RT9742 - Richtek

®
RT9742
Ω, 3A/2A/1.5A/1A High-Side Power Switches
70mΩ
Ω/55mΩ
with Flag
General Description
Features
The RT9742 is a cost-effective, low-voltage, single
N-MOSFET high-side Power Switch IC for USB application.
Low switch-on resistance and low supply current are
realized in this IC.





The RT9742 integrates an over-current protection circuit,
a short fold back circuit, a thermal shutdown circuit and
an under-voltage lockout circuit for overall protection.
Besides, a flag output is available to indicate fault
conditions to the local USB controller. Furthermore, the
chip also integrates an embedded delay function to prevent
miss-operation from happening due to inrush-current. The
RT9742 is an ideal solution for USB power supply and
can support flexible applications since it is available in
TSOT-23-5, TSOT-23-5 (FC) and SOT-23-3 package.



Ω (typ.) N-MOSFET Switch
70mΩ
Ω/55mΩ
Operating Range : 2.7V to 6V
Reverse Blocking Current
Under Voltage Lockout
Deglitched Fault Report (FLG)
Thermal Protection with Fold-back
Over Current Protection
Short Circuit Protection
Applications


USB Peripherals
Notebook PCs
Pin Configurations
(TOP VIEW)
VIN
EN/EN
VOUT
EN
GND
5
4
5
4
3
2
3
2
2
3
VOUT GND FLG
VOUT GND VIN
TSOT-23-5 / TSOT-23-5 (FC)
TSOT-23-5
VIN
VOUT
SOT-23-3
(For RT9742M Only)
Simplified Application Circuit
USB Controller
Supply Voltage
2.7V to 6V
CIN
Chip Enable
Over-Current
FLG
VIN
RT9742
VBUS
VOUT
GND
+
EN/EN
D+
DGND
COUT
Data
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9742-00 July 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
1
RT9742
Ordering and Marking Information
Version
EN Function
Package
Discharge
Product
Current
Function Active Active Internal TSOT-23-5 TSOT-23-5 SOT-23-3
Code
High
Low Pull High
(FC)
RT9742AGJ5F
07=
3A
Yes
RT9742BGJ5F
06=
3A
Yes
RT9742ANGJ5F
0F=
3A
No
RT9742BNGJ5F
0E=
3A
No
RT9742CGJ5F
05=
2A
Yes
RT9742DGJ5F
04=
2A
Yes
RT9742CNGJ5F
0D=
2A
No
RT9742DNGJ5F
0C=
2A
No
RT9742CGJ5
0K=
2A
Yes
RT9742DGJ5
0J=
2A
Yes
RT9742CNGJ5
11=
2A
No
RT9742DNGJ5
10=
2A
No
RT9742JNGV
6A=
2A
No
RT9742EGJ5F
03=
1.5A
Yes
RT9742FGJ5F
02=
1.5A
Yes
RT9742ENGJ5F
0B=
1.5A
No
RT9742FNGJ5F
0A=
1.5A
No
RT9742EGJ5
0H=
1.5A
Yes
RT9742FGJ5
0G=
1.5A
Yes
RT9742ENGJ5
0Z=
1.5A
No
RT9742FNGJ5
0Y=
1.5A
No
RT9742KNGV
69=
1.5A
No
RT9742GGJ5F
01=
1A
Yes
RT9742HGJ5F
00=
1A
Yes
RT9742GNGJ5F
09=
1A
No
RT9742HNGJ5F
08=
1A
No
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
RT9742GGJ5
0F=
1A
Yes
RT9742HGJ5
0E=
1A
Yes
RT9742GNGJ5
0X=
1A
No
RT9742HNGJ5
0W=
1A
No
RT9742LNGV
68=
1A
No
RT9742MGJ5
14=
1.5A
Yes
V
V
RT9742MNGJ5
15=
1.5A
No
V
V
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
www.richtek.com
2
V
V
V
V
V
V
V
V
V
V
is a registered trademark of Richtek Technology Corporation.
DS9742-00 July 2015
RT9742
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.
Functional Pin Description
Pin Name
Pin Function
VOUT
Output Voltage
GND
Ground.
FLG
Fault FLAG Output.
EN/EN
Chip Enable (Active High/Low).
VIN
Power Input Voltage.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9742-00 July 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
3
RT9742
Function Block Diagram
TSOT-23-5 / TSOT-23-5 (FC) Package
VIN
EN/EN
Bias
UVLO
Oscillator
Charge
Pump
Current
Limiting
Gate
Control
Output Voltage
Detection
Thermal
Protection
VOUT
Auto Discharge
FLG
Delay
GND
SOT-23-3 Package
VIN
UVLO
Current
Limiting
Bias
Charge
Pump
Oscillator
Gate
Control
Thermal
Protection
Output Voltage
Detection
Auto
Discharge
VOUT
GND
TSOT-23-5 Package (For RT9742M Only)
VIN
EN
GND
Bias
UVLO
Oscillator
Charge
Pump
Thermal
Protection
Current
Limiting
Gate
Control
Output Voltage
Detector
VOUT
VOUT
Auto
Discharge
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
www.richtek.com
4
is a registered trademark of Richtek Technology Corporation.
DS9742-00 July 2015
RT9742
Operation
Charge Pump 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 above 2.4V, UVLO turns on the
MOSFET switch.
Thermal Shutdown
Current Limit
The RT9742 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.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9742-00 July 2015
The RT9742 continuously monitors the operating
temperature of the power switch for over-temperature
protection. The RT9742 turns off the power switch to
prevent the device from damage if the junction temperature
rises to approximately 140°C due to over-current or shortcircuit conditions. The pass element turns on again after
the junction temperature cools to 120°C.
FLAG
The RT9742 pulls low the open drain output FLAG after
over current or over temperature condition occurring over
approximately 10ms.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
5
RT9742
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------EN Voltage ----------------------------------------------------------------------------------------------------------------- FLAG Voltage ------------------------------------------------------------------------------------------------------------- Power Dissipation, PD @ TA = 25°C
TSOT-23-5 ------------------------------------------------------------------------------------------------------------------TSOT-23-5 (FC) -----------------------------------------------------------------------------------------------------------SOT-23-3 ------------------------------------------------------------------------------------------------------------------- Package Thermal Resistance (Note 2)
TSOT-23-5, θJA ------------------------------------------------------------------------------------------------------------TSOT-23-5 (FC), θJA -----------------------------------------------------------------------------------------------------SOT-23-3, θJA -------------------------------------------------------------------------------------------------------------- Junction Temperature ---------------------------------------------------------------------------------------------------- Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------ Storage Temperature Range ------------------------------------------------------------------------------------------- ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------------

