RT5710C - Richtek

®
RT5710C
1A, 1.5MHz, 5.5V CMCOT Synchronous Step-Down Converter
General Description
Features
The RT5710C is a high efficiency synchronous step-down
DC/DC converter. Its input voltage range is from 2.5V to
5.5V and provides an adjustable regulated output voltage
from 0.6V to 3.4V while delivering up to 1A of output
current.





The internal synchronous low on-resistance power
switches increase efficiency and eliminate the need for
an external Schottky diode. The Current Mode ConstantOn-time (CMCOT) operation with internal compensation
allows the transient response to be optimized over a wide
range of loads and output capacitors.



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

Ordering Information
RT5710C
Applications
Package Type
QW : WDFN-6L 2x2 (W-Type)

Lead Plating System
G : Green (Halogen Free and Pb Free)
Note :
Efficiency Up to 95%
Ω LS
RDS(ON) 160mΩ
Ω HS / 110mΩ
VIN Range 2.5V to 5.5V
VREF 0.6V with ±2% Accuracy
CMCOTTM Control Loop Design for Best Transient
Response, Robust Loop Stability with Low-ESR
(MLCC) COUT
Fixed Soft-Start 1.2ms
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
Output Under Voltage Protection (UVP Hiccup)
Thermal Shutdown Protection
Power Saving at Light Load
UVP Option
H : Hiccup


STB, Cable Modem, & xDSL Platforms
LCD TV Power Supply & Metering Platforms
General Purpose Point of Load (POL)
Pin Configurations
(TOP VIEW)

RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.

Suitable for use in SnPb or Pb-free soldering processes.
IC
1
EN
VIN
2
GND
Richtek products are :
3
7
6
FB
5
GND
LX
4
WDFN-6L 2x2
Marking Information
3D : Product Code
3DW
W : Date Code
Simplified Application Circuit
VIN
L
VIN
CIN
LX
RT5710C
EN
DS5710C-00 July 2015
R1
FB
GND
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VOUT
COUT
R2
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1
RT5710C
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
IC
No Internal Connection.
2
EN
Enable Control Input.
3
VIN
Supply Voltage Input. The RT5710C operates from a 2.5V to 5.5 input.
4
LX
Switch Node.
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum thermal dissipation.
5, 7 (Exposed Pad) GND
6
FB
Feedback.
Function Block Diagram
EN
VIN
UVLO
Shut Down
Control
OTP
FB
-
VREF
Error
Amplifier
Ton
Comparator
+
RC
CCOMP
+
-
Logic
Control
LX
VIN
Driver
Current
Limit
Detector
Current
Sense
LX
GND
LX
Operation
The RT5710C is a synchronous low voltage step-down
converter that can support the input voltage range from
2.5V to 5.5V and the output current can be up to 1A. The
RT5710C uses a constant on-time, current mode
architecture. In normal operation, the high side P-MOSFET
is turned on when the switch controller is set by the
comparator and is turned off when the Ton comparator
resets the switch controller.
Low side MOSFET peak current is measured by internal
RSENSE. The error amplifier EA adjusts COMP voltage
by comparing the feedback signal (VFB) from the output
voltage with the internal 0.6V reference. When the load
current increases, it causes a drop in the feedback voltage
relative to the reference, then the COMP voltage rises to
allow higher inductor current to match the load current.
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2
UV Comparator
If the feedback voltage (VFB) is lower than threshold voltage
0.2V, the UV comparator’s output will go high and the
switch controller will turn off the high side MOSFET. The
output under voltage protection is designed to operate in
Hiccup mode.
Enable Comparator
A logic-high enables the converter; a logic-low forces the
IC into shutdown mode.
Soft-Start (SS)
An internal current source charges an internal capacitor
to build the soft-start ramp voltage. The VFB voltage will
track the internal ramp voltage during soft-start interval.
The typical soft-start time is 1.2ms.
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DS5710C-00 July 2015
RT5710C
Over Current Protection (OCP)
The RT5710C provides over current protection by detecting
low side MOSFET valley inductor current. If the sensed
valley inductor current is over the current limit threshold
(1.5A typ.), the OCP will be triggered. When OCP is
tripped, the RT5710C will keep the over current threshold
level until the over current condition is removed.
Thermal Shutdown (OTP)
The device implements an internal thermal shutdown
function when the junction temperature exceeds 150°C.
The thermal shutdown forces the device to stop switching
when the junction temperature exceeds the thermal
shutdown threshold. Once the die temperature decreases
below the hysteresis of 20°C, the device reinstates the
power up sequence.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS5710C-00 July 2015
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3
RT5710C
Absolute Maximum Ratings








