pixalynx/cm5-minimal-carrier
A 4-layer Raspberry Pi CM5 carrier board routes USB‑C 5V power through an RT9742 load switch with TVS protection and capacitive filtering, while providing ESD-protected HDMI output, CM5 connectors, test points, and ground/power planes.
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references/rt9742.txt
®
RT9742
70mΩ/55mΩ, 3A/2.5A/2A/1.5A/1A/0.5A High-Side Power
Switches with Flag
General Description Features
The RT9742 is a cost-effective, low-voltage, single 70mΩ/55mΩ (typ.) N-MOSFET Switch
N-MOSFET high-side Power Switch IC for USB application. Operating Range : 2.7V to 6V
Low switch-on resistance and low supply current are Reverse Blocking Current
realized in this IC. Under Voltage Lockout
Deglitched Fault Report (FLG)
The RT9742 integrates an over-current protection circuit,
Thermal Protection with Fold-back
a short fold back circuit, a thermal shutdown circuit and
Over Current Protection
an under-voltage lockout circuit for overall protection.
Short Circuit Protection
Besides, a flag output is available to indicate fault
UL Approved−E219878
conditions to the local USB controller. Furthermore, the
Nemko Approved-NO109777
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 Applications
can support flexible applications since it is available in USB Peripherals
TSOT-23-5, TSOT-23-5 (FC) and SOT-23-3 package. Notebook PCs
Pin Configuration
(TOP VIEW)
VIN EN/EN VOUT EN VOUT VIN GND
5 4 5 4 5 4 3
2 3 2 3 2 3 2
VOUT GND FLG VOUT GND VIN EN GND FLG VIN VOUT
TSOT-23-5 / TSOT-23-5 TSOT-23-5
SOT-23-3
TSOT-23-5 (FC) For RT9742M/V only For RT9742U only
Simplified Application Circuit
USB Controller
Supply Voltage Over-Current
2.7V to 6V VIN FLG
CIN RT9742
Chip Enable VOUT VBUS
EN/EN +
D+
GND COUT
D-
GND
Data
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RT9742
Ordering and Marking Information
EN Function Package
Product Discharge
Version Current
Code Function Active Active Internal TSOT-23-5 TSOT-23-5 SOT-23-3
High Low Pull High (FC)
RT9742AGJ5F 07= 3A Yes V V
RT9742BGJ5F 06= 3A Yes V V
RT9742ANGJ5F 0F= 3A No V V
RT9742BNGJ5F 0E= 3A No V V
RT9742CGJ5F 05= 2A Yes V V
RT9742DGJ5F 04= 2A Yes V V
RT9742CNGJ5F 0D= 2A No V V
RT9742DNGJ5F 0C= 2A No V V
RT9742CGJ5 0K= 2A Yes V V
RT9742DGJ5 0J= 2A Yes V V
RT9742CNGJ5 11= 2A No V V
RT9742DNGJ5 10= 2A No V V
RT9742JNGV 6A= 2A No V V
RT9742EGJ5F 03= 1.5A Yes V V
RT9742FGJ5F 02= 1.5A Yes V V
RT9742ENGJ5F 0B= 1.5A No V V
RT9742FNGJ5F 0A= 1.5A No V V
RT9742EGJ5 0H= 1.5A Yes V V
RT9742FGJ5 0G= 1.5A Yes V V
RT9742ENGJ5 0Z= 1.5A No V V
RT9742FNGJ5 0Y= 1.5A No V V
RT9742KNGV 69= 1.5A No V V
RT9742GGJ5F 01= 1A Yes V V
RT9742HGJ5F 00= 1A Yes V V
RT9742GNGJ5F 09= 1A No V V
RT9742HNGJ5F 08= 1A No V V
RT9742GGJ5 0F= 1A Yes V V
RT9742HGJ5 0E= 1A Yes V V
RT9742GNGJ5 0X= 1A No V V
RT9742HNGJ5 0W= 1A No V V
RT9742LNGV 68= 1A No V V
RT9742MGJ5 14= 1.5A Yes V V
RT9742MNGJ5 15= 1.5A No V V
RT9742VGJ5 9S= 2A Yes V V
RT9742NGJ5F 43= 2.5A Yes V V
RT9742PGJ5F DD= 2.5A Yes V V
RT9742NNGJ5F 42= 2.5A No V V
RT9742PNGJ5F CC= 2.5A No V V
RT9742NGJ5 9H 2.5A Yes V V
RT9742QGJ5 47= 0.5A Yes V V
RT9742RGJ5 45= 0.5A Yes V V
RT9742QNGJ5 46= 0.5A No V V
RT9742RNGJ5 44= 0.5A No V V
RT9742SNGV 6V= 0.5A No V V
RT9742UNGJ5 9F= 1.5A No V V
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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.
