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RT9702/A
80m, 500mA/1.1A High-Side Power Switches with Flag
General Description
The RT9702 and RT9702A are cost-effective, low voltage, single N-Channel MOSFET high-side power switches, optimized for self-powered and bus- powered Universal Serial Bus (USB) applications. The RT9702/A equipped with a charge pump circuitry to drive the internal MOSFET switch; the switch's low RDS(ON), 80m, meets USB voltage drop requirements; and a flag output is available to indicate fault conditions to the local USB controller. 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, fault current is limited to typically 800mA for RT9702 in single port and 1.5A for RT9702A in dual ports in accordance with the USB power requirements, lower quiescent current as 25A making this device ideal for portable battery-operated equipment. The RT9702/A is available in SOT-23-5 and TSOT-23-5 packages requiring minimum board space and smallest components.
Features
Compliant to USB Specifications Built-In (Typically 80m) N-Channel MOSFET Output Can Be Forced Higher Than Input (Off-State) Low Supply Current : 25A Typical at Switch On State 1A Typical at Switch Off State Guaranteed 500mA/RT9702 and 1.1A/RT9702A Continuous Load Current Wide Input Voltage Ranges : 2V to 5.5V Open-Drain Fault Flag Output Hot Plug-In Application (Soft-Start) 1.7V Typical Under-Voltage Lockout (UVLO) Current Limiting Protection Thermal Shutdown Protection Reverse Current Flow Blocking (no body diode) Smallest SOT-23-5 and TSOT-23-5 Packages Minimizes Board Space UL Approved-E219878 - TUV IEC60950-1 : 2005 Certified RoHS Compliant and 100% Lead (Pb)-Free
Applications
USB Bus/Self Powered Hubs USB Peripherals ACPI Power Distribution PC Card Hot Swap Notebook, Motherboard PCs Battery-Powered Equipment Hot-Plug Power Supplies Battery-Charger Circuits
Ordering Information
RT9702/A Package Type B : SOT-23-5 J5 : TSOT-23-5 Operating Temperature Range P : Pb Free with Commercial Standard G : Green (Halogen Free with Commercial Standard) 1.1A Output Current 500mA Output Current
Marking Information
For marking information, contact our sales representative directly or through a RichTek distributor located in your area, otherwise visit our website for detail.
Note : RichTek Pb-free and Green 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. 100% matte tin (Sn) plating.
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RT9702/A
Pin Configurations
(TOP VIEW)
VOUT 5 1 EN 2 VIN
Functional Pin Description
Pin Name VIN VOUT
4 3
Pin Function Power Input Voltage Output Voltage Ground Chip Enable (Active High) Open-Drain Fault Flag Output
GND EN FLG
GND FLG
SOT-23-5/TSOT-23-5
Typical Application Circuit
Pull-Up Resistor (10K to 100K) (Optional) Flag Transient Filtering) USB Controller Supply Voltage 5V VIN 1uF FLG 0.1uF RT9702/A VOUT GND 10uF 150uF VBUS D+ DGND Ferrite Beades 10K Over -Current
+
Chip Enable
EN
Data
Note: A low-ESR 150F aluminum electrolytic or tantalum 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)
Function Block Diagram
VIN EN Bias UVLO Current Limiting
Oscillator
Charge Pump
Gate Control Output Voltage Detection
VOUT
Thermal Protection
FLG Delay GND
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Test Circuits
1
RFG
+
2
ISupply
A
VIN
FLG
VFLG ILEAK AGE
VIN CIN
VIN
FLG
VFLG S1 IOUT VOUT
VIN
CIN
+
RT9702/A VOUT GND
RT9702/A VOUT GND
Chip Enable
EN
A
COUT
EN Chip Enable
A
RL
+
RL
IL
3
VRDS(ON)
4
V
IOUT VIN VOUT
VIN
+ +
+
RFG
FLG
VFLG VOUT
CIN VIN
RT9702/A
COUT
VIN
CIN
RT9702/A VOUT GND COUT
EN Chip Enable GND
FLG
VCE
EN
+
RL
IL
5
S2 VIN
RFG
FLG
VFLG IOUT VOUT
+
VIN
CIN
RT9702/A VOUT GND COUT
EN
A
S3 RL IL
