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RT8267GS

P1-P3P4-P6P7-P9P10-P12
RT8267
1
DS8267-02 March 2011 www.richtek.com
Ordering Information
Pin Configurations
(TOP VIEW)
SOP-8
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.
2A, 22V, 400kHz Step-Down Converter
Applications
z Distributive Power Systems
z Battery Charger
z DSL Modems
z Pre-regulator for Linear Regulators
General Description
The RT8267 is an asynchronous high voltage buck
converter that can support the input voltage range from
4.75V to 22V and the output current can be up to 2A.
Current Mode operation provides fast transient response
and eases loop stabilization.
The chip provides protection functions such as cycle-by-
cycle current limiting and thermal shutdown protection.
In shutdown mode, the regulator draws 25μA of supply
current. The RT8267 is available in a SOP-8 surface mount
package.
Features
zz
zz
z
Wide Operating Input Range : 4.75V to 22V
zz
zz
z Adjustable Output Voltage Range : 1.222V to 16V
zz
zz
z Output Current up to 2A
zz
zz
z 25
μμ
μμ
μA Low Shutdown Current
zz
zz
z Power MOSFET : 0.18
ΩΩ
ΩΩ
Ω
zz
zz
z High Efficiency up to 95%
zz
zz
z 400kHz Fixed Switching Frequency
zz
zz
z Stable with Low ESR Output Ceramic Capacitors
zz
zz
z Thermal Shutdown Protection
zz
zz
z Cycle-By-Cycle Over Current Protection
zz
zz
z RoHS Compliant and Halogen Free
Typical Application Circuit
BOOT
VIN
SW
GND
NC
EN
FB
COMP
2
3
4
5
6
7
8
Package Type
S : SOP-8
RT8267
Lead Plating System
G : Green (Halogen Free and Pb Free)
VIN
EN
GND
BOOT
FB
SW
7
5
2
3
1
L1
15µH
C
B
10nF
C
OUT
22µF
R1
17k
R2
10k
V
OUT
3.3V/2A
C
IN
10µF
Chip Enable
V
IN
4.75V to 22V
RT8267
D1
B330
COMP
C
C
1.5nF
R
C
10k
C
P
NC
6
4
RT8267
2
DS8267-02 March 2011www.richtek.com
Functional Pin Description
Function Block Diagram
Pin No. Pin Name Pin Function
1 BOOT
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 hi
g
h side switch.
2 VIN
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.
3 SW
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.
4 GND
Ground. The exposed pad must be soldered to a large PCB and connected to GND for
maximum power dissipation.
5 FB
Feedback Input. FB senses the output voltage to regulate said voltage. The feedback
reference voltage is 1.222V typically.
6 COMP
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.
7 EN
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.
8 NC No Internal Connection.
V
OUT
(V) R1 (kΩ) R2 (kΩ) R
C
(kΩ) C
C
(nF) C
OUT
(μF) L1 (μH)
12 88.7 10 62 0.82 22 33
5 30 10 20 2.2 22 22
3.3 17 10 10 1.5 22 15
2.5 10.45 10 7.5 1.5 22 10
1.8 4.75 10 6 1.5 22 10
1.222 0 10 6 3.9 22 6.8
Table 1. Recommended Component Selection
R
QS
Q
VA
+
-
+
-
+
-
+
-
EA
UV
Comparator
Oscillator
400kHz/120kHz
Foldback
Control
0.6V
Internal
Regulator
+
-
1V
1µA
Shutdown
Comparator
Current Sense
Amplifier
BOOT
VIN
GND
SW
FB
EN
COMP
1.222V
3V
10k
VA
V
CC
V
CC
Slope Comp
Current
Comparator
Gm = 780µA/V
RT8267
3
DS8267-02 March 2011 www.richtek.com
Electrical Characteristics
Parameter Symbol Test Conditions Min Typ Max Unit
Feedback Reference Voltage V
FB
4.75V ≤ V
IN
≤ 22V 1.184 1.222 1.258 V
High Side Switch-On Resistance R
DS(ON)1
-- 0.18 -- Ω
Low Side Switch-On Resistance R
DS(ON)2
-- 10 -- Ω
Switch Leakage V
EN
= 0V, V
SW
= 0V -- -- 10 μA
Current Limit I
LIM
Duty = 90%; V
BOOT−SW
= 4.8V -- 2.7 -- A
Current Sense Transconductance G
CS
Output Current to V
COMP
-- 2.5 -- A/V
Error Amplifier Tansconductance G
m
ΔI
C
= ±10μA -- 780 -- μA/V
Oscillator Frequency f
SW
320 400 460 kHz
Short Circuit Oscillation Frequency V
FB
= 0V -- 120 -- kHz
Maximum Duty Cycle D
MAX
V
FB
= 0.8V -- 90 -- %
Minimum On-Time t
ON
-- 100 -- ns
Under Voltage Lockout Threshold
Rising
4 4.2 4.5 V
Under Voltage Lockout Threshold
Hysteresis
-- 300 -- mV
En input Low Voltage -- -- 0.4 V
En input High Voltage 1.4 -- -- V
Enable Pull Up Current -- 1 -- μA
(V
IN
= 12V, T
A
= 25°C unless otherwise specified)
Absolute Maximum Ratings (Note 1)
z Supply Voltage, V
IN
-----------------------------------------------------------------------------------------23V
z Switching Voltage, SW -------------------------------------------------------------------------------------−0.3V to (V
IN
+ 0.3V)
z BOOT Voltage ------------------------------------------------------------------------------------------------(V
SW
− 0.3V) to (V
SW
+ 6V)
z All Other Voltage---------------------------------------------------------------------------------------------−0.3V to 6V
z Power Dissipation, P
D
@ T
A
= 25°C
SOP-8 ----------------------------------------------------------------------------------------------------------0.833W
z Package Thermal Resistance (Note 2)
SOP-8, θ
JA
----------------------------------------------------------------------------------------------------120°C/W
z Junction Temperature ---------------------------------------------------------------------------------------150°C
z Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------260°C
z Storage Temperature Range -------------------------------------------------------------------------------−65°C to 150°C
z ESD Susceptibility (Note 3)
HBM (Human Body Mode) ---------------------------------------------------------------------------------2kV
MM (Machine Mode) ----------------------------------------------------------------------------------------200V
Recommended Operating Conditions (Note 4)
z Supply Voltage, V
IN
-----------------------------------------------------------------------------------------22V
z Enable Voltage, V
EN
-----------------------------------------------------------------------------------------0V to 5.5V
z Junction Temperature Range ------------------------------------------------------------------------------−40°C to 125°C
z Ambient Temperature Range ------------------------------------------------------------------------------ −40°C to 85°C
To be continued
P1-P3P4-P6P7-P9P10-P12

RT8267GS

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IC REG BUCK ADJ 2A 8SOP
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