LM3526
LM3526 Dual Port USB Power Switch and Over-Current Protection
Literature Number: SNVS054D
LM3526
October 20, 2011
Dual Port USB Power Switch and Over-Current Protection
General Description
The LM3526 provides Universal Serial Bus standard power
switch and over-current protection for all host port applica-
tions. The dual port device is ideal for Notebook and desktop
PC's that supply power to more than one port.
A 1 ms delay on the fault flag output prevents erroneous over-
current reporting caused by in-rush currents during hot-plug
events.
The dual stage thermal protection circuit in the LM3526 pro-
vides individual protection to each switch and the entire de-
vice. In a short-circuit/over-current event, the switch dissipat-
ing excessive heat is turned off, allowing the second switch
to continue to function uninterrupted.
The LM3526 accepts an input voltage between 2.7V and 5.5V
allowing use as a device-based in-rush current limiter for 3.3V
USB peripherals, as well as Root and Self-Powered Hubs at
5.5V. The Enable inputs accept both 3.3V and 5.0V logic
thresholds.
The small size, low RON, and 1 ms fault flag delay make the
LM3526 a good choice for root hubs as well as per-port power
control in embedded and stand-alone hubs.
Features
■Compatible with USB1.1 and USB 2.0
■1 ms fault flag delay filters Hot-Plug events
■Smooth turn-on eliminates in-rush induced voltage drop
■UL recognized component: REF# 205202
■1A nominal short circuit output current protects PC power
supplies
■Thermal shutdown protects device in direct short condition
■500mA minimum continuous load current
■Small SO-8 package minimizes board space
■2.7V to 5.5V input voltage range
■140 mΩ Max. switch resistance
■1 µA Max. standby current
■200 µA Max. operating current
■Under-voltage lockout (UVLO)
Applications
■Universal Serial Bus (USB) Root Hubs including Desktop
and Notebook PC
■USB Monitor Hubs
■Other Self-Powered USB Hub Devices
■High Power USB Devices Requiring In-rush Limiting
■General Purpose High Side Switch Applications
Typical Operating Circuit and Connection Diagram
10109701
© 2011 National Semiconductor Corporation 101097 www.national.com
LM3526 Dual Port USB Power Switch and Over-Current Protection
10109702
LM3526-H
10109740
10109728
LM3526-L
Ordering Information
Part Number Enable, Delivery Option Package Type
LM3526M-H Active High Enable, 95 units per rail
SO-8,
NS Package Number
M08A
LM3526M-L Active Low Enable, 95 units per rail
LM3526MX-H Active High Enable, 2500 units per reel
LM3526MX-L Active Low Enable, 2500 units per reel
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LM3526
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage −0.3V to 6V
Output Voltage −0.3V to 6V
Voltage at All Other Pins −0.3V to 5.5V
Power Dissipation (TA = 25°C)
(Note 2) 700 mW
TJMAX (Note 2)150°C
Operating Ratings
Supply Voltage Range 2.7V to 5.5V
Operating Ambient Range −40°C to 85°C
Operating Junction Temperature
Range −40°C to 125°C
Storage Temperature Range −65°C to +150°C
Lead Temperature
(Soldering, 5 seconds) 260°C
ESD Rating (Note 3)
ESD Rating Output Only
2kV
8kV
DC Electrical Characteristics
Limits in standard typeface are for TJ = 25°C, and limits in boldface type apply over the full operating temperature range. Unless
otherwise specified: VIN = 5.0V, VEN = 0V (LM3526-L) or VEN = VIN (LM3526-H).
Symbol Parameter Conditions Min Typ Max Units
RON On Resistance VIN = 5V, IOUT = 500mA, each switch 100 140 mΩ
VIN = 2.7V, IOUT = 500mA, each switch 110 180
IOUT OUT pins continuous output
current
Each Output 0.5 A
ISC Short Circuit Output Current Each Output (enable into Load) (Note 4)
VOUT = 4.0V
VOUT = 0.1V
0.5 1.2
1
1.9
1.5
A
OCTHRESH Over-current Threshold 2.2 3.2 A
ILEAK OUT pins Output Leakage
Current
VEN = VIN (LM3526-L)
VEN = 0V (LM3526-H)
0.01 10 µA
RFO FLAG Output Resistance
IFO = 10 mA, VIN = 5.0V 10 25
Ω
IFO = 10 mA, VIN = 3.3V 11 35
IFO = 10 mA, VIN = 2.7V 12 40
IEN EN/EN Leakage Current VEN/VEN = 0V or VEN/VEN = VIN −0.5 0.5 µA
VIH EN/EN Input Logic High (Note 5)2.4 1.9 V
VIL EN/EN Input Logic Low (Note 5) 1.7 0.8 V
VUVLO Under-Voltage Lockout
Threshold
1.8 V
IDDOFF Supply Current Switch-Off
−40°C ≤ TJ ≤ 85°C
0.2 1
2
µA
IDDON Supply Current Switch-On 115 200 µA
ThSD Over-temperature
Shutdown Threshold
TJ Increasing, with no shorted output
TJ Increasing, with shorted output (s)
TJ Decreasing (Note 4)
150
145
135
°C
IFH Error Flag Leakage Current Vflag = 5V 0.01 1 µA
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
beyond its rated operating conditions.