(Note 1)
Supply Input Voltage ----------------------------------------------------------------------------------------------LX Pin Switch Voltage --------------------------------------------------------------------------------------------<20ns ----------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
WDFN-6L 2x2 ------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
WDFN-6L 2x2, θJA -------------------------------------------------------------------------------------------------WDFN-6L 2x2, θJC -------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------
Recommended Operating Conditions



−0.3V to 6.5V
−0.3V to (VIN + 0.3V)
−4.5V to 7.5V
0.833W
120°C/W
7°C/W
260°C
−40°C to 150°C
−65°C to 150°C
2kV
(Note 4)
Supply Input Voltage ----------------------------------------------------------------------------------------------- 2.5V to 5.5V
Ambient Temperature Range ------------------------------------------------------------------------------------- −40°C to 85°C
Junction Temperature Range ------------------------------------------------------------------------------------- −40°C to 125°C
Electrical Characteristics
(VIN = 3.6V, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Min
Typ
Max
Unit
2.5
--
5.5
V
0.588
0.6
0.612
V
VFB = 3.3V
--
--
1
A
Active, VFB = 0.63V, Not Switching
--
22
--
Shutdown
--
--
1
Switching Leakage Current
--
--
1
A
Switching Frequency
--
1.5
--
MHz
Input Voltage
VIN
Feedback Reference Voltage
VREF
Feedback Leakage Current
IFB
DC Bias Current
Test Conditions
A
Switch On Resistance, High
RPMOS
ISW = 0.3A
--
160
--
m
Switch On Resistance, Low
RNMOS
ISW = 0.3A
--
110
--
m
Valley Current Limit
ILIM
1.1
1.5
2
A
Under-Voltage Lockout
Threshold
VUVLO
VDD Rising
--
2.25
2.5
VDD Falling
--
2
--
--
150
--
Over-Temperature Threshold
Enable Input
Voltage
Logic-High
VIH
1.5
--
--
Logic-Low
VIL
--
--
0.4
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V
C
V
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DS5710C-00 July 2015
RT5710C
Parameter
Min
Typ
Max
Unit
--
1.2
--
ms
Minimum Off Time
--
120
--
ns
Output Discharge Switch On
Resistance
--
1.8
--
k
Soft-Start Time
Symbol
Test Conditions
TSS
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. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC 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 © 2015 Richtek Technology Corporation. All rights reserved.
DS5710C-00 July 2015
is a registered trademark of Richtek Technology Corporation.
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RT5710C
Typical Application Circuit
VIN
2.5V to 5.5V
3
CIN
10µF
VIN
LX
4
EN
FB
GND
VOUT
CFF*
RT5710C
2
L
R1
6
COUT
5
R2
*CFF : Optional for performance fine-tune
Table 1. Suggested Component Values
VOUT (V)
R1 (k)
R2 (k)
L (H)
COUT (F)
3.3
90
20
1 to 3.3
10
1.8
100
50
1 to 3.3
10
1.5
100
66.6
1 to 3.3
10
1.2
100
100
1 to 3.3
10
1.05
100
133
1 to 3.3
10
1
100
148
1 to 3.3
10
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is a registered trademark of Richtek Technology Corporation.
DS5710C-00 July 2015
RT5710C
Typical Operating Characteristics
Efficiency vs. Output Current
Efficiency vs. Output Current
100
100
90
90
