RT8279
5A, 36V, 500kHz Step-Down Converter
General Description
The RT8279 is a step-down regulator with an internal power
MOSFET. It achieves 5A of continuous output current over
a wide input supply range with excellent load and line
regulation. Current mode operation provides fast transient
response and eases loop stabilization.
For protection, the RT8279 provides cycle-by-cycle current
limiting and thermal shutdown protection. An adjustable
soft-start reduces the stress on the input source at
startup. In shutdown mode, the regulator draws only 25μA
of supply current.
The RT8279 requires a minimum number of readily
available external components, providing a compact
solution. The RT8279 is available in the SOP-8 (Exposed
Pad) package.
Features
5A Output Current
Internal Soft-Start
110mΩ Internal Power MOSFET Switch
Ω
Internal Compensation Minimizes External Parts
Count
High Efficiency up to 90%
25μA Shutdown Mode
μ
Fixed 500kHz Frequency
Thermal Shutdown
Cycle-by-Cycle Over Current Protection
Wide 5.5V to 36V Operating Input Range
Adjustable Output Voltage from 1.222V to 26V
Available In an SOP8 (Exposed Pad) Package
RoHS Compliant and Halogen Free
Ordering Information
RT8279
Package Type
SP : SOP-8 (Exposed Pad-Option 1)
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
NC
NC
FB
2
3
4
8
SW
VIN
GND
EN
GND
9
7
6
5
SOP-8 (Exposed Pad)
Marking Information
RT8279GSP : Product Number
RT8279
GSPYMDNN
YMDNN : Date Code
DS8279-01
December 2011
www.richtek.com
1
RT8279
Typical Application Circuit
V
IN
5.5V to 36V
Chip Enable
7
C
IN
4.7µF/
50V x 2
VIN
BOOT
RT8279
5 EN
1
C
BOOT
10nF
D1
B550A
FB 4
R2
L1
SW 8
V
OUT
C
FF
R1
C
OUT
22µF x 2
Open = Automatic
Startup
6, 9 (Exposed Pad)
GND
V
OUT
(V)
2.5
3.3
5
8
Table 1. Recommended Component Selection
R1 (kΩ)
R2 (kΩ)
C
FF
(pF)
L (μH)
100
100
82
6.8
100
58.6
82
10
100
31.6
82
15
100
18
82
22
C
OUT
(μF)
22 x 2
22 x 2
22 x 2
22 x 2
Functional Pin Description
Pin No.
1
2, 3
4
5
6,
9 (Exposed Pad)
7
8
Pin Name
BOOT
NC
FB
EN
GND
VIN
SW
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.
No Internal Connection.
Feedback Input. The feedback threshold is 1.222V.
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. For
automatic startup, leave EN unconnected.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
Power Input. A suitable large capacitor should be bypassed from VIN to GND to
eliminate noise on the input to the IC.
Power Switching Output. Note that a capacitor is required from SW to BOOT to
power the high side switch.
www.richtek.com
2
DS8279-01
December 2011
RT8279
Function Block Diagram
VIN
Ramp
Generator
Current Sense
Amplifier
-
+
BOOT
EN
Regulator
Oscillator
500kHz
+
S
Q
R
-
PWM
Comparator
Bootstrap
Control
GND
Driver
Reference
FB
12k
Error
+
Amplifier
-
SW
400k
30pF
13pF
DS8279-01
December 2011
www.richtek.com
3
RT8279
Absolute Maximum Ratings
(Note 1)
−0.3V
to 40V
−0.3V
to V
IN
+
0.3V
(V
SW
−
0.3V) to (V
SW
+
6V)
−0.3V
to 6V
1.333W
Supply Voltage, V
IN
------------------------------------------------------------------------------------------
Switching Voltage, SW -------------------------------------------------------------------------------------
BOOT Voltage -------------------------------------------------------------------------------------------------
The Other Pins ------------------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------
Package Thermal Resistance (Note 2)
SOP-8 (Exposed Pad),
θ
JA
--------------------------------------------------------------------------------- 75°C/W
SOP-8 (Exposed Pad),
θ
JC
-------------------------------------------------------------------------------- 15°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
------------------------------------------------------------------------------------------ 5.5V to 36V
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
Reference Voltage
High Side Switch-On Resistance
Low Side Switch-On Resistance
High Side Switch Leakage
Current Limit
Oscillator Frequency
Short Circuit Frequency
Maximum Duty Cycle
Minimum On-Time
Under Voltage Lockout Threshold
Rising
Under Voltage Lockout Threshold
Hysteresis
Logic-High
EN Threshold
Voltage
Logic-Low
Enable Pull Up Current
Shutdown Current
Quiescent Current
Soft-Start Period
Thermal Shutdown
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4
Symbol
V
REF
R
DS(ON)1
R
DS(ON)2
I
LIM
f
OSC
D
MAX
t
ON
Test Conditions
5.5V
≤
V
IN
≤
36V
Min
Typ
Max
Unit
V
mΩ
Ω
μA
A
kHz
kHz
%
ns
V
mV
V
μA
μA
mA
ms
°C
1.202 1.222 1.239
--
110
160
--
10
--
7.5
500
150
90
100
4.2
315
--
--
1
25
0.6
5
150
15
10
9
575
--
95
150
4.5
--
--
0.4
--
45
1
8.2
--
--
6
425
--
85
--
3.8
--
V
EN
= 0V, V
SW
= 0V
Duty = 90%, V
BOOT−SW
= 4.8V
V
FB
= 0V
V
FB
= 0.8V
V
IH
V
IL
I
SHDN
I
Q
T
SD
EN_hys = 350mV
1.4
--
--
--
--
3
--
V
EN
= 0V
V
EN
= 2V, V
FB
= 1.5V
C
SS
= 0.1μF
DS8279-01
December 2011
RT8279
Note 1.
Stresses beyond those listed
“Absolute
Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only, and 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 may
affect device reliability.
Note 2.
θ
JA
is measured at T
A
= 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7.
θ
JC
is
measured at the exposed pad of the package.
Note 3.
Devices are ESD sensitive. Handling precaution is recommended.
Note 4.
The device is not guaranteed to function outside its operating conditions.
DS8279-01
December 2011
www.richtek.com
5
测试/测量
