RT9721A/B
80mΩ
Ω, 500mA High-Side Power Switches with Flag
General Description
Features
The RT9721A/B are low voltage, single N-MOSFET highside power switches, optimized for self-powered and buspowered Universal Serial Bus (USB) applications. The
RT9721A/B series provides a charge pump circuitry to drive
the internal MOSFET switch; the switch's low RDS(ON),
80mΩ, meets USB voltage drop requirements; and a flag
output is available to indicate fault conditions to the local
USB controller.
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Compliant to USB Specifications
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Built-In N-MOSFET
Ω
` Typical RDS(ON) : 80mΩ
Output Can Be Forced to Higher Than Input (OffState)
Low Supply Current :
` 50μ
μA Typical at Switch On State
` 0.1μ
μA Typical at Switch Off State
Guaranteed 500mA Continuous Load Current
Wide Input Voltage Ranges : 2.5V to 5.5V
Open-Drain Fault Flag Output
Hot Plug-In Application (Soft-Start)
2.15V Typical Under-Voltage Lockout (UVLO)
Current Limiting Protection
Thermal Shutdown Protection
Reverse Current Flow Blocking (no body diode)
UL Approved−E219878
RoHS Compliant and Halogen Free
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Additional features include soft-start to limit inrush current
during plug-in, thermal shutdown to prevent catastrophic
switch failure from high-current loads, under-voltage lockout
(UVLO) to ensure that the device remains off unless there
is a valid input voltage present. The maximum current is
limited to typically 750mA in dual ports in accordance with
the USB power requirements, lower quiescent current as
50uA making this device ideal for portable battery-operated
equipment.
The RT9721A is designed without output auto-discharge
function and RT9721B is designed with output autodischarge function.
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Applications
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The RT9721A/B are available in SOT-23-5 package
requiring minimum board space and smallest components.
Ordering Information
RT9721
Package Type
B : SOT-23-5
Lead Plating System
G : Green (Halogen Free and Pb Free)
Output Discharge Function
A : Without Auto-Discharge Function
B : With Auto-Discharge Function
Note :
Richtek products are :
`
RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.
`
Suitable for use in SnPb or Pb-free soldering processes.
DS9721A/B-02 April 2011
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USB Bus/Self Powered Hubs
USB Peripherals
Notebook, Motherboard PCs
Pin Configurations
(TOP VIEW)
VOUT
FLG
5
4
2
3
VIN GND EN
SOT-23-5
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
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1
RT9721A/B
Typical Application Circuit
Pull-Up Resistor (10k to 100k)
USB Controller
Supply
Voltage 5V
1
FLG
VIN
C IN
1µF
4
Over -Current
RT9721A/B
3
VOUT
EN
5
V BUS
+
Chip Enable
C OUT
10µF
GND
2
D+
DGND
150µF
Ferrite
Beads
Data
Functional Pin Description
Pin No.
Pin Name
Pin Function
1
VIN
Switch Input Voltage.
2
GND
Ground.
3
EN
Chip Enable (Active High).
4
FLG
Open-Drain Fault Flag Output.
5
VOUT
Switch Output Voltage.
