Preliminary
RT9702/A
80mΩ
Ω, 500mA/1.1A High-Side Power Switches with Flag
General Description
Features
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), 80mΩ, meets USB
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voltage drop requirements; and a flag output is available
to indicate fault conditions to the local USB controller.
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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 25μA
making this device ideal for portable battery-operated
equipment.
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The RT9702/A is available in SOT-23-5 and TSOT-23-5
packages requiring minimum board space and smallest
components.
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RT9702/A
Package Type
B : SOT-23-5
J5 : TSOT-23-5
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
RoHS Compliant and 100% Lead (Pb)-Free
Applications
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Ordering Information
Compliant to USB Specifications
Ω) N-Channel MOSFET
Built-In (Typically 80mΩ
Output Can Be Forced Higher Than Input (Off-State)
Low Supply Current :
25μ
μA Typical at Switch On State
1μ
μA Typical at Switch Off State
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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
Operating Temperature Range
C : Commercial Standard
P : Pb Free with Commercial Standard
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1.1A Output Current
Marking Information
500mA Output Current
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 products are :
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−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.
DS9702/A-08 February 2006
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1
RT9702/A
Preliminary
Pin Configurations
Functional Pin Description
(TOP VIEW)
Pin Name
Pin Function
VIN
Power Input Voltage
VOUT
VIN
VOUT
Output Voltage
5
4
GND
Ground
3
EN
Chip Enable (Active High)
FLG
Open-Drain Fault Flag Output
1
2
EN
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
10K
VIN
Over -Current
FLG
0.1uF
1uF
RT9702/A
EN
VOUT
GND
VBUS
+
Chip Enable
10uF
D+
D-
150uF
GND
Ferrite
Beades
Data
Note: 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. (see Application Information Section for further details)
Function Block Diagram
VIN
EN
Bias
UVLO
Oscillator
Charge
Pump
Thermal
Protection
Current
Limiting
Gate
Control
Output Voltage
Detection
VOUT
FLG
Delay
GND
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DS9702/A-08 February 2006
RT9702/A
Preliminary
Test Circuits
1
2
RFG
ISupply
+
VIN
+
VIN
CIN
VFLG
FLG
VIN
S1
RT9702/A
A
EN
GND
COUT
RT9702/A
A
VOUT
EN
Chip Enable
RL
VFLG
FLG
ILEAK AGE
+
Chip Enable
VIN
VOUT
IOUT
VOUT
A
CIN
GND
RL
IL
3
4
VRDS(ON)
RFG
V
IOUT
CIN
VIN
VOUT
GND
VCE
+
VOUT
EN
GND
5
VFLG
FLG
RT9702/A
FLG
EN
Chip Enable
COUT
RT9702/A
VIN
+
VIN
+
+
CIN
VOUT
VIN
COUT
RL
IL
RFG
S2
+
VIN
CIN
VIN
VFLG
FLG
RT9702/A
VOUT
IOUT
GND
+
VOUT
EN
COUT
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
2 −Supply Current vs. Input Voltage & Temperature, Switch Off Supply Current vs. Temperature, Turn-Off Leakage Current
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-08 February 2006
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3
RT9702/A
Preliminary
Absolute Maximum Ratings
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(Note 1)
Supply Voltage --------------------------------------------------------------------------------------------------------- 6.5V
Chip Enable Input Voltage ------------------------------------------------------------------------------------------- −0.3V to 6.5V
Flag Voltage ------------------------------------------------------------------------------------------------------------ 6.5V
Power Dissipation, PD @ TA = 25°C
SOT-23-5, TSOT-23-5 ------------------------------------------------------------------------------------------------- 0.4W
Package Thermal Resistance (Note 4)
SOT-23-5, TSOT-23-5, θJA ------------------------------------------------------------------------------------------- 250°C/W
Junction Temperature ------------------------------------------------------------------------------------------------- 150°C
Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260°C