Recommended Operating Conditions




7V
−0.3V to 7V
7V
0.43W
0.57W
0.41W
230.6°C/W
174°C/W
243.3°C/W
150°C
260°C
−65°C to 150°C
2kV
(Note 4)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------EN Voltage -----------------------------------------------------------------------------------------------------------------Junction Temperature Range -------------------------------------------------------------------------------------------Ambient Temperature Range --------------------------------------------------------------------------------------------
2.7V to 6V
0V to 6V
−40°C to 125°C
−40°C to 85°C
Electrical Characteristics
(VIN = 5V, CIN = 10μF, COUT = 0.1μF, TA = 25°C, unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Input Quiescent Current
IQ
Switch On, VOUT = Open
--
30
40
Input Shutdown Current
ISHDN
VIN = 5V, No Load on OUT, Device
OFF, VEN = 0V or VEN = 5V
--
0.1
1
--
55
--
--
70
--
ILIM
1.4
1.5
ILIM
2.1
2.25
ILIM
2.8
3
ILIM
4.2
4.5
1
1.1
1.2
1.5
1.65
1.8
2
2.2
2.4
3
3.3
3.6
1.8
2.15
2.5
Switch On
Resistance
RT9742XXJ5F
RT9742XXJ5/V
RDS(ON)
RT9742G/H/L
Over Current Trip
Threshold
RT9742E/F/K/M
RT9742C/D/J
ITRIP
VIN = 5V, 100A/s
RT9742A/B
RT9742G/H/L
Current
Limit
RT9742E/F/K/M
RT9742C/D
ILIM
RT9742A/B
RT9742J
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
www.richtek.com
6
VOUT = 1V
Unit
A
m
A
A
is a registered trademark of Richtek Technology Corporation.
DS9742-00 July 2015
RT9742
Parameter
Symbol
Test Conditions
Logic_High
Voltage
VIH
Logic_Low
Voltage
VIL
VIN = 2.7V to 6V
EN/EN Input Current
IEN/EN
VEN = 0V, VEN = 5V
Output Leakage Current
ILEAKAGE
Output Turn-On Rise Time
EN/EN Threshold
VIN = 2.7V to 6V
Min
Typ
Max
2
--
--
Unit
V
--
--
0.8
0.5
--
0.5
A
VEN = 0V, RLOAD = 0
--
0.5
1
A
TON_RISE
10% to 90% of VOUT Rising
--
300
--
s
FLG Output Resistance
RFLG
ISINK = 1mA
--
10
--