Function Block Diagram
VIN
EN
Bias
UVLO
Oscillator
Charge
Pump
Current
Limiting
Gate
Control
Output Voltage
Detection
VOUT
Thermal
Protection
Auto Discharge
RT9721B Only
FLG
Delay
GND
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DS9721A/B-02 April 2011
RT9721A/B
Absolute Maximum Ratings
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(Note 1)
Supply Input Voltage, VIN -----------------------------------------------------------------------------------------------EN Input Voltage ----------------------------------------------------------------------------------------------------------Flag Voltage ---------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
SOT-23-5 -------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2)
SOT-23-5, θJA --------------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3)
HBM -------------------------------------------------------------------------------------------------------------------------MM ----------------------------------------------------------------------------------------------------------------------------
Recommended Operating Conditions
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6V
−0.3V to 6V
6V
0.4W
250°C/W
260°C
150°C
−65°C to 150°C
4kV
400V
(Note 4)
Supply Input Voltage Range, VIN --------------------------------------------------------------------------------------EN Input Voltage Range -------------------------------------------------------------------------------------------------Junction Temperature Range -------------------------------------------------------------------------------------------Ambient Temperature Range --------------------------------------------------------------------------------------------
2.5V to 5.5V
0V to 5.5V
−40°C to 125°C
−40°C to 85°C
Electrical Characteristics
(VIN = 5V, CIN = 1μF, COUT = 10μF, TA = 25°C, unless otherwise specified)
Parameter
Switch On Resistance
Symbol
Test Conditions
Min
Typ
Max
Unit
mΩ
RDS(ON)
VIN = 5V, IOUT = 100mA
--
80
100
ISW_ON
Switch On, VOUT = Open
--
50
70
ISW_OFF
Switch Off, VOUT = Open
--
0.1
1
Logic-Low Voltage
VIL
VIN = 2.5V to 5.5V, Switch Off
--
--
0.8
V
Logic-High Voltage
VIH
VIN = 2.5V to 5.5V, Switch On
2
--
--
V
EN Input Current
IEN
VEN = 5V
--
0.01
0.1
μA
Output Leakage Current
ILEAKAGE
VEN = 0V, RLOAD = 0Ω
--
0.5
1
μA
Output Turn-On Rise Time
T ON_RISE
10% to 90% of V OUT Rising
--
200
--
μs
Current Limit Detect Threshold
ILIM_THRES
IOUT Rising
--
--
1
A
Current Limit
ILIM
VOUT = 4V
500
--
900
mA
FLG Output Resistance
RFLG
ISINK = 1mA
--
10
--
Ω
FLG Off Current
IFLG_OFF
VFLG = 5V
--
0.01
1
μA
tD
From fault condition to FLG
assertion
5
12
20
ms
RDischarge
VEN = 0V
--
100
150
Ω
Supply Current
EN
Threshold
FLG Delay Time
(Note 5)
Shutdown Auto-Discharge
Resistance
HOLD
μA
To be continued
DS9721A/B-02 April 2011
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3
RT9721A/B
Parameter
Symbol
Test Conditions
Min
Typ
Max
Unit
Under-Voltage Lockout
VUVLO
VIN Increasing
1.9
2.15
2.4
V
Under-Voltage Hysteresis
ΔVUVLO
VIN Decreasing
--
0.1
--
V
Thermal Shutdown Protection
T SD
--
150
--
°C
Thermal Shutdown Hysteresis
ΔTSD
--
25
--
°C
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. 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.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. The FLAG delay time is input voltage dependent, see “Typical Operating Characteristics” graph for further details.
