RT9741

®
RT9741
100mΩ
Ω, 1.5A/0.7A High-Side Power Switches
General Description
Features
The RT9741 is a cost-effective, low-voltage, single NMOSFET high-side Power Switch IC for USB application.
Low switch-on resistance (typ. 100mΩ) and low supply
current (typ. 50μA) are realized in this IC.

The RT9741 integrates an over-current protection circuit,
a short fold back circuit, a thermal shutdown circuit and
an under-voltage lockout circuit for overall protection.
Furthermore, the chip also integrates an embedded delay
function to prevent miss-operation from happening due to
inrush-current. The RT9741 is an ideal solution for USB
power supply and can support flexible applications since
it is available in the SOT-23-3 package.







100mΩ
Ω (typ.) N-MOSFET Switch
Operating Range : 2.7V to 5.5V
Reverse Blocking Current
Under-Voltage Lockout
Thermal Protection with Foldback
Over-Current Protection
Short-Circuit Protection
RoHS Compliant and Halogen Free
Applications


USB Peripherals
Notebook PCs
Marking Information
Ordering Information
RT9741AGV
RT9741
4F= : Product Code
Package Type
V : SOT-23-3
4F=DNN
Lead Plating System
G : Green (Halogen Free and Pb Free)
Output Current
A : 1.5A
C : 0.7A
DNN : Date Code
RT9741CGV
4D= : Product Code
4D=DNN
DNN : Date Code
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.
Simplified Application Circuit
RT9741
VIN
VOUT
CIN
VBUS
FB
+
Supply Voltage
2.7V to 5.5V
GND
D+
DGND
COUT
FB
Data
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9741-01 March 2015
is a registered trademark of Richtek Technology Corporation.
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RT9741
Functional Pin Description
Pin Configurations
(TOP VIEW)
Pin No.
GND
3
2
VIN
Pin Name
Pin Description
1
VIN
Power Input.
2
VOUT
Output Voltage.
3
GND
Ground.
VOUT
SOT-23-3
Function Block Diagram
VIN
UVLO
Current
Limiting
Bias
Oscillator
Charge
Pump
Thermal
Protection
Gate
Control
Output Voltage
Detection
Auto
Discharge
VOUT
GND
Operation
Charge Pumps and Drivers
Under-Voltage Lockout
An internal charge pump supplies power to the driver circuit
and provides the necessary voltage to pull the gate of the
MOSFET above the source. The driver controls the gate
voltage of the power switch.
A voltage-sense circuit monitors the input voltage. When
the input voltage is below approximately 1.3V, UVLO turns
off the MOSFET switch.
Thermal Shutdown
Current Limit
The RT9741 continuously monitors the output current for
over-current protection to protect the system power, the
power switch, and the load from damage during output
short circuit. When an overload or short circuit occurs,
the current-sense circuitry sends a control signal to the
driver. The driver reduces the gate voltage and drives the
power MOSFET into its saturation region, which switches
the output into a constant-current mode and holds the
current constant until the thermal shutdown occurs or the
fault is removed.
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The RT9741 continuously monitors the operating
temperature of the power switch for over-temperature
protection. The RT9741 turns off the power switch to
prevent the device from damage if the junction temperature
rises to approximately 120°C due to over-current or shortcircuit conditions.
The pass element turns on again after the junction
temperature cools to 80°C. The
RT9741 lowers its OTP trip level from 120°C to 100°C
when output short circuit occurs (VOUT < 1V).
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DS9741-01 March 2015
RT9741
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C
SOT-23-3 ------------------------------------------------------------------------------------------------------------------- Package Thermal Resistance (Note 2)
SOT-23-3, θJA -------------------------------------------------------------------------------------------------------------- Junction Temperature ---------------------------------------------------------------------------------------------------- Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------ Storage Temperature Range ------------------------------------------------------------------------------------------- ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------------
6V

