®
RT7259
10A, 24V, 600kHz Step-Down Converter with Synchronous
Gate Driver
General Description
The RT7259 is a synchronous step-down DC/DC converter
with an integrated high side internal power MOSFET and
a gate driver for a low side external power MOSFET. It
can deliver up to
10A
output current from a 4.5V to 24V
input supply. The RT7259's current mode architecture
allows the transient response to be optimized over a wider
input voltage and load range. Cycle-by-cycle current limit
provides protection against shorted outputs and soft-start
eliminates input current surge during start-up. The RT7259
is synchronizable to an external clock with frequency
ranging from 300kHz to 1.5MHz.
The RT7259 is available in WDFN-14L 4x3 package.
Features
4.5V to 24V Input Voltage Range
10A Output Current
45mΩ Internal High Side N-MOSFET
Ω
Current Mode Control
600kHz Switching Frequency
Adjustable Output from 0.808V to 15V
Up to 95% Efficiency
Internal Compensation
Stable with Ceramic Capacitors
Synchronous External Clock : 300kHz to 1.5MHz
Cycle-by-Cycle Current Limit
Input Under Voltage Lockout
Output Under Voltage Protection
Power Good Indicator
Thermal Shutdown Protection
RoHS Compliant and Halogen Free
Applications
Point of Load Regulator in Distributed Power System
Digital Set top Boxes
Personal Digital Recorders
Broadband Communications
Flat Panel TVs and Monitors
Simplified Application Circuit
RT7259
BOOT
C
BOOT
SW
VCC
C
VCC
Power Good
Chip Enable
EN/SYNC
GND
PGOOD
FB
R2
BG
Q1
R1
C
OUT
L
V
OUT
V
IN
C
IN
VIN
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7259-01
November 2013
www.richtek.com
1
RT7259
Ordering Information
RT7259
Package Type
QW : WDFN-14L 4x3 (W-Type)
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.
FB
PGOOD
EN/SYNC
VIN
VIN
VIN
NC
Marking Information
14= : Product Code
14=YM
DNN
YMDNN : Date Code
Pin Configurations
(TOP VIEW)
1
2
3
4
5
6
7
14
13
12
GND
15
11
10
9
8
GND
BG
VCC
BOOT
SW
SW
SW
WDFN-14L 4x3
Functional Pin Description
Pin No.
1
Pin Name
FB
Pin Function
Feedback Input. 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 divider. The feedback reference voltage is 0.808V typically.
Power Good Indicator with Open Drain. A 100kΩ pull-high resistor is needed.
The output of this pin is pulled to low when the FB is lower than 0.75V; otherwise
it is high impedance.
Enable or External Frequency Synchronization Input. A logic-high (2V < EN <
5.5V) enables the converter; a logic-low forces the IC into shutdown mode
reducing the supply current to less than 3μA. For external frequency
synchronization operation, the available frequency range is from 300kHz to
1.5MHz.
Power Input. The available input voltage range is from 4.5V to 24V. A 22μF or
larger input capacitor is needed to reduce voltage spikes at the input.
No Internal Connection.
Switching Node. Output of the internal high side MOSFET. Connect this pin to
external low side N-MOSFET, inductor and bootstrap capacitor.
Bootstrap for High side Gate Driver. Connect a 1μF ceramic capacitor between
the BOOT pin and SW pin.
BG Driver Bias Supply. Decouple with a 1μF X5R/X7R ceramic capacitor
between the VCC pin and GND.
Gate Driver Output. Connect this pin to the gate of the external low side
N-MOSFET.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum thermal dissipation.
2
PGOOD
3
EN/SYNC
4, 5, 6
7
8, 9, 10
11
12
13
VIN
NC
SW
BOOT
VCC
BG
14,
GND
15 (Exposed Pad)
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
2
DS7259-01
November 2013
RT7259
Function Block Diagram
VIN
VCC
V
CC
Internal
Regulator
OSC
Slope
Current Sense
Compensator Amplifier
+
-
Enable
Comparator
+
1.7V
EN/SYNC
5k
3V
-
R
SENSE
Foldback
Control
OTP
V
CC
BOOT
UV Comparator
V
CC
0.4V
+
-
Switch
Controller
Current
Signal
COMP
+
-
45m
SW
0.808V
V
SS
54pF
FB
+
+
EA
-
Current
Comparator
BG
Driver
BG
300k
1pF
PGOOD
Comparator
0.75V
+
-
PGOOD
GND
Operation
The RT7259 is a synchronous high voltage Buck Converter
that can support the input voltage range from 4.5V to 24V
and the output current can be up to 10A. The RT7259
uses a constant frequency, current mode architecture. In
normal operation, the high side N-MOSFET is turned on
when the Switch Controller is set by the oscillator (OSC)
and is turned off when the current comparator resets the
Switch Controller. While the N-MOSFET is turned off, the
external low side N-MOSFET is turned on by BG Driver
with 5V driving voltage from Internal Regulator (V
CC
) until
next cycle begins.