Note 2: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX (Maximum junction temperature), θJA (junction to
ambient thermal resistance), and TA (ambient temperature). The maximum allowable power dissipation at any temperature is PDMAX = (TJMAX − TA)/θJA or the
number given in the Absolute Maximum Ratings, which ever is lower. θJA = 150°C/W.
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. Enable pin ESD threshold is 1.7kV.
Note 4: Thermal Shutdown will protect the device from permanent damage.
Note 5: For LM3526-L, OFF is EN ≥ 2.4V and ON is EN ≤ 0.8V. For LM3526-H, OFF is EN ≤ 0.8V and ON is EN ≥ 2.4V.
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LM3526
AC Electrical Characteristics
Limits in standard typeface are for TJ = 25°C, and limits in boldface type apply over the full operating temperature range. Unless
otherwise specified: VIN = 5.0V.
Symbol Parameter Conditions Min Typ Max Units
trOUT Rise Time RL = 10Ω 100 µs
tfOUT Fall Time RL = 10Ω 5 µs
tON Turn on Delay, EN to OUT RL = 10Ω 150 µs
tOFF Turn off Delay, EN to OUT RL = 10Ω 5 µs
tOC Over Current Flag Delay RL = 0 1 ms
Pin Descriptions
Pin Number Pin Name Pin Function
1, 4 ENA, ENB
(LM3526-L)
ENA, ENB
(LM3526-H)
Enable (Input): Logic-compatible enable inputs.
2, 3 FLAG A
FLAG B
Fault Flag (Output): Active-low, open-drain outputs. Indicates overcurrent, UVLO or thermal
shutdown. *See application section for more information.
6 GND Ground
7 IN Supply Input: This pin is the input to the power switch and the supply voltage for the IC.
8, 5 OUT A
OUT B
Switch Output: These pins are the outputs of the high side switch.
Typical Application Circuit
10109703
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LM3526
Typical Performance Characteristics VIN = 5.0V, IL = 500 mA, TA = 25°C unless otherwise specified.
RON vs Temperature
10109704
RON vs Temperature
10109705
Quiescent Current vs Input Voltage
10109706
Quiescent Current vs Temperature
10109707
Current Limit vs Output Voltage
10109708
OC Threshold vs Temperature
10109709
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LM3526
Fault Flag Delay vs Temperature
10109735
Fault Flag Delay vs Temperature
10109736
Under Voltage Lockout (UVLO)
10109734
Under Voltage Lockout Threshold vs Temperature
10109737
Over Current/Current Limit Response*
10109710
* Output is shorted to Ground through a 100 mΩ resistor
Short Circuit Response with
Thermal Cycling*
10109711
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LM3526
Turn-ON/OFF Response with
47Ω/10µF Load
10109712
Turn-ON/OFF Response with
47Ω/150µF Load
10109713
Thermal Shutdown Response
(Port A output shorted*)
10109714
* Port A is shorted to GND through a 100 mΩ resistor
Thermal Shutdown Response (See Notes)
10109729
Enable into a short
10109730
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LM3526
Functional Description
The LM3526-H and LM3526-L are high side P-Channel
switches with active-high and active-low enable inputs, re-
spectively. Fault conditions turn-off and inhibit turn-on of the
output transistor and activate the open-drain error flag tran-
sistor sinking current to the ground.
INPUT AND OUTPUT
IN (Input) is the power supply connection to the control cir-
cuitry and the source of the output MOSFET.
OUT (Output) is the connection to the drain of the output
MOSFET. In a typical application circuit, current flows through
the switch from IN to OUT towards the load.
If VOUT is greater than VIN when the switch is enabled, current
will flow from OUT to IN since the MOSFET is bidirectional.
THERMAL SHUTDOWN
The LM3526 is internally protected against excessive power
dissipation by a two-stage thermal protection circuit. If the
device temperature rises to approximately 145°C, the thermal
shutdown circuitry turns off any switch that is current limited.
Non-overloaded switches continue to function normally. If the
die temperature rises above 150°C, both switches are turned
off and both fault flag outputs are activated. Hysteresis en-
sures that a switch turned off by thermal shutdown will not be
turned on again until the die temperature is reduced to 135°
C. Shorted switches will continue to cycle off and on, due to
the rising and falling die temperature, until the short is re-
moved.