Functional Block Diagram
TSOT-23-5 / TSOT-23-5 (FC) Package
VIN
EN/EN Bias UVLO Current
Limiting
Gate
Charge
Oscillator Control
Pump
Output Voltage
Detection VOUT
Thermal
Protection Auto Discharge
FLG
Delay
GND
SOT-23-3 Package
VIN
UVLO Current
Limiting
Bias
Charge Gate
Oscillator Control
Pump
Thermal
Protection Output Voltage
VOUT
Detection
Auto
Discharge
GND
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RT9742
TSOT-23-5 Package (For RT9742M/V Only)
VIN
EN Bias UVLO Current
Limiting
Charge Gate
Oscillator Control
Pump
GND
Thermal
Protection Output Voltage
VOUT
Detector
VOUT
Auto
Discharge
Operation
Charge Pump and Drivers Under-Voltage Lockout
An internal charge pump supplies power to the driver circuit A voltage-sense circuit monitors the input voltage. When
and provides the necessary voltage to pull the gate of the the input voltage is above 2.4V, UVLO turns on the
MOSFET above the source. The driver controls the gate MOSFET switch.
voltage of the power switch.
Thermal Shutdown
Current Limit The RT9742 continuously monitors the operating
The RT9742 continuously monitors the output current for temperature of the power switch for over-temperature
over-current protection to protect the system power, the protection. The RT9742 turns off the power switch to
power switch, and the load from damage during output prevent the device from damage if the junction temperature
short circuit. When an overload or short circuit occurs, rises to approximately 140°C due to over-current or short-
the current-sense circuitry sends a control signal to the circuit conditions. The pass element turns on again after
driver. The driver reduces the gate voltage and drives the the junction temperature cools to 120°C.
power MOSFET into its saturation region, which switches
the output into a constant-current mode and holds the FLAG
current constant until the thermal shutdown occurs or the The RT9742 pulls low the open drain output FLAG after
fault is removed. over current or over temperature condition occurring over
approximately 10ms.
