ETC RT9293

RT9293
Conceptual
Small Package, High Performance, Asynchronies Boost
for 10 WLED Driver
General Description
Features
The RT9293 is a high frequency, asynchronous boost
converter. The internal MOSFET can support up to 10
White LEDs for backlighting and OLED power application,
and the internal soft start function can reduce the inrush
current. The device operates with 1-MHz fixed switching
frequency to allow small external components and to
simplify possible EMI problems. Moreover, the IC comes
with 46V over voltage protection to allow inexpensive and
small-output capacitors with lower voltage ratings. The
LED current is initially set with the external sense resistor
RSET . The RT9293 is available in the tiny package type
TSOT-23-6 and WDFN-8L 2x2 packages to provide the
best solution for PCB space saving and total BOM cost.
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Ordering Information
RT9293
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Applications
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Package Type
J6 : TSOT-23-6
QW : WDFN-8L 2x2 (W-Type)
Operating Temperature Range
G : Green (Halogen Free with Commercial Standard)
VIN Operating Range : 2.5V to 5.5V
Internal Power N-MOSFET Switch
Wide Range for PWM Dimming (100Hz to200kHz)
Minimize the External Component Counts
Internal Soft Start
Internal Compensation
Under Voltage Protection
Over Voltage Protection
Over Temperature Protection
Small TSOT-23-6 and 8-Lead WDFN Packages
RoHS Compliant and Halogen Free
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Cellular Phones
Digital Cameras
PDAs and Smart Phones and MP3 and OLED.
Probable Instruments
Pin Configurations
(TOP VIEW)
Feedback Voltage Reference
A : 104mV
B : 300mV
C : 200mV
VIN VOUT EN
Note :
Richtek Green products are :
6
5
4
1
2
3
LX
GND
FB
TSOT-23-6
}RoHS compliant and compatible with the current require-
GND 1
VIN 2
VOUT 3
EN 4
}Suitable for use in SnPb or Pb-free soldering processes.
}100% matte tin (Sn) plating.
GND
ments of IPC/JEDEC J-STD-020.
9
8
7
6
5
LX
NC
FB
GND
WDFN-8L 2x2
Marking Information
Note : There is no pin1 indicator on top mark for TSOT-23-6
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area, otherwise visit our website for detail.
DS9293-03C April 2008
type, and pin 1 will be lower left pin when reading top mark
from left to right.
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1
RT9293
Conceptual
Typical Application Circuit
L
22uH
D
V OUT
LX
V IN
VOUT
VIN
C IN
2.2uF
C OUT
1uF
RT9293
10 WLEDs
Chip Enable
EN
GND
FB
R SET
Functional Pin Description
Pin No.
Pin Name
Pin Function
RT9293□ GJ6
RT9293□ GQW
1
8
1, 5,
Exposed pad (9)
LX
3
6
FB
Feed Back Pin, put a resistor to GND to setting the current.
4
4
EN
Chip Enable (Active High).
5
3
VOUT
Output Voltage Pin.
6
2
VIN
Input Supply.
--
7
NC
No Internal Condition.
2
Switching Pin.
Ground Pin. The exposed pad must be soldered to a large
PCB and connected to GND for maximum power dissipation.
