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RT7277GSP

P1-P3P4-P6P7-P9P10-P12P13-P14
RT7277
®
DS7277-01 March 2013 www.richtek.com
1
Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
©
3A, 18V, 700kHz ACOT
TM
Synchronous Step-Down Converter
Features
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zz
z
ACOT
TM
Mode Enables Fast Transient Response
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z 4.5V to 18V Input Voltage Range
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z 3A Output Current
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zz
z 60m
ΩΩ
ΩΩ
Ω Internal Low Site N-MOSFET
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z Advanced Constant On-Time Control
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z Support All Ceramic Capacitors
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z Up to 95% Efficiency
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z 700kHz Switching Frequency
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z Adjustable Output Voltage from 0.765V to 8V
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z Adjustable Soft-Start
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z Cycle-by-Cycle Current Limit
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z Input Under Voltage Lockout
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z Thermal Shutdown
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z RoHS Compliant and Halogen Free
Applications
z Industrial and Commercial Low Power Systems
z Computer Peripherals
z LCD Monitors and TVs
z Green Electronics/Appliances
z Point of Load Regulation for High-Performance DSPs,
FPGAs, and ASICs
Simplified Application Circuit
EN
RT7277
PVCC
FB
GND
VIN
V
IN
C1 C2
BOOT
L1
C6
C7
SW
Chip Enable
SS
C5
C4
V
OUT
R1
R2
C3
V
PVCC
General Description
The RT7277 is a synchronous step-down DC/DC converter
with Advanced Constant On-Time (ACOT
TM
) mode control.
It achieves high power density to deliver up to 3A output
current from a 4.5V to 18V input supply. The proprietary
ACOT
TM
mode offers an optimal transient response over a
wide range of loads and all kinds of ceramic capacitors,
which allows the device to adopt very low ESR output
capacitors for ensuring performance stabilization. In
addition, RT7277 keeps an excellent constant switching
frequency under line and load variation and the integrated
synchronous power switches with the ACOT
TM
mode
operation provides high efficiency in whole output current
load range. Cycle-by-cycle current limit provides an
accurate protection by a valley detection of low side
MOSFET and external soft-start setting eliminates input
current surge during startup. Protection functions also
include output under voltage protection, output over voltage
protection, and thermal shutdown.
Marking Information
RT7277GSP : Product Number
YMDNN : Date Code
RT7277
GSPYMDNN
RT7277
2
DS7277-01 March 2013www.richtek.com
©
Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
Pin No. Pin Name Pin Function
1 EN
Enable Input. A logic-high enables the converter; a logic-low forces the IC into
shutdown mode reducing the supply current to less than 10μA.
2 FB
Feedback Input. It is used to regulate the output of the converter to a set value via
an external resistive voltage divider. The feedback threshold voltage is 0.765V
typically.
3 PVCC
Internal Regulator Output. Connect a 1μF capacitor to GND to stabilize output
voltage.
4 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 3.9nF capacitor sets the soft-start period of
V
OUT
to 2.6ms.
5, 9
(Exposed Pad)
GND
Ground. The Exposed pad should be soldered to a large PCB and connected to
GND for maximum thermal dissipation.
6 SW Switch Node. Connect this pin to an external L-C filter.
7 BOOT
Bootstrap Supply for High Side Gate Driver. Connect a 0.1μF or greater ceramic
capacitor from BOOT to SW pins.
8 VIN
Power Input. The input voltage range is from 4.5V to 18V. Must bypass with a
suitably large ( ≥10μF x 2) ceramic capacitor.
Functional Pin Description
Pin Configurations
(TOP VIEW)
SOP-8 (Exposed Pad)
EN
FB
PVCC
SS
VIN
BOOT
GND
SW
GND
2
3
4
5
6
7
8
9
Ordering Information
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.
RT7277
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
Lead Plating System
G : Green (Halogen Free and Pb Free)
RT7277
3
DS7277-01 March 2013 www.richtek.com
©
Copyright 2013 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
Function Block Diagram
UGATE
LGATE
Driver
SW
BOOT
PVCC
Switch
Controller
On-Time
EN
FB
Comparator
SW
GND
Internal
Regulator
PVCC
VIBIAS
V
REF
PVCC
+
--
2µA
PVCC
Ripple
Gen.
VIN
FB
SS
Over Current
Protection
EN
Operation
In normal operation, the high side N-MOSFET is turned
on when the FB Comparator sets the Switch Controller,
and it is turned off when On-Time Controller resets the
Switch Controller. While the high side N-MOSFET is turned
off, the low side N-MOSFET is turned on and waits for the
FB Comparator to set the beginning of next cycle.
The FB Comparator sets the Switch Controller by
comparing the feedback signal (FB) from output voltage
with the internal 0.765V reference. When load transient
induces VOUT drop, the FB voltage will be less than its
threshold voltage. This means that the high side N-MOSFET
will turn on again immediately after minimum off-time
expired. The switching frequency will vary during the
transient period thus can provide a very fast transient
response. After the load transient finished, the RT7277
will be back to steady state with a constant switching
frequency.
Enable
Activate internal regulator once EN input level is higher
than the target level. Force IC to enter shutdown mode
when the EN input level is lower than 0.4V
Internal Regulator
Provide internal power for logic control and switch gate
drivers.
On-Time Controller
Control on-time according to VIN and SW to obtain
constant switching frequency.
P1-P3P4-P6P7-P9P10-P12P13-P14

RT7277GSP

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IC REG BUCK ADJUSTABLE 3A 8SOP
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