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RT9742
Absolute Maximum Ratings (Note 1)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 7V
EN Voltage ------------------------------------------------------------------------------------------------------------------ −0.3V to 7V
FLAG Voltage -------------------------------------------------------------------------------------------------------------- 7V
Power Dissipation, PD @ TA = 25°C
TSOT-23-5 ------------------------------------------------------------------------------------------------------------------- 0.49W
TSOT-23-5 (FC) ------------------------------------------------------------------------------------------------------------ 0.79W
SOT-23-3 -------------------------------------------------------------------------------------------------------------------- 0.41W
Package Thermal Resistance (Note 2)
TSOT-23-5, θJA ------------------------------------------------------------------------------------------------------------- 203°C/W
TSOT-23-5 (FC), θJA ------------------------------------------------------------------------------------------------------ 126.5°C/W
SOT-23-3, θJA --------------------------------------------------------------------------------------------------------------- 243.3°C/W
Junction Temperature ----------------------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------- 260°C
Storage Temperature Range -------------------------------------------------------------------------------------------- −65°C to 150°C
ESD Susceptibility (Note 3)
HBM (Human Body Model) ---------------------------------------------------------------------------------------------- 2kV
Recommended Operating Conditions (Note 4)
Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------- 2.7V to 6V
EN Voltage ------------------------------------------------------------------------------------------------------------------ 0V to 6V
Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------------- −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 Unit
Input Quiescent Current IQ Switch on, VOUT = open -- 30 40
VIN = 5V, no load on OUT, device A
Input Shutdown Current ISHDN -- 0.1 1
OFF, VEN = 0V or VEN = 5V
Switch On RT9742XXJ5F -- 55 --
RDS(ON) m
Resistance RT9742XXJ5/V -- 70 --
RT9742Q/R/S 0.65 0.89 1
RT9742G/H/L 1.05 1.4 1.5
Over Current RT9742E/F/K/M/U 1.55 2.1 2.25
Trip Threshold ITRIP VIN = 5V, 100A/s A
(Note 5) RT9742C/D/J/V 2.05 2.8 3
RT9742N/P 2.55 3.5 3.75
RT9742A/B 3.05 4.2 4.5
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RT9742
Parameter Symbol Test Conditions Min Typ Max Unit
RT9742Q/R/S 0.6 0.7 0.8
RT9742G/H/L 1 1.1 1.2
RT9742E/F/K/M/U 1.5 1.65 1.8
Current
RT9742C/D/V ILIM VOUT = 1V 2 2.2 2.4 A
Limit
RT9742N/P 2.5 2.75 3
RT9742A/B 3 3.3 3.6
RT9742J 1.8 2.15 2.5
Logic_High Voltage VIH VIN = 2.7V to 6V 1.5 -- --
EN/EN Threshold V
Logic_Low Voltage VIL VIN = 2.7V to 6V -- -- 0.75
EN/EN Input Current IEN/EN VEN = 0V, VEN = 5V 0.5 -- 0.5 A
Output Leakage Current ILEAKAGE VEN = 0V, RLOAD = 0 -- 0.5 1 A
Reverse Leakage Current IREV VOUT = 5V, VIN = 0V -- -- 1 A
Reverse Voltage Trip Point VREV VOUT VIN -- 200 -- mV
Output Turn-On Rise Time tON_RISE 10% to 90% of VOUT rising -- 1.5 -- ms
Turn-On Time tON From enable to 90% of VOUT -- 2.1 -- ms
FLG Output Resistance RFLG ISINK = 1mA -- 10 --
FLG Off Current IFLG_OFF VFLG = 5V -- 0.01 1 A
From fault condition to FLG
FLG Delay Time tD -- 10 -- ms
assertion
Shutdown Auto-Discharge Resistance RDischarge VEN = 0V, VEN = 5V -- 100 --
Under-Voltage Lockout VUVLO VIN rising -- -- 2.4 V
Under-Voltage Hysteresis VUVLO VIN decreasing -- 0.1 -- V
Thermal Shutdown Protection TSD (Note 6) -- 140 -- °C
Thermal Shutdown Hysteresis TSD (Note 6) -- 20 -- °C
Note 1. Stresses beyond those listed under “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.
Note 5. For a specific sample, Current Trip Threshold (ITRIP) is always higher than Current Limit Threshold (ILIM).
Note 6. Guarantee by design.
