RT8290A - Richtek

®
RT8290A
3A, 23V, 340kHz Synchronous Step-Down Converter
General Description
Features
The RT8290A is a high efficiency synchronous step-down
DC/DC converter that can deliver up to 3A output current
from 4.5V to 23V input supply. The RT8290A's current
mode architecture and external compensation allow the
transient response to be optimized over a wide range of
loads and output capacitors. Cycle-by-cycle current limit
provides protection against shorted outputs and soft-start
eliminates input current surge during start-up. The
RT8290A also provides output 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
RT8290A is awailable in an SOP-8 (Exposed Pad)
package.
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Ordering Information
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RT8290A

Package Type
SP : SOP-8 (Exposed Pad-Option 1)
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Note :
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Richtek products are :
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RoHS compliant and compatible with the current require-

ments of IPC/JEDEC J-STD-020.

1.5% High Accuracy Feedback Voltage
3A Output Current
Integrated N-MOSFET Switches
Current Mode Control
Fixed Frequency Operation : 340kHz
Output Adjustable from 0.925V to 20V
Up to 95% Efficiency
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
PSM / PWM Auto-Switched
Thermally Enhanced SOP-8 (Exposed Pad) Package
RoHS Compliant and Halogen Free
Applications
Lead Plating System
G : Green (Halogen Free and Pb Free)

