RT7257D
Typical Application Circuit
1
3
V
2
IN
VIN
BOOT
RT7257D
4.5V to 18V
C
C
BOOT
0.1µF
IN
L
10µF x 2
3.6µH
V
3.3V
OUT
SW
Chip Enable
R1
7
8
EN
SS
75k
C
OUT
22µF x 2
5
6
FB
C
C
C
0.1µF
R
SS
C
R2
2.2nF
22k
24k
4, 9 (Exposed Pad)
COMP
GND
C
P
Open
Table 1. Suggested Components Selection
VOUT (V) R1 (k) R2 (k) RC (k) CC (nF) L (H)
COUT (F)
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
22 x 2
8
27
3
11.8
24
51
33
22
16
10
8.2
6.8
2.2
2.2
2.2
2.2
2.2
2.2
2.2
10
6.8
3.6
3.6
2
5
62
3.3
2.5
1.5
1.2
1
75
25.5
10.5
12
12
12
24
12
2
2
3
Functional Pin Description
Pin No.
Pin Name
Pin Function
Bootstrap for High Side Gate Driver. Connect a 0.1F or greater ceramic
capacitor from BOOT to SW pins.
1
BOOT
Input Supply Voltage, 4.5V to 18V. Must bypass with a suitable large ceramic
capacitor.
2
3
VIN
SW
Switch Node. Connect this pin to an external L-C filter.
4,
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
GND
9 (Exposed Pad)
Feedback Input. It is used to regulate the output of the converter to a set value
via an external resistive voltage divider.
5
6
FB
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.
COMP
Enable Input. A logic high enables the converter; a logic low forces the
RT7257D into shutdown mode reducing the supply current to less than 3A.
Attach this pin to VIN with a 100k 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 0.1F capacitor sets the
soft-start period to 13.5ms.
7
8
EN
SS
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is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS7257D-05 October 2016
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