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RT9742
Typical Application Circuit
Pull-Up Resistor (10k to 100k)
USB Controller
Supply Voltage Over -Current
2.7V to 6V VIN FLG
CIN RT9742A/B/
10µF C/D/E/F/G/H/
N/P/Q/R/U
RT9742A/C/E/G/N/Q/U
VOUT VBUS
Chip Enable EN/EN +
COUT D+
GND 0.1µF D-
GND
RT9742B/D/F/H/P/R
Chip Enable Ferrite
Beads Data
RT9742J/K/L/S
Supply Voltage
2.7V to 6V VIN
CIN VOUT + VBUS
10µF COUT D+
GND 0.1µF D-
GND
Ferrite
Beads Data
Supply Voltage VIN VOUT VBUS
2.7V to 6V
CIN D+
10µF RT9742M/V COUT
0.1µF
D-
GND GND
EN
Ferrite
Beads Data
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RT9742
Typical Operating Characteristics
On Resistance vs. Input Voltage On Resistance vs. Temperature
120 100
110
90
100 TSOT-23-5
On Resistance (mΩ ) On Resistance (mΩ)
80
90
TSOT-23-5
80 70
70 60 TSOT-23-5 (FC)
60
TSOT-23-5 (FC) 50
50
40
40
VIN = 5V
30 30
2.5 3 3.5 4 4.5 5 5.5 -50 -25 0 25 50 75 100 125
Input Voltage (V) Temperature (°C)
Quiescent Current vs. Input Voltage Quiescent Current vs. Temperature
29.5 28.4
29.0 28.2
Quiescent Current (μA)
28.5
Quiescent Current (μA)
28.0
28.0
27.5 27.8
27.0 27.6
26.5
27.4
26.0
27.2
25.5
25.0 27.0
No Load VIN = 5V, No Load
24.5 26.8
2.5 3 3.5 4 4.5 5 5.5 -50 -25 0 25 50 75 100 125
Input Voltage (V) Temperature (°C)
Shutdown Current vs. Input Voltage Shutdown Current vs. Temperature
0.9 1.2
0.8
1
Shutdown Current (μA)1 Shutdown Current (μA)1
0.7
0.6 0.8
0.5
0.6
0.4
0.3 0.4
0.2
0.2
0.1
VEN = 0V VIN = 5V, VEN = 0V
0 0
2.5 3 3.5 4 4.5 5 5.5 -50 -25 0 25 50 75 100 125
Input Voltage (V) Temperature (°C)
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RT9742
Output Voltage vs. Output Current UVLO Threshold vs. Temperature
6 2.8
VIN = 5V 2.6
5
2.4 Rising
Output Voltage (V) UVLO Threshold (V)
2.2
4
2.0
3 1.8 Falling
VIN = 3.3V
1.6
2
1.4
1.2
1
1.0
0 0.8
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 -50 -25 0 25 50 75 100 125
Output Current (A) Temperature (°C)
Current Limit Threshold vs. Input Voltage Current Limit Threshold vs. Temperature
3.6 3.6
3.5
3.4
Current Limit Threshold (A)
3.4
3.2
Current Limit (A)
3.3
3.2
3.0
3.1
2.8
3.0
2.9 2.6
2.8
2.4
2.7
VIN = 5V
2.6 2.2
2.5 3 3.5 4 4.5 5 5.5 6 -50 -25 0 25 50 75 100
Input Voltage (V) Temperature (°C)
Over Current Trip Threshold vs. Temperature FLAG Delay Time vs. Input Voltage
5.0 9.9
Over Current Trip Threshold (A)
4.8 9.8
FLAG Delay Time (ms)
9.7
4.6
9.6
4.4
9.5
4.2
9.4
4.0
9.3
3.8 9.2
VIN = 5V
3.6 9.1
-50 -25 0 25 50 75 100 2.5 3 3.5 4 4.5 5 5.5
Temperature (°C) Input Voltage (V)
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RT9742
Power On from VIN Power Off from VIN
VIN VIN
(2V/Div) (2V/Div)
VOUT VOUT
(2V/Div) (2V/Div)
No Load No Load
Time (2ms/Div) Time (10ms/Div)
Power On from EN FLG Response
FLG
(5V/Div)
EN
(2V/Div)
VOUT
(2V/Div)
VOUT
(2V/Div)
I IN
No Load
(2A/Div) VIN = 5V
Time (1ms/Div) Time (2ms/Div)
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RT9742
Application Information
The RT9742 is a single N-MOSFET high-side power switch Reverse Voltage Protection
with enable input, optimized for self-powered and bus- When the output voltage exceeds than input voltage by
powered Universal Serial Bus (USB) applications. The reverse voltage trip point (VREV), the reverse voltage
RT9742 is equipped with a charge pump circuitry to drive protection circuitry will turn off MOSFET to protect the
the internal N-MOSFET switch; the switch's low RDS(ON), input power supply. The MOSFET will turn on again when
70mΩ/55mΩ, meets USB voltage drop requirements; and output voltage return to the same level with input voltage.
