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Preliminary
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 buspowered 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-25 package 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 0.1A 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-25 Package Minimizes Board Space UL Approved - E219878
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-25 Operating Temperature Range C: Commercial Standard 1.1A Output Current 500mA Output Current
Pin Configurations
Part Number RT9702/ACB (Plastic SOT-25)
5
Pin Configurations
4
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.
1
2
3
TOP VIEW 1. CE 2. GND 3. FLG 4. VIN 5. VOUT
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RT9702/A
Typical Application Circuit
Pull-Up Resistor (10k to 100k)
Preliminary
(Optional) Flag Transient Filtering Supply Voltage 5V 1F + 10k VIN FLG 0.1F
USB Controller Ov er-current
RT9702/A
VOUT CE GND 10F +
VBUS + 150F D+ D- GND
On Off
Ferrite Beads
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)
Pin Description
Pin Name VIN VOUT GND CE FLG Pin Function Supply Input Switch Output Common Ground Chip Enable Control Input Open-Drain Fault Flag Output
Function Block Diagram
VIN Current Limiting
CE
Bias
UVLO
Oscillator
Charge Pump
Gate Control
Thermal Protection
Output Voltage Detection
VOUT
FLG Delay
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Preliminary Test Circuits
RFG V FLG
S1
RT9702/A
I SUPPLY
VIN CIN
On Off +
FLG VIN
VOUT
VIN
A CIN
+
VIN
FLG
RT9702/A
VOUT CE GND
IOUT A COUT
+
RT9702/A
VOUT On CE GND
I LEAK AGE A RL
RL
IL
Off
VRDS(ON) V I OUT
VIN VOUT +
RFG V FLG VOUT
VOUT
FLG VIN
VIN
CIN
On Off
+
RT9702/A
CE GND FLG
C OUT
VIN
CIN
+
RT9702/A
CE GND
VCE
C OUT
+
RL
IL
RFG V FLG VOUT I OUT A C OUT
+ S3 VOUT CE GND
S2 VIN
FLG +
VIN
C IN
RT9702/A
RL
IL
Note: Above test circuits reflected the graphs shown on "Typical Operating Characteristics" are as follows: - Turn-On Rising & Falling Time vs. Temperature, Turn-On & Off Response, Flag Response - Supply Current vs. Input Voltage & Temperature, Switch Off Supply Current vs. Temperature, Turn-Off Leakage Current vs. Temperature - On-Resistance vs. Input Voltage & Temperature - CE Threshold Voltage vs. Input Voltage & Temperature, Flag Delay Time vs. Input Voltage & Temperature, UVLO Threshold vs. Temperature, UVLO at Rising & Falling - 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
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RT9702/A
Supply Voltage Chip Enable Input Voltage Flag Voltage Power Dissipation, PD @ TA = 25C SOT-25 Package Thermal Resistance SOT-25, JA Junction Temperature Lead Temperature (Soldering, 10 sec.) Storage Temperature Range ESD Susceptibility (Note 2) HBM (Human Body Mode) MM (Machine Mode)
Preliminary
6.5V -0.3V to 6.5V 6.5V 0.25W 250C/W 150C 260C -65C to 150C 8kV 800V
Absolute Maximum Ratings (Note 1)
Recommended Operating Conditions (Note 3)
Supply Input Voltage Chip Enable Input Voltage Junction Temperature Range 2V to 5.5V 0V to 5.5V -20C to 100C
Electrical Characteristics
(VIN = 5V, CIN = COUT = 1F, TA = 25C, unless otherwise specified) Parameter Switch On Resistance Supply Current CE Threshold Logic-Low Voltage RT9702 RT9702A Symbol RDS(ON) ISW_ON ISW_OFF VIL ICE ILEAKAGE TON_RISE ILIM ISC_FB RFLG IFLG_OFF tD Logic-High Voltage VIH 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 VCE = 0V to 5.5V VCE = 0V, RLOAD = 0 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 Min ----2.0 ---0.5 1.1 ----2 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 A A mS
CE Input Current Output Leakage Current Output Turn-On Rise Time Current Limit Short Circuit FoldBack Current RT9702 RT9702A RT9702 RT9702A
FLAG Output Resistance FLAG Off Current FLAG Delay Time (Note 4)
To be continued
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Preliminary
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 ----
RT9702/A
Typ 1.7 0.1 130 20 Max ----Units V V C 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 for extended periods may affect device reliability. Note 2. Devices are ESD sensitive. Handling precaution recommended. The human body model is a 100pF capacitor discharged through a 1.5k resistor into input and output pins. Note 3. The device is not guaranteed to function outside its operating conditions. Note 4. The FLAG delay time is input voltage dependent, see "Typical Operating Characteristics" graph for further details.