VIN = 5V, VOUT = 3.3V
VIN = 3.3V, VOUT = 1.2V
70
80
Efficiency (%)
Efficiency (%)
80
60
50
40
30
60
50
40
30
20
20
10
10
0
0
0.2
0.4
0.6
0.8
VIN = 5V, VOUT = 3.3V
VIN = 3.3V, VOUT = 1.2V
70
0
0.001
1
0.01
Output Current (A)
1
10
Output Voltage vs. Output Current
1.28
3.40
1.26
3.38
1.24
Output Voltage (V)
Output Voltage (V)
Output Voltage vs. Output Current
1.22
1.20
1.18
1.16
3.36
3.34
3.32
3.30
3.28
1.14
VIN = 5V, VOUT = 3.3V
VIN = 3.3V, VOUT = 1.2V
1.12
0
0.2
0.4
0.6
0.8
3.26
1
0
0.2
Output Current (A)
0.4
0.6
0.8
1
Output Current (A)
Output Voltage vs. Input Voltage
Output Voltage vs. Input Voltage
1.25
3.50
1.24
3.45
1.23
3.40
Output Voltage (V)
Output Voltage (V)
0.1
Output Current (A)
1.22
1.21
1.20
1.19
1.18
1.17
3.35
3.30
3.25
3.20
3.15
3.10
1.16
VIN = 2.5V to 5.5V, VOUT = 1.2V, IOUT = 1A
1.15
2.5
3
3.5
4
4.5
5
Input Voltage (V)
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DS5710C-00 July 2015
5.5
3.05
VIN = 4.5V to 5.5V, VOUT = 3.3V, IOUT = 1A
3.00
4.5
4.6
4.7
4.8
4.9
5
5.1
5.2
5.3
5.4
5.5
Input Voltage (V)
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RT5710C
Switching Frequency vs. Temperature
1.8
0.64
1.7
Switching Frequency (MHz)1
Reference Voltage (V)
Reference Voltage vs. Input Voltage
0.65
0.63
0.62
0.61
0.60
0.59
0.58
0.57
0.56
VIN = 2.5V to 5.5V, IOUT = 1A
0.55
2.5
3
3.5
4
4.5
5
1.6
1.5
VIN = 5V, VOUT = 3.3V
VIN = 3.3V, VOUT = 1.2V
1.4
1.3
1.2
1.1
IOUT = 0.5A
1.0
-50
5.5
-25
0
VEN = 0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
2.5
3
3.5
4
4.5
5
5.0
100
125
VEN = 0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-50
5.5
-25
0
25
50
75
100
125
Temperature (°C)
Input Voltage (V)
Quiescent Current vs. Input Voltage
Quiescent Current vs. Temperature
35
40
30
35
Quiescent Current (µA)
Quiescent Current (µA)
75
Shutdown Quiescent Current vs. Temperature
Shutdown Quiescent Current (μA)1
Shutdown Quiescent Current (μA)1
Shutdown Quiescent Current vs. Input Voltage
0.9
50
Temperature (°C)
Input Voltage (V)
1.0
25
25
20
15
10
5
30
VIN = 5V
25
VIN = 3.3V
20
15
10
5
VFB = 0.63V, LX No Switch
0
0
2.5
3
3.5
4
4.5
5
Input Voltage (V)
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5.5
-50
-25
0
25
50
75
100
125
Temperature (°C)
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DS5710C-00 July 2015
RT5710C
Inductor Current Limit vs. Temperature
3.0
2.5
2.5
Inductor Current (A)
Inductor Current (A)
Inductor Current Limit vs. Input Voltage
3.0
2.0
1.5
1.0
2.0
1.5
1.0
0.5
0.5
VOUT = 1.2V
0.0
2.5
3
3.5
4
4.5
5
VOUT = 1.2V
0.0
-50
5.5
-25
0
Input Voltage (V)
50
75
100
125
Temperature (°C)
Input UVLO vs. Temperature
Enable Threshold vs. Temperature
2.5
1.4
2.4
Enable Threshold (V) 1
1.2
2.3
Input UVLO (V)
25
Turn Off
2.2
2.1
2.0
1.9
Turn On
1.8
1.7
1.0
Enable On
0.8
Enable Off
0.6
0.4
0.2
1.6
VEN = 3.3V
1.5
-50
-25
0
25
50
75
100
125
VIN = 3.3V
0.0
-50
-25
0
25
50
75
100
Temperature (°C)
Temperature (°C)
Load Transient Response
Load Transient Response
VIN = 3.3V, VOUT = 1.2V, IOUT = 0A to 1A, Cff = 22pF
VOUT
(50mV/Div)
VOUT
(50mV/Div)
IOUT
(500mA/Div)
IOUT
(500mA/Div)
Time (100μs/Div)
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125
VIN = 3.3V, VOUT = 1.2V,