Note: Above test circuits reflected the graphs shown on " Typical Operating Characteristics " are as follows: 1 -Turn-On Rising & Falling Time vs. Temperature, Turn-On & Off Response, Flag Response vs. Temperature 3 -On-Resistance vs. Input Voltage & Temperature 4 -EN Threshold Voltage vs. Input Voltage & Temperature, Flag Delay Time vs. Input Voltage & Temperature, UVLO Threshold vs. Temperature, UVLO at Rising & Falling 5 -Current Limit vs. Input Voltage/Temperature, Short Circuit Current Response, Short Circuit Current vs. Temperature, Inrush Current Response, Soft-start Response, Ramped Load Response, Current Limit Transient Response, Thermal Shutdown Response DS9702/A-11 June 2007 www.richtek.com 3 2 -Supply Current vs. Input Voltage & Temperature, Switch Off Supply Current vs. Temperature, Turn-Off Leakage Current
+
RT9702/A
Absolute Maximum Ratings
(Note 1) Supply Voltage --------------------------------------------------------------------------------------------------------- 6.5V Chip Enable Input Voltage ------------------------------------------------------------------------------------------- -0.3V to 6.5V Flag Voltage ------------------------------------------------------------------------------------------------------------ 6.5V Power Dissipation, PD @ TA = 25C SOT-23-5, TSOT-23-5 ------------------------------------------------------------------------------------------------- 0.4W Package Thermal Resistance (Note 4) SOT-23-5, TSOT-23-5, JA ------------------------------------------------------------------------------------------- 250C/W Junction Temperature ------------------------------------------------------------------------------------------------- 150C Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260C Storage Temperature Range ---------------------------------------------------------------------------------------- -65C to 150C ESD Susceptibility (Note 2) HBM (Human Body Mode) ------------------------------------------------------------------------------------------ 8kV MM (Machine Mode) -------------------------------------------------------------------------------------------------- 800V
Recommended Operating Conditions
(Note 3)
Supply Input Voltage -------------------------------------------------------------------------------------------------- 2V to 5.5V Chip Enable Input Voltage ------------------------------------------------------------------------------------------- 0V to 5.5V Junction Temperature Range ---------------------------------------------------------------------------------------- -20C to 100C Ambient Temperature Range ---------------------------------------------------------------------------------------- -40C to 85C
Electrical Characteristics
(VIN = 5V, CIN = COUT = 1F, TA = 25C, unless otherwise specified)
Parameter Switch On Resistance RT9702 RT9702A Supply Current Logic-Low Voltage
Symbol RDS(ON) ISW_ON ISW_OFF
Test Conditions IOUT = 500mA IOUT = 1.1A switch on, VOUT = Open switch off, VOUT = Open VIN = 2V to 5.5V, switch off VIN = 2V to 5.5V, switch on VEN = 0V to 5.5V
Min ----2.0 ---0.5
Typ 80 25 0.1 --0.01 0.5 400 0.8 1.5 0.8 1.0 20 0.01 10
Max 100 45 1 0.8 --10 -1.1 2.0 --400 1 15
Units m A V V A A s A
EN Threshold
VIL
Logic-High Voltage VIH EN Input Current Output Leakage Current Output Turn-On Rise Time Current Limit Short Circuit FoldBack Current RT9702 RT9702A RT9702 RT9702A ISC_FB RFLG IFLG_OFF tD ILIM IEN
ILEAKAGE VEN = 0V, RLOAD = 0 TON_RISE 10% to 90% of VOUT rising RLOAD = 1 VOUT = 0V, measured prior to thermal shutdown ISINK = 1mA VFLG = 5V From fault condition to FLG assertion
1.1 ----2
A A ms
FLAG Output Resistance FLAG Off Current FLAG Delay Time (Note 5)
To be continued
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Parameter Under-voltage Lockout Under-voltage Hysteresis Thermal Shutdown Protection Thermal Shutdown Hysteresis Symbol VUVLO VUVLO TSD TSD Test Conditions VIN increasing VIN decreasing Min 1.3 ---Typ 1.7 0.1 130 20 Max ----Units V V C 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. Devices are ESD sensitive. Handling precaution recommended. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. JA is measured in the natural convection at TA = 25C on a low effective thermal conductivity single layer test board of JEDEC 51-3 thermal measurement standard. Note 5. The FLAG delay time is input voltage dependent, see" Typical Operating Characteristics" graph for further details.
