RT9706
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Pin Configurations
80mΩΩ
ΩΩ
Ω, 500mA High-Side Power Switch with Flag
Marking Information
For marking information, contact our sales representative
directly or through a Richtek distributor located in your
area.
Ordering Information
General Description
The RT9706 is a cost-effective, low voltage, single
N-Channel MOSFET high-side power switch, optimized
for self-powered and bus-powered Universal Serial Bus
(USB) applications. The RT9706 equipped with a charge
pump circuitry to drive the internal MOSFET 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.
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, lower
quiescent current as 25μA making this device ideal for
portable battery operated equipment.
The RT9706 is available in SOT-23-5 package requiring
minimum board space and smallest components.
Features
zz
zz
zCompliant to USB Specifications
zz
zz
zBuilt-In (Typically 80mΩΩ
ΩΩ
Ω) N-Channel MOSFET
zz
zz
zOutput Can Be Forced Higher than Input (Off-State)
zz
zz
zLow Supply Current :
` 25μμ
μμ
μA Typical at Switch On State
` 0.1μμ
μμ
μA Typical at Switch Off State
zz
zz
zGuaranteed 500mA Continuous Load Current
zz
zz
zWide Input Voltage Ranges : 2V to 5.5V
zz
zz
zOpen-Drain Fault Flag Output
zz
zz
zHot Plug-In Application (Soft-Start)
zz
zz
z1.7V Typical Under-Voltage Lockout (UVLO)
zz
zz
zCurrent Limiting Protection
zz
zz
zThermal Shutdown Protection
zz
zz
zReverse Current Flow Blocking (no body diode)
zz
zz
zSmalle st SOT-23-5 Package Minimizes Board Space
zz
zz
zUL Approved−−
−−
−E219878
zz
zz
zRoHS Compliant and 100% Lead (Pb)-Free
Applications
zUSB Bus/Self Powered Hubs
zUSB Peripherals
zACPI Power Distribution
zPC Card Hot Swap
zNotebook, Motherboard PCs
zBattery-Powered Equipment
zHot-Plug Power Supplies
zBattery-Charger Circuits
Note :
Richtek products are :
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes. (TOP VIEW)
SOT-23-5
GND
VOUT VIN
4
23
5
EN FLG
RT9706
Package Type
B : SOT-23-5
Lead Plating System
P : Pb Free
G : Green (Halogen Free and Pb Free)
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Function Block Diagram
Functional Pin Description
Typical Application Circuit
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)
Pin Name Pin Function
VIN Power Input Voltage
VOUT Output Voltage
GND Ground
EN Chip Enable (Active Low)
FLG Open-Drain Fault Flag Output
VIN
EN
FLG
VOUT
GND
RT9706
+
Over -Current
VBUS
D+
D-
GND
USB Controller
1uF
150uF
10uF
Supply Voltage 5V
Pull-Up Resistor (10K to 100k)
Ferrite
Beades Data
OFF
ON
Gate
Control
Output Voltage
Detection
Delay
Oscillator
UVLO
Charge
Pump
Bias
Thermal
Protection
Current
Limiting
FLG
VOUT
VIN
EN
GND
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Test Circuits
12
34
5
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
−EN 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
1
2
3
4
5
VIN
EN
FLG
VOUT
GND
RT9706
+
+
RL
COUT IL
VOUT
RFG
CIN
VIN
VCE
VFLG
VIN
EN
FLG
VOUT
GND
RT9706
+
+
RL
A
IOUT
S1
COUT IL
VOUT
RFG
CIN
VIN VFLG
OFF
ON
VIN
EN
FLG
VOUT
GND
RT9706
+
RL
A
ISupply
CIN
VIN
A
ILEAK AGE
VFLG
OFF
ON
VIN
EN FLG
VOUT
GND
RT9706
+
+
IOUT
COUT
VRDS(ON)
CIN
VIN
V
OFF
ON
VIN
EN
FLG
VOUT
GND
RT9706
+
+
RL
A
IOUT
S3
COUT IL
VOUT
RFG
CIN
VIN
S2
VFLG
OFF
ON
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Absolute Maximum Ratings (Note 1)