FLG Off Current
IFLG_OFF
VFLG = 5V
--
0.01
1
A
FLG Delay Time
TD
From fault condition to FLG
Assertion
--
10
--
ms
Shutdown Auto-Discharge
Resistance
RDischarge
VEN = 0V, VEN = 5V
--
10
--

Under-Voltage Lockout
VUVLO
VIN Rising
--
--
2.4
V
Under-Voltage Hysteresis
VUVLO
VIN Decreasing
--
0.1
--
V
Thermal Shutdown Protection
TSD
--
140
--
°C
Thermal Shutdown Hysteresis
TSD
--
20
--
°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.
The thermal shutdown protection will react at high Ambient Temperature or low VIN due to RDS(ON) variation.
Please refer to Application Information and Typical Operating Characteristics.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9742-00 July 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
7
RT9742
Typical Application Circuit
Pull-Up Resistor (10k to 100k)
USB Controller
Supply Voltage
2.7V to 6V
CIN
10µF
RT9742A/B/
C/D/E/F/G/H
VOUT
EN/EN
GND
RT9742B/D/F/H
Chip Enable
VBUS
+
RT9742A/C/E/G
Chip Enable
Over -Current
FLG
VIN
D+
DGND
COUT
0.1µF
Ferrite
Beads
Data
RT9742J/K/L
Supply Voltage
2.7V to 6V
VIN
GND
VBUS
+
VOUT
CIN
10µF
D+
D-
COUT
0.1µF
GND
Ferrite
Beads
Supply Voltage
2.7V to 6V
VIN
CIN
10µF
Data
VOUT
RT9742M
EN
VBUS
www.richtek.com
8
D-
GND
GND
Ferrite
Beads
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
D+
COUT
0.1µF
Data
is a registered trademark of Richtek Technology Corporation.
DS9742-00 July 2015
RT9742
Typical Operating Characteristics
On Resistance vs. Input Voltage
On Resistance vs. Temperature
120
100
90
100
On Resistance (mΩ)
On Resistance (mΩ )
110
90
TSOT-23-5
80
70
60
TSOT-23-5 (FC)
50
TSOT-23-5
80
70
60
TSOT-23-5 (FC)
50
40
40
VIN = 5V
30
30
2.5
3
3.5
4
4.5
5
5.5
-50
-25
0
Input Voltage (V)
50
100
125
Quiescent Current vs. Temperature
28.4
29.0
28.2
Quiescent Current (μA)
29.5
28.5
28.0
27.5
27.0
26.5
26.0
25.5
28.0
27.8
27.6
27.4
27.2
27.0
25.0
75
Temperature (°C)
Quiescent Current vs. Input Voltage
Quiescent Current (μA)
25
VIN = 5V, No Load
No Load
24.5
26.8
2.5
3
3.5
4
4.5
5
5.5
-50
-25
0
Input Voltage (V)
25
50
75
100
125
Temperature (°C)
Shutdown Current vs. Input Voltage
Shutdown Current vs. Temperature
0.9
1.2
Shutdown Current (μA)1
Shutdown Current (μA)1
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
1
0.8
0.6
0.4
0.2
VEN = 0V
0
VIN = 5V, VEN = 0V
0
2.5
3
3.5
4
4.5
5
Input Voltage (V)
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9742-00 July 2015
5.5
-50
-25
0
25
50
75
100
125
Temperature (°C)
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
9
RT9742
Output Voltage vs. Output Current
UVLO Threshold vs. Temperature
6
2.8
UVLO Threshold (V)
Output Voltage (V)
2.6
VIN = 5V
5
4
3
VIN = 3.3V
2
1
2.4
Rising
2.2
2.0
1.8
Falling
1.6
1.4
1.2
1.0
0
0.8
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
-50
-25
Output Current (A)
Current Limit Threshold vs. Input Voltage
50
75
100
125
Current Limit Threshold vs. Temperature
3.6
3.5
3.4
3.4
Current Limit (A)
Current Limit Threshold (A)
25
Temperature (°C)
3.6
3.3
3.2
3.1
3.0
2.9
2.8
3.2
3.0
2.8
2.6
2.4
2.7
VIN = 5V
2.2
2.6
2.5
3
3.5
4
4.5
5
5.5
-50
6
-25
0
25
50
75
100
Temperature (°C)
Input Voltage (V)
Over Current Trip Threshold vs. Temperature
FLAG Delay Time vs. Input Voltage
5.0
9.9
4.8
9.8
FLAG Delay Time (ms)
Over Current Trip Threshold (A)
0
4.6
4.4
4.2
4.0
3.8
9.7
9.6
9.5
9.4
9.3
9.2
VIN = 5V
9.1
3.6
-50
-25
0
25
50
75
Temperature (°C)
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
www.richtek.com
10
100
2.5
3
3.5
4
4.5
5
5.5
Input Voltage (V)
is a registered trademark of Richtek Technology Corporation.
DS9742-00 July 2015
RT9742
Power Off from VIN
Power On from VIN
VIN
(2V/Div)
VIN
(2V/Div)
VOUT
(2V/Div)
VOUT
(2V/Div)
No Load
No Load
Time (2ms/Div)
Time (10ms/Div)
Power On from EN
FLG Response
FLG
(5V/Div)
EN
(5V/Div)
VOUT
(2V/Div)
VOUT
(2V/Div)
I IN
(2A/Div)
I IN
(2A/Div)
Time (200μs/Div)
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9742-00 July 2015
VIN = 5V
Time (2ms/Div)
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
11
RT9742
Application Information
The RT9742 is a single N-MOSFET high-side power switch
with enable input, optimized for self-powered and buspowered Universal Serial Bus (USB) applications. The
RT9742 is equipped with a charge pump circuitry to drive
the internal N-MOSFET switch; the switch's low RDS(ON),
70mΩ/55mΩ, 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 parasitic body diode
between drain and source of the MOSFET, the RT9742
prevents reverse current flow if VOUT is externally forced
to a higher voltage than VIN when the chip is disabled
(VEN <0.8V or VEN > 2V).
S
D
S
D
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.
Fault Flag
The RT9742 series provides a FLG signal pin which is an
N-Channel open drain MOSFET output. This open drain
output goes low when current limit or the die temperature
exceeds 140°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 over-current 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 10ms.
Under-Voltage Lockout
G
Normal MOSFET
G
RT9742
Chip Enable Input
The switch will be disabled when the EN/EN pin is in a