Storage Temperature Range ---------------------------------------------------------------------------------------- −65°C to 150°C
ESD Susceptibility (Note 2)
HBM (Human Body Mode) ------------------------------------------------------------------------------------------ 8kV
MM (Machine Mode) -------------------------------------------------------------------------------------------------- 800V
Recommended Operating Conditions
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(Note 3)
Supply Input Voltage -------------------------------------------------------------------------------------------------- 2V to 5.5V
Chip Enable Input Voltage ------------------------------------------------------------------------------------------- 0V to 5.5V
Junction Temperature Range ---------------------------------------------------------------------------------------- −20°C to 100°C
Ambient Temperature Range ---------------------------------------------------------------------------------------- −40°C to 85°C
Electrical Characteristics
(VIN = 5V, CIN = COUT = 1μF, TA = 25°C, unless otherwise specified)
Parameter
Switch On Resistance
Symbol
RT9702
RT9702A
IOUT = 500mA
Min
Typ
Max
Units
--
80
100
mΩ
IOUT = 1.1A
ISW_ON
switch on, VOUT = Open
--
25
45
ISW_OFF
switch off, VOUT = Open
--
0.1
1
VIL
VIN = 2V to 5.5V, switch off
--
--
0.8
V
Logic-High Voltage VIH
VIN = 2V to 5.5V, switch on
2.0
--
--
V
--
0.01
--
μA
Supply Current
EN Threshold
RDS(ON)
Test Conditions
Logic-Low Voltage
μA
EN Input Current
IEN
Output Leakage Current
ILEAKAGE VEN = 0V, RLOAD = 0Ω
--
0.5
10
μA
Output Turn-On Rise Time
TON_RISE 10% to 90% of VOUT rising
--
400
--
μs
0.5
0.8
1.1
1.1
1.5
2.0
Current Limit
VEN = 0V to 5.5V
RT9702
A
ILIM
RLOAD = 1Ω
VOUT = 0V, measured prior to
thermal shutdown
--
0.8
--
ISC_FB
--
1.0
--
FLAG Output Resistance
RFLG
ISINK = 1mA
--
20
400
Ω
FLAG Off Current
IFLG_OFF
VFLG = 5V
--
0.01
1
μA
FLAG Delay Time (Note 5)
tD
From fault condition to FLG
assertion
2
10
15
ms
RT9702A
Short Circuit FoldBack Current
RT9702
RT9702A
A
To be continued
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DS9702/A-08 February 2006
RT9702/A
Preliminary
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
Under-voltage Lockout
VUVLO
VIN increasing
1.3
1.7
--
V
Under-voltage Hysteresis
ΔVUVLO
VIN decreasing
--
0.1
--
V
Thermal Shutdown Protection
TSD
--
130
--
°C
Thermal Shutdown Hysteresis
ΔTSD
--
20
--
°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. θJA is measured in the natural convection at TA = 25°C 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.
DS9702/A-08 February 2006
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5
RT9702/A
Preliminary
Typical Operating Characteristics
(U.U.T: RT9702ACB, unless otherwise indicated)
40
40
VIN = VEN = 5V
VIN = VEN = 5V, RL = Open
35
35
30
Supply Current (uA)1
CIN = 33uF
Supply Current (uA)
2
Supply Current vs. Temperature
2
Supply Curent vs. Input Voltage
RL = Open
25
20
15
10
5
CIN = 33uF, COUT = 33uF
30
25
20
15
10
5
0
0
2
2.5
3
3.5
4
4.5
5
5.5
-40
-20
0
20
100
120
Current Limit vs. Input Voltage
5
Input Voltage (V)
40
60
80
Temperature (° C)
5
Current Limit vs. Input Voltage
1.6
2.0
RT9702
1.4
Current Limit (A)
Current Limit (A)
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
1.2
CIN = 33uF, COUT= 33uF
CIN = 33uF, COUT= 33uF
0.2
S2 = On, S3 = Off, RL = 1Ω
S2 = On, S3 = Off, RL = 1Ω
0
1.0
2
2.5
3
3.5
4
4.5
5
2
5.5
2.5
3
Input Voltage (V)
On-Resistance vs. Input Voltage
3
4
4.5
5
5.5
3
On-Resistance vs. Temperature
160
160
CIN = COUT = 33uF
140
VIN = 5V
140
IOUT = 1.1A
On-Resistance (mΩ)
On-Resistance (mΩ)
3.5
Input Voltage (V)
120
100
80
60
CIN = COUT = 33uF
120
IOUT = 1.1A
100
80
60
40
40
20
20
0
0
2
2.5
3
3.5
4
4.5
Input Voltage (V)
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5
5.5
-40
-20
0
20
40
60
80
100
120
Temperature (° C)
DS9702/A-08 February 2006
RT9702/A
Preliminary
Short Circuit Current Response
Short Circuit Current vs. Temperature 5
5
2.00
VIN = 5V
0
VIN=5V, S2=S3=On
IOUT (A)
2
CIN=33uF
1
1.80
Short Circuit Current (A)
VOUT (V)
5
COUT=0.1uF
CIN = COUT = 33uF
S2 = S3 = On
1.60
1.40
1.20
1.00
0.80
0
0.60
-40
-20
0
20
40
60
80
100
120
Temperature(° C)
4
EN Threshold
Pin Threshold
Voltage
vs. Input
CE
Voltage
vs. Input
Voltage
4
EN Pin
CE Threshold
ThreshholdVoltage
Voltage vs.