zSupply Voltage --------------------------------------------------------------------------------------------------------- 6.5V
zChip Enable Input Voltage ------------------------------------------------------------------------------------------- −0.3V to 6.5V
zFlag Voltage ------------------------------------------------------------------------------------------------------------ 6.5V
zPower Dissipation, PD @ TA = 25°C
SOT-23-5 ---------------------------------------------------------------------------------------------------------------- 0.4W
zPackage Thermal Resistance (Note 2)
SOT-23-5, θJA ---------------------------------------------------------------------------------------------------------- 250°C/W
zJunction Temperature ------------------------------------------------------------------------------------------------- 150°C
zLead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260°C
zStorage Temperature Range ---------------------------------------------------------------------------------------- −65°C to 150°C
zESD Susceptibility (Note 3)
HBM (Human Body Mode) ------------------------------------------------------------------------------------------ 2kV
MM (Machine Mode) -------------------------------------------------------------------------------------------------- 200V
Electrical Characteristics
Recommended Operating Conditions (Note 4)
zSupply Input Voltage -------------------------------------------------------------------------------------------------- 2V to 5.5V
zChip Enable Input Voltage ------------------------------------------------------------------------------------------- 0V to 5.5V
zJunction Temperature Range ---------------------------------------------------------------------------------------- −40°C to 125°C
zAmbient Temperature Range ---------------------------------------------------------------------------------------- −40°C to 85°C
Parameter Symbol Test Conditions Min Typ Max Unit
Switch On Resistance RDS(ON) I
OUT = 500mA -- 100 130 mΩ
ISW_ ON switch on, VOUT = Open -- 25 45
Supply Current
ISW_ OFF switch off, VOUT = Open -- 0.1 1
μA
Logic-Low Voltage VIL V
IN = 2V to 5.5V, switch off -- -- 0.8 V
EN Threshold
Logic-High Voltage VIH V
IN = 2V to 5.5V, switch on 2.0 -- -- V
EN Input Current IEN V
EN = 0V to 5.5V -- 0.01 -- μA
Output Leakage Current ILEAKAGE V
EN = 5V, RLOAD = 0Ω -- 0.5 10 μA
Output Turn-On Rise Time TON_RISE 10% to 90% of VOUT rising -- 400 -- μs
Current Limit ILIM R
LOAD =1Ω 0.5 0.8 1.25 A
FLAG Output Resistance RFLG ISINK = 1mA -- 20 400 Ω
FLAG Off Current IFLG_OFF VFL G = 5V -- 0.01 1 μA
FLAG Delay Time (Note 5) tD From fault condition to FLG
assertion 5 12 20 ms
Under-voltage Lockout VUVLO V
IN Rising 1.3 1.7 -- V
Under-voltage Hysteresis ΔVUVLO -- 0.1 -- V
(VIN = 5V, CIN = COUT = 1μF, T A = 25°C, unless otherwise specified)
To be continued
RT9706
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Parameter Symbol Test Conditions Min Typ Max Unit
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. θJA is measured in the natural convection at TA = 25°C on a low effective single layer thermal conductivity test board of
JEDEC 51-3 thermal measurement standard.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. The FLAG delay time is input voltage dependent, see“ Typical Operating Characteristics” graph for further details.
