SW
Pin Function
No Internal Connection.
High Side Gate Drive Boost Input. BOOT supplies the drive for the high side N-MOSFET
switch. Connect a 10nF or greater capacitor from SW to BOOT to power the high side
swi tc h.
Power Input. VIN supplies the power to the IC, as well as the step-down converter
switches. Bypass VIN to GND with a suitable large capacitor to eliminate noise on the
input to the IC.
Power Switching Output. SW is the switching node that supplies power to the output.
Connect the output LC filter from SW to the output load. Note that a capacitor is required
from SW to BOOT to power the high side switch.
5
GND
Ground.
6
FB
Feedback Input. FB senses the output voltage to regulate said voltage. The feedback
reference voltage is 1.222V typically.
Compensation Node. COMP is used to compensate the regulation control loop. Connect
7
COMP
a series RC network from COMP to GND to compensate the regulation control loop. In
some cases, an additional capacitor from COMP to GND is required.
8
EN
Enable Input. EN is a digital input that turns the regulator on or off. Drive EN higher than
1.4V to turn on the regulator, lower than 0.4V to turn it off. If the EN pin is open, it will be
pulled to high by internal circuit.
Function Block Diagram
VIN
1µA
Internal
Regulator
Oscillator
400kHz/120kHz
Current Sense
Slope Comp Amplifier
+
-
VA
10k
EN
-
Foldback
Control
1V +
0.6V +
3V
Shutdown
Comparator
-
UV
Comparator
1.222V +
EA
-
SQ
+
RQ
-
Current
Comparator
Gm = 780µA/V
VA
BOOT
SW
GND
www.richtek.com
2
FB
COMP
DS8256-01 March 2011
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