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RT9702/A
Supply Curent vs. Input Voltage
40 35
Preliminary
Typical Operating Characteristics (U.U.T: RT9702ACB, unless otherwise indicated)
2
40 35 30
Supply Current vs. Temperature 2
VIN = VCE = 5V CIN = 33F COUT = 33F RL = Open
Supply Current (A)
30 25 20 15 10 5 0 2
VIN = VCE = 5V CIN = 33F RL = Open
Supply Current
25 20 15 10 5 0
2.5
3
3.5
4
4.5
5
5.5
-40
-20
0
20
40
60
80
100
120
Input Voltage (V)
C) Temperature (X
Current Limit vs. Input Voltage
2
5
2.4 2.2 2
Current Limit vs. Temperature
VIN = 5V CIN = COUT = 33F RL = 1 S2 = On S3 = Off
5
1.8
Current Limit (A)
Current Limit (A)
CIN = 33F COUT = 33F RL = 1 S2 = On S3 = Off
1.8 1.6 1.4 1.2 1 0.8 0.6
1.6
1.4
1.2
1 2 2.5 3 3.5 4 4.5 5 5.5
0.4 -40 -20 0 20 40 60 80 100 120
Input Voltage (V)
Temperature(X C)
On-Resistance vs. Input Voltage
160 140
3
160 140
On-Resistance vs. Temperature
VIN = 5V CIN = COUT = 33F IOUT = 1.1A
3
CIN = COUT = 33F IOUT = 1.1A
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)
120 100 80 60 40 20 0
-40
-20
0
20
40
60
80
100
120
Input Voltage (V)
C) Temperature (X
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Preliminary
RT9702/A
Short Circuit Current vs. Temperature 5
2
Short Circuit Current Response
5
Short Circuit Current (A)
1.8 1.6 1.4 1.2 1 0.8 0.6
IOUT (1A/DIV)
VOUT (5V/DIV)
VIN = 5V CIN = 33F COUT = 0.1F S2 = S3 = On
VIN = 5V CIN = COUT = 33F S2 = S3 = On
Time (10ms/DIV)
-40
-20
0
20
40
60
80
100
120
C) Temperature(X
CE Threshold Voltage vs. Input Voltage
2.4
4
CE Threshhold Voltage vs. Temperature 4
2.4 2 1.6 1.2 0.8 0.4 0
CE Threshold Voltage (V)
1.6 1.2 0.8 0.4 0 2 2.5 3 3.5 4 4.5 5 5.5
CE Threshold Voltage (V)
2
CIN = COUT = 33F IL = 100mA
VIN = 5V CIN = COUT = 33F IL = 100mA
-40
-20
0
20
40
60
80
100
120
Input Voltage (V)
C) Temperature(X
Turn-On Rising Time vs. Temperature
720
1
Turn-Off Falling Time (s)
Turn-Off Falling Time vs. Temperature 1
140 120 100 80 60 40 20 0
Turn-On Rising Time (s)
630 540 450 360 270 180 90 0 -40 -20 0 20 40 60
VIN = 5V CIN = 33F COUT = 1F RL = 30 S1 = On
VIN = 5V CIN = 33F COUT = 1F RL = 30 S1 = On
80
100
120
-40
-20
0
20
40
60
80
100
120
C) Temperature(X
C) Temperature (X
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RT9702/A
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Preliminary
Switch Off Supply Current vs. Temperature 2
Switch Off Supply Current (A)
0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1 -40 -20 0 20 40 60 80 100 120
Turn-Off Leakage Current vs. Temperature 2
Turn-off Leakage Current (A)
3.5 3 2.5 2 1.5 1 0.5 0 -40 -20 0 20 40 60 80 100 120
VIN = 5V CIN = COUT = 33F VCE = 0V RL = Open
VIN = 5V CIN = COUT = 33F VCE = 0V RL = 0
C) Temperature (X
C) Temperature(X
FLAG Delay Time vs. Input Voltage
24 20
4
FLAG Delay Time vs. Temperature
16 15 14
4
VCE = 5V CIN = COUT = 33F
VIN = VCE = 5V CIN = COUT = 33F
Delay Time (ms)
Delay Time (ms)
16 12 8 4 0 2 2.5 3 3.5 4 4.5 5 5.5
13 12 11 10 9 8 7 -40 -20 0 20 40 60 80 100 120
Input Voltage (V)
C) Temperature(X
3.5 3
UVLO Threshold vs. Temperature 4
CIN = COUT = 33F RL = 1k
Inrush Current Response
VIN = 5V CIN = 33F RL = 1 S2 = On S3 = Off
5
COUT = 1000F COUT = 220F
UVLO Threshold (V)
2.5 2 1.5
IOUT (1A/DIV)
1 0.5 0 -40 -20 0 20 40 60 80 100 120
COUT = 1F
C) Temperature(X
Time (10ms/DIV)
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Preliminary
RT9702/A
Turn-Off Response
Turn-On Response
1
IL VCE VOUT (0.5A/DIV) (5V/DIV) (5V/DIV)
1
VCE (5V/DIV)
VOUT (1V/DIV)
VIN = 5V CIN = 33F COUT = 1F RL = 30 S1 = On
VIN = 5V RL = 30 S1 = Off
CIN = 33F COUT = 1F
Time (100s/DIV)
Time (100s/DIV)
UVLO at Rising
4
VIN
UVLO at Falling
4
VIN = 5V CIN = 33F COUT = 1F RL = 30
VIN (1V/DIV)
VOUT (1V/DIV)
VOUT
VIN = 5V CIN = 33F COUT = 1F RL = 30
VOUT VIN (1V/DIV) (1V/DIV)
VIN
VOUT
Time (1ms/DIV)
Time (10ms/DIV)
Soft-Start Response
5
Ramped Load Response
