®
RT7264E
4A, 21V, 500kHz Synchronous Step-Down Converter
General Description
The RT7264E is a synchronous step-down regulator with
an internal power MOSFET. It achieves 4A 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.
Fault condition protection includes cycle-by-cycle current
limiting and thermal shutdown. An adjustable soft-start
reduces the stress on the input source at startup.
The RT7264E requires a minimal number of readily
available external components, providing a compact
solution.
Features
Wide Input Range : 4.5V to 21V
Adjustable Output from 0.808V to 15V
4A Output Current
120mΩ/40mΩ Internal Power MOSFET Switch
Ω
Ω
Internal Compensation Minimizes External Parts
500kHz Fixed Switching Frequency
Synchronized External Clock from 300kHz to 2MHz
Adjustable Soft-Start
Cycle-by-Cycle Over Current Limit
Thermal Shutdown Protection
Available in SOP-8 (Exposed Pad) and 14-Lead
WDFN Packages
RoHS Compliant and Halogen Free
Ordering Information
RT7264E
Package Type
QW : WDFN-14L 4x3 (W-Type)
SP : SOP-8 (Exposed Pad-Option 2)
Lead Plating System
Z : ECO (Ecological Element with
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
Simplified Application Circuit
V
IN
C
IN
Chip Enable
BOOT
RT7264E
SW
EN/SYNC
VCC
C
C
GND
FB
R
T
R1
R2
C
OUT
C
BOOT
L
V
OUT
VIN
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7264E-00
November 2012
www.richtek.com
1
RT7264E
Marking Information
RT7264EZQW
03 : Product Code
YMDNN : Date Code
Pin Configurations
(TOP VIEW)
VIN
SW
SW
SW
SW
BOOT
EN/SYNC
1
2
3
4
5
6
7
14
13
03 YM
DNN
GND
15
12
11
10
9
8
AGND
GND
GND
VCC
SS
PGOOD
FB
RT7264EZSP
RT7264EZSP : Product Number
WDFN-14L 4x3
VIN
SW
SW
BOOT
2
3
4
8
RT7264E
ZSPYMDNN
YMDNN : Date Code
GND
VCC
FB
EN/SYNC
GND
9
7
6
5
SOP-8 (Exposed Pad)
Functional Pin Description
Pin No.
WDFN-14L 4x3
SOP-8
(Exposed Pad)
1
Pin Name
Pin Function
Power Input. VIN supplies the power to the IC, as well as the
step-down converter switches. Drive VIN with a 4.5V to 21V
power source. Bypass VIN to GND with a suitably large
capacitor to eliminate noise on the input to the IC.
Switch Node. 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.
Bootstrap for High Side Gate Driver. Connect a 100nF or greater
capacitor from SW to BOOT to power the high side switch driver.
Enable or External Frequency Synchronization Input. For
automatic start-up, connect the EN/SYNC pin to VIN with a
100kΩ resistor. The switching frequency can be changed by an
external clock applying to the SYNC pin.
Feedback Input. FB senses the output voltage via an external
resistive voltage divider. The feedback reference voltage is
0.808V typically.
Power Good Indicator is an Open Drain Output. The power good
rising/falling threshold is 90%/70% of regulation output voltage.
Soft-Start Control Input. Connect a capacitor from SS to GND to
set the soft-start period.
Bias Supply. Decouple with 0.1μF to 0.22μF capacitor between
this pin and GND.
Ground. The exposed pad must be soldered to a large PCB and
connected to GND for maximum power dissipation.
Analog Ground. Connect this pin to the system ground in PCB
layout.
is a registered trademark of Richtek Technology Corporation.
