®
RT2862
3A, 36V, Synchronous Step-Down Converter
General Description
The RT2862 is a high efficiency, current-mode
synchronous step-down DC/DC converter that can deliver
up to 3A output current over a wide input voltage range
from 4.5V to 36V. The device integrates 105mΩ high-side
and 80mΩ low-side MOSFETs to achieve high conversion
efficiency. The current-mode control architecture supports
fast transient response and simple external compensation.
A cycle-by-cycle current limit function provides protection
against shorted output and an internal soft-start eliminates
input current surge during start-up. The RT2862 provides
complete protection functions such as input under-voltage
lockout, output under-voltage protection, over-current
protection and thermal shutdown.
The RT2862 is available in the thermal enhanced SOP-8
(Exposed Pad) package.
Features
4.5V to 36V Input Voltage Range
3A Output Current
Internal N-MOSFETs
Current Mode Control
Frequency Operation : 300kHz to 1MHz
Adjustable Output Voltage from 0.8V to 30V
High Efficiency Up to 95%
Stable with Low ESR Ceramic Output Capacitors
Cycle-by-Cycle Current Limit
Input Under-Voltage Lockout
Output Under-Voltage Protection
Thermal Shutdown
Applications
Ordering Information
RT2862
Package Type
SP: SOP-8 (Exposed Pad-Option 2)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Richtek products are :
½
Point of Load Regulator in Distributed Power Systems
Digital Set Top Boxes
Broadband Communications
Vehicle Electronics
Automotive Audio, Navigation, and Information Systems
Enterprise Datacom Platforms Point of Load (POL)
Industrial Grade General Purpose Point of Load
Marking Information
RT2862GSP : Product Number
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.
RT2862
GSPYMDNN
YMDNN : Date Code
½
Simplified Application Circuit
V
IN
C
IN
VIN
BOOT
RT2862
SW
R1
RT
R
T
GND
COMP
FB
C
C
R
C
R2
C
OUT
C
B
L
V
OUT
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS2862-00 July 2014
www.richtek.com
1
RT2862
Pin Configurations
(TOP VIEW)
SW
BOOT
EN
GND
2
3
4
8
VIN
RT
COMP
FB
GND
9
7
6
5
SOP-8 (Exposed Pad)
Functional Pin Description
Pin No.
1
2
3
4,
9 (Exposed Pad)
5
Pin Name
SW
BOOT
EN
GND
FB
Pin Function
Switch Node. Connect to external L-C filter.
Bootstrap Supply for the High-Side MOSFET. Connect a 100nF or greater
capacitor between the BOOT and SW pins.
Enable Control Input. A logic-high enables the converter; a logic-low forces the
device into shutdown mode.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum thermal dissipation.
Feedback Voltage Input. This pin is used to set the output voltage of the
converter to regulate to the desired value via an resistive divider.
Compensation Node. COMP is used to compensate the regulation control loop.
Connect a R-C network from the COMP to GND. In some cases, an additional
capacitor from COMP to GND is required.
Switching Frequency Setting. Connect an external resistor to set the switching
frequency from 300kHz to 1MHz.
Power Input. The input voltage range is from 4.5V to 36V. Must bypass with a
suitable large ceramic capacitor at this pin.
6
COMP
7
8
RT
VIN
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS2862-00 July 2014
RT2862
Function Block Diagram
VIN
V
CC
Internal
Regulator
Shutdown
Comparator
1.2V
V
A
V
CC
+
-
Oscillator
Foldback
Control
0.4V
+
Slope Comp
Current Sense
Amplifier
+
-
R
SENSE
VA
5k
EN
Lockout
Comparator
-
+
1.7V
UV
S
+
-
Current
Comparator
BOOT
Q
SW
R
Q
GND
-
UV
Comparator
3.6V
SS
0.8V
+
+
EA
-
RT
FB
COMP
Operation
The RT2862 is a constant frequency, current-mode
synchronous step-down converter. In normal operation,
the high-side N-MOSFET is turned on when the S-R latch
is set by the oscillator and is turned off when the current
comparator resets the S-R latch. While the high-side
N-MOSFET is turned off, the low-side N-MOSFET is turned
on to conduct the inductor current until next cycle begins.
Error Amplifier
The error amplifier adjusts its output voltage by comparing
the feedback signal (V
FB
) with the internal 0.8V reference.
When the load current increases, it causes a drop in the
feedback voltage relative to the reference, and then the
error amplifier's output voltage rises to allow higher inductor
current to match the load current.
Oscillator
The oscillator frequency can be set by using an external
resister R
T
. Oscillator frequency range is from 300kHz to
1MHz.
Internal Regulator
The regulator provides low voltage power to supply the
internal control circuits and the bootstrap power for high-
side gate driver.