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DS9721A/B-02 April 2011
RT9721A/B
Typical Operating Characteristics
On Resistance vs. Temperature
On Resistance vs. Input Voltage
110
150
IOUT = 100mA
On Resistance (mΩ)
On Resistance (mΩ)
105
100
95
90
85
VIN = 5V, IOUT = 100mA
130
110
90
70
50
80
2.5
3
3.5
4
4.5
5
-50
5.5
-25
0
Switch On Supply Current vs. Input Voltage
Switch On Supply Current (uA)
Switch On Supply Current (uA)1
75
100
125
Switch On Supply Current vs. Temperature
45.0
No Load
42.5
40
37.5
35
32.5
30
27.5
25
VIN = 5V, No Load
42.5
40.0
37.5
35.0
32.5
30.0
27.5
25.0
2.5
3
3.5
4
4.5
5
5.5
-50
-25
0
Input Voltage (V)
25
50
75
100
125
Tmeperature (°C)
Switch Off Supply Current vs. Input Voltage
0.30
Switch Off Supply Current vs. Temperature
0.8
No Load
Switch Off Supply Current (uA)
Switch Off Supply Current (uA)
50
Temperature (°C)
Input Voltage (V)
45
25
0.25
0.20
0.15
0.10
0.05
VIN = 5V, No Load
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.00
2.5
3
3.5
4
4.5
Input Voltage (V)
DS9721A/B-02 April 2011
5
5.5
-50
-25
0
25
50
75
100
125
Temperature (°C)
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RT9721A/B
UVLO Threshold vs. Temperature
Output Voltage vs. Output Current
6
2.5
VIN = 5V
UVLO Threshold (V)
Output Volttage (V)
5
4
3
2
1
0
2.3
Rising
2.1
Falling
1.9
1.7
1.5
0
100 200 300 400 500 600 700 800 900 1000
100
0
-50
-25
0
Output Turn-On Rise Time vs. Input Voltage
No Load
200
180
160
140
120
100
75
100
125
Output Turn-On Rise Time vs. Temperature
VIN = 5V, No Load
230
210
190
170
150
80
2.5
3
3.5
4
4.5
5
-50
5.5
-25
0
Current Limit Detect Threshold vs. Input Voltage
900
800
700
600
500
3
3.5
4
4.5
Input Voltage (V)
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6
50
75
100
125
Current Limit Detect Threshold vs. Temperature
Current Limit Detect Threshold (mA)
1000
2.5
25
Temperature (°C)
Input Voltage (V)
Current Limit Detect Threshold (mA)
50
250
Output Turn-On Rise Time (us)
Output Turn-On Rise Time (us)1
220
25
Temperature (°C)
Output Current (mA)
5
5.5
1000
VIN = 5V
900
800
700
600
500
-50
-25
0
25
50
75
100
125
Temperature (°C)
DS9721A/B-02 April 2011
RT9721A/B
Current Limit vs. Input Voltage
Current Limit vs. Temperature
900
VIN − VOUT = 1V
850
850
800
800
Current Limit (mA)
Current Limit (mA)
900
750
700
650
600
550
VIN = 5V, VOUT = 4V
750
700
650
600
550
500
500
2.5
3
3.5
4
4.5
5
5.5
-50
-25
0
Input Voltage (V)
75
100
125
VIN = 5V, RLOAD = 0Ω
13.5
12
FLAG Delay Time (ms)
FLAG Delay Time (ms)
14.0
RLOAD = 0Ω
10
8
6
4
13.0
12.5
12.0
11.5
11.0
10.5
2
10.0
2.5
3
3.5
4
4.5
5
5.5
-50
Input Voltage (V)
-25
0
25
50
75
100
125
Temperature (°C)
EN Threshold Volatge vs. Input Voltage
Power On from VIN
2.0
EN Threshold Voltage (V)
50
FLAG Delay Time vs. Temperature
FLAG Delay Time vs. Input Voltage
14
25
Temperature (°C)
1.8
Rising
1.6
VIN
(2V/Div)
1.4
Falling
1.2
VOUT
(2V/Div)
1.0
RLOAD = 200Ω
0.8
2.5
3
3.5
4
4.5
5
5.5
Time (2ms/Div)
Input Voltage (V)
DS9721A/B-02 April 2011
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RT9721A/B
Power Off from VIN
Turn On from EN
VEN
(5V/Div)
VIN
(2V/Div)
VOUT
(2V/Div)
VOUT
(2V/Div)
I IN
(500mA/Div)
RLOAD = 200Ω
COUT = 10μF, RLOAD = 10Ω
Time (2ms/Div)
Time (100μs/Div)
Turn Off from EN
Current Limit Response
COUT = 10μF, RLOAD = 10Ω
VIN = 5V, COUT = 10μF, RLOAD = 4Ω
VEN
(5V/Div)
VOUT
(2V/Div)
VOUT
(2V/Div)
IOUT
(500mA/Div)
I IN
(500mA/Div)
Time (100μs/Div)
Time (100μs/Div)
FLAG Response
Thermal Shutdown Response
VIN = 5V, RLOAD = 4Ω
VIN = 5V, RLOAD = 0Ω
VOUT
(5V/Div)
VOUT
(5V/Div)
VFLG
(5V/Div)
VFLG
(5V/Div)
IOUT
(500mA/Div)
IOUT
(1A/Div)
Time (2ms/Div)
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Time (400ms/Div)
DS9721A/B-02 April 2011
RT9721A/B
Applications Information
The RT9721A/B are single N-MOSFET high-side power
switch with active-high enable input, optimized for selfpowered and bus-powered Universal Serial Bus (USB)
applications. The RT9721A/B series equipped with a charge
pump circuitry to drive the internal N-MOSFET switch; the
switch's low RDS(ON), 80mΩ, meets USB voltage drop
requirements; and a flag output is available to indicate fault
conditions to the local USB controller.