logic low/high condition. During this condition, the internal
circuitry and MOSFET will be turned off. Floating the
EN/EN may cause unpredictable operation. EN should
not be allowed to go negative with respect to GND. The
EN/EN pin may be directly tied to VIN (GND) to keep the
part on.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
www.richtek.com
12
Under-voltage lockout (UVLO) prevents the MOSFET
switch from turning on until input the voltage exceeds 2.4V.
If input voltage drops below than UVLO threshold, UVLO
turns off the MOSFET switch. Under-voltage detection
functions only when the switch is enabled.
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 3A through the
switch of the RT9742A/B, 2A for RT9715C/D/J, 1.5A for
RT9742E/F/K/M and 1A for RT9742G/H/L respectively.
When a heavy load or short circuit is applied to an enabled
switch, a large transient current may flow until the current
is a registered trademark of Richtek Technology Corporation.
DS9742-00 July 2015
RT9742
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.
Thermal Shutdown
Thermal protection limits the power dissipation in RT9742.
When the operation junction temperature exceeds 140°C,
the OTP circuit starts the thermal shutdown function and
turns the pass element off. The pass element turn on again
after the junction temperature cools to 120°C.
Power Dissipation
The junction temperature of the RT9742 series depend
on several factors such as the load, PCB layout, ambient
temperature and package type. The output pin of the
RT9742 can deliver the current of up to 3A (RT9742A/B),
2A (RT9742C/D/J), 1.5A (RT9742E/F/K/M) and 1A
(RT9742G/H/L) respectively over the full operating junction
temperature range. However, the maximum output current
must be derated at higher ambient temperature to ensure
the junction temperature does not exceed 125°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
Although the devices are rated for 3A, 2A, 1.5A 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 (125°C) and T A is the maximum ambient
temperature.
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
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 polyfuse or polyswitch) have slow
trip times, high on-resistance, and lack the necessary
circuitry for USB-required fault reporting.
The junction to ambient thermal resistance (θJA) for TSOT23-5 package at recommended minimum footprint is
250°C/W (θJA is layout dependent).
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9742-00 July 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
13
RT9742
The faster trip time of the RT9742 power distribution allows
designers to design hubs that can operate through faults.
The RT9742 provides low on-resistance and internal faultreporting circuitry to meet voltage regulation and fault
notification requirements.
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 (see Figure 7-47 of Universal
Serial Specification Revision 2.0).
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.
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) :
Supply Filter/Bypass Capacitor
VOUT (MIN) = 4.75V − [ II x ( 4 x RCONN + 2 x RCABLE ) ] −
A 10μF 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 7V
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 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.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
www.richtek.com
14
(0.1A x NPORTS x RSWITCH ) − VPCB
Where
RCONN = Resistance of connector contacts
(two contacts per connector)
RCABLE = Resistance of upstream cable wires
(one 5V and one GND)
RSWITCH = Resistance of power switch
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 RT9742, with its maximum
100mΩ on-resistance over temperature, can fit the demand
of this requirement.
is a registered trademark of Richtek Technology Corporation.
DS9742-00 July 2015
RT9742
0.6
Maximum Power Dissipation (W)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.
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
243.3°C/W on a standard JEDEC 51-7 four-layer thermal
test board. For TSOT-23-5 package, the thermal
resistance, θJA, is 230.6°C/W on a standard JEDEC 51-7
four-layer thermal test board. For TSOT-23-5 (FC) package,
the thermal resistance, θJA, is 174°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 :
PD(MAX) = (125°C − 25°C) / (243.3°C/W) = 0.41W for
SOT-23-3 package
PD(MAX) = (125°C − 25°C) / (230.6°C/W) = 0.43W for
TSOT-23-5 package
PD(MAX) = (125°C − 25°C) / (174°C/W) = 0.57W for
TSOT-23-5 (FC) package
The maximum power dissipation depends on the operating
ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 1 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9742-00 July 2015
Four-Layer PCB
TSOT-23-5 (FC)
0.5
TSOT-23-5
0.4
SOT-23-3
0.3
0.2
0.1
0.0
0
25
50
75
100
125
Ambient Temperature (°C)
Figure 1. Derating Curve of Maximum Power Dissipation
Layout Consideration
In order to meet the voltage drop, droop, and EMI
requirements, careful PCB layout is necessary. The
following guidelines must be followed :