vs. Temperature
Temperature
2.4
2.4
VIN = 5V
2
ENThreshold
Pin Threshold
Voltage
CE
Voltage
(V) (V)
EN
Threshold
Voltage(V)
(V)
CEPin
Threshold
Voltage
CIN = COUT = 33uF
IL = 100mA
1.6
1.2
0.8
0.4
0
2
CIN = COUT = 33uF
IL = 100mA
1.6
1.2
0.8
0.4
0
2
2.5
3
3.5
4
4.5
5
-40
5.5
-20
0
Turn-Off Falling Time (us)
Turn-On Rising Time (us)
60
80
100
120
140
VIN = 5V, RL = 30Ω
540
40
Turn-Off Falling Time vs. Temperature 1
Turn-On Rising Time vs. Temperature 1
720
630
20
Temperature (° C)
Input Voltage (V)
CIN = 33uF, COUT = 1uF
S1 = On
450
360
270
180
VIN = 5V, RL = 30Ω
120
CIN = 33uF, COUT= 1uF
100
S1 = On
80
60
40
20
90
0
0
-40
-20
0
20
40
60
80
Temperature (° C)
DS9702/A-08 February 2006
100
120
-40
-20
0
20
40
60
80
100
120
Temperature(° C)
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RT9702/A
Preliminary
Turn-Off Leakage Current vs. Temperature
Switch Off Supply Current vs. Temperature
Switch Off Supply Current (uA)
0.8
VIN = 5V, VEN = 0V
0.6
CIN = COUT = 33uF
0.4
RL = Open
0.2
0
-0.2
-0.4
-0.6
2
3.5
Turn-off Leakage Current (uA)
2
1
VIN = 5V, VEN = 0V
3
CIN = COUT = 33uF
RL= 0Ω
2.5
2
1.5
1
0.5
-0.8
0
-1
-40
-20
0
20
40
60
80
100
-40
120
-20
0
20
40
60
80
100
120
Temperature (° C)
Temperature(° C)
FLAG Delay Time vs. Input Voltage
4
4
FLAG Delay Time vs. Temperature
24
16
VEN = 5V
VIN = VEN = 5V
15
CIN = COUT = 33uF
20
CIN = COUT = 33uF
Delay Time (ms)
Delay Time (ms)
14
16
12
8
13
12
11
10
9
4
8
7
0
2
2.5
3
3.5
4
4.5
5
-40
5.5
-20
0
UVLO Threshold vs. Temperature
2.40
CIN=COUT=33uF
60
80
100
120
RL=1kΩ
CIN = COUT = 33uF
2.00
2.5
2
1.5
1
5
VIN = 5V, RL = 1Ω
2.20
Current Limit (A)
UVLO Threshold (V)
40
Current Limit vs. Temperature
4
3.5
3
20
Temperature(° C)
Input Voltage (V)
S2 = On,S3 = Off
1.80
1.60
1.40
1.20
1.00
0.80
0.5
0.60
0
0.40
-40
-20
0
20
40
60
80
Temperature (° C)
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100
120
-40
-20
0
20
40
60
80
100
120
Temperature (° C)
DS9702/A-08 February 2006
RT9702/A
Preliminary
1
VEN
VOUT
VOUT
IL
(1V/DIV)
V
=5V,
30Ω
Ω
VIN
=5V, R
RLL=
=30
IN
1
Turn- Off Response
C
=33uF,C
=1uF
CIN
=33uF, COUT
=1uF
IN
OUT
S
S11=On
=On
(0.5A/DIV) (5V/DIV) (5V/DIV)
VEN
(5V/DIV)
Turn- On Response
VIN=5V, RL= 30Ω
CIN=33uF COUT=1uF
S1=Off
Time (100μs / DIV)
Time (100μs / DIV)
UVLO at Rising
4
UVLO at Falling
4
VIN=5V, RL= 30Ω
VIN
VIN
VIN
VOUT
VIN=5V, RL= 30Ω
VOUT
CIN=33uF, COUT=1uF
(1V/DIV) (1V/DIV)
VIN
VOUT
(1V/DIV) (1V/DIV)
CIN=33uF, COUT=1uF
Time (10ms / DIV)
Time (1ms / DIV)
5
Soft- Start Response
Ramped Load Response
On
4.9V
(5V/DIV)
(5V/DIV)
S3= Off
VOUT
↓
S2:Off
VEN
VOUT
Time (50μs / DIV)
DS9702/A-08 February 2006
IL
VIN=5V
RL=1kΩ
1Ω
↓
VIN=5V, RL=1Ω
CIN=33uF, COUT=1uF
(0.5A/DIV)
IL
(0.5A/DIV)
1.1A
CIN=33uF,COUT=1uF
Time (100ms / DIV)
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9
5
RT9702/A
Preliminary
Flag Response (Enable into Short Circuit) 1
VOUT
RL=0Ω , S1=On
(5V/DIV) (5V/DIV)
VFLG
IL
CIN=33uF,COUT=1uF
12ms
CIN=0.1uF,
RL=1Ω
COUT=33uF
S1=On
Time (2.5ms / DIV)
Time (10ms / DIV)
5
VEN
IOUT(1A/DIV) IOUT(1A/DIV)
(5V/DIV)
VTRIGGER
IOUT
(1A/DIV)
VIN=5V,CIN=COUT=33uF
S2=On ,S3=Off,RL=1Ω
Time (5us / DIV)
Current Limit (5V/DIV)
Thermal Shutdown Response
S2=On
S3=Off
RL=1Ω
S3=On
Short
Current Limit Transient Respones
CIN=33uF
COUT=1uF
Time (50ms / DIV)
Short Circuit Current Response
IOUT (A)
1
(1A/DIV)
VEN
12ms (tD)
(0.5A/DIV)
VFLG
(5V/DIV) (5V/DIV)
RT9702CB
IL
Flag Response
5
COUT=1000uF
4
COUT=220uF
5
3
2
1
0
COUT=1uF
VIN=5V, RL=1Ω
CIN=33uF
S2=On, S3=Off
Time (10ms / DIV)
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DS9702/A-08 February 2006
5
Preliminary
RT9702/A
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), 80mΩ, 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).