Input and Output
VIN (input) is the power source connection to the internal
circuitry and the drain of the MOSFET. VOUT (output) is
the source of the MOSFET. In a typical application, current
flows through the switch from VIN to VOUT toward the load.
If VOUT is greater than VIN, current will flow from VOUT to
VIN since the MOSFET is bidirectional when on.
Unlike a normal MOSFET, there is no a parasitic body
diode between drain and source of the MOSFET, the
RT9721A/B prevent reverse current flow if VOUT being
externally forced to a higher voltage than VIN when the
chip is disabled (VEN < 0.8V).
D
S
start” feature effectively isolates the power source from
extremely large capacitive loads, satisfying the USB voltage
droop requirements.
Fault Flag
The RT9721A/B series provides a FLG signal pin which is
an N-Channel open drain MOSFET output. This open drain
output goes low when VOUT < VIN − 1V, current limit or the
die temperature exceeds 150°C approximately. The FLG
output is capable of sinking a 10mA load to typically 200mV
above ground. The FLG pin requires a pull-up resistor, this
resistor should be large in value to reduce energy drain. A
100kΩ pull-up resistor works well for most applications. In
the case of an over-current condition, FLG will be asserted
only after the flag response delay time, tD, has elapsed.
This ensures that FLG is asserted only upon valid overcurrent conditions and that erroneous error reporting is
eliminated.
For example, false over-current conditions may occur
during hot-plug events when extremely large capacitive
loads are connected and causes a high transient inrush
current that exceeds the current limit threshold. The FLG
response delay time tD is typically 12ms.
S
D
Under-Voltage Lockout
G
G
Normal MOSFET
RT9721A/B
Chip Enable Input
The switch will be disabled when the EN pin is in a logic
low condition. During this condition, the internal circuitry
and MOSFET are turned off, reducing the supply current
to 0.1μA typical. The maximum guaranteed voltage for a
logic low at the EN pin is 0.8V. A minimum guaranteed
voltage of 2V at the EN pin will turn the RT9721A/B on.
Floating the input may cause unpredictable operation. EN
should not be allowed to go negative with respect to GND.
Soft Start for Hot Plug-In Applications
In order to eliminate the upstream voltage droop caused
by the large inrush current during hot-plug events, the “softDS9721A/B-02 April 2011
Under-voltage lockout (UVLO) prevents the MOSFET switch
from turning on until input voltage exceeds approximately
2.15V. If input voltage drops below approximately 2.05V,
UVLO turns off the MOSFET switch, FLG will be asserted
accordingly. Under-voltage detection functions only when
the switch is enabled.
Current Limiting Protection
The current limit circuitry prevents damage to the MOSFET
switch and the hub downstream port but can deliver load
current up to the current limit threshold of typically 700mA
through the switch of RT9721A/B series. When a heavy
load or short circuit is applied to an enabled switch, a
large transient current may flow until the current limit
circuitry responds. Once this current limit threshold is
exceeded, the device enters constant current mode until
the thermal shutdown occurs or the fault is removed.
