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RT7248
2A, 18V, 340kHz Synchronous Step-Down Converter
General Description
The RT7248 is a high efficiency, monolithic synchronous
step-down DC/DC converter that can deliver up to 2A output
current from a 4.5V to 18V input supply. The RT7248's
current mode architecture and external compensation
allow the transient response to be optimized over a wide
input range and loads. Cycle-by-cycle current limit
provides protection against shorted outputs and soft-start
eliminates input current surge during start up. The RT7248
also provides under voltage protection and thermal
shutdown protection. The low current (< 3μA) shutdown
mode provides output disconnection, enabling easy power
management in battery-powered systems. The RT7248
is available in SOP-8 (Exposed Pad) package.
Features
±
1.5% High Accuracy Feedback Voltage
Input Voltage Range : 4.5V to 18V
2A Output Current
Integrated N-MOSFETs
Current Mode Control
340kHz Fixed Frequency Operation
Output Adjustable Voltage Range : 0.923V to 15V
Efficiency Up to 95%
Programmable Soft-Start
Stable with Low ESR Ceramic Output Capacitors
Cycle-by Cycle Over Current Protection
Input Under Voltage Lockout
Output Under Voltage Protection
Thermal Shutdown Protection
RoHS Compliant and Halogen Free
Marking Information
RT7248xGSP : Product Number
RT7248x
GSPYMDNN
x : H or N
YMDNN : Date Code
Applications
Wireless AP/Router
Set-Top-Box
Industrial and Commercial Low Power Systems
LCD Monitors and TVs
Green Electronics/Appliances
Point of Load Regulation of High-Performance DSPs
Simplified Application Circuit
V
IN
C
IN
Chip Enable
VIN
BOOT
RT7248
SW
C
BOOT
L
V
OUT
R1
FB
C
C
COMP
C
P
R
C
R2
C
OUT
EN
SS
C
SS
GND
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7248-02
October 2016
www.richtek.com
1
RT7248
Ordering Information
RT7248
Package Type
SP : SOP-8 (Exposed Pad-Option 2)
Lead Plating System
G : Green (Halogen Free and Pb Free)
H : UVP Hiccup
N : UVP Disabled
Note :
Richtek products are :
½
Pin Configurations
(TOP VIEW)
BOOT
VIN
SW
GND
2
3
4
8
SS
EN
COMP
FB
GND
9
7
6
5
SOP-8 (Exposed Pad)
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.
½
Functional Pin Description
Pin No.
1
2
3
4, 9 (Exposed Pad)
Pin Name
BOOT
VIN
SW
GND
Pin Function
Bootstrap for High Side Gate Driver. Connect a 100nF or greater ceramic
capacitor from BOOT to SW pins.
Input Supply Voltage, 4.5V to 18V. Must bypass with a suitable large
ceramic capacitor.
Phase Node. Connect this pin to external L-C filter.
Ground. The exposed pad must be soldered to a large PCB and connected
to GND for maximum power dissipation.
Feedback Input Pin. This pin is connected to the converter output. It is used
to set the output of the converter to regulate to the desired value via an
external resistive voltage divider. For an adjustable output, an external
resistive voltage divider is connected to this pin.
Compensation Node. COMP is used to compensate the regulation control
loop. Connect a series RC network from COMP to GND. In some cases, an
additional capacitor from COMP to GND is required.
Enable Input pin. A logic high enables the converter; a logic low forces the
IC into shutdown mode reducing the supply current to less than 3A. Attach
this pin to VIN with a 100k pull up resistor for automatic startup.
Soft-Start Control Input. SS controls the soft-start period. Connect a
capacitor from SS to GND to set the soft-start period. A 0.1F capacitor
sets the soft-start period to 15.5ms.
5
FB
6
COMP
7
EN
8
SS
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS7248-02
October 2016
RT7248
Function Block Diagram
VIN
Internal
Regulator
Shutdown
V
A
V
CC
Comparator
1.2V
+
-
Lockout
Comparator
-
2.5V +
V
CC
6µA
SS
0.923V
+
+
-
Error Amp
COMP
0.4V
Oscillator
Slope Comp
Foldback
Control
+
-
UV
Comparator
Current Sense
Amplifier
+
-
R
SENSE
V
A
BOOT
S
+
-
Current
Comparator
R
Q
Q
150m
EN
5k
SW
130m
GND
FB
Operation
Shutdown Comparator
Activate internal regulator once EN input level is larger
than the target level. Force IC to enter shutdown mode
when the EN input level is lower than 0.4V.