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
Enable
The converter is turned on when the EN pin is higher than
2V. When the EN pin is lower than 0.4V, the converter will
enter shutdown mode and reduce the supply current to
0.5μA.
Soft-Start (SS)
An internal current source charges an internal capacitor
to build a soft-start ramp voltage. The FB voltage will track
the internal ramp voltage during soft-start interval. The
typical soft-start time is 2ms.
UV Comparator
If the feedback voltage is lower than 0.4V, the UV
Comparator will go high to turn off the high-side MOSFET.
The output under voltage protection is designed to operate
in hiccup mode. When the UV condition is removed, the
converter will resume switching.
Thermal Shutdown
The over-temperature protection function will shut down
the switching operation when the junction temperature
exceeds 150°C. Once the junction temperature cools
down by approximately 20°C, the converter will
automatically resume switching.
is a registered trademark of Richtek Technology Corporation.
DS2862-00 July 2014
www.richtek.com
3
RT2862
Absolute Maximum Ratings
(Note 1)
−0.3V
to 40V
−0.3V
to (V
IN
+ 0.3V)
−0.3V
to 46.3V
−0.3V
to 40V
−5V
to 46.3V
−0.3V
to 3.6V
−0.3V
to 40V
Supply Voltage, VIN ------------------------------------------------------------------------------------------------
Switch Voltage, SW ------------------------------------------------------------------------------------------------
BOOT Pin -------------------------------------------------------------------------------------------------------------
EN Pin (with REN (150kΩ to 600kΩ) to VIN) -----------------------------------------------------------------
SW Voltage (t < 10ns) ---------------------------------------------------------------------------------------------
EN Pin ------------------------------------------------------------------------------------------------------------------
Other Pins -------------------------------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------------- 2.041W
Package Thermal Resistance (Note 2)
SOP-8 (Exposed Pad),
θ
JA
---------------------------------------------------------------------------------------- 49°C/W
SOP-8 (Exposed Pad),
θ
JC
--------------------------------------------------------------------------------------- 8°C/W
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------- 260°C
Junction Temperature ----------------------------------------------------------------------------------------------- 150°C
Storage Temperature Range --------------------------------------------------------------------------------------
−65°C
to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------- 2kV
Recommended Operating Conditions
(Note 4)
Supply Input Voltage, VIN
-----------------------------------------------------------------------------------------
4.5V to 36V
Junction Temperature Range --------------------------------------------------------------------------------------
−40°C
to 125°C
Ambient Temperature Range --------------------------------------------------------------------------------------
−40°C
to 85°C
Electrical Characteristics
(V
IN
= 12V, C
IN
= 20μF, T
A
=
−40°C
to 85°C, unless otherwise specified)
Parameter
Shutdown Supply Current
Quiescent Current
Feedback Reference Voltage
Switch
On-Resistance
High-Side
Low-Side
Symbol
Test Conditions
V
EN
= 0V
Min
--
--
0.784
--
--
4.25
Typ
--
1
0.8
105
80
5
1.7
300
500
1000
50
95
100
Max
10
1.3
0.816
190
145
5.75
--
336
560
1120
--
--
120
Unit
A
mA
V
m
A
A
I
Q
V
REF
R
DS(ON)1
R
DS(ON)2
U
OC
V
EN
= 3V, V
FB
= 0.9V
4.5V
V
IN
36V
High-Side Switch Current Limit
Range
Low-Side Switch Current Limit
From Drain to Source
R
T
= 191k
--
264
440
880
--
--
--
Oscillation Frequency
f
OSC1
R
T
= 113k
R
T
= 51k
kHz
Short-Circuit Oscillation
Frequency
Maximum Duty Cycle
Minimum On-Time
f
OSC2
D
MAX
t
ON
V
FB
= 0V, R
T
= 113k
V
FB
= 0.7V
kHz
%
ns
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS2862-00 July 2014
RT2862
Parameter
EN Input Voltage
Logic-High
Logic-Low
Input Under-Voltage Lockout
Threshold
Input Under-Voltage Lockout
Hysteresis
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
COMP to Current Sense
Trans-conductance
Symbol
V
IH
V
IL
V
UVLO
V
UVLO
T
SD
T
SD
G
CS
I
COMP
= ±10A
V
IN
Rising
Test Conditions
Min
2
--
3.7
--
--
--
--
--
Typ
--
--
4.2
250
150
25
4.1
950
Max
3.3
0.4
4.5
--
--
--
--
--
V
mV
C
C
A/V
A/V
Unit
V
Error Amplifier Trans-conductance G
EA
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. The PCB copper area with exposed pad is 70mm
2
.
Note 3.
Devices are ESD sensitive. Handling precaution is recommended.
Note 4.
The device is not guaranteed to function outside its operating conditions.
Copyright
©
2014 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS2862-00 July 2014
www.richtek.com
5
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