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RT7257DLZSP 数据手册 - Richtek（立锜）
制造商:
Richtek（立锜）
分类:
稳压芯片
封装:
SOP-8
描述:
RICHTEK RT7257DLZSP 直流-直流开关降压(逐步递减)稳压器, 可调, 4.5V-18V输入, 800mV-12V输出, 3A输出, SOP-8
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RT7257DLZSP数据手册
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RT7257D
2
DS7257D-04 September 2012www.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 0.1μF 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. 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.
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 0.1μF capacitor sets the
soft-start period to 13.5ms.
Typical Application Circuit
V
OUT
(V) R1 (kΩ) R2 (kΩ) R
C
(kΩ) C
C
(nF) L (μH) C
OUT
(μF)
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
RT7257D
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
Chip Enable
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