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Typical Operating Characteristics
Supply Curent vs. Input Voltage
40
(U.U.T: RT9702ACB, unless otherwise indicated)
2
40 35
Supply Current vs. Temperature
VIN = VEN = 5V, RL = Open CIN = 33uF, COUT = 33uF
2
VIN = VEN = 5V
35
CIN = 33uF
Supply Current (uA)
Supply Current (uA)1
3 3.5 4 4.5 5 5.5
30 25 20 15 10 5 0 2
RL = Open
30 25 20 15 10 5 0
2.5
-40
-20
0
20
40
60
80
100
120
Input Voltage (V)
Temperature (C)
Current Limit vs. Input Voltage
2.0
5
1.6
Current Limit vs. Input Voltage
RT9702
1.4
5
1.8
Current Limit (A)
Current Limit (A)
CIN = 33uF, COUT= 33uF S2 = On, S3 = Off, RL = 1
1.2 1 0.8 0.6 0.4
1.6
1.4
1.2
CIN = 33uF, COUT= 33uF
0.2 0
S2 = On, S3 = Off, RL = 1
2 2.5 3 3.5 4 4.5 5 5.5
1.0 2 2.5 3 3.5 4 4.5 5 5.5
Input Voltage (V)
Input Voltage (V)
3
160 140
On-Resistance vs. Input Voltage
160
On-Resistance vs. Temperature
VIN = 5V
3
CIN = COUT = 33uF
140
On-Resistance (m)
120 100 80 60 40 20 0 2 2.5 3 3.5 4 4.5 5 5.5
On-Resistance (m)
IOUT = 1.1A
CIN = COUT = 33uF IOUT = 1.1A
120 100 80 60 40 20 0 -40
-20
0
20
40
60
80
100
120
Input Voltage (V)
Temperature (C)
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Short Circuit Current Response
5
5
2.00
Short Circuit Current vs. Temperature 5
VIN = 5V
1.80 1.60 1.40 1.20 1.00 0.80 0.60 -40 -20 0 20 40 60 80 100 120
Short Circuit Current (A)
CIN = COUT = 33uF S2 = S3 = On
VOUT (V)
0
2
VIN=5V, S2=S3=On CIN=33uF
IOUT (A)
1 0
COUT=0.1uF
Temperature(C)
EN Pin Threshold Voltage vs. Voltage 4 CE Threshold Voltage vs. Input Input
2.4
EN Pin Threshold Voltage vs. Temperature 4 CE Threshhold Voltage vs. Temperature
2.4
CIN = COUT = 33uF
VIN = 5V
EN Pin Threshold Voltage CE Threshold Voltage (V) (V)
EN Pin Threshold Voltage(V) CE Threshold Voltage (V)
2 1.6 1.2 0.8 0.4 0 2
IL = 100mA
2 1.6 1.2 0.8 0.4 0
CIN = COUT = 33uF IL = 100mA
2.5
3
3.5
4
4.5
5
5.5
-40
-20
0
20
40
60
80
100
120
Input Voltage (V)
Temperature (C)
Turn-On Rising Time vs. Temperature 1
720
Turn-Off Falling Time vs. Temperature 1
140
Turn-On Rising Time (us)
630 540 450 360 270 180 90 0
Turn-Off Falling Time (us)
VIN = 5V, RL = 30 CIN = 33uF, COUT = 1uF S1 = On
VIN = 5V, RL = 30
120 100 80 60 40 20 0
CIN = 33uF, COUT= 1uF S1 = On
-40
-20
0
20
40
60
80
100
120
-40
-20
0
20
40
60
80
100
120
Temperature (C)
Temperature(C)
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Switch Off Supply Current vs. Temperature
1
Turn-Off Leakage Current vs. Temperature
3.5
Switch Off Supply Current (uA)
0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1
VIN = 5V, VEN = 0V CIN = COUT = 33uF RL = Open
Turn-off Leakage Current (uA)
2
2
VIN = 5V, VEN = 0V CIN = COUT = 33uF RL= 0
3 2.5 2 1.5 1 0.5 0
-40
-20
0
20
40
60
80
100
120
-40
-20
0
20
40
60
80
100
120
Temperature(C)
Temperature (C)
FLAG Delay Time vs. Input Voltage
24
4
16 15 14
FLAG Delay Time vs. Temperature
VIN = VEN = 5V CIN = COUT = 33uF
4
VEN = 5V
20
CIN = COUT = 33uF
Delay Time (ms)
Delay Time (ms)
16 12 8 4
13 12 11 10 9 8
0 2 2.5 3 3.5 4 4.5 5 5.5
7 -40 -20 0 20 40 60 80 100 120
Input Voltage (V)
Temperature(C)
4
2.40 2.20 2.00
UVLO Threshold vs. Temperature
3.5
Current Limit vs. Temperature
VIN = 5V, RL = 1 CIN = COUT = 33uF S2 = On,S3 = Off
5
CIN=COUT=33uF
3
RL=1k
UVLO Threshold (V)
Current Limit (A)
-40 -20 0 20 40 60 80 100 120
2.5 2 1.5 1 0.5 0
1.80 1.60 1.40 1.20 1.00 0.80 0.60 0.40 -40 -20 0 20 40
60
80
100
120
Temperature (C)
Temperature (C)
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Turn- On Response
(5V/DIV)
1
Turn- Off Response
1
(1V/DIV)
VOUT
CIN=33uF,COUT=1uF CIN=33uF, COUT=1uF S1=On S 1=On
IL
VIN=5V, RL= 30 VIN=5V, RL=30
(0.5A/DIV) (5V/DIV) (5V/DIV)
VEN
VOUT
VEN
VIN=5V, RL= 30 S1=Off CIN=33uF COUT=1uF
Time (100s / DIV)
Time (100s / DIV)
UVLO at Rising
4
VIN
UVLO at Falling
VIN=5V, RL= 30 CIN=33uF, COUT=1uF
4
(1V/DIV) (1V/DIV)
VIN
VOUT
VIN=5V, RL= 30 CIN=33uF, COUT=1uF
(1V/DIV) (1V/DIV)
VIN
VOUT
VIN
VOUT
VOUT
Time (1ms / DIV)
Time (10ms / DIV)
Soft- Start Response
S2:Off On
5