4.5V to 23V Input Voltage Range
Suitable for use in SnPb or Pb-free soldering processes.
Industrial and Commercial Low Power Systems
Computer Peripherals
LCD Monitors and TVs
Green Electronics/Appliances
Point of Load Regulation of High-Performance DSPs,
FPGAs and ASICs.
Simplified Application Circuit
VIN
VIN
REN
CIN
BOOT
RT8290A
SW
EN
SS
CSS
GND
CBOOT
L1
VOUT
R1
FB
CC
RC
COMP
COUT
R2
CP
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RT8290A
Pin Configurations
Marking Information
RT8290AGSP : Product Number
(TOP VIEW)
BOOT
VIN
2
SW
3
GND
4
GND
9
8
SS
7
EN
6
COMP
5
FB
RT8290A
GSPYMDNN
YMDNN : Date Code
SOP-8 (Exposed Pad)
Functional Pin Description
Pin No.
Pin Name
Pin Function
Bootstrap for High Side Gate Driver. Connect a 10nF or greater ceramic capacitor
from the BOOT pin to SW pin.
Voltage Supply Input. The input voltage range is from 4.5V to 23V. A suitable large
capacitor must be bypassed with this pin.
1
BOOT
2
VIN
3
SW
Switching Node. Connect the output LC filter between the SW pin and output load.
GND
Ground. The exposed pad must be soldered to a large PCB and connected to
GND for maximum power dissipation.
5
FB
Output Voltage Feedback Input. The feedback reference voltage is 0.925V
typically.
6
COMP
Compensation Node. This pin is used for compensating the regulation control
loop. A series RC network is required to be connected from COMP to GND. If
needed, an additional capacitor can be connected from COMP to GND.
7
EN
Enable Input. A logic high enables the converter, a logic low forces the converter
into shutdown mode reducing the supply current to less than 3A. For automatic
startup, connect this pin to VIN with a 100k pull up resistor.
8
SS
Soft-Start Control Input. The soft-start period can be set by connecting a capacitor
from SS to GND. A 0.1F capacitor sets the soft-start period to 15.5ms typically.
4,
9 (Exposed Pad)
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DS8290A-01 November 2014
RT8290A
Function Block Diagram
VIN
Internal
Regulator
Shutdown
Comparator
1.2V +
EN
VA VCC
Foldback
Control
3V
VA
-
-
5k
Current Sense
Slope Comp Amplifier
+
Oscillator
0.5V
+
Lockout
Comparator
2.5V
BOOT
S
Q
100m
SW
+
+
UV
Comparator
Current
Comparator
VCC
R
Q
85m
GND
7µA
SS
0.925V
+
+ EA
-
COMP
FB
Absolute Maximum Ratings
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(Note 1)
Supply Voltage, VIN -----------------------------------------------------------------------------------------Switching Voltage, SW ------------------------------------------------------------------------------------SW (AC) 30ns ------------------------------------------------------------------------------------------------BOOT Voltage ------------------------------------------------------------------------------------------------The Other Pins -----------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
SOP-8 (Exposed Pad), θJA --------------------------------------------------------------------------------SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM (Human Body Model) --------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------
Recommended Operating Conditions
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DS8290A-01 November 2014
1.333W
75°C/W
15°C/W
150°C
260°C
−65°C to 150°C
2kV
200V
(Note 4)
Supply Voltage, VIN -----------------------------------------------------------------------------------------Enable Voltage, VEN ----------------------------------------------------------------------------------------Junction Temperature Range ------------------------------------------------------------------------------Ambient Temperature Range -------------------------------------------------------------------------------
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
−0.3V to 25V
−0.3V to (VIN + 0.3V)
−5V to 30V
(VSW − 0.3V) to (VSW + 6V)
−0.3V to 6V
4.5V to 23V
0V to 5.5V
−40°C to 125°C
−40°C to 85°C
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RT8290A
Electrical Characteristics
(VIN = 12V, TA = 25°C unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Shutdown Supply Current
VEN = 0V
--
0.3
3
A
Supply Current
VEN = 3V, VFB = 1V
--
0.8
1.2
mA
0.911
0.925
0.939
V
--
940
--
A/V
Feedback Voltage
VFB
4.5V  VIN  23V
Error Amplifier Transconductance
GEA
I C = ±10A
High Side Switch On-Resistance
RDS(ON)1
--
100
--
m
Low Side Switch On-Resistance
RDS(ON)2
--
85
--
m
--
0
10
A
--
5.1
--
A
--
1.5
--
A
High Side Switch Leakage Current
VEN = 0V, VSW = 0V
Min. Duty Cycle
VBOOT  VSW = 4.8V
From Drain to Source
Upper Switch Current Limit
Lower Switch Current Limit
COMP to Current Sense
Transconductance
Oscillation Frequency
GCS
--
5.4
--
A/V
f OSC1
300
340
380
kHz
Short Circuit Oscillation Frequency
f OSC2
VFB = 0V
--
100
--
kHz
Maximum Duty Cycle
DMAX
VFB = 0.8V
--
90
--
%
Minimum On Time
tON
--
100
--
ns
EN Input Threshold Logic-High
Voltage
Logic-Low
Input Under Voltage Lockout
Threshold
Input Under Voltage Lockout
Threshold Hysteresis
Soft-Start Current
VIH
2.7
--
--
VIL
--
--
0.4
3.8
4.2
4.5
V
--
320
--
mV
ISS
VSS = 0V
--
6
--
A
Soft-Start Period
tSS
CSS = 0.1F
--
15.5
--
ms
Thermal Shutdown
TSD
--
150
--
°C
VUVLO
VIN Rising
VUVLO
V
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.
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RT8290A
Typical Application Circuit
2
VIN
4.5V to 23V
REN
100k
CIN
10µFx2
BOOT
VIN
RT8290A
7 EN
8 SS
CSS
0.1µF
4,
9 (Exposed Pad)
GND
1
SW 3
CBOOT L1
10nF 10µH
R1
26.1k
FB 5
COMP
6
CC
RC
3.9nF 6.8k
VOUT
3.3V/3A
COUT
22µFx2
R2
10k
CP
NC
Table 1. Recommended Component Selection
VOUT (V)
R1 (k)
R2 (k)
RC (k)
CC (nF)
L (μH)
COUT (μF)
15
153
10
30
3.9
33
22 x 2
10
97.6
10
20
3.9
22
22 x 2
8
76.8
10
15
3.9
22
22 x 2
5
45.3
10
13
3.9
15
22 x 2
3.3
26.1
10
6.8
3.9
10
22 x 2
2.5
16.9
10
6.2
3.9
6.8
22 x 2
1.8
9.53
10
4.3
3.9
4.7
22 x 2
1.2
3
10
3
3.9
3.6
22 x 2
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RT8290A
Typical Operating Characteristics
Reference Voltage vs. Input Voltage
Efficiency vs. Output Current
0.932
100
90
VIN = 4.5V
VIN = 12V
VIN = 23V
70
60
0.930
Reference Voltage (V)
Efficiency (%)
80
50
40
30
20
0.928
0.926
0.924
0.922
10
0.920
0
0.01
0.1
1
4
10
6
8
10
12
14
16
18
20
22
24
Input Voltage (V)
Output Current (A)
Reference Voltage vs. Temperature
Output Voltage vs. Output Current
0.940
3.40
3.38
3.36
Output Voltage (V)
Reference Voltage (V)
0.935
0.930
0.925
0.920
3.34
3.32
3.30
VIN = 4.5V
VIN = 12V
VIN = 23V
3.28
3.26
3.24
0.915
3.22
0.910
3.20
-50
-25
0
25
50
75
100
125
0.0
0.3
0.6
0.9
Temperature (C)
1.5
1.8
2.1
2.4
2.7
3.0
Output current (A)
Frequency vs. Input Voltage
Frequency vs. Temperature
350
350
345
345
340
340
Frequency (kHz)1
Frequency (kHz)1
1.2
335
330
325
320
315
335
330
VIN = 4.5V
VIN = 12V
VIN = 23V
325
320
315
310
310
305
VOUT = 3.3V, IOUT = 0.5A
305
VOUT = 3.3V, IOUT = 0.5A
300
300
4
6
8
10
12
14
16
18
20
22
Input Voltage (V)
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24
-50
-25
0
25
50
75
100
125
Temperature (C)
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RT8290A
Current Limit vs. Temperature
Load Transient Response
7.0
Current Limit (A)
6.5
VOUT
(100mV/Div)
6.0
5.5
5.0
4.5
IOUT
(2A/Div)
4.0
3.5
VIN = 12V, VOUT = 3.3V, IOUT = 0.3A to 3A
VOUT = 3.3V, VIN = 12V
3.0
-50
-25
0
25
50
75
100
125
Time (100μs/Div)
Temprature (C)
Load Transient Response
Switching Waveform
VOUT
(10mV/Div)
VOUT
(100mV/Div)
VSW
(10V/Div)
IOUT
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 1.5A to 3A
IL
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 3A
Time (100μs/Div)
Time (1μs/Div)
Power On from VIN
Power Off from VIN
VIN
(5V/Div)
VOUT
(2V/Div)
VIN
(5V/Div)
VOUT
(2V/Div)
IL
(2A/Div)
IL
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 3A
Time (5ms/Div)
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DS8290A-01 November 2014
VIN = 12V, VOUT = 3.3V, IOUT = 3A
Time (5ms/Div)
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RT8290A
Power On from EN
Power Off from EN
VEN
(2V/Div)
VEN
(2V/Div)
VOUT
(2V/Div)
VOUT
(2V/Div)
IOUT
(2A/Div)
IOUT
(2A/Div)
VIN = 12V, VOUT = 3.3V, IOUT = 3A
Time (10ms/Div)
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VIN = 12V, VOUT = 3.3V, IOUT = 3A
Time (10ms/Div)
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RT8290A
Application Information
The RT8290A is a synchronous high voltage buck converter
that can support the input voltage range from 4.5V to 23V
and the output current can be up to 3A.
SS pin and GND. The chip provides a 6μA charge current
for the external capacitor. If a 0.1μF capacitor is used to
set the soft-start, the period will be 15.5ms (typ.).
Output Voltage Setting
Inductor Selection
The resistive voltage divider allows the FB pin to sense
the output voltage as shown in Figure 1.
The inductor value and operating frequency determine the
ripple current according to a specific input and output
voltage. The ripple current ΔIL increases with higher VIN
and decreases with higher inductance.
V
V
IL =  OUT   1 OUT 
f