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9
RT9721A/B
Thermal Shutdown
Thermal shutdown is employed to protect the device from
damage if the die temperature exceeds approximately
150°C. The power switch will auto-recover when the IC is
cooling down. The thermal hysteresis temperature is about
25°C.
Universal Serial Bus (USB) & Power Distribution
The goal of USB is to enable devices from different vendors
to interoperate in an open architecture. USB features
include ease of use for the end user, a wide range of
workloads and applications, robustness, synergy with the
PC industry, and low-cost implementation. Benefits include
self-identifying peripherals, dynamically attachable and
reconfigurable peripherals, multiple connections (support
for concurrent operation of many devices), support for as
many as 127 physical devices, and compatibility with PC
Plug-and-Play architecture.
The Universal Serial Bus connects USB devices with a
USB host: each USB system has one USB host. USB
devices are classified either as hubs, which provide
additional attachment points to the USB, or as functions,
which provide capabilities to the system (for example, a
digital joystick). Hub devices are then classified as either
Bus-Power Hubs or Self-Powered Hubs.
A Bus-Powered Hub draws all of the power to any internal
functions and downstream ports from the USB connector
power pins. The hub may draw up to 500mA from the
upstream device. External ports in a Bus-Powered Hub
can supply up to 100mA per port, with a maximum of four
external ports.
Self-Powered Hub power for the internal functions and
downstream ports does not come from the USB, although
the USB interface may draw up to 100mA from its upstream
connect, to allow the interface to function when the
remainder of the hub is powered down. The hub must be
able to supply up to 500mA on all of its external
downstream ports. Please refer to Universal Serial
Specification Revision 2.0 for more details on designing
compliant USB hub and host systems.
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Over-Current protection devices such as fuses and PTC
resistors (also called polyfuse or polyswitch) have slow
trip times, high on-resistance, and lack the necessary
circuitry for USB-required fault reporting.
The faster trip time of the RT9721A/B power distribution
allow designers to design hubs that can operate through
faults. The RT9721A/B have low on-resistance and internal
fault-reporting circuitry that help the designer to meet
voltage regulation and fault notification requirements.
Because the devices are also power switches, the designer
of self-powered hubs has the flexibility to turn off power to
output ports. Unlike a normal MOSFET, the devices have
controlled rise and fall times to provide the needed inrush
current limiting required for the bus-powered hub power
switch.
Supply Filter/Bypass Capacitor
A 1uF low-ESR ceramic capacitor from VIN to GND, located
at the device is strongly recommended to prevent the input
voltage drooping during hot-plug events. However, higher
capacitor values will further reduce the voltage droop on
the input. Furthermore, without the bypass capacitor, an
output short may cause sufficient ringing on the input (from
source lead inductance) to destroy the internal control
circuitry. The input transient must not exceed 6.5V of the
absolute maximum supply voltage even for a short duration.
Output Filter Capacitor
A low-ESR 150uF aluminum electrolytic or tantalum
between VOUT and GND is strongly recommended to meet
the 330mV maximum droop requirement in the hub VBUS
(Per USB 2.0, output ports must have a minimum 120uF
of low-ESR bulk capacitance per hub). Standard bypass
methods should be used to minimize inductance and
resistance between the bypass capacitor and the
downstream connector to reduce EMI and decouple voltage
droop caused when downstream cables are hot-insertion
transients. Ferrite beads in series with VBUS, the ground
line and the 0.1μF bypass capacitors at the power
connector pins are recommended for EMI and ESD
protection. The bypass capacitor itself should have a low
dissipation factor to allow decoupling at higher frequencies.
DS9721A/B-02 April 2011
RT9721A/B
Voltage Drop
Thermal Considerations
The USB specification states a minimum port-output voltage
in two locations on the bus, 4.75V output of a Self-Powered
Hub port and 4.4V output of a Bus-Powered Hub port. As
with the Self-Powered Hub, all resistive voltage drops for
the Bus-Powered Hub must be accounted for to guarantee
voltage regulation (see Figure 7-47 of Universal Serial
Specification Revision 2.0 ).