Recommended Operating Conditions



0.41W
243.3°C/W
150°C
260°C
−65°C to 150°C
2kV
(Note 4)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 2.7V to 5.5V
Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 5V, CIN = 1μF, COUT = 10μF, TA = 25°C, unless otherwise specified)
Parameter
Input Quiescent Current
Switch OnResistance
Current Limit
RT9741A
RT9741C
RT9741A
Symbol
IQ
RDS(ON)
Test Conditions
Min
Typ
Max
Unit
Switch On, VOUT = Open
--
50
70
A
VIN = 5V, IOUT = 1.3A
--
100
120
VIN = 5V, IOUT = 0.6A
--
120
140
1.5
2
--
0.7
1
--
m
ILIM
VOUT = 4V
ISC_FB
VOUT = 0V, Measured Prior
to Thermal Shutdown
--
1.4
--
--
0.7
--
Output Turn-On Rising Time
TON_RISE 10% to 90% of VOUT Rising
--
200
--
s
Under-Voltage Lockout
VUVLO
VIN Rising
1.3
1.7
2.1
V
Under-Voltage Hysteresis
VUVLO
VIN Decreasing
--
0.1
--
V
Thermal Shutdown Protection
TSD
VOUT > 1V
--
120
--
VOUT = 0V
--
100
--
Thermal Shutdown Hysteresis
TSD
VOUT = 0V
--
20
--
Short Current
RT9741C
RT9741A
RT9741C
A
A
C
C
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.
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.
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RT9741
Typical Application Circuit
RT9741
CIN
1µF
1 VIN
VOUT
GND
3
2
VBUS
FB
+
Supply Voltage
2.7V to 5.5V
COUT
10µF
150µF
FB
D+
DGND
Data
Note : A low-ESR 150μF aluminum electrolytic or tantalum capacitor between VOUT and GND is strongly recommended
to meet the 330mV maximum droop requirement in the hub VBUS. (see Application Information Section for further
details)
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is a registered trademark of Richtek Technology Corporation.
DS9741-01 March 2015
RT9741
Typical Operating Characteristics
On Resistance vs. Input Voltage
125
RT9741A
130
121
On Resistance (mΩ)
On Resistance (mΩ)
123
On Resistance vs. Temperature
140
119
117
115
113
111
109
120
110
100
90
80
70
107
IOUT = 1.5A
105
2.7
3.1
3.5
3.9
4.3
4.7
5.1
VIN = 5V, IOUT = 1.5A
60
5.5
-40
-20
0
Input Voltage (V)
Quiescent Current vs. Input Voltage
46
40
60
80
Quiescent Current vs. Temperature
45
RT9741A
44
Quiescent Current (µA)
44
Quiescent Current (µA)
20
Temperature (°C)
42
40
38
36
34
32
43
42
41
40
39
38
37
36
No Load
30
VIN = 5V, No Load
35
2.7
3.1
3.5
3.9
4.3
4.7
5.1
-40
5.5
-20
Input Voltage (V)
0
20
40
60
80
100
Temperature (°C)
Output Voltage vs. Output Current
UVLO Threshold vs. Temperature
2.2
5.5
5.0
UVLO Threshold (V)
Output Voltage (V)
2.0
VIN = 5V
4.5
4.0
3.5
3.0
VIN = 3.3V
2.5
2.0
1.5
1.0
Rising edge
1.8
1.6
Falling edge
1.4
1.2
0.5
0.0
1.0
0.5
0.75
1
1.25
1.5
1.75
2
Output Current (A)
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2.25
-40
-20
0
20
40
60
80
Temperature (°C)
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RT9741
Current Limit vs. Input Voltage
2.3
Current Limit vs. Temperature
2.00
RT9741A
1.90
2.1
Current Limit (A)
Current Limit (A)
RT9741A
1.95
2.2
2.0
1.9
1.8
1.7
1.85
1.80
1.75
1.70
1.65
1.60
1.6
1.55
1.5
1.50
2.7
3.1
3.5
3.9
4.3
4.7
5.1
-40
5.5
-20
Input Voltage (V)
1.48
40
60
80
Short Current vs. Temperature
1.50
RT9741A
RT9741A
1.48
1.46
Short Current (A)
1.46
Short Current (A)
20
Temperature (°C)
Short Current vs. Input Voltage
1.50
0
1.44
1.42
1.40
1.38
1.36
1.44
1.42
1.40
1.38
1.36
1.34
1.34
1.32
1.32
1.30
1.30
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
-40
0
20
40
Temperature (°C)
Power On from VIN
Power Off from VIN
VIN
(2V/Div)
VIN
(2V/Div)
VOUT
(2V/Div)
VOUT
(2V/Div)
No Load
Time (25ms/Div)
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-20
Input Voltage (V)
60
80
No Load
Time (25ms/Div)
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DS9741-01 March 2015
RT9741
Application Information
The RT9741 is a single N-MOSFET high-side power
switches, optimized for self-powered and bus-powered
Universal Serial Bus (USB) applications. The RT9741 is
equipped with a charge pump circuitry to drive the internal
N-MOSFET switch; the switch's low RDS(ON) meets USB
voltage drop requirements.
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.
Thermal Shutdown
Thermal protection limits the power dissipation in RT9741.
When the operation junction temperature exceeds 120°C,
the OTP circuit starts the thermal shutdown function and
turns the pass element off. The pass element turns on
again after the junction temperature cools to 80°C. The
RT9741 lowers its OTP trip level from 120°C to 100°C
when output short circuit occurs (VOUT < 1V) as shown in
Figure 1.
V OUT Short to GND
1V
V OUT
IOUT
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
“soft-start” feature effectively isolates the power source
from extremely large capacitive loads, satisfying the USB
voltage droop requirements.
Thermal
Shutdown
120  C 100 C