Internal Regulator
Provide internal power for logic control and switch gate
drivers.
Lockout Comparator
Activate the Current Comparator, release lock-out logic,
and enable the switches as EN input level is larger than
lockout voltage. Otherwise, the switches still locks out.
Oscillator
The oscillator provides internal clock and controls the
converter's switching frequency.
Foldback Control
Dynamically adjust the internal clock. It provides a slower
frequency as a lower FB voltage.
UV Comparator
As FB voltage is lower than the UV voltage, it will activate
a UV protect scheme.
Error Amp
The output voltage COMP of the error amplifier is adjusted
comparing FB signal with the internal reference voltage
and SS signal.
Current Sense Amplifier
R
SENSE
detects the peak current of the high-side switch.
This signal is amplified by the Current Sense Amplifier
and added with a Slope Compensation. Then, it controls
the switches by comparing this signal with the COMP
voltage.
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7248-02
October 2016
www.richtek.com
3
RT7248
Absolute Maximum Ratings
(Note 1)
−0.3V
to 20V
−0.3V
to (V
IN
+
0.3V)
−0.3V
to 6V
−0.3V
to 20V
Supply Voltage, VIN -----------------------------------------------------------------------------------------------
Input Voltage, SW --------------------------------------------------------------------------------------------------
V
BOOT
−
V
SW
---------------------------------------------------------------------------------------------------------
Other Pins Voltages -----------------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------------- 1.333W
Package Thermal Resistance (Note 2)
SOP-8 (Exposed Pad),
θ
JA
---------------------------------------------------------------------------------------- 75°C
SOP-8 (Exposed Pad),
θ
JC
---------------------------------------------------------------------------------------
Junction Temperature ----------------------------------------------------------------------------------------------
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------
Storage Temperature Range -------------------------------------------------------------------------------------
15°C
150°C
260°C
−65°C
to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model) --------------------------------------------------------------------------------------- 2kV
(Note 4)
Recommended Operating Conditions
Supply Voltage, VIN ----------------------------------------------------------------------------------------------- 4.5V to 18V
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
Shutdown Supply Current
Supply Current
Feedback Voltage
Symbol
Test Conditions
V
EN
= 0V
Min
--
--
0.909
--
--
--
Typ
0.5
0.8
0.923
940
150
130
0
4
3.7
340
100
93
100
Max
3
1.2
0.937
--
--
--
10
--
--
380
--
--
--
Unit
A
mA
V
A/V
m
m
A
A
A/V
kHz
kHz
%
ns
I
CC
V
FB
R
DS(ON)1
R
DS(ON)2
V
EN
= 3 V, V
FB
= 1V
4.5V
V
IN
23V
I
C
=
10A
Error Amplifier Transconductance G
EA
High Side Switch-On Resistance
Low Side Switch-On Resistance
High Side Switch Leakage Current
Upper Switch Current Limit
COMP to Current Sense
Transconductance
Oscillator Frequency
Short Circuit Oscillation
Frequency
Maximum Duty Cycle
Minimum On-Time
V
EN
= 0V, V
SW
= 0V
Min.Duty Cycle, V
BOOTSW
= 4.8V
G
CS
f
OSC1
f
OSC2
D
MAX
V
FB
= 0V
V
FB
= 0.7V
--
--
--
300
--
--
--
t
ON
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS7248-02
October 2016
RT7248
Parameter
EN Input Threshold
Voltage
Logic High
Logic Low
Symbol
V
IH
V
IL
V
UVLO
V
UVLO
I
SS
t
SS
T
SD
V
SS
= 0V
C
SS
= 0.1F
V
IN
Rising
Test Conditions
Min
2.7
--
3.8
--
--
--
--
Typ
--
--
4.2
320
6
15.5
150
Max
18
0.4
4.5
--
--
--
--
Unit
V
V
mV
A
ms
C
Input Under Voltage Lockout Threshold
Input Under Voltage Lockout Hysteresis
Soft-Start Current
Soft-Start Period
Thermal Shutdown
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..
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7248-02
October 2016
www.richtek.com
5
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