L
VIN 

 
VOUT
R1
FB
RT8290A
R2
GND
Figure 1. Output Voltage Setting
The output voltage is set by an external resistive voltage
divider according to the following equation :
VOUT = VFB  1 R1 
 R2 
where VFB is the feedback reference voltage (0.925V typ.).
External Bootstrap Diode
Connect a 10nF low ESR ceramic capacitor between the
BOOT pin and SW pin. This capacitor provides the gate
driver voltage for the high side MOSFET.
It is recommended to add an external bootstrap diode
between an external 5V and the BOOT pin for efficiency
improvement when input voltage is lower than 5.5V or duty
ratio is higher than 65%. The bootstrap diode can be a
low cost one such as 1N4148 or BAT54.
The external 5V can be a 5V fixed input from system or a
5V output of the RT8290A. Note that the external boot
voltage must be lower than 5.5V.
5V
BOOT
RT8290A
10nF
SW
Figure 2. External Bootstrap Diode
Soft-Start
The RT8290A contains an external soft-start clamp that
gradually raises the output voltage. The soft-start timing
can be programmed by the external capacitor between
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Having a lower ripple current reduces not only the ESR
losses in the output capacitors but also the output voltage
ripple. High frequency with small ripple current can achieve
highest efficiency operation. However, it requires a large
inductor to achieve this goal.
For the ripple current selection, the value of ΔIL = 0.2375
(IMAX) will be a reasonable starting point. The largest ripple
current occurs at the highest VIN. To guarantee that the
ripple current stays below the specified maximum, the
inductor value should be chosen according to the following
equation :
 VOUT  
VOUT 
L =
  1  VIN(MAX) 
f
I