Locate the ceramic bypass capacitors as close as
possible to the VIN pins of the RT9742.

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).

Keep all VBUS traces as short as possible and use at
least 50-mil, 2 ounce copper for all VBUS traces.

Avoid vias as much as possible. If vias are necessary,
make them as large as feasible.

Place cuts in the ground plane between ports to help
reduce the coupling of transients between ports.

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 RT9742 as close as possible to the output
port to limit switching noise.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
15
RT9742
The input capacitor should
be placed as close as
possible to the IC.
VIN
VOUT
VBUS
GND
GND_BUS
FLG
EN
VIN
The input capacitor should be
placed as close as possible to
the IC.
VBUS
+
+
+
VIN
VOUT
GND
GND_BUS
Figure 2. PCB Layout Guide
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
www.richtek.com
16
is a registered trademark of Richtek Technology Corporation.
DS9742-00 July 2015
RT9742
Outline Dimension
H
D
L
B
C
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-23-5 Surface Mount Package
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
DS9742-00 July 2015
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
17
RT9742
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-23-5 (FC) Surface Mount Package
Copyright © 2015 Richtek Technology Corporation. All rights reserved.
www.richtek.com
18
is a registered trademark of Richtek Technology Corporation.
DS9742-00 July 2015
RT9742
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.
DS9742-00 July 2015
www.richtek.com
19