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 following
formula :
The following calculation determines VOUT(MIN) for multiple
ports (NPORTS) ganged together through one switch (if using
one switch per port, NPORTS is equal to 1) :
PD(MAX) = (TJ(MAX) − TA) / θJA
VOUT(MIN) = 4.75V − [ II x (4 x RCONN + 2 x RCABLE) ] −
(0.1A x NPORTS x RSWITCH) − VPCB
Where
RCONN : Resistance of connector contacts (two contacts
per connector)
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 of
RT9721A/B, the maximum junction temperature is 125°C.
The junction to ambient thermal resistance θJA is layout
RCABLE : Resistance of upstream cable wires (one 5V and
one GND)
dependent. For SOT-23-5 package, the thermal resistance
θJA is 250°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 :
RSWITCH : Resistance of power switch (80mΩ typical for
RT9721A/B)
P D(MAX) = (125°C - 25°C) / (250°C/W) = 0.4W for
SOT-23-5 package
VPCB : PCB voltage drop
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal resistance
θJA. For the RT9721A/B, Figure 1 shows the maximum
power dissipation allowed under various ambient
temperatures.
If the hub consumes the maximum current (II) of 500mA,
the maximum resistance of the cable is 90mΩ.
The resistance of the switch is defined as follows :
RSWITCH = { 4.75V − 4.4V − [ 0.5A x (4 x 30mΩ + 2 x
90mΩ)] − V PCB } / (0.1A x N PORTS )
= (200mV − VPCB ) / (0.1A x NPORTS )
If the voltage drop across the PCB is limited to 100mV,
the maximum resistance for the switch is 250mΩ for four
ports ganged together. The RT9721A/B, with its maximum
110mΩ on-resistance over temperature, easily meets this
requirement.
DS9721A/B-02 April 2011
0.50
Maximum Power Dissipation (W)
The USB specification defines the maximum resistance
per contact (RCONN) of the USB connector to be 30mΩ
and the drop across the PCB and switch to be 100mV.
This basically leaves two variables in the equation : the
resistance of the switch and the resistance of the cable.
Single Layers PCB
0.45
0.40
0.35
SOT-23-5
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 1. Maximum Power Dissipation Derating Curve
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11
RT9721A/B
Layout Considerations
For best performance of the RT9721A/B series, the following
guidelines must be strictly followed.
` Input and output capacitors should be placed close to
the IC and connected to ground plane to reduce noise
coupling.
` The GND should be connected to a strong ground plane
for heat sink.
` Keep the main current traces as possible as short and
wide.
V OUT
GND
V IN
FLG
EN
V IN
GND
Figure 2
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DS9721A/B-02 April 2011
RT9721A/B
Outline Dimension
H
D
L
B
C
b
A
A1
e
Symbol
Dimensions In Millimeters
Dimensions In Inches
Min
Max
Min
Max
A
0.889
1.295
0.035
0.051
A1
0.000
0.152
0.000
0.006
B
1.397
1.803
0.055
0.071
b
0.356
0.559
0.014
0.022
C
2.591
2.997
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
SOT-23-5 Surface Mount Package
Richtek Technology Corporation
Richtek Technology Corporation
Headquarter
Taipei Office (Marketing)
5F, No. 20, Taiyuen Street, Chupei City
5F, No. 95, Minchiuan Road, Hsintien City
Hsinchu, Taiwan, R.O.C.
Taipei County, Taiwan, R.O.C.
Tel: (8863)5526789 Fax: (8863)5526611
Tel: (8862)86672399 Fax: (8862)86672377
Email: [email protected]
Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design,
specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed
by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek.
DS9721A/B-02 April 2011
www.richtek.com
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