L(MAX)

 

Inductor Core Selection
The inductor type must be selected once the value for L
is known. Generally speaking, high efficiency converters
can not afford the core loss found in low cost powdered
iron cores. So, the more expensive ferrite or
mollypermalloy cores will be a better choice.
The selected inductance rather than the core size for a
fixed inductor value is the key for actual core loss. As the
inductance increases, core losses decrease. Unfortunately,
increase of the inductance requires more turns of wire
and therefore the copper losses will increase.
Ferrite designs are preferred at high switching frequency
due to the characteristics of very low core losses. So,
design goals can focus on the reduction of copper loss
and the saturation prevention.
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RT8290A
Ferrite core material saturates “hard”, which means that
inductance collapses abruptly when the peak design
current is exceeded. The previous situation results in an
abrupt increase in inductor ripple current and consequent
output voltage ripple.
Do not allow the core to saturate!
Different core materials and shapes will change the size/
current and price/current relationship of an inductor.
Toroid or shielded pot cores in ferrite or permalloy materials
are small and do not radiate energy. However, they are
usually more expensive than the similar powdered iron
inductors. The rule for inductor choice mainly depends
on the price vs. size requirement and any radiated field/
EMI requirements.
CIN and COUT Selection
The input capacitance, C IN, is needed to filter the
trapezoidal current at the source of the high side MOSFET.
To prevent large ripple current, a low ESR input capacitor
sized for the maximum RMS current should be used. The
RMS current is given by :
V
VIN
IRMS = IOUT(MAX) OUT
1
VIN
VOUT
This formula has a maximum at VIN = 2VOUT, where
I RMS = I OUT/2. This simple worst-case condition is
commonly used for design because even significant
deviations do not offer much relief.
Choose a capacitor rated at a higher temperature than
required. Several capacitors may also be paralleled to
meet size or height requirements in the design.
For the input capacitor, a 10μF x 2 low ESR ceramic
capacitor is recommended. For the recommended
capacitor, please refer to table 3 for more detail.
The selection of COUT is determined by the required ESR
to minimize voltage ripple.
Moreover, the amount of bulk capacitance is also a key
for COUT selection to ensure that the control loop is stable.
Loop stability can be checked by viewing the load transient
response as described in a later section.
The output ripple, ΔVOUT , is determined by :
1

VOUT  IL ESR 
8fCOUT 

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The output ripple will be highest at the maximum input
voltage since ΔIL increases with input voltage. Multiple
capacitors placed in parallel may be needed to meet the
ESR and RMS current handling requirement. Dry tantalum,
special polymer, aluminum electrolytic and ceramic
capacitors are all available in surface mount packages.
Special polymer capacitors offer very low ESR value.
However, it provides lower capacitance density than other
types. Although Tantalum capacitors have the highest
capacitance density, it is important to only use types that
pass the surge test for use in switching power supplies.
Aluminum electrolytic capacitors have significantly higher
ESR. However, it can be used in cost-sensitive applications
for ripple current rating and long term reliability
considerations. Ceramic capacitors have excellent low
ESR characteristics but can have a high voltage coefficient
and audible piezoelectric effects. The high Q of ceramic
capacitors with trace inductance can also lead to significant
ringing.
Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at input and
output. When a ceramic capacitor is used at the input
and the power is supplied by a wall adapter through long
wires, a load step at the output can induce ringing at the
input, VIN. At best, this ringing can couple to the output
and be mistaken as loop instability. At worst, a sudden
inrush of current through the long wires can potentially
cause a voltage spike at VIN large enough to damage the
part.
Checking Transient Response
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to ΔILOAD (ESR) and COUT also begins to be charged
or discharged to generate a feedback error signal for the
regulator to return VOUT to its steady-state value. During
this recovery time, VOUT can be monitored for overshoot or
ringing that would indicate a stability problem.
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RT8290A
Thermal Considerations
Layout Considerations
For continuous operation, do not exceed the maximum
operation junction temperature 125°C. 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
following formula :
Follow the PCB layout guidelines for optimal performance
of the RT8290A.
PD(MAX) = (TJ(MAX) − TA) / θJA

Keep the traces of the main current paths as short and
wide as possible.

