RT7297B
2
DS7297B-02 September 2012
www.richtek.com
©
Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
Functional Pin Description
Pin No.
Pin Name
Pin Function
1 BOOT
Bootstrap for High Side Gate Driver. Connect a 0.1
μ
F or greater ceramic
capacitor from BOOT to SW pins.
2 VIN
Input Supply Voltage, 4.5V to 18V. Must bypass with a suitable large ceramic
capacitor.
3
SW
Switch Node. Connect this pin to an external L-C filter.
4,
9 (Exposed Pad)
GND
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
5 FB
Feedback Input. It is used to regulate the output of the converter to a set value
via an external resistive voltage divider.
6 COMP
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.
7 EN
Enable Input Pin. A logic high enables the converter; a logic low forces the IC
into shutdown mode reducing the supply current to less than 3
μ
A. Attach this
pin to VIN with a 100k
Ω
pull up resistor for automatic startup.
8 SS
Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor
from SS to GND to set the soft-start period. A 0.1
μ
F capacitor sets the
soft-start period to 13.5ms.
Typical Application Circuit
V
OUT
(V) R1 (k
Ω
) R2
(k
Ω
) R
C
(k
Ω
) C
C
(nF)
L (
μ
H) C
OUT
(
μ
F)
8
27
3
51
2.2
10
22 x 2
5
62
11.8
33
2.2
6.8
22 x 2
3.3
75
24
22
2.2
3.6
22 x 2
2.5
25.5
12
16
2.2
3.6
22 x 2
1.5
10.5
12
10
2.2
2
22 x 2
1.2
12
24
8.2
2.2
2
22 x 2
1
3
12
6.8
2.2
2
22 x 2
Table 1. Suggested Components Selection
VIN
EN
GND
BOOT
FB
SW
7
5
2
3
1
L
3.6µH
0.1µF
22µF x 2
R1
75k
R2
24k
V
OUT
3.3V
10µF x 2
V
IN
4.5V to 18V
RT7297B
SS
8
C
SS
COMP
C
C
2.2nF
R
C
22k
C
P
Open
6
4, 9 (Exposed Pad)
C
BOOT
C
IN
0.1µF
C
OUT
R
EN
100k