GND
Function Block Diagram
LX
VIN
UVLO
VOUT
OCP
Internal
Compensation
Internal
Soft Start
OVP
OTP
Logic Control,
Minimum On
Time
PWM
CurrentSense
+
+
EA
GM
Driver
GND
+
-
Slope
Compensation
LPF
Enable
Logic
Shutdown
20ms
PWM
Oscillator
Reference
Voltage
VREF
1uA
FB
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2
Bias
Current
EN
DS9293-03C April 2008
RT9293
Conceptual
Absolute Maximum Ratings
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(Note 1)
Supply Input Voltage, VIN ---------------------------------------------------------------------------------------------- −0.3V to 6V
Switching Pin, LX -------------------------------------------------------------------------------------------------------- −0.3V to 50V
VOUT ----------------------------------------------------------------------------------------------------------------------- −0.3V to 46V
Other Pins ----------------------------------------------------------------------------------------------------------------- −0.3V to 6V
Power Dissipation, PD @ TA = 25°C
TSOT-23-6 ----------------------------------------------------------------------------------------------------------------- 0.392W
WDFN−8L 2x2 ------------------------------------------------------------------------------------------------------------ 0.606W
Package Thermal Resistance (Note 3)
TSOT-23-6, θJA ----------------------------------------------------------------------------------------------------------- 255°C/W
WDFN−8L 2x2, θJA ------------------------------------------------------------------------------------------------------- 165°C/W
WDFN−8L 2x2, θJC ------------------------------------------------------------------------------------------------------ 20°C/W
Lead Temperature (Soldering, 10 sec.)------------------------------------------------------------------------------ 260°C
Junction Temperature --------------------------------------------------------------------------------------------------- 150°C
Storage Temperature Range ------------------------------------------------------------------------------------------- −65°C to 150°C
Recommended Operating Conditions
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(Note 2)
Junction Temperature Range ------------------------------------------------------------------------------------------ −40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------------------ −40°C to 85°C
Electrical Characteristics
(VIN = 3.7V, CIN = 2.2uF, COUT = 0.47uF, IOUT = 20mA, L = 22uH, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Input Voltage
VIN
Under Voltage Lock Out
VUVLO
Conditions
UVLO Hystersis
Min
Typ
Max
Unit
2.5
--
5.5
V
2
2.2
2.45
V
--
0.1
--
V
Quiescent Current
IQ
FB = 1.5V, No Switching
--
400
600
uA
Supply Current
IIN
FB = 0V, Switching
--
1
2
mA
Shutdown Current
ISHDN
VEN < 0.4V
--
1
4
uA
Line Regulation
VIN = 3 to 4.3V
--
1
--
%
Load Regulation
1mA to 20mA
--
1
--
%
0.75
1
1.25
MHz
Maximum Duty Cycle
90
92
--
%
Clock Rate
0.1
--
200
kHz
94
104
114
285
300
315
190
200
210
Operation Frequency
fOSC
RT9293A
Feedback Reference
Voltage
RT9293B
RT9293C
VREF
mV
To be continued
DS9293-03C April 2008
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3
RT9293
Conceptual
Parameter
On R esistance
EN Threshold
Symbol
Conditions
RDS(ON)
Min
Typ
Max
Unit
--
0.7
1.2
Ω
Logic-High Voltage
V IH
1.4
--
--
V
Logic-Low Voltage
V IL
--
--
0.5
V
IIH
--
1
--
uA
--
0.1
--
V
42
1
46
1.2
50
--
V
A
----
160
30
20
----
°C
°C
ms
EN Sink Current
EN Hystersis
Over-Voltage Threshold
Over-C urrent Threshold
OTP
OTP H ystersis
Shutdown Delay
V OVP
IOCP
T OTP
T SHDN
Note 1. Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for
stress ratings. 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 for extended
periods may remain possibility to affect device reliability.
Note 2. The device is not guaranteed to function outside its operating conditions.
Note 3. θJA is measured in the natural convection at TA = 25°C on a low effective single layer thermal conductivity test board of
JEDEC 51-3 thermal measurement standard. The case point of θJC is on the expose pad for the WDFN package.
