RT7297B
Typical Application Circuit
V
IN
4.5V to 18V
2
C
IN
10µF x 2
R
EN
100k
VIN
BOOT
RT7297B
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
C
SS
0.1µF
4, 9 (Exposed Pad)
C
P
Open
Table 1. Suggested Components Selection
V
OUT
(V) R1 (kΩ)
8
5
3.3
2.5
1.5
1.2
1
27
62
75
25.5
10.5
12
3
R2 (kΩ)
3
11.8
24
12
12
24
12
R
C
(kΩ)
51
33
22
16
10
8.2
6.8
C
C
(nF)
2.2
2.2
2.2
2.2
2.2
2.2
2.2
L (μH)
10
6.8
3.6
3.6
2
2
2
C
OUT
(μF)
22 x 2
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
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 Pin. A logic high enables the converter; a logic low forces the IC
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
DS7297B-02
September 2012
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