High side MOSFET peak current is measured by internal
R
SENSE
. The Current Signal is where Slope Compensator
works together with sensing voltage of R
SENSE
. The error
amplifier EA adjusts COMP voltage by comparing the
feedback signal (V
FB
) from the output voltage with the
internal 0.808V reference. When the load current
increases, it causes a drop in the feedback voltage relative
to the reference, the COMP voltage then rises to allow
higher inductor current to match the load current.
UV Comparator : If the feedback voltage (V
FB
) is lower
than threshold voltage 0.4V, the UV Comparator's output
will go high and the Switch Controller will turn off the high
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
side MOSFET. The output under voltage protection is
designed to operate in Hiccup mode.
Oscillator (OSC) : The internal oscillator runs at nominal
frequency 600kHz and can be synchronized by an external
clock in the range between 300kHz and 1.5MHz from EN/
SYNC pin.
PGOOD Comparator : When the feedback voltage (V
FB
)
is higher than threshold voltage 0.75V, the PGOOD open
drain output will be high impedance.
Enable Comparator : Internal 5kΩ resistor and Zener diode
are used to clamp the input signal to 3V. A 1.7V reference
voltage is for EN logic-high threshold voltage. The EN pin
can be connected to VIN through a 100kΩ resistor for
automatic startup.
Foldback Control : When V
FB
is lower than 0.7V, the
oscillation frequency will be proportional to the feedback
voltage.
Soft-Start (SS) : An internal current source charges an
internal capacitor to build the soft-start ramp voltage (V
SS
).
The V
FB
voltage will track the internal ramp voltage during
soft-start interval. The typical soft-start time is 2ms.
is a registered trademark of Richtek Technology Corporation.
DS7259-01
November 2013
www.richtek.com
3
RT7259
Absolute Maximum Ratings
(Note 1)
–0.3V
to 26V
–0.3V
to (V
IN
+ 0.3V)
−5V
to 30V
–0.3V
to 6V
−0.3V
to 6V
1.667W
Supply Input Voltage, V
IN
------------------------------------------------------------------------------------------
Switching Voltage, SW --------------------------------------------------------------------------------------------
SW (AC) < 20ns -----------------------------------------------------------------------------------------------------
BOOT to SW ---------------------------------------------------------------------------------------------------------
All Other Voltage ----------------------------------------------------------------------------------------------------
Power Dissipation, P
D
@ T
A
= 25°C
WDFN-14L 4x3 -------------------------------------------------------------------------------------------------------
Package Thermal Resistance (Note 2)
WDFN-14L 4x3,
θ
JA
------------------------------------------------------------------------------------------------- 60°C/W
WDFN-14L 4x3,
θ
JC
------------------------------------------------------------------------------------------------- 7.5°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 Mode) ---------------------------------------------------------------------------------------- 2kV
MM (Machine Mode) ------------------------------------------------------------------------------------------------ 200V
Recommended Operating Conditions
(Note 4)
Supply Input Voltage, V
IN
------------------------------------------------------------------------------------------ 4.5V to 24V
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
Reference Voltage
Feedback Current
High Side Switch On Resistance
High Side Switch Current Limit
Oscillation Frequency
Short Circuit Oscillation Frequency
Maximum Duty Cycle
Minimum On-Time
Symbol
Test Conditions
V
EN
= 0V
V
EN
= 3V, V
FB
= 1V
Min
--
--
--
--
--
--
--
--
--
4
--
2
--
0.3
--
Typ
1
0.9
10
45
16
600
190
90
100
4.2
400
--
--
--
10
Max
--
--
0.82
--
--
--
--
--
--
--
4.4
--
5.5
0.4
1.5
--
Unit
μA
mA
V
nA
mΩ
A
kHz
kHz
%
ns
V
mV
V
MHz
μs
V
REF
I
FB
R
DS(ON)
4.5V
≤
V
IN
≤
24V
V
FB
= 0.8V
BOOT
−
SW = 4.8V
0.796 0.808
f
OSC1
f
OSC2
D
MAX
t
ON
V
FB
= 0V
V
FB
= 0.6V
V
FB
= 1V
Input Under Voltage Lockout Threshold V
UVLO
Input Under Voltage Lockout Threshold
ΔV
UVLO
Hysteresis
EN Threshold
Voltage
Logic-High
Logic-Low
V
IH
V
IL
f
Sync
t
OFF
Sync Frequency Range
EN Turn-Off Delay
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS7259-01
November 2013
RT7259
Parameter
EN Pull Low Current
Thermal Shutdown
Thermal Shutdown Hysteresis
Power Good Threshold Rising
Power Good Threshold Hysteresis
Power Good Pin Level
BG Driver Bias Supply Voltage
Gate Driver Sink Impedance
Gate Driver Source Impedance
V
CC
R
Sink
R
Source
PGOOD Sink 10mA
T
SD
ΔT
SD
Symbol
Test Conditions
V
EN
= 2V
Min
--
--
--
--
--
--
4.5
--
--
Typ
1
150
20
0.75
40
--
5
0.9
3.3
Max
--
--
--
--
--
0.125
--
--
--
Unit
μA
°C
°C
V
mV
V
V
Ω
Ω
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
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS7259-01
November 2013
www.richtek.com
5
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