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4
DS9293-03C April 2008
RT9293
Conceptual
Typical Operating Characteristics
Efficiency vs. Input Voltage
Efficiency vs. Output Current
100
100
VIN = 4.5V
VIN = 4V
80
80
Efficiency (%)
70
Efficiency (%)
ILOAD = 30mA
90
90
60
50
40
30
ILOAD = 10mA
70
ILOAD = 20mA
60
50
40
30
20
20
10
10
VOUT = 10V
VOUT = 34V
0
0
0
0.05
0.1
0.15
0.2
0.25
2.5
0.3
3
3.5
4.5
5
Output Voltage vs. Output Current
Quiescent Current vs. Input Voltage
500
35
450
Quiescent Current (uA)
40
30
25
20
15
400
350
300
250
VFB = 1.5V
VIN = 3.7V, VOUT = 34V
200
10
5
15
25
35
45
55
65
75
2.5
85
3
3.5
4
4.5
5
5.5
Input Voltage (V)
Output Current (mA)
Frequency vs. Input Voltage
Frequency vs. Temperature
1100
1100
1050
1050
Frequency (kHz)
Frequency (kHz)
5.5
Input Voltage (V)
Output Current (A)
Output Voltage (V)
4
1000
950
900
1000
950
900
850
850
VIN = 3.7V, ILED = 20mA
ILED = 20mA
800
800
2.5
3
3.5
4
4.5
Input Voltage (V)
DS9293-03C April 2008
5
5.5
-40 -25 -10
5
20
35
50
65
80
95 110 125
Temperature (°C)
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5
RT9293
Conceptual
VFB vs. Input Voltage
VFB vs. Temperature
0.34
0.32
0.33
0.29
0.26
V FB (V)
V FB (V)
VOUT = 34V, IOUT = No Load
10WLED, ILED = 20mA
0.23
0.32
VIN = 3V
0.31
VIN = 3.7V
0.30
VIN = 4.2V
0.29
0.28
0.2
0.27
ILED = 20mA
0.17
0.26
2.5
3
3.5
4
4.5
5
-40
5.5
-15
10
60
85
Temperature (°C)
Input Voltage (V)
Enable Voltage vs. Input Voltage
VFB vs. Output Current
0.314
1.00
0.98
VIN = 3V
0.310
Rising
VIN = 4.2V
VIN = 3.7V
0.302
0.298
Enable Voltage (V)
0.96
0.306
V FB (V)
35
0.94
0.92
0.90
0.88
Falling
0.86
0.84
0.294
VOUT = 34V
0.290
0.82
0.80
0
5
10
15
20
25
30
2.5
3
3.5
4
4.5
Output Current (mA)
Input Voltage (V)
LED Current vs. Duty
Power On from EN
5
5.5
25
LED Current (mA)
20
VEN
(2V/Div)
15
f
f
f
f
10
= 200Hz
= 2kHz
= 20kHz
= 200kHz
5
VOUT
(10V/Div)
VIN = 3.7V, ILED = 20mA
VIN = 3.7V, ILED = 20mA
0
0
10
20
30
40
50
60
70
80
90
100
Time (1ms/Div)
Duty (%)
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6
DS9293-03C April 2008
RT9293
Conceptual
Power Off from EN
Ripple
VIN
(20mV/Div)
VEN
(2V/Div)
VOUT
(20mV/Div)
VOUT
(10V/Div)
VIN = 3.7V, ILED = 20mA
VIN = 3.7V, ILED = 20mA
Time (1ms/Div)
Time (500ns/Div)
PWM Dimming
PWM Dimming
f = 20kHz
f = 200Hz
VEN
(4V/Div)
VEN
(4V/Div)
ILED
(10mA/Div)
ILED
(10mA/Div)
VIN = 3.7V, ILED = 20mA
Time (1ms/Div)
DS9293-03C April 2008
VIN = 3.7V, ILED = 20mA
Time (10us/Div)
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7
RT9293
Conceptual
Applications Information
LED Current Setting
V IN
2.5V to 5.5V
The loop of Boost structure will keep the FB pin voltage
equal to the reference voltage VREF. Therefore, when RREF
connects FB pin and GND, the current flows from VOUT
through LED and RREF to GND will be decided by the
current on RREF, which is equal to following equation.