D
S
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 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 130°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
G
Normal MOSFET
RT9702/A
Chip Enable Input
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 0.1μA 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.
DS9702/A-08 February 2006
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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11
RT9702/A
Preliminary
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
130°C. If enabled, the switch automatically restarts when
the die temperature falls 20°C. 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 100°C. With all possible conditions, the
junction temperature must be within the range specified
under operating conditions. Power dissipation can be
calculated based on the output current and the RDS(ON) of
switch as below.
2
PD = RDS(ON) x IOUT
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 ) / θJA
Where TJ (MAX) is the maximum junction temperature of
the die (100°C) and T A is the maximum ambient
temperature. The junction to ambient thermal resistance
(θJA) for SOT-23-5 and TSOT-23-5 package at recommended
minimum footprint is 250°C/W (θJA is layout dependent).
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12
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.
DS9702/A-08 February 2006
RT9702/A
Preliminary
Because the devices are also power switches, the designer
of self-powered hubs has the flexibility to turn off power to
output ports. Unlike a normal MOSFET, the devices have
controlled rise and fall times to provide the needed inrush
current limiting required for the bus-powered hub power
switch.
Supply Filter/Bypass Capacitor
A 1μF low-ESR ceramic capacitor from VIN to GND,
located at the device is strongly recommended to prevent
the input voltage drooping during hot-plug events. However,
higher capacitor values will further reduce the voltage droop
on the input. Furthermore, without the bypass capacitor,
an output short may cause sufficient ringing on the input
(from source lead inductance) to destroy the internal
control circuitry. The input transient must not exceed 6.5V
of the absolute maximum supply voltage even for a short
duration.
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)
Output Filter Capacitor
RCABLE = Resistance of upstream cable wires
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.
(one 5V and one GND)
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 (10kΩ and 0.1μF) in the flag line (see Typical
Application Circuit) eliminates short-duration transients.
DS9702/A-08 February 2006
RSWITCH = Resistance of power switch
(80mΩ typical for RT9702/A)
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 • 30mΩ + 2 • 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 RT9702/A, with its maximum
100mΩ on-resistance over temperature, easily meets this
requirement.
www.richtek.com
13
RT9702/A
Preliminary
PCB Layout
ESD
In order to meet the voltage drop, droop, and EMI
requirements, careful PCB layout is necessary. The
following guidelines must be considered:
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.
z
Keep all VBUS traces as short as possible and use at
least 50-mil, 2 ounce copper for all VBUS traces.
z
Avoid vias as much as possible. If vias are necessary,
make them as large as feasible.
z
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).
z
Place cuts in the ground plane between ports to help
reduce the coupling of transients between ports.
z
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.
z
Locate the RT9702/A as close as possible to the output
port to limit switching noise.
z
Locate the ceramic bypass capacitors as close as
possible to the VIN pins of the RT9702/A.
VBUS
VOUT
Low-ESR 1μF 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.
VIN
FLG
GND_BUS
EN
Board Layout
www.richtek.com
14
GND
USB
Controller
DS9702/A-08 February 2006
RT9702/A
Preliminary
Outline Dimension
H
D
L
B
C
b
A
A1
e
Symbol
Dimensions In Millimeters
Dimensions In Inches
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
0.559
0.014
0.022
C
2.591
2.997
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
SOT-23-5 Surface Mount Package
DS9702/A-08 February 2006
www.richtek.com
15
RT9702/A
Preliminary
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
www.richtek.com
16
DS9702/A-08 February 2006