RT7257D
Typical Application Circuit
V
IN
4.5V to 18V
2
C
IN
10µF x 2
VIN
BOOT
RT7257D
SW 3
7 EN
8 SS
GND
1
C
BOOT
L
0.1µF 3.6µH
R1
75k
FB 5
COMP
6
C
C
2.2nF
R
C
22k
R2
24k
V
OUT
3.3V
C
OUT
22µF x 2
Chip Enable
C
SS
0.1µF
4, 9 (Exposed Pad)
C
P
Open
V
OUT
(V)
8
5
3.3
2.5
1.5
1.2
1
Table 1. Suggested Components Selection
R1 (kΩ) R2 (kΩ) R
C
(kΩ) C
C
(nF)
L (μH)
C
OUT
(μF)
27
3
51
2.2
10
22 x 2
62
11.8
33
2.2
6.8
22 x 2
75
24
22
2.2
3.6
22 x 2
25.5
12
16
2.2
3.6
22 x 2
10.5
12
10
2.2
2
22 x 2
12
24
8.2
2.2
2
22 x 2
3
12
6.8
2.2
2
22 x 2
Functional Pin Description
Pin No.
1
2
3
4,
9 (Exposed Pad)
5
6
Pin Name
BOOT
VIN
SW
GND
FB
COMP
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 18V. Must bypass with a suitable 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.
Compensation Node. COMP is used to compensate the regulation control
loop. Connect a series RC network from COMP to GND. In some cases, an
additional capacitor from COMP to GND is required.
Enable Input. A logic high enables the converter; a logic low forces the
RT7257D 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.
7
EN
8
SS
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS7257D-04
September 2012
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