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Supply Current vs . Input Vo ltage
0
5
10
15
20
25
30
2 2.5 3 3.5 4 4.5 5 5.5
Input Voltage (V)
Supply Current (uA)
Current Limit vs. Input Voltage
0
0.25
0.5
0.75
1
1.25
1.5
2 2.5 3 3.5 4 4.5 5 5.5
Input Voltage (V)
Current Limit (A)
Typical Operating Characteristics
Supply Current vs. Temperature
0
10
20
30
40
50
-40-20 0 20406080100120
Temperature
Supply Current (uA)
(°C)
Curren t L im it vs. Te m p e rature
0
0.5
1
1.5
2
2.5
-40 -20 0 20 40 60 80 100 120
Temperature
Current Limit (A)
(°C)
Switch On Resistance vs. Temperature
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
-40 -20 0 20 40 60 80 100 120
Temperature
Switch On Resistance (Ω)
(°C)
(Ω)
Switch On Resistance vs. Input Voltage
20
40
60
80
100
120
140
160
2 2.5 3 3.5 4 4.5 5 5.5
Input Voltage (V)
Switch On Resistance (mΩ)
(mΩ)
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EN Pin Threshold Voltage vs. Input Voltage
0
0.4
0.8
1.2
1.6
2
22.5 33.5 44.5 55.5
Input Voltage (V)
EN Pin Threshold Voltage (V)
FLAG Delay Time vs. Input Voltage
0
4
8
12
16
20
2 2.5 3 3.5 4 4.5 5 5.5
Input Voltage (V)
FLAG Delay Time (ms)
Flag Delay Time vs. Temperature
0
5
10
15
20
25
-40 -20 0 20 40 60 80 100 120
Temperature
Flag Delay Time (ms)
(°C)
EN Pin Threshold Voltage vs. Temperature
0
0.4
0.8
1.2
1.6
2
-40 -20 0 20 40 60 80 100 120
Temperature
EN Pin Threshold Voltage (V)
(°C)
Switch Off Supply Current vs. Tem perature
-0.1
-0.06
-0.02
0.02
0.06
0.1
-40-200 20406080100120
Temperature
Switch Off Supply Current (uA)
(°C)
Turn-Off Leak a ge Current vs. Tempe rature
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
-40 -20 0 20 40 60 80 100 120
Temperature
Turn-Off Leakage Current (uA)
(°C)
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Turn-On Rising Time vs . Te m perature
0
100
200
300
400
500
600
-40 -20 0 20 40 60 80 100 120
Temperature
Turn-On Rising Time (us)
(°C)
Turn- Off Falling Time vs. Temperature
0
20
40
60
80
100
-40 -20 0 20 40 60 80 100 120
Temperature
Turn Off Falling Time (us)
(°C)
UVLO at Falling
Time (10ms/Div)
VIN
(1V/Div)
VOUT
(1V/Div)
CIN = 33uF, COUT = 1uF
UVLO at Rising
Time (1ms/Div)
VEN
(1V/Div)
VOUT
(1V/Div)
CIN = 33uF, COUT = 1uF
Turn-On Response
Time (100μs/Div)
VEN
(5V/Div)
VOUT
(5V/Div)
CIN = 33uF, COUT = 1uF
RL = 30Ω
Turn-Off Response
Time (25μs/Div)
VEN
(5V/Div)
VOUT
(5V/Div)
CIN = 33uF, COUT = 1uF
RL = 30Ω
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Ramped Load Response
Time (50ms/Div)
IOUT
(500mA/Div)
VEN
(5V/Div)
IOUT
(1A/Div)
RL = 1Ω
RL = Short
Inrush Current Response
Time (1ms/Div)
IOUT
(1A/Div)
COUT = 1000uF
COUT = 220uF
COUT = 1uF
Ramped Load Response
Time (50μs/Div)
IOUT
(500mA/Div)
VOUT
(1V/Div)
RL(H) = 5Ω, RL(L) = 100Ω
Short Circuit Current Response
Time (5ms/Div)
IOUT
(1A/Div)
VEN
(5V/Div)
CIN = COUT = 33uF
Flag Response with Over Current
Time (2.5ms/Div)
IOUT
(500mA/Div)
VOUT
(5V/Div)
VEN
(5V/Div)
FLAG
(5V/Div)
CIN = COUT = 1uF
Flag Response with Turn-On Short Current
Time (10ms/Div)
IOUT
(500mA/Div)
VEN
(5V/Div)
FLAG
(5V/Div)
RL = 0Ω
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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 RT9706 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 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. The FLG response delay time tD
is typically 12ms.
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.
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 RT9706. 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.
Applications Information
The RT9706 is a single N-Channel MOSFET high-side
power switch with active-low enable input, optimized for
self-powered and bus-powered Universal Serial Bus (USB)
applications. The RT9706 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
RT9706 prevents reverse current flow if VOUT being
externally forced to a higher voltage than VIN when the
output disabled (VEN > 2V).
Chip Enable Input
The switch will be disabled when the EN pin is in a logic
high 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 RT9706 off. Floating
the input may cause unpredictable operation. EN should
not be allowed to go negative with respect to GND.
D
G
S
D
G
S
Normal MOSFET RT9706
Figure 1
RT9706
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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
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 and Thermal Consideration
The device “S” junction temperature depends on several
factors such as the load, PCB layout, ambient temperature
and package type. The output pin of RT9706 can deliver a
current of up to 500mA, 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.
