RT8270
2A, 22V, 1.2MHz Step-Down Converter
General Description
The RT8270 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 RT8270 is available in a SOP-8 surface mount
package.
Features
Wide Operating Input Range : 4.75V to 22V
Adjustable Output Voltage Range : 1.222V to 16V
Output Current up to 2A
25μA Low Shutdown Current
μ
Power MOSFET : 0.18Ω
Ω
High Efficiency up to 95%
1.2MHz Fixed Switching Frequency
Stable with Low ESR Output Ceramic Capacitors
Thermal Shutdown Protection
Cycle-By-Cycle Over Current Protection
RoHS Compliant and Halogen Free
Ordering Information
RT8270
Package Type
S : SOP-8
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)
BOOT
VIN
SW
GND
2
3
4
8
7
6
5
NC
EN
COMP
FB
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.
SOP-8
Typical Application Circuit
V
IN
4.75V to 22V
2
C
IN
10µF
7 EN
FB 5
4 GND
COMP
6
VIN
BOOT
RT8270
SW 3
1
C
B
10nF
D1
B330
R
C
C
C
18k 1.8nF
L1
4.7µH
R1
17k
R2
10k
V
OUT
3.3V/2A
C
OUT
22µF
Chip Enable
C
P
NC
DS8270-01 March 2011
www.richtek.com
1
RT8270
Table 1. Recommended Component Selection
V
OUT
(V)
12
5
3.3
2.5
1.8
1.222
R1 (kΩ)
88.7
30
17
10.45
4.75
0
R2 (kΩ)
10
10
10
10
10
10
R
C
(kΩ)
51
23.1
18
12
10
9.1
C
C
(nF)
0.86
1.2
1.8
2.2
2.2
2.2
L1 (μH)
10
6.8
4.7
4.7
2.2
2.2
C
OUT
(μF)
22
22
22
22
22
22
Functional Pin Description
Pin No.
1
Pin Name
BOOT
Pin Function
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.
Feedback Input. FB senses the output voltage to regulate said voltage. The feedback
reference voltage is 1.222V 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.
No Internal Connection.
2
VIN
3
4
5
SW
GND
FB
6
COMP
7
8
EN
NC
Function Block Diagram
VIN
V
CC
1µA
EN
10k
1V
3V
VA V
CC
-
+
Shutdown
Comparator
Foldback
Control
0.6V
+
Logic
+
-
Current
Comparator
Internal
Regulator
Oscillator
1.2MHz/440kHz
Current Sense
Slope Comp Amplifier
+
-
BOOT
SW
VA
-
UV
Comparator
1.222V
+
-
EA
GND
Gm = 780µA/V
FB
COMP
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DS8270-01 March 2011
RT8270
Absolute Maximum Ratings
(Note 1)
Supply Voltage, V
IN
----------------------------------------------------------------------------------------- 23V
Switching Voltage, SW -------------------------------------------------------------------------------------
−0.3V
to (V
IN
+
0.3V)
BOOT Voltage ------------------------------------------------------------------------------------------------ (V
SW
−
0.3V) to (V
SW
+
6V)
All Other Voltage ---------------------------------------------------------------------------------------------
−0.3V
to 6V
Power Dissipation, P
D
@ T
A
= 25°C
SOP-8 ---------------------------------------------------------------------------------------------------------- 0.833W
Package Thermal Resistance (Note 2)
SOP-8,
θ
JA
---------------------------------------------------------------------------------------------------- 120°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 22V
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
≤
22V
Min
1.184
--
--
--
--
--
--
--
--
--
--
4
--
--
1.4
--
Typ
0.18
10
--
3
2.5
780
1.2
440
80
100
4.2
300
--
--
1
Max
--
--
10
--
--
--
--
--
--
--
4.5
--
0.4
--
--
Unit
V
Ω
Ω
μA
A
A/V
μA/V
MHz
kHz
%
ns
V
mV
V
V
μA
1.222 1.258
V
EN
= 0V, V
SW
= 0V
I
LIM
G
CS
G
m
f
SW
V
FB
= 0V
V
FB
= 0.8V
Duty = 90%; 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
En input Low Voltage
En input High Voltage
Enable Pull Up Current
t
ON
To be continued
DS8270-01 March 2011
www.richtek.com
3
RT8270
Parameter
Shutdown Current
Quiescent Current
Thermal Shutdown
I
Q
T
SD
Symbol
I
SHDN
Test Conditions
V
EN
= 0V
V
EN
= 2V, V
FB
= 1.5V
Min
--
--
--
Typ
25
0.7
150
Max
50
1
--
Unit
μA
mA
°C
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 four layers thermal conductivity test board of
JEDEC 51-7 thermal measurement standard.
Note 3.
Devices are ESD sensitive. Handling precaution is recommended.
Note 4.
The device is not guaranteed to function outside its operating conditions.
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DS8270-01 March 2011
RT8270
Typical Operating Characteristics
Efficiency vs. Output Current
100
90
1.226
1.224
Reference Voltage vs. Input Voltage
Efficiency (%)
70
60
50
40
30
20
10
0
0
Reference Voltage (V)
80
V
IN
= 4.75V
V
IN
= 12V
V
IN
= 22V
1.222
1.220
1.218
1.216
V
OUT
= 3.3V
1.214
V
IN
= 4.75V to 22V, V
OUT
= 3.3V
2
4
7
10
13
16
19
22
0.4
0.8
1.2
1.6
Output Current (A)
Input Voltage (V)
Output Voltage vs. Output Current
3.300
3.297
Output Voltage vs. Temperature
3.400
3.375
Output Voltage (V)
3.294
3.291
3.288
3.285
3.282
Output Voltage (V)
3.350
3.325
3.300
3.275
3.250
3.225
V
IN
= 9V
V
IN
= 12V
V
IN
= 22V
V
OUT
= 3.3V
3.279
0
0.4
0.8
1.2
1.6
2
V
IN
= 12V, V
OUT
= 3.3V, I
OUT
= 0A
3.200
-50
-25
0
25
50
75
100
125
Output Current (A)
Temperature
(°C)
Frequency vs. Input Voltage
1.40
1.35
Frequency vs. Temperature
1.40
1.35
Frequency (MHz)
Frequency (MHz)
1.30
1.25
1.20
1.15
1.10
1.05
1.30
1.25
1.20
1.15
1.10
1.05
V
IN
= 4.75V to 22V, V
OUT
= 3.3V
1.00
4
6
8
10
12
14
16
18
20
22
V
IN
= 12V, V
OUT
= 3.3V
1.00
-50
-25
0
25
50
75
100
125
Input Voltage (V)
Temperature
(°C)
DS8270-01 March 2011
www.richtek.com
5
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