1
VIN
2, 3, 4, 5
2, 3
SW
6
4
BOOT
7
5
EN/SYNC
8
6
FB
9
10
11
--
--
7
PGOOD
SS
VCC
12, 13, 15
8,
GND
(Exposed Pad) 9 (Exposed Pad)
14
--
AGND
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
DS7264E-00
November 2012
RT7264E
Function Block Diagram
For WDFN-14L 4x3 Package
VIN
Shutdown
Comparator
1.2V
+
-
Ramp
Generator
Current Sense
Amplifier
-
+
V
A
Oscillator
+
-
Regulator
V
C
V
A
BOOT
EN/SYNC
5k
1µA
3V
1.7V
-
+
S
Q
R
SW
PWM
Comparator
Driver
Lockout
Comparator
VCC
PGOOD
+
-
Reference
Error
+
Amplifier
+
-
V
C
10µA
30pF
400k
GND
FB
SS
1pF
For SOP-8 (Exposed Pad) Package
VIN
Shutdown
Comparator
+
Regulator
-
Ramp
Generator
Current Sense
Amplifier
-
+
BOOT
Oscillator
-
1.2V
EN/SYNC
5k
1µA
3V
1.7V
S
Q
+
-
Driver
+
Lockout
Comparator
R
SW
PWM
Comparator
VCC
Reference
FB
Error
Amplifier
+
-
30pF
400k
GND
1pF
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7264E-00
November 2012
www.richtek.com
3
RT7264E
Operation
The RT7264E 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 reference. When
the load current increases, it causes a drop in the feedback
voltage relative to the reference. The error amplifier's output
voltage then rises to allow higher inductor current to match
the load current.
Oscillator
The internal oscillator runs at fixed frequency 500kHz. In
short circuit condition, the frequency is reduced to 150kHz
for low power consumption.
Internal Regulator
The regulator provides low voltage power to supply the
internal control circuits and the bootstrap power for high
side gate driver.
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
be less than 1μA.
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 4ms.
UV Comparator
If the feedback voltage (V
FB
) 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 30°C, the converter will
automatically resume switching.
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS7264E-00
November 2012
RT7264E
Absolute Maximum Ratings
(Note 1)
−0.3V
to 26V
−0.3V
to (V
IN
+ 0.3V)
(SW
−
0.3V) to (SW + 6V)
−0.3V
to 6V
3.33W
1.63W
Supply Input Voltage, VIN ----------------------------------------------------------------------------------
Switch Voltage, SW -----------------------------------------------------------------------------------------
Boot Voltage, BOOT -----------------------------------------------------------------------------------------
Other Pins ------------------------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
WDFN-14L 4x3 ------------------------------------------------------------------------------------------------
SOP-8 (Exposed Pad) --------------------------------------------------------------------------------------
Package Thermal Resistance (Note 2)
WDFN-14L 4x3,
θ
JA
------------------------------------------------------------------------------------------ 30°C/W
WDFN-14L 4x3,
θ
JC
------------------------------------------------------------------------------------------ 7.5°C/W
SOP-8 (Exposed Pad),
θ
JA
--------------------------------------------------------------------------------- 61.2°C/W
SOP-8 (Exposed Pad),
θ
JC
-------------------------------------------------------------------------------- 6.5°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 Model) --------------------------------------------------------------------------------- 2kV
Recommended Operating Conditions
(Note 4)
Supply Input Voltage, VIN ---------------------------------------------------------------------------------- 4.5V to 21V
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 Current
Quiescent Current
Upper Switch On Resistance
Lower Switch On Resistance
Switch Leakage
Current Limit
Oscillator Frequency
Short Circuit Frequency
Maximum Duty Cycle
Minimum On Time
Feedback Voltage
Feedback Current
EN Threshold
Voltage
Logic-High
Logic-Low
Symbol
I
SHDN
I
Q
R
DS(ON)1
R
DS(ON)2
I
LEAK
I
LIM
f
SW
V
EN
= 0
Test Conditions
Min
--
--
--
--
Typ
0
0.7
120
40
0
7.5
500
150
90
100
Max
1
--
--
--
10
--
575
--
--
--
0.82
50
5.5
0.4
Unit
μA
mA
mΩ
mΩ
μA
A
kHz
kHz
%
ns
V
nA
V
V
EN
= 2V, V
FB
= 1V
V
EN
= 0V, V
SW
= 0V or 12V
V
BOOT
−
V
SW
= 4.8V
V
FB
= 0.75V
V
FB
= 0V
--
5.9
425
--
--
--
D
MAX
t
ON
V
FB
I
FB
V
IH
V
IL
V
FB
= 0.8V
4.5V
≤
V
IN
≤
21V
0.796 0.808
--
2
--
10
--
--
Copyright
©
2012 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7264E-00
November 2012
www.richtek.com
5
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