RT7256B
Typical Application Circuit
V
IN
4.5V to 17V
2
C
IN
10µF x 2
R
EN
100k
VIN
RT7256B
BOOT
7 EN
8 SS
GND
1
C
BOOT
L
0.1µF 2µH
R1
22k
FB 5
R2
6.8k
V
OUT
3.3V
C
OUT
22µF x 2
SW 3
C
SS
0.1µF
4, 9 (Exposed Pad)
Table 1. Suggested Component Selection
V
OUT
(V)
8
5
3.3
2.5
1.8
1.2
R1 (kΩ)
9
10.5
22
25.5
31.25
35.7
R2 (kΩ)
1
2
6.8
12
25
68
L (μH)
3.6
2
2
1
0.68
0.68
C
OUT
(μF)
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
Functional Pin Description
Pin No.
1
2
3
4,
9 (Exposed Pad)
5
6
7
Pin Name
BOOT
VIN
SW
GND
FB
NC
EN
Pin Function
Bootstrap for High Side Gate Driver. Connect a 0.1μF or greater ceramic
capacitor from BOOT to SW pins.
Input Supply Voltage, 4.5V to 17V. Must bypass with a suitably large ceramic
capacitor.
Switch Node. Connect this pin to an external L-C filter.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
Feedback Input. It is used to regulate the output of the converter to a set value
via an external resistive voltage divider.
No Internal Connection.
Enable Input Pin. A logic high enables the converter; a logic low forces the
RT7256B into shutdown mode reducing the supply current to less than 3μA.
Attach this pin to VIN with a 100kΩ pull up resistor for automatic startup.
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 13.5ms.
8
SS
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS7256B-00
February 2012
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