D
C OUT
1uF
C IN
2.2uF
RT9293
LX
VIN
GND
VOUT
EN
FB
ILED
V OUT
L
10uH to 22uH
WLEDs
Chip Enable
V
= REF
RSET
R3
10k
R4
82k
Dimming Control
V DC Dimming
0V to 2.8V
a. Using a PWM Signal to EN Pin
For controlling the LED brightness, the RT9293 can perform
the dimming control by applying a PWM signal to EN pin.
A low pass filter is implemented inside chip to reduce the
slew rate of IWLED for preventing the audio noise. The
internal soft start and the wide range dimming frequency
from 200 to 200kHz can eliminate inrush current and audio
noise when dimming. The average LED current is
proportional to the PWM signal duty cycle. The magnitude
of the PWM signal should be higher than the maximum
enable voltage of EN pin, in order to let the dimming control
perform correctly.
EN
IWLED,AVG = Duty of EN
IWLED
Figure 1. PWM Dimming
b. Using a DC Voltage
Using a variable DC voltage to adjust the brightness is a
popular method in some applications. The dimming control
using a DC voltage circuit is shown in Figure 2. As the DC
voltage increases, the current pass through R3 increasingly
and the voltage drop on R3 increase, i.e. the LED current
decreases. For example, if the VDC range is from 0V to
2.8V and assume the RT9293B is selected which VREF is
equal to 0.3V, the selection of resistors in Figure 2 sets
the LED current from 21mA to 0mA. The LED current can
be calculated by the following equation.
VREF −
ILED =
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8
R SET
16
R3 × (VDC − VREF )
R4
RSET
Figure 2. Dimming Control Using a DC Voltage for the
RT9293
c. Using a Filtered PWM signal
Another common application is using a filtered PWM
signal as an adjustable DC voltage for LED dimming control.
A filtered PWM signal acts as the DC voltage to regulate
the output current. The recommended application circuit
is shown as Figure 3. In this circuit, the output ripple
depends on the frequency of PWM signal. For smaller
output voltage ripple (<100mV), the recommended
frequency of 2.8V PWM signal should be above 2kHz. To
fix the frequency of PWM signal and change the duty cycle
of PWM signal can get different output current. The LED
current can be calculated by the following equation.
R3 × (VPWM × Duty − VREF )
VREF −
R4 + RDC
ILED =
R SET
V IN
2.5V to 5.5V
L
10uH to 22uH
V OUT
D
C OUT
1uF
C IN
2.2uF
RT9293
VIN
GND
FB
LX
VOUT
EN
WLEDs
Chip Enable
R3
10k
R4
3k
R DC
82k
R SET
16
C DC
1uF
2.8V
0V
PWM Signal
Figure 3. Filtered PWM Signal for LED Dimming Control
of the RT9293
DS9293-03C April 2008
RT9293
Conceptual
By the above equation and the application circuit shown
in Figure 3, and assume the RT9293B is selected which
VREF is equal to 0.3V. Figure 4 shows the relationship
between the LED current and PWM duty cycle. For
example, when the PWM duty is equal to 60%, the LED
current will be equal to 8.6mA. When the PWM duty is
equal to 40%, the LED current will be equal to 12.7mA.
Application for Driving 3 x 13 WLEDs
The RT9293 can driver different WLEDs topology. For
example, the Figure 6 shows the 3x13 WLEDs and total
current is equal to 260mA. The total WLEDs current can
be set by the RREF which is equal to following equation.
ITotal =
VREF
RSET
20
V IN
18
LED Current (mA)
16
D
C OUT
1uF
C IN
2.2uF
14
V OUT
L
22uH
RT9293
LX
VIN
12
GND
10
8
…
VOUT
FB
EN
Chip Enable
3 x 13 WLEDs
6
4
R SET
2
0
Figure 6. Application for Driving 3 X 13 WLEDs
0
20
40
60
80
100
PWM Duty (%)
Soft-Start
Figure 4
Constant Output Voltage Control
The output voltage of R9293 can be adjusted by the divider
circuit on FB pin. Figure 5 shows the application circuit
for the constant output voltage. The output voltage can be
calculated by the following Equations.