Ramped Load Response
4.9V
5
(5V/DIV)
VEN
(5V/DIV)
VOUT
S3= Off
1.1A
(0.5A/DIV)
(0.5A/DIV)
VIN=5V RL=1k
IL
CIN=33uF, COUT=1uF
IL
VIN=5V, RL=1
1
CIN=33uF,COUT=1uF
Time (50s / DIV)
Time (100ms / DIV)
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RT9702/A
Flag Response (Enable into Short Circuit) 1
RT9702CB
Flag Response
(5V/DIV) (5V/DIV)
1
(5V/DIV) (5V/DIV)
VEN
12ms (tD)
VFLG
VOUT
12ms CIN=0.1uF, COUT=33uF RL=1 S1=On
VFLG
(0.5A/DIV)
IL
RL=0 , S1=On
Time (2.5ms / DIV)
IL
CIN=33uF,COUT=1uF
(1A/DIV)
Time (10ms / DIV)
Current Limit Transient Respones
5
Current Limit (5V/DIV)
Thermal Shutdown Response
S2=On
5
VTRIGGER
(5V/DIV)
IOUT(1A/DIV) IOUT(1A/DIV)
VEN
S3=Off RL=1
S3=On
Short
(1A/DIV)
IOUT
VIN=5V,CIN=COUT=33uF S2=On ,S3=Off,RL=1
CIN=33uF COUT=1uF
Time (5us / DIV)
Time (50ms / DIV)
Short Circuit Current Response
5 4 3 2 1 0 COUT=1uF VIN=5V, RL=1 CIN=33uF S2=On, S3=Off COUT=1000uF COUT=220uF
5
IOUT (A)
Time (10ms / DIV)
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Applications Information
The RT9702 and RT9702A are single N-Channel MOSFET high-side power switches with active-high enable input, optimized for self-powered and bus-powered Universal Serial Bus (USB) applications. The RT9702/A equipped with a charge pump circuitry to drive the internal NMOS switch; the switch's low RDS(ON), 80m, 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 RT9702/A prevents reverse current flow if VOUT being externally forced to a higher voltage than VIN when the output disabled (VEN < 0.8V). 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 RT9702/A provides a FLG signal pin which is an NChannel open drain MOSFET output. This open drain output goes low when VOUT < VIN - 1V, current limit or the die temperature exceeds 130C 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 100k 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 G
D
S
D
S
Normal MOSFET
Chip Enable Input
RT9702/A
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 0.1A 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 RT9702/A back on. Floating the input may cause unpredictable operation. EN should not be allowed to go negative with respect to GND. The EN pin may be directly tied to VIN to keep the part on.
Under-voltage lockout (UVLO) prevents the MOSFET switch from turning on until input voltage exceeds approximately 1.7V. If input voltage drops below approximately 1.3V, UVLO turns off the MOSFET switch, FLG will be asserted accordingly. 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 typically 800mA through the switch of RT9702 and 1.5A for RT9702A respectively. When a heavy load or short circuit is applied to an enabled switch, a large transient current may flow
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RT9702/A
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. Thermal Shutdown Thermal shutdown is employed to protect the device from damage if the die temperature exceeds approxi- mately 130C. If enabled, the switch automatically restarts when the die temperature falls 20C. The output and FLG signal will continue to cycle on and off until the device is disabled or the fault is removed. Power Dissipation The device s junction temperature depends on several factors such as the load, PCB layout, ambient temperature and package type. The output pin of RT9702/A can deliver a current of up to 500mA, and 1.1A 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 100C. 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 switch as below. PD = RDS(ON) x IOUT
2
Universal Serial Bus (USB) & Power Distribution The goal of USB is to be enabled 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 implement- ation. 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 faster trip time of the RT9702/A power distribution allow designers to design hubs that can operate through faults. The RT9702/A have low on-resistance and internal fault-reporting circuitry that help the designer to meet voltage regulation and fault notification requirements.
