RT8271
2A, 24V, 1.2MHz Step-Down Converter
General Description
The RT8271 is a high voltage buck converter that can
support the input voltage range from 4.75V to 24V and the
output current can be up to 2A. Current Mode operation
provides fast transient response and eases loop
stabilization. The RT8271 also provides adjustable soft-
start to be a flexible solution for customers.
The chip provides protection functions such as cycle-by-
cycle current limiting and thermal shutdown protection.
In shutdown mode, the regulator draws 22μA of supply
current. The RT8271 is available in the SOP-8 and
MSOP-10 (Exposed Pad) surface mount package.
Features
Wide Operating Input Range : 4.75V to 24V
Adjustable Output Voltage Range : 0.92V to 16V
Output Current up to 2A
22μA Low Shutdown Current
μ
Power MOSFET : 0.18Ω
Ω
High Efficiency up to 92%
1.2MHz Fixed Switching Frequency
Stable with Low ESR Output Ceramic Capacitors
Programmable Soft-Start
Thermal Shutdown Protection
Cycle-By-Cycle Over Current Protection
RoHS Compliant and Halogen Free
Ordering Information
RT8271
Package Type
S : SOP-8
FP : MSOP-10 (Exposed Pad)
Lead Plating System
G : Green (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.
Applications
Distributive Power Systems
Battery Charger
DSL Modems
Pre-regulator for Linear Regulators
Pin Configurations
(TOP VIEW)
NC
BOOT
NC
VIN
SW
10
2
3
4
5
9
GND
8
11 7
6
SS
EN
COMP
FB
GND
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area, otherwise visit our website for detail.
MSOP-10 (Exposed Pad)
BOOT
VIN
SW
GND
2
3
4
8
7
6
5
SS
EN
COMP
FB
SOP-8
DS8271-02 March 2011
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1
RT8271
Typical Application Circuit
V
IN
4.75V to 24V
Chip Enable
C
IN
10µF/25V
VIN
BOOT
RT8271
SW
EN
SS
GND
FB
C
C
1.5nF
COMP
R
C
15k
R2
10k
C
BOOT
L1
10nF 4.7µH
D1
B230A
R1
16.9k
V
OUT
2.5V
C
OUT
22µF/6.3V
C
SS
10nF
C
P
NC
Table 1. Recommended Component Selection
V
OUT
(V)
R1 (kΩ)
R2 (kΩ)
R
C
(kΩ)
C
C
(nF)
L (μH)
C
OUT
(μF)
15
10
8
5
3.3
2.5
1.8
1.2
154
100
76.8
44.2
25.5
16.9
9.53
3
10
10
10
10
10
10
10
10
68
49.9
49.9
33
22
15
12
12
0.56
0.82
1
1.2
1.5
1.5
1.5
1.5
22
15
10
6.8
4.7
4.7
2.2
2.2
22
22
22
22
22
22
22
22
Function Block Diagram
VIN
V
CC
1µA
EN
10k
VA V
CC
-
+
1V
Shutdown
Comparator
V
CC
10µA
SS
+
+
EA
-
Gm = 920µA/V
0.92V
Foldback
Control
0.5V
+
-
UV
Comparator
Internal
Regulator
Oscillator
1.2MHz/440kHz
Current Sense
Slope Comp Amplifier
+
-
VA
BOOT
SW
3V
+
-
Current
Comparator
Logic
GND
FB
COMP
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DS8271-02 March 2011
RT8271
Functional Pin Description
Pin No.
PMSOP-10
1, 3
2
SOP-8
--
1
NC
BOOT
No Internal Connection.
High Side Gate Drive Boost Input. BOOT supplies the drive for the
high side N-MOSFET switch. Connect a 10nF or greater capacitor
from SW to BOOT to power the high side switch.
Power Input. V
IN
supplies the power to the IC, as well as the
step-down converter switches. Bypass VIN to GND with a suitable
large capacitor to eliminate noise on the input to the IC.
Power Switching Output. SW is the switching node that supplies
power to the output. Connect the output LC filter from SW to the
output load. Note that a capacitor is required from SW to BOOT to
power the high side switch.
Ground. The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
Feedback Input. FB senses the output voltage to regulate said
voltage. The feedback reference voltage is 0.92V typically.
Compensation Node. COMP is used to compensate the regulation
control loop. Connect a series RC network from COMP to GND to
compensate the regulation control loop. In some cases, an additional
capacitor from COMP to GND is required.
Enable Input. EN is a digital input that turns the regulator on or off.
Drive EN higher than 1.4V to turn on the regulator, lower than 0.4V to
turn it off. If the EN pin is open, it will be pulled to high by internal
circuit.