VOUT = VREF ×
V IN
2.5V to 5.5V
R1 + R2
; R2 >10k
R2
L
10uH to 22uH
V OUT
D
GND
FB
limiting threshold.
LX
VOUT
EN
R1
Chip Enable
R2
Figure 5. Application for Constant Output Voltage
DS9293-03C April 2008
across the current limiting threshold, the N-MOSFET will
be turned off so that the inductor will be forced to leave
charging stage and enter discharging stage. Therefore,
the inductor current will not increase over the current
RT9293
VIN
Current Limiting
The current flow through inductor as charging period is
detected by a current sensing circuit. As the value comes
COUT
1uF
CIN
2.2uF
The function of soft-start is made for suppressing the inrush
current to an acceptable value at the beginning of poweron. The soft-start function is built-in the RT9293 by
clamping the output voltage of error amplifier so that the
duty cycle of the PWM will be increased gradually in the
soft-start period.
OVP/UVLO/OTP
The Over Voltage Protection is detected by a junction
breakdown detecting circuit. Once VOUT goes over the
detecting voltage, LX pin stops switching and the power
N-MOSFET will be turned off. Then, the VOUT will be
clamped to be near VOVP. As the output voltage is higher
than a specified value or input voltage is lower than a
specified value, the chip will enter protection mode to
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9
RT9293
Conceptual
prevent abnormal function. As the die temperature >
160°C, the chip also will enter protection mode. The power
MOSFET will be turned off during protection mode to
prevent abnormal operation.
PD(MAX) = (125°C − 25°C) / (165°C/W) = 0.606W for
WDFN-8L 2x2 packages
Inductor Selection
The maximum power dissipation depends on operating
ambient temperature for fixed T J(MAX) and thermal
resistance θJA. For RT9293 packages, the Figure 7 of
derating curves allows the designer to see the effect of
rising ambient temperature on the maximum power
allowed.
Capacitor Selection
Input ceramic capacitor of 2.2uF and output ceramic
capacitor of 1uF are recommended for the RT9293
applications for driving 10 series WLEDs. For better
voltage filtering, ceramic capacitors with low ESR are
recommended. X5R and X7R types are suitable because
of their wider voltage and temperature ranges.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum operation junction temperature. The maximum
power dissipation depends on the thermal resistance of
IC package, PCB layout, the rate of surroundings airflow
and temperature difference between junction to ambient.
The maximum power dissipation can be calculated by
0.8
Maximum Power Dissipation (W)
The recommended value of inductor for 10 WLEDs
applications is from 10uH to 22uH. Small size and better
efficiency are the major concerns for portable devices,
such as the RT9293 used for mobile phone. The inductor
should have low core loss at 1MHz and low DCR for better
efficiency. The inductor saturation current rating should
be considered to cover the inductor peak current.
PD(MAX) = (125°C − 25°C) / (255°C/W) = 0.392W for
TSOT-23-6 packages
Single Layer PCB
0.7
WDFN-8L 2x2
0.6
0.5
0.4
TSOT-23-6
0.3
0.2
0.1
0
0
25
50
75
Figure 7. Derating Curves for RT9293 Packages
Layout Considerations
PD(MAX) = ( TJ(MAX) − TA ) / θJA
} A full GND plane without gap break.
temperature 125°C, TA is the ambient temperature and the
θJA is the junction to ambient thermal resistance.
For recommended operating conditions specification of
RT9293, where T J(MAX) is the maximum junction
temperature of the die (125°C) and TA is the maximum
ambient temperature. The junction to ambient thermal
resistance θJA is layout dependent. For WDFN-8L 2x2
packages, the thermal resistance θJA is 165°C/W on the
standard JEDEC 51-3 single layer thermal test board. The
maximum power dissipation at TA = 25°C can be calculated
by following formula :
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10
125
Ambient Temperature (°C)
following formula :
Where T J(MAX) is the maximum operation junction
100
} LX node copper area should be minimized for reducing
EMI.