IOUT = 0.5A to 1A, Cff = 22pF
Time (100μs/Div)
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RT5710C
Voltage Ripple
Voltage Ripple
VIN = 3.3V, VOUT = 1.2V, IOUT = 1A
VIN = 5V, VOUT = 3.3V, IOUT = 1A
VOUT
(10mV/Div)
VOUT
(10mV/Div)
VLX
(2V/Div)
VLX
(2V/Div)
Time (500ns/Div)
Time (500ns/Div)
Power On from EN
Power Off from EN
VIN = 3.3V, VOUT = 1.2V, IOUT = 1A
VIN = 3.3V, VOUT = 1.2V, IOUT = 1A
VEN
(5V/Div)
VEN
(5V/Div)
VOUT
(1V/Div)
VOUT
(1V/Div)
IOUT
(1A/Div)
IOUT
(1A/Div)
Time (500μs/Div)
Time (10μs/Div)
Power On from EN
Power Off from EN
VIN = 5V, VOUT = 3.3V, IOUT = 1A
VIN = 5V, VOUT = 3.3V, IOUT = 1A
VEN
(5V/Div)
VEN
(5V/Div)
VOUT
(2V/Div)
IOUT
(1A/Div)
VOUT
(2V/Div)
IOUT
(1A/Div)
Time (500μs/Div)
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Time (10μs/Div)
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DS5710C-00 July 2015
RT5710C
Application Information
The RT5710C is a single-phase step-down converter. It
provides single feedback loop, constant on-time current
mode control with fast transient response. An internal 0.6V
reference allows the output voltage to be precisely
regulated for low output voltage applications. A fixed
switching frequency (1.5MHz) oscillator and internal
compensation are integrated to minimize external
component count. Protection features include over current
protection, under voltage protection and over temperature
protection.
Output Voltage Setting
Connect a resistive voltage divider at the FB between VOUT
and GND to adjust the output voltage. The output voltage
is set according to the following equation :
VOUT = VREF   1 R1 
 R2 
where VREF is the feedback reference voltage 0.6V (typ.).
VOUT
R1
causing PWM pulse width to increase slowly and in turn
reduce the input surge current. The internal 0.6V reference
takes over the loop control once the internal ramping-up
voltage becomes higher than 0.6V.
UVLO Protection
The RT5710C has input Under Voltage Lockout protection
(UVLO). If the input voltage exceeds the UVLO rising
threshold voltage (2.25V typ.), the converter resets and
prepares the PWM for operation. If the input voltage falls
below the UVLO falling threshold voltage during normal
operation, the device will stop switching. The UVLO rising
and falling threshold voltage has a hysteresis to prevent
noise-caused reset.
Inductor Selection
The switching frequency (on-time) and operating point (%
ripple or LIR) determine the inductor value as shown below:
VOUT   VIN  VOUT 
L=
fSW  LIR  ILOAD(MAX)  VIN
where LIR is the ratio of the peak-to-peak ripple current to
the average inductor current.
FB
R2
GND
Figure 1. Setting VOUT with a Voltage Divider
Chip Enable and Disable
The EN pin allows for power sequencing between the
controller bias voltage and another voltage rail. The
RT5710C remains in shutdown if the EN pin is lower than
400mV. When the EN pin rises above the VEN trip point,
the RT5710C begins a new initialization and soft-start
cycle.
Find a low loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. The core
must be large enough not to saturate at the peak inductor
current (IPEAK) :
IPEAK = ILOAD(MAX) +  LIR  ILOAD(MAX) 
 2

