DS6257AB Datasheet, PDF (2/15 Pages) –

RT6257A/B
Typical Application Circuit
V_IN
4.5V to 18V
Enable
C1
10µF/50V
RT6257A/B
4 _VIN
BOOT
6
C2
10µF/50V
2 _EN
LX ⁵
3 _GND
FB ¹
C_BOOT
0.1µF
L
3.3µH
R_T
4.99k
R1
147k
R2
20k
C_FF
47pF
C3
22µF/25V
V_OUT
C4
5V
22µF/25V
V_OUT (V)
1
1.2
1.8
2.5
3.3
5
Table 1. Suggested Component Values
R1 (k)
13.3
R2 (k)
20
L (H)
1.2
C_OUT (F)
44
20
20
1.2
44
40.2
20
1.5
44
63.4
20
2.2
44
90.9
20
2.8
44
147
20
3.3
44
R_T (k)
4.99
4.99
4.99
4.99
4.99
4.99
C_FF (pF)
--
--
--
47 to 82
47 to 82
47 to 82
Note :
(1) All the input and output capacitors are the suggested values, referring to the effective capacitances, subject to any
de-rating effect, like a DC bias.
(2) Considering the noise immunity, it is necessary to add R_T = 4.99k between feedback network and chip FB pin.
Functional Pin Description
Pin No.
1
Pin Name
FB
Pin Function
Feedback voltage input. This pin is used to set the desired output voltage via an
external resistive divider.
2
EN
3
GND
Enable control input. Floating this pin or connecting this pin to logic high can enable
the device and connecting this pin to GND can disable the device.
System ground. Provides the ground return path for the control circuitry and low-side
power MOSFET.
4
VIN
Power input. Supplies the power switches of the device.
5
LX
Switch node. LX is the switching node that supplies power to the output and connect
the output LC filter from LX to the output load.
6
BOOT
Bootstrap supply for high-side gate driver. Connect a 0.1F ceramic capacitor from LX
to BOOT to power the high-side switch.
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is a registered trademark of Richtek Technology Corporation.
DS6257A/B-00 September 2016