Soft-Start Control Input. SS controls the soft start period. Connect a
capacitor from SS to GND to set the soft-start period. A 10nF
capacitor sets the soft-start period to 1ms.
Pin Name
Pin Function
4
2
VIN
5
6,
11 (Exposed Pad)
7
3
SW
4
5
GND
FB
8
6
COMP
9
7
EN
10
8
SS
DS8271-02 March 2011
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RT8271
Absolute Maximum Ratings
(Note 1)
Supply Voltage, V
IN
-----------------------------------------------------------------------------------------
−0.3V
to 26V
Switching Voltage, SW -------------------------------------------------------------------------------------
−0.3V
to (V
IN
+
0.3V)
BOOT Voltage ------------------------------------------------------------------------------------------------ (V
SW
−
0.3V) to (V
SW
+
6V)
The Other Pins Voltage -------------------------------------------------------------------------------------
−0.3V
to 6V
Power Dissipation, P
D
@ T
A
= 25°C
SOP-8 ---------------------------------------------------------------------------------------------------------- 0.833W
MSOP-10 (Exposed Pad) ---------------------------------------------------------------------------------- 1.163W
Package Thermal Resistance (Note 2)
SOP-8,
θ
JA
---------------------------------------------------------------------------------------------------- 120°C/W
MSOP-10 (Exposed Pad),
θ
JA
---------------------------------------------------------------------------- 86°C/W
MSOP-10 (Exposed Pad),
θ
JC
---------------------------------------------------------------------------- 30°C/W
Junction Temperature --------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------- 260°C
Storage Temperature Range -------------------------------------------------------------------------------
−65°C
to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Mode) --------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ---------------------------------------------------------------------------------------- 200V
Recommended Operating Conditions
(Note 4)
Supply Voltage, V
IN
----------------------------------------------------------------------------------------- 4.75V to 24V
Enable Voltage, V
EN
----------------------------------------------------------------------------------------- 0V to 5.5V
Junction Temperature Range ------------------------------------------------------------------------------
−
40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------
−
40°C to 85°C
Electrical Characteristics
(V
IN
= 12V, T
A
= 25°C unless otherwise specified)
Parameter
Feedback Reference Voltage
High Side Switch-On Resistance
Low Side Switch-On Resistance
Switch Leakage
Current Limit
Current Sense Transconductance
Error Amplifier Tansconductance
Oscillator Frequency
Symbol
V
FB
R
DS(ON)1
R
DS(ON)2
Test Conditions
4.75V
≤
V
IN
≤
24V
Min
0.902
--
--
--
--
--
620
--
--
--
--
3.8
--
Typ
0.92
0.18
10
--
3
2.5
920
1.2
440
75
90
4.2
250
Max
0.938
--
--
10
--
--
1220
--
--
--
--
4.5
--
Unit
V
Ω
Ω
μA
A
A/V
μA/V
MHz
kHz
%
ns
V
mV
V
EN
= 0V, V
SW
= 0V
I
LIM
G
CS
G
m
f
SW
V
FB
= 0V
V
FB
= 0.8V
Duty = 75%; V
BOOT−SW
= 4.8V
Output Current to V
COMP
ΔI
C
= ±10μA
Short Circuit Oscillation Frequency
Maximum Duty Cycle
D
MAX
Minimum On-Time
Under Voltage Lockout Threshold
Rising
Under Voltage Lockout Threshold
Hysteresis
t
ON
To be continued
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4
DS8271-02 March 2011
RT8271
Parameter
EN Input Voltage
Logic High
Logic Low
I
SHDN
I
Q
T
SD
V
EN
= 0V
V
EN
= 0V
V
EN
= 2V, V
FB
= 1V
C
SS
= 10nF
Symbol
Test Conditions
Min
1.4
--
--
--
--
--
--
Typ
--
--
1
22
0.6
1
150
Max
5.5
0.4
--
36
1
--
--
Unit
V
μA
μA
mA
ms
°C
Enable Pull Up Current
Shutdown Current
Quiescent Current
Soft-Start Period
Thermal Shutdown
Note 1.
Stresses listed as the above "Absolute Maximum Ratings" may cause permanent damage to the device. These are for
stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended
periods may remain possibility to affect device reliability.
Note 2.
θ
JA
is measured in the natural convection at T
A
= 25°C on a high effective thermal conductivity four layers test board of
JEDEC 51-7 thermal measurement standard. The case point of
θ
JC
is on the expose pad for MSOP-10 (Exposed Pad)
package.
Note 3.
Devices are ESD sensitive. Handling precaution is recommended.
Note 4.
The device is not guaranteed to function outside its operating conditions.
DS8271-02 March 2011
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