} The input capacitor CIN should be placed as closed as
possible to Pin 6.
} The output capacitor COUT should be connected directly
from the Pin 5 to ground rather than across the LEDs.
} FB node copper area should be minimized and kept far
away from noise sources (Pin 1, Pin 5, Pin 6).
} The Inductor is far away receiver and microphone.
} RSET should be placed as close as possible to the
RT9293.
DS9293-03C April 2008
Conceptual
RT9293
} Traces in bold need to be routed first and should be
kept as short as possible.
} VDD to GND noise bypass : Short and wide connection
for the 1uF MLCC capacitor between Pin 6 and Pin 2 is
recommended.
} The voice trace should be far away from the RT9293.
} The embedded antenna should be kept far away from
and at different side of the RT9293.
} The through hole of the RT9293's GND pin is
recommended to be large and as many as possible.
The inductor should be placed as close as
possible to the switch pin to minimize the
noise coupling into other circuits.
LX node copper area should be minimized
for reducing EMI.
GND
The C OUT should be connected
directly from the output schottky
diode to ground rather than
across the WLEDs
C OUT
V IN
C IN should be placed
as closed as possible
to VIN pin for good
filtering.
D
L
LX
1
6
VIN
GND
2
5
VOUT
3
4
EN
CIN
RSET
FB
WLEDs
FB node copper area should be
minimized and keep far away
from noise sources (LX pin) and
RS should be as close as
possible to FB pin.
Figure 8. The Layout Consideration of the RT9293
DS9293-03C April 2008
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11
RT9293
Conceptual
Datasheet Revision History
Version
Data
00C
2008/1/16
Page No.
Item
Description
First Edition
Headline
General Description
01C
2008/2/13
Features
Absolute Maximum Ratings
Modify
Recommended Operating
Conditions
Electrical Characteristics
02C
03C
2008/3/18
2008/4/10
General Description
Ordering Information
Typical Application Circuit
Electrical Characteristics
Typical Application Circuit
Absolute Maximum Ratings
Typical Operating Characteristics
Applications Information
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12
Change from RT9293A/B to RT9293
Modify. Previous RT9293 Phase Out_by
Eric/PME
Modify
Add Typical Operating Characteristics
and Applications Information
DS9293-03C April 2008
RT9293
Conceptual
Outline Dimension
H
D
L
C
B
b
A
A1
e
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min
Max
Min
Max
A
0.700
1.000
0.028
0.039
A1
0.000
0.100
0.000
0.004
B
1.397
1.803
0.055
0.071
b
0.300
0.559
0.012
0.022
C
2.591
3.000
0.102
0.118
D
2.692
3.099
0.106
0.122
e
0.838
1.041
0.033
0.041
H
0.080
0.254
0.003
0.010
L
0.300
0.610
0.012
0.024
TSOT-23-6 Surface Mount Package
DS9293-03C April 2008
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13
RT9293
Conceptual
D2
D
L
E2
E
1
e
SEE DETAIL A
b
2
1
2
1
A
A1
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
0.300
0.008
0.012
D
1.950
2.050
0.077
0.081
D2
1.000
1.250
0.039
0.049
E
1.950
2.050
0.077
0.081
E2
0.400
0.650
0.016
0.026
e
L
0.500
0.300
0.020
0.400
0.012
0.016
W-Type 8L DFN 2x2 Package
Richtek Technology Corporation
Richtek Technology Corporation
Headquarter
Taipei Office (Marketing)
5F, No. 20, Taiyuen Street, Chupei City
8F, No. 137, Lane 235, Paochiao Road, Hsintien City
Hsinchu, Taiwan, R.O.C.
Taipei County, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
Tel: (8862)89191466 Fax: (8862)89191465
Email: [email protected]
www.richtek.com
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DS9293-03C April 2008