a flag output is available to indicate fault conditions to the
local USB controller. Soft-Start for Hot Plug-In Applications
In order to eliminate the upstream voltage droop caused
Input and Output
by the large inrush current during hot-plug events, the
VIN (input) is the power source connection to the internal “soft-start” feature effectively isolates the power source
circuitry and the drain of the MOSFET. VOUT (output) is from extremely large capacitive loads, satisfying the USB
the source of the MOSFET. In a typical application, current voltage droop requirements.
flows through the switch from VIN to VOUT toward the load.
If VOUT is greater than VIN, current will flow from VOUT to Fault Flag
VIN since the MOSFET is bidirectional when on. The RT9742 series provides a FLG signal pin which is an
Unlike a normal MOSFET, there is no parasitic body diode N-Channel open drain MOSFET output. This open drain
between drain and source of the MOSFET, the RT9742 output goes low when current limit or the die temperature
prevents reverse current flow if VOUT is externally forced exceeds 140°C approximately. The FLG output is capable
to a higher voltage than VIN when the chip is disabled. 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
D S
D S 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.
G G
Normal MOSFET RT9742 For example, false over-current conditions may occur
during hot-plug events when extremely large capacitive
Chip Enable Input loads are connected and causes a high transient inrush
current that exceeds the current limit threshold. The FLG
The switch will be disabled when the EN/EN pin is in a
response delay time tD is typically 10ms.
logic low/high condition. During this condition, the internal
circuitry and MOSFET will be turned off. Floating the Under-Voltage Lockout
EN/EN may cause unpredictable operation. EN should
Under-voltage lockout (UVLO) prevents the MOSFET
not be allowed to go negative with respect to GND. The
switch from turning on until input the voltage exceeds 2.4V.
EN/EN pin may be directly tied to VIN (GND) to keep the
If input voltage drops below than UVLO threshold, UVLO
part on.
turns off the MOSFET switch. Under-voltage detection
functions only when the switch is enabled.
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RT9742
Current Limiting and Short-Circuit Protection The junction to ambient thermal resistance (θJA) for TSOT-
The current limit circuitry prevents damage to the MOSFET 23-5 package at recommended minimum footprint is
switch and the hub downstream port but can deliver load 203°C/W (θJA is layout dependent).
current up to the current limit threshold. When a heavy
Universal Serial Bus (USB) & Power Distribution
load or short circuit is applied to an enabled switch, a
large transient current may flow until the current limit The goal of USB is to enable device from different vendors
circuitry responds. Once this current limit threshold is to interoperate in an open architecture. USB features
exceeded, the device enters constant current mode until include ease of use for the end user, a wide range of
the thermal shutdown occurs or the fault is removed. workloads and applications, robustness, synergy with the
PC industry, and low-cost implementation. Benefits
Thermal Shutdown include self-identifying peripherals, dynamically attachable
Thermal protection limits the power dissipation in the and reconfigurable peripherals, multiple connections
RT9742. When the operation junction temperature (support for concurrent operation of many devices), support
exceeds 140°C, the OTP circuit starts the thermal for as many as 127 physical devices, and compatibility
shutdown function and turns the pass element off. The with PC Plug-and-Play architecture.
pass element turn on again after the junction temperature The Universal Serial Bus connects USB devices with a
cools to 120°C. USB host: each USB system has one USB host. USB
devices are classified either as hubs, which provide
Power Dissipation
additional attachment points to the USB, or as functions,
The junction temperature of the RT9742 series depend which provide capabilities to the system (for example, a
on several factors such as the load, PCB layout, ambient digital joystick). Hub devices are then classified as either
temperature and package type. The output pin of the Bus-Power Hubs or Self-Powered Hubs.