Although the devices are rated for 500mA and 1.1A 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 ) / JA Where TJ (MAX) is the maximum junction temperature of the die (100C) and T A is the maximum ambient temperature. The junction to ambient thermal resistance (JA) for SOT-23-5 and TSOT-23-5 package at recommended minimum footprint is 250C/W (JA is layout dependent).
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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 1F 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 150F 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 120F 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 0.1F 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. Fault Flag Filtering (Optional) The transient inrush current to downstream capacitance may cause a short-duration error flag, which may cause erroneous over-current reporting. A simple 1ms RC lowpass filter (10k and 0.1F) in the flag line (see Typical Application Circuit) eliminates short-duration transients. 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 ). 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) : VOUT (MIN) = 4.75V - [ II x ( 4 * RCONN + 2 * RCABLE ) ] - (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 (80m typical for RT9702/A) VPCB = PCB voltage drop The USB specification defines the maximum resistance per contact (RCONN) of the USB connector to be 30m 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 90m. The resistance of the switch is defined as follows: RSWITCH = { 4.75V - 4.4V -[ 0.5A x ( 4 * 30m + 2 * 90m ) ]-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 250m for four ports ganged together. The RT9702/A, with its maximum 100m on-resistance over temperature, easily meets this requirement.
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PCB Layout In order to meet the voltage drop, droop, and EMI requirements, careful PCB layout is necessary. The following guidelines must be considered: 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 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). 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 RT9702/A as close as possible to the output port to limit switching noise. Locate the ceramic bypass capacitors as close as possible to the VIN pins of the RT9702/A.
VBUS VOUT VIN
ESD Because USB is a hot insertion and removal system, USB components (especially the connector pins) are subject to electrostatic discharge (ESD) and should be qualified to IEC801.2. The RT9702/A is designed to withstand a 8kV human body mode, as defined in MIL-STD-883C. The requirements in IEC801.2 are much more stringent and require additional capacitors for the RT9702/A to withstand the higher ESD energy. Low-ESR 1F ceramic bypass capacitors and output capacitors should be placed as closely as possible to the VIN and VOUT pins to increase the ESD immunity. The RT9702/A may pass the requirements of IEC 1000-4-2 (EN 50082-1) level-4 for 15kV air discharge and 8kV contact discharge tests when these capacitors are added.
FLG
GND_BUS EN Board Layout GND USB Controller
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DS9702/A-11 June 2007
RT9702/A
Outline Dimension
H D L C B
b A A1 e
Symbol A A1 B b C D e H L
Dimensions In Millimeters Min 0.889 0.000 1.397 0.356 2.591 2.692 0.838 0.080 0.300 Max 1.295 0.152 1.803 0.559 2.997 3.099 1.041 0.254 0.610
Dimensions In Inches Min 0.035 0.000 0.055 0.014 0.102 0.106 0.033 0.003 0.012 Max 0.051 0.006 0.071 0.022 0.118 0.122 0.041 0.010 0.024
SOT-23-5 Surface Mount Package
DS9702/A-11 June 2007
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RT9702/A
H D L C B
b A A1 e
Symbol A A1 B b C D e H L
Dimensions In Millimeters Min 0.700 0.000 1.397 0.300 2.591 2.692 0.838 0.080 0.300 Max 1.000 0.100 1.803 0.559 3.000 3.099 1.041 0.254 0.610
Dimensions In Inches Min 0.028 0.000 0.055 0.012 0.102 0.106 0.033 0.003 0.012 Max 0.039 0.004 0.071 0.022 0.118 0.122 0.041 0.010 0.024
TSOT-23-5 Surface Mount Package
Richtek Technology Corporation
Headquarter 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611
Richtek Technology Corporation
Taipei Office (Marketing) 8F, No. 137, Lane 235, Paochiao Road, Hsintien City Taipei County, Taiwan, R.O.C. Tel: (8862)89191466 Fax: (8862)89191465 Email: marketing@richtek.com
www.richtek.com 16
DS9702/A-11 June 2007

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