4.9V
5
VCE (5V/DIV)
VOUT (5V/DIV)
IL (0.5A/DIV)
RL = 1 VIN = 5V
Time (50s/DIV)
IL (0.5A/DIV)
CIN = 33F COUT = 1F S2 : Off On S3 = Off
1.1A V = 5V IN CIN = 33F COUT = 1F RL : 1k 1
Time (10ms/DIV)
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RT9702/A
Preliminary
Flag Response (Enable into Short Circuit) RT9702CB
VCE VFLG (5V/DIV) (5V/DIV)
12ms (tD)
1
VOUT VFLG (5V/DIV) (5V/DIV)
Flag Response
1
12ms (tD) CIN = 0.1F COUT = 33F S1 = On RL = 1
IL (0.5A/DIV)
Time (2.5ms/DIV)
IL (1A/DIV)
CIN = 33F COUT = 1F S1 = On RL = 0
Time (10ms/DIV)
Current Limit Transient Response
VIN = 5V RL = 1 S2 = On S3 = Off CIN = 0.1F COUT = 33F
5
VCE IOUT(1A/DIV) IOUT(1A/DIV) Current Limit (5V/DIV) Short
Thermal Shutdown Response
S2 = On
5
VTRIGGER (5V/DIV)
S3 = Off RL = 1
S3 = On CIN = 33F COUT = 1F
IOUT (1A/DIV)
Time (5s/DIV)
Time (50ms/DIV)
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Preliminary 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 (VCE < 0.8V).
RT9702/A
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 N-Channel 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 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
D
S
D
S
G Normal MOSFE T
G RT9702/A
Chip Enable Input The switch will be disabled when the CE 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 CE pin is 0.8V. A minimum guaranteed voltage of 2V at the CE pin will turn the RT9702/A back on. Floating the input may cause unpredictable operation. CE should not be allowed to go negative with respect to GND. The CE pin may be directly tied to VIN to keep the part on.
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RT9702/A
Preliminary
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 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.
1.5A for RT9702A respectively. When a heavy load or short circuit is applied to an enabled switch, a large transient current may flow until the current limit circuitry responds. Once this current limit threshold is exceeded the device enters constant current mode until the thermal shutdown occurs or the fault is removed. Thermal Shutdown Thermal shutdown is employed to protect the device from damage if the die temperature exceeds approximately 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 IOUT2 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 TA is the maximum ambient temperature. The junction to ambient thermal resistance (JA) for SOT-25 package at recommended minimum footprint is 250C/W (JA is layout dependent).
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Preliminary
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. 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.
RT9702/A
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 low-pass 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 Self-Powered 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 )
*
-
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RT9702/A
Preliminary
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.
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. 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
FLG
GND_BUS
CE
GND
USB Controller
Board Layout
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Preliminary Package Information
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 0.889 0.000 1.397 0.356 2.591 2.692 0.838 0.102 0.356 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 0.004 0.014 Max 0.051 0.006 0.071 0.022 0.118 0.122 0.041 0.010 0.024
SOT- 25 Surface Mount Package
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RT9702/A
Preliminary
RICHTEK TECHNOLOGY CORP.
Headquarter
5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611
RICHTEK TECHNOLOGY CORP.
Taipei Office (Marketing)
8F-1, 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
DS9702A-01
March 2003
16

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