PD = RDS(ON) x (IOUT)2
Although the devices are rated for 500mA 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
PD(MAX) = ( TJ(MAX) − TA ) / θJA
Where TJ(MAX) is the maximum operation junction
temperature, TA is the ambient temperature and the θJA is
the junction to ambient thermal resistance.
For recommended operating conditions specification of
RT9706, where TJ(MAX) is the maximum junction
temperature of the die (125°C) and TA is the maximum
ambient temperature. The junction to ambient thermal
resistance θJA is layout dependent. For SOT-23-5
packages, the thermal resistance θJA is 250°C/W on the
standard JEDEC 51-3 single-layer thermal test board.
The maximum power dissipation at TA = 25°C can be
calculated by following formula :
PD(MAX) = (125°C − 25°C) / 250°C/W = 0.4 W for
SOT-23-5 packages
The maximum power dissipation depends on operating
ambient temperature for fixed TJ(MAX) and thermal
resistance θJA. For RT9706 packages, the Figure 2 of
derating curves allows the designer to see the effect of
rising ambient temperature on the maximum power
allowed.
Figure 2. Derating Curves for RT9706 Package
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.
0
0.1
0.2
0.3
0.4
0.5
0.6
0 25 50 75 100 125
Ambient Temperature
Maximum Power Dissipation (W)
Single Layer PCB
(°C)
SOT-23-5
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Output Filter Capacitor
A low-ESR 150μF aluminum electrolytic or tantalum
between VOUT and GND is strongly recommended to meet
the 330mV maximum droop requirement in the hub VBUS
(Per USB 2.0, output ports must have a minimum 120μF
of low-ESR bulk capacitance per hub). Standard bypass
methods should be used to minimize inductance and
resistance between the bypass capacitor and the
downstream connector to reduce EMI and decouple voltage
droop caused when downstream cables are hot-insertion
transients. Ferrite beads in series with VBUS, the ground
line and the 0.1μF bypass capacitors at the power
connector pins are recommended for EMI and ESD
protection. The bypass capacitor itself should have a low
dissipation factor to allow decoupling at higher frequencies.
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 (10kΩ and 0.1μF) 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 4.4V 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 multi-
ple 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 x RCONN + 2 x 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)
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 RT9706 power distribution allow
designers to design hubs that can operate through faults.
The RT9706 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/Bypa ss Ca pa citor
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.
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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 :
zKeep all VBUS traces as short as possible and use at
least 50-mil, 2 ounce copper for all VBUS traces.
zAvoid vias as much as possible. If vias are necessary,
make them as large as feasible.
zPlace 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).
zPlace cuts in the ground plane between ports to help
reduce the coupling of transients between ports.
zLocate 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.
zLocate the RT9706 as close as possible to the output
port to limit switching noise.
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 RT9706 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 RT9706 to withstand
the higher ESD energy.
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
RT9706 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.
GND
EN
FLG
GND_BUS
USB
Controller
Board Layout
VIN
VOUT
VBUS
RSWITCH : Resistance of power switch
(80mΩ typical for RT9706)
VPCB : PCB voltage drop
The USB specification defines the maximum resistance
per contact (RCONN) of the USB connector to be 30mΩ
and the drop across the PCB and switch to be 100mV.
This basically leaves two variables in the equation : the
resistance of the switch and the resistance of the cable.
If the hub consumes the maximum current (II) of 500mA,
the maximum resistance of the cable is 90mΩ.
The resistance of the switch is defined as follows :
RSWITCH = { 4.75V − 4.4V − [ 0.5A x ( 4 x 30mΩ + 2 x
90mΩ) ] − VPCB } ÷( 0.1A x NPORTS )
= (200mV − VPCB ) ÷( 0.1A x NPORTS )
If the voltage drop across the PCB is limited to 100mV,
the maximum resistance for the switch is 250mΩ for four
ports ganged together. The RT9706, with its maximum
100mΩ on-resistance over temperature, easily meets this
requirement.
zLocate the ceramic bypass capacitors as close as
possible to the VIN pins of the RT9706.
RT9706
14
DS9706-04 April 2011www.richtek.com
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Outline Dimension
AA1
e
b
B
D
C
H
L
SOT-23-5 Surface Mount Package
Dimensions In Millimeter s 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 0.559 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
