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  Richtek Technology Electronic Components Datasheet  

RT7257E Datasheet

Synchronous Step-Down Converter

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RT7257E pdf
SacPower
Preliminary
RT7257E
3A, 17V, 340kHz Synchronous Step-Down Converter
General Description
The RT7257E is a high efficiency, monolithic synchronous
step-down DC/DC converter that can deliver up to 3A
output current from a 4.5V to 17V input supply. The
RT7257E's current mode architecture and external
compensation allow the transient response to be
optimized over a wide range of loads and output capacitors.
Cycle-by-cycle current limit provides protection against
shorted outputs, and soft-start eliminates input current
surge during start-up. The RT7257E provides thermal
shutdown protection. The low current (<3μA) shutdown
mode provides output disconnection, enabling easy power
management in battery-powered systems. The RT7257E
is available in an SOP-8 (Exposed Pad) package.
Ordering Information
RT7257EN
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
Lead Plating System
Z : ECO (Ecological Element with
Halogen Free and Pb free)
Note :
Richtek products are :
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
Features
z ±1.5% High Accuracy Feedback Voltage
z 4.5V to 17V Input Voltage Range
z 3A Output Current
z Integrated N-MOSFET Switches
z Current Mode Control
z Fixed Frequency Operation : 340kHz
z Output Adjustable from 0.8V to 15V
z Up to 95% Efficiency
z Programmable Soft-Start
z Stable with Low ESR Ceramic Output Capacitors
z Cycle-by-Cycle Over Current Protection
z Input Under Voltage Lockout
z Thermal Shutdown Protection
z RoHS Compliant and Halogen Free
Applications
z Wireless AP/Router
z Set-Top-Box
z Industrial and Commercial Low Power Systems
z LCD Monitors and TVs
z Green Electronics/Appliances
z Point of Load Regulation of High-Performance DSPs
Pin Configurations
(TOP VIEW)
BOOT
VIN
SW
GND
8
27
GND
36
9
45
SS
EN
COMP
FB
SOP-8 (Exposed Pad)
0755-83983280
1
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  Richtek Technology Electronic Components Datasheet  

RT7257E Datasheet

Synchronous Step-Down Converter

No Preview Available !

RT7257E pdf
RT7257E
Typical Application Circuit
Preliminary
VIN
4.5V to 17V
Chip Enable
CIN
10µF x 2
2 VIN
BOOT 1
RT7257E
SW 3
7 EN
CSS
0.1µF
8 SS
4, 9 (Exposed Pad)
GND
FB 5
COMP 6
CBOOT L
100nF 10µH
CC
4.7nF
RC
12k
R1
75k
R2
24k
VOUT
3.3V
COUT
22µF x 2
CP
Open
VOUT (V)
8
5
3.3
2.5
1.5
1.2
1
Table 1. Recommended Components Selection
R1 (kΩ)
27
62
75
25.5
10.5
R2 (kΩ)
3
11.8
24
12
12
RC (kΩ)
24
18
12
8.2
3.6
CC (nF)
4.7
4.7
4.7
4.7
4.7
L (μH)
22
15
10
6.8
3.6
12 24 3 4.7 3.6
3 12 2.7 4.7 3.6
COUT (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
Pin Name
BOOT
VIN
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 17V. Must bypass with a suitably 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 internal resistive voltage divider.
Compensation Node. COMP is used to compensate the regulation control
6
COMP
loop. Connect a series RC network from COMP to GND. In some cases, an
additional capacitor from COMP to GND is required.
Enable Input. A logic high enables the converter; a logic low forces the
7 EN RT7257E 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
8 SS from SS to GND to set the soft-start period. A 0.1μF capacitor sets the
soft-start period to 13.5ms.
2
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Part Number RT7257E
Description Synchronous Step-Down Converter
Maker Richtek
Total Page 15 Pages
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