RT9742 can deliver the current of up to the current limit
A Bus-Powered Hub draws all of the power to any internal
threshold over the full operating junction temperature range.
functions and downstream ports from the USB connector
However, the maximum output current must be derated
power pins. The hub may draw up to 500mA from the
at higher ambient temperature to ensure the junction
upstream device. External ports in a Bus-Powered Hub
temperature does not exceed 125°C. With all possible
can supply up to 100mA per port, with a maximum of four
conditions, the junction temperature must be within the
external ports.
range specified under operating conditions. Power
dissipation can be calculated based on the output current Self-Powered Hub power for the internal functions and
and the RDS(ON) of the switch as below. downstream ports does not come from the USB, although
the USB interface may draw up to 100mA from its
PD = RDS(ON) x IOUT2
upstream connect, to allow the interface to function when
Although the devices are rated for 3A, 2.5A, 2A, 1.5A, 1A the remainder of the hub is powered down. The hub must
and 0.5A , of output current, but the application may limit be able to supply up to 500mA on all of its external
the amount of output current based on the total power downstream ports. Please refer to Universal Serial
dissipation and the ambient temperature. The final Specification Revision 2.0 for more details on designing
operating junction temperature for any set of conditions compliant USB hub and host systems.
can be estimated by the following thermal equation :
Over-Current protection devices such as fuses and PTC
PD (MAX) = ( TJ (MAX) - TA ) / θJA resistors (also called polyfuse or polyswitch) have slow
Where TJ (MAX) is the maximum junction temperature of trip times, high on-resistance, and lack the necessary
the die (125°C) and T A is the maximum ambient circuitry for USB-required fault reporting.
temperature. The faster trip time of the RT9742 power distribution allows
designers to design hubs that can operate through faults.
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RT9742
The RT9742 provides low on-resistance and internal fault- Output Filter Capacitor
reporting circuitry to meet voltage regulation and fault The output capacitance should be optimized for the
notification requirements. different applications. For the USB application, the
Because the devices are also power switches, the designer minimum output capacitance between VOUT and GND has
of self-powered hubs has the flexibility to turn off power to been determining. Each downstream facing port is required
output ports. Unlike a normal MOSFET, the devices have at least 120μF to meet the minimum drop voltage of VBUS
controlled rise and fall times to provide the needed inrush (330mV). However, the maximum output capacitance is
current limiting required for the bus-powered hub power also constrained from the applications. The first is larger
switch. output capacitance causes higher inrush current during
turn on period. Based on the acceptable inrush current
Supply Filter/Bypass Capacitor and VOUT rising time, the maximum output capacitor is
A 10μF low-ESR ceramic capacitor from VIN to GND, obtained. Second, the VIN spike is also considered as
located at the device is strongly recommended to prevent VOUT short-circuit occurring. Greater output capacitance
the input voltage drooping during hot-plug events. However, induces greater VIN spike. Thus, the recommend output
higher capacitor values will further reduce the voltage droop capacitance is defined from 120μF to 330μF.
on the input. Furthermore, without the bypass capacitor, For the general application, bypassing the output with a
an output short may cause sufficient ringing on the input 0.01μF to 0.1μF ceramic capacitor improves the immunity
(from source lead inductance) to destroy the internal of the device to short-circuit transients.
control circuitry. The input transient must not exceed 7V
of the absolute maximum supply voltage even for a short
duration.