Put the input capacitor as close as possible to the device
pins (VIN and GND).

SW node is with high frequency voltage swing and
should be kept in a small area. Keep sensitive
components away from the SW node to prevent stray
capacitive noise pick-up.

Place the feedback components as close to the FB pin
and COMP pin as possible.

The GND pin and Exposed Pad should be connected to
a strong ground plane for heat sinking and noise
protection.
where T J(MAX) is the maximum operation junction
temperature, TA is the ambient temperature and the θJA is
the junction to ambient thermal resistance.
For recommended operating conditions specification, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance θJA is layout dependent. For
SOP-8 (Exposed Pad) package, the thermal resistance
θJA is 75°C/W on the standard JEDEC 51-7 four-layers
thermal test board. The maximum power dissipation at TA
= 25°C can be calculated by following formula :
PD(MAX) = (125°C − 25°C) / (75°C/W) = 1.333W for
SOP-8 (Exposed Pad) package
The maximum power dissipation depends on operating
ambient temperature for fixed T J(MAX) and thermal
resistance θJA. The derating curve in Figure 3 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Maximum Power Dissipation (W)1
1.6
Four-Layer PCB
1.4
Input capacitor must be placed
as close to the IC as possible.
SW
GND
V IN
CS
The feedback
components must be
connected as close to
the device as possible.
C IN
BOOT
L1
V OUT
C OUT
VIN
2
SW
3
GND
4
GND
8
SS
7
EN
6
COMP
5
FB
CC
CP
RC
R1
V OUT
SW should be connected to inductor by
wide and short trace. Keep sensitive
components away from this trace.
R2
GND
Figure 4. PCB Layout Guide
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 3. Derating Curve of Maximum Power Dissipation
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RT8290A
Table 2. Suggested Inductors for Typical Application Circuit
Component Supplier
Series
Dimensions (mm)
TDK
VLF10045
10 x 9.7 x 4.5
TAIYO YUDEN
NR8040
8x8x4
Table 3. Suggested Capacitors for CIN and COUT
Component Supplier
Part No.
Capacitance (μF)
Case Size
MURATA
GRM31CR61E106K
10
1206
TDK
C3225X5R1E106K
10
1206
TAIYO YUDEN
TMK316BJ106ML
10
1206
MURATA
GRM31CR60J476M
47
1206
TDK
C3225X5R0J476M
47
1210
TAIYO YUDEN
EMK325BJ476MM
47
1210
MURATA
GRM32ER71C226M
22
1210
TDK
C3225X5R1C226M
22
1210
Copyright © 2013 Richtek Technology Corporation. All rights reserved.
www.richtek.com
12
is a registered trademark of Richtek Technology Corporation.
DS8290A-01 November 2014
RT8290A
Outline Dimension
H
A
M
EXPOSED THERMAL PAD
(Bottom of Package)
Y
J
X
B
F
C
I
D
Dimensions In Millimeters
Symbol
Dimensions In Inches
Min
Max
Min
Max
A
4.801
5.004
0.189
0.197
B
3.810
4.000
0.150
0.157
C
1.346
1.753
0.053
0.069
D
0.330
0.510
0.013
0.020
F
1.194
1.346
0.047
0.053
H
0.170
0.254
0.007
0.010
I
0.000
0.152
0.000
0.006
J
5.791
6.200
0.228
0.244
M
0.406
1.270
0.016
0.050
X
2.000
2.300
0.079
0.091
Y
2.000
2.300
0.079
0.091
X
2.100
2.500
0.083
0.098
Y
3.000
3.500
0.118
0.138
Option 1
Option 2
8-Lead SOP (Exposed Pad) Plastic 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.
DS8290A-01 November 2014
www.richtek.com
13