The calculation above serves as a general reference. To
further improve transient response, the output inductor
can be further reduced. This relation should be considered
along with the selection of the output capacitor.
Inductor saturation current should be chosen over IC’s
current limit.
Internal Soft-Start
Input Capacitor Selection
The RT5710C provides an internal soft-start function to
prevent large inrush current and output voltage overshoot
when the converter starts up. The soft-start (SS)
automatically begins once the chip is enabled. During softstart, the internal soft-start capacitor becomes charged
and generates a linear ramping up voltage across the
capacitor. This voltage clamps the voltage at the FB pin,
High quality ceramic input decoupling capacitor, such as
X5R or X7R, with values greater than 10μF are
recommended for the input capacitor. The X5R and X7R
ceramic capacitors are usually selected for power regulator
capacitors because the dielectric material has less
capacitance variation and more temperature stability.
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RT5710C
The input capacitor is used to supply the input RMS
current, which can be approximately calculated using the
following equation :
V
  1 OUT 
VIN 

The next step is selecting a proper capacitor for RMS
current rating. One good design uses more than one
capacitor with low equivalent series resistance (ESR) in
parallel to form a capacitor bank.
IIN_RMS = ILOAD 
VOUT
VIN
The input capacitance value determines the input ripple
voltage of the regulator. The input voltage ripple can be
approximately calculated using the following equation :
IOUT(MAX) VOUT  VOUT 
VIN =

 1
CIN  fSW
VIN 
VIN 
Output Capacitor Selection
The output capacitor and the inductor form a low pass
filter in the Buck topology. In steady state condition, the
ripple current flowing into/out of the capacitor results in
ripple voltage. The output voltage ripple (VP-P) can be
calculated by the following equation :
1

VP_P = LIR  ILOAD(MAX)   ESR +

8

C

f
OUT SW 

When load transient occurs, the output capacitor supplies
the load current before the controller can respond.
Therefore, the ESR will dominate the output voltage sag
during load transient. The output voltage undershoot (VSAG)
can be calculated by the following equation :
VSAG = ILOAD  ESR
For a given output voltage sag specification, the ESR value
can be determined.
Another parameter that has influence on the output voltage
sag is the equivalent series inductance (ESL). The rapid
change in load current results in di/dt during transient.
Therefore, the ESL contributes to part of the voltage sag.
Using a capacitor with low ESL can obtain better transient
performance. Generally, using several capacitors
connected in parallel can have better transient performance
than using a single capacitor for the same total ESR.
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Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
WDFN-6L 2x2 package, the thermal resistance, θJA, is
120°C/W on a standard four-layer thermal test board. The
maximum power dissipation at TA = 25°C can be calculated
by the following formula :
PD(MAX) = (125°C − 25°C) / (120°C/W) = 0.833W for
WDFN-6L 2x2 package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 2 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
1.0
Maximum Power Dissipation (W)1
Voltage rating and current rating are the key parameters
when selecting an input capacitor. Generally, selecting an
input capacitor with voltage rating 1.5 times greater than
the maximum input voltage is a conservatively safe design.
Four-Layer PCB
0.8
0.6
0.4
0.2
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 2. Derating Curve of Maximum Power Dissipation
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RT5710C
Outline Dimension
D2
D
L
E
E2
1
e
b
A
A1
SEE DETAIL A
2
1
2
1
A3
DETAIL A
Pin #1 ID and Tie Bar Mark Options
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min
Max
Min
Max
A
0.700
0.800
0.028
0.031
A1
0.000
0.050
0.000
0.002
A3
0.175
0.250
0.007
0.010
b
0.200
0.350
0.008
0.014
D
1.950
2.050
0.077
0.081
D2
1.000
1.450
0.039
0.057
E
1.950
2.050
0.077
0.081
E2
0.500
0.850
0.020
0.033
e
L
0.650
0.300
0.026
0.400
0.012
0.016
W-Type 6L DFN 2x2 Package
Richtek Technology Corporation
14F, No. 8, Tai Yuen 1st Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: (8863)5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should
obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot
assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be
accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third
parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
DS5710C-00 July 2015
www.richtek.com
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