10k
USB Controller
5V VIN Over-Current
CIN
RT9742 USB Port
Connector
Chip Enable
VOUT VBUS
EN
COUT1 COUT2 D+
GND 0.1µF 120µF
D-
GND
Ferrite
USB requirement only*
Beads
*USB requirement that downstream
facing ports are bypassed with at
least 120µF per hub
Figure 1. USB Power Switch Application Circuit
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RT9742
Voltage Drop Thermal Considerations
The USB specification states a minimum port-output For continuous operation, do not exceed absolute
voltage in two locations on the bus, 4.75V out of a Self- maximum junction temperature. The maximum power
Powered Hub port and 4.40V out of a Bus-Powered Hub dissipation depends on the thermal resistance of the IC
port. As with the Self-Powered Hub, all resistive voltage package, PCB layout, rate of surrounding airflow, and
drops for the Bus-Powered Hub must be accounted for to difference between junction and ambient temperature. The
guarantee voltage regulation (see Figure 7-47 of Universal maximum power dissipation can be calculated by the
Serial Specification Revision 2.0). following formula :
The following calculation determines VOUT(MIN) for multi- PD(MAX) = (TJ(MAX) − TA) / θJA
ple ports (NPORTS) ganged together through one switch (if where TJ(MAX) is the maximum junction temperature, TA is
using one switch per port, NPORTS is equal to 1) : the ambient temperature, and θJA is the junction to ambient
VOUT (MIN) = 4.75V − [ II x ( 4 x RCONN + 2 x RCABLE ) ] − thermal resistance.
(0.1A x NPORTS x RSWITCH ) − VPCB For recommended operating condition specifications, the
Where maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
RCONN = Resistance of connector contacts
SOT-23-3 package, the thermal resistance, θ JA, is
(two contacts per connector) 243.3°C/W on a standard JEDEC 51-7 four-layer thermal
RCABLE = Resistance of upstream cable wires test board. For TSOT-23-5 package, the thermal
resistance, θJA, is 203°C/W on a standard JEDEC 51-7
(one 5V and one GND)
four-layer thermal test board. For TSOT-23-5 (FC) package,
RSWITCH = Resistance of power switch the thermal resistance, θJA, is 126.5°C/W on a standard
VPCB = PCB voltage drop JEDEC 51-7 four-layer thermal test board. The maximum
power dissipation at TA = 25°C can be calculated by the
The USB specification defines the maximum resistance
following formula :
per contact (RCONN) of the USB connector to be 30mΩ
and the drop across the PCB and switch to be 100mV. PD(MAX) = (125°C − 25°C) / (243.3°C/W) = 0.41W for
This basically leaves two variables in the equation: the SOT-23-3 package
resistance of the switch and the resistance of the cable. If PD(MAX) = (125°C − 25°C) / (203°C/W) = 0.49W for
the hub consumes the maximum current (II) of 500mA, TSOT-23-5 package
the maximum resistance of the cable is 90mΩ.
PD(MAX) = (125°C − 25°C) / (126.5°C/W) = 0.79W for
The resistance of the switch is defined as follows : TSOT-23-5 (FC) package
RSWITCH = { 4.75V − 4.4V − [ 0.5A x ( 4 x 30mΩ + 2 x The maximum power dissipation depends on the operating
90mΩ) ] − VPCB } ( 0.1A x NPORTS ) ambient temperature for fixed T J(MAX) and thermal
resistance, θJA. The derating curve in Figure 2 allows the
= (200mV − VPCB ) ( 0.1A x NPORTS )
designer to see the effect of rising ambient temperature
If the voltage drop across the PCB is limited to 100mV, on the maximum power dissipation.
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.
Copyright © 2020 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
www.richtek.com DS9742-10 January 2020
14
RT9742
0.9
TSOT-23-5 (FC) Four-Layer PCB
Maximum Power Dissipation (W)1
0.8
0.7
0.6
TSOT-23-5
0.5
0.4
SOT-23-3
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
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.
Copyright © 2020 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
DS9742-10 January 2020 www.richtek.com
15
RT9742
The input capacitor should
be placed as close as
possible to the IC.
VBUS VOUT VIN
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 3. PCB Layout Guide
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www.richtek.com DS9742-10 January 2020
16
RT9742
Outline Dimension
Dimensions In Millimeters Dimensions In Inches
Symbol
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 © 2020 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
DS9742-10 January 2020 www.richtek.com
17
RT9742
Dimensions In Millimeters Dimensions In Inches
Symbol
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 © 2020 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
www.richtek.com DS9742-10 January 2020
18
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. 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.
DS9742-10 January 2020 www.richtek.com
19
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