RT8272
Table 1. Recommended Component Selection
V
OUT
(V)
R1 (kΩ)
R2 (kΩ)
R
C
(kΩ)
C
C
(nF)
C
OUT
(μF)
L (μH)
15
10
8
5
3.3
2.5
1.8
1.2
153
100
77
43
25.8
17
9.1
3
10
10
10
10
10
10
10
10
82
62
62
41
39
21
15
15
0.82
1.2
1.5
2.2
2.2
2.2
2.2
2.2
47
47
47
47
47
47
47
47
10
10
6.8
6.8
4.7
4.7
2.2
2.2
Functional Pin Description
Pin No.
1
Pin Name
BOOT
Pin Function
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 switch.
Power Input. V
IN
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.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
Feedback Input. FB senses the output voltage to regulate said voltage. The
feedback reference voltage is 0.92V typically.
Compensation Node. COMP is used to compensate the regulation control loop.
Connect 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.
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.
Soft-Start Control Input. SS controls the soft start period. Connect a capacitor
from SS to GND to set the soft-start period. A 0.1μF capacitor sets the soft-start
period to 10ms.
2
VIN
3
4,
9 (Exposed Pad)
5
SW
GND
FB
6
COMP
7
EN
8
SS
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2
DS8272-02 March 2011
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