OTP Trip Point
IC Temperature
100 C
80 C
Under-Voltage Lockout
Under-Voltage Lockout (UVLO) prevents the MOSFET
switch from turning on until input the voltage exceeds
approximately 1.7V. If input voltage drops below
approximately 1.3V, UVLO turns off the MOSFET switch.
Current Limiting and Short-Circuit 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 2A
through the switch of the RT9741A and 1A for RT9741C
respectively. When a heavy load or short circuit is applied
to 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.
Figure 1. Short Circuit Thermal Folded Back Protection
when Output Short Circuit Occurs (Patent)
Power Dissipation
The junction temperature of the RT9741 series depends
on several factors such as the load, PCB layout, ambient
temperature and package type. The output pin of the
RT9741 can deliver the current of up to 2A (RT9741A) and
1A (RT9741C) respectively over the full operating junction
temperature range. However, the maximum output current
must be decreased at higher ambient temperature to
ensure the junction temperature does not exceed 100°C.
With all possible conditions, the junction temperature must
be within the range specified under operating conditions.
Power dissipation can be calculated based on the output
current and the RDS(ON) of the switch as below.
PD = RDS(ON) x IOUT2
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RT9741
Although the devices are rated for 2A and 1A of output
current, but the application may limit the amount of output
current based on the total power dissipation and the
ambient temperature. The final operating junction
temperature for any set of conditions can be estimated
by the following thermal equation:
PD(MAX) = ( TJ (MAX) − TA ) / θJA
Where TJ (MAX) is the maximum junction temperature of
the die (100°C) and TA is the
maximum ambient temperature. The junction to ambient
thermal resistance (θJA) for SOT-23-3 at recommended
minimum footprint is 243.3°C/W (θJA is layout dependent).
Universal Serial Bus (USB) & Power Distribution
The goal of USB is to enable device 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
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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.
Over-Current protection devices such as fuses and PTC
resistors (also called poly-fuse or poly-switch) have slow
trip times, high on-resistance, and lack the necessary
circuitry for USB-required fault reporting.
The faster trip time of the RT9741 power distribution allows
designers to design hubs that can operate through faults.
The RT9741 provides low on-resistance 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 1μF 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 6V of the
absolute maximum supply voltage even for a short duration.
Output Filter Capacitor
A low-ESR 150μF 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 120μF
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
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DS9741-01 March 2015
RT9741
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.
Voltage Drop
The USB specification states a minimum port-output
voltage in two locations on the bus, 4.75V out of a SelfPowered Hub port and 4.40V out 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.
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) :
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.
(0.1A x NPORTS x RSWITCH) − VPCB
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
SOT-23-3 package, the thermal resistance, θ JA, is
RCONN = Resistance of connector contacts (two contacts
per connector)
243.3°C/W on a standard JEDEC 51-7 four-layer thermal
test board. The maximum power dissipation at TA = 25°C
can be calculated by the following formula :
RCABLE = Resistance of upstream cable wires (one 5V
and one GND)
PD(MAX) = (125°C − 25°C) / (243.3°C/W) = 0.41W for
SOT-23-3 package
Where
RSWITCH = Resistance of power switch (typical 100mΩ for
RT9741A and 120mΩ for RT9741C)
VPCB = PCB voltage drop
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. 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) ] − VPCB }  ( 0.1A x NPORTS )
= (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 RT9741, with its maximum
120mΩ on resistance can fit the demand of this
requirement.
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DS9741-01 March 2015
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.
0.5
Maximum Power Dissipation (W)1
VOUT(MIN) = 4.75V − [II x ( 4 x RCONN + 2 x RCABLE )] −
Four-Layer PCB
0.4
0.3
0.2
0.1
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 2. Derating Curve of Maximum Power Dissipation
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RT9741
Layout Consideration

Avoid via as much as possible. If via are necessary,
make them as large as feasible.

Locate the ceramic bypass capacitors as close as
possible to the VIN pins of the RT9741.
Place cuts in the ground plane between ports to help
reduce the coupling of transients between ports.

Place a ground plane under all circuitry to lower both
resistance and inductance and improve DC and transient
performance (Use a separate ground and power plans if
possible).
Locate the output capacitor and ferrite beads as close
to the USB connectors as possible to lower impedance
(mainly inductance) between the port and the capacitor
and improve transient load performance.

Locate the RT9741 as close as possible to the output
port to limit switching noise.
In order to meet the voltage drop, droop, and EMI
requirements, careful PCB layout is necessary. The
following guidelines must be followed :



Keep all VBUS traces as short as possible and use at
least 50-mil, 2 ounce copper for all VBUS traces.
The input capacitor should be
placed as close as possible to
the IC.
VBUS
+
+
+
VIN
VOUT
GND
GND_BUS
Figure 3. PCB Layout Guide
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is a registered trademark of Richtek Technology Corporation.
DS9741-01 March 2015
RT9741
Outline Dimension
H
D
L
C
B
e
A
A1
b
Dimensions In Millimeters
Dimensions In Inches
Symbol
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
0.508
0.014
0.020
C
2.591
2.997
0.102
0.118
D
2.692
3.099
0.106
0.122
e
1.803
2.007
0.071
0.079
H
0.080
0.254
0.003
0.010
L
0.300
0.610
0.012
0.024
SOT-23-3 Surface Mount 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.
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