UNDERVOLTAGE LOCKOUT
UVLO prevents the MOSFET switch from turning on until in-
put voltage exceeds 1.8V (typical).
If input voltage drops below 1.8V (typical), UVLO shuts off the
MOSFET switch and signals the fault flag. UVLO functions
only when device is enabled.
CURRENT LIMIT
The current limit circuit is designed to protect the system sup-
ply, the MOSFET switches and the load from damage caused
by excessive currents. The current limit threshold is set inter-
nally to allow a minimum of 500 mA through the MOSFET but
limits the output current to approximately 1.0A typical.
FAULT FLAG
The fault flag is an open-drain output capable of sinking
10 mA load current to typically 100 mV above ground.
A parasitic diode exists between the flag pins and VIN pin.
Pulling the flag pins to voltages higher than VIN will forward
bias this diode and will cause an increase in supply current.
This diode will also clamp the voltage on the flag pins to a
diode drop above VIN.
The fault flag is active (pulled low) when any of the following
conditions are present: under-voltage, current limit, or thermal
shutdown.
A 1ms (typ.) delay in reporting the fault condition prevents
erroneous fault flags and eliminates the need for an external
RC delay network.
Application Information
FILTERING
The USB specification indicates that “no less than 120 µF
tantalum capacitors” must be used on the output of each
downstream port. This bulk capacitance provides the short-
term transient current needed during a hot plug-in. Current
surges caused by the input capacitance of the down stream
device could generate undesirable EMI signals. Ferrite beads
in series with all power and ground lines are recommended
to eliminate or significantly reduce EMI.
In selecting a ferrite bead, the DC resistance of the wire used
must be kept to a minimum to reduce the voltage drop.
A 0.01 µF ceramic capacitor is recommended on each port
directly between the Vbus and ground pins to prevent EMI
damage to other components during the hot-detachment.
Adequate capacitance must be connected to the input of the
device to limit the input voltage drop during a hot-plug event
to less than 330 mV. For a few tens of µs, the host must supply
the in-rush current to the peripheral, charging its bulk capac-
itance to Vbus. This current is initially supplied by the input
capacitor. A 33 µF 16V tantalum capacitor is recommended.
In choosing the capacitors, special attention must be paid to
the Effective Series Resistance, ESR, of the capacitors to
minimize the IR drop across the capacitor's ESR.
SOFT START
To eliminate the upstream voltage droop caused by the high
in-rush current drawn by the output capacitors, the maximum
in-rush current is internally limited to 1.5A.
TRANSIENT OVER-CURRENT DELAY
High transient current is also generated when the switch is
enabled and large values of capacitance at the output have
to be rapidly charged. The in-rush currents created could ex-
ceed the short circuit current limit threshold of the device
forcing it into the current limit mode. The capacitor is charged
with the maximum available short circuit current set by the
LM3526. The duration of the in-rush current depends on the
size of the output capacitance and load current. Since this is
not a valid fault condition, the LM3526 delays the generation
of the fault flag for 1 ms. If the condition persists due to other
causes such as a short, a fault flag is generated after a 1 ms
delay has elapsed.
The LM3526's 1 ms delay in issuing the fault flag is adequate
for most applications. If longer delays are required, an RC
filter as shown in Figure 1 may be used.
10109724
FIGURE 1.
PCB LAYOUT CONSIDERATIONS
In order to meet the USB requirements for voltage drop, droop
and EMI, each component used in this circuit must be evalu-
ated for its contribution to the circuit performance. The PCB
layout rules and guidelines must be followed.
•Place the switch as close to the USB connector as
possible. Keep all Vbus traces as short as possible and use
at least 50-mil, 1 ounce copper for all Vbus traces. Solder
plating the traces will reduce the trace resistance.
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LM3526
•Avoid vias as much as possible. If vias are used, use
multiple vias in parallel and/or make them as large as
possible.
•Place the output capacitor and ferrite beads as close to
the USB connector as possible.
•If ferrite beads are used, use wires with minimum
resistance and large solder pads to minimize connection
resistance.
10109723
FIGURE 2. Self-Powered Hub Per-Port Voltage Drop
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LM3526
Typical Applications
10109725
FIGURE 3. Dual-Port USB Self-Powered Hub
10109726
FIGURE 4. Soft-Start Application (Single port shown)
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LM3526
10109727
FIGURE 5. In-rush Current-limit Application
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LM3526
Physical Dimensions inches (millimeters) unless otherwise noted
See Order Information Table
NS Package Number M08A
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LM3526
Notes
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LM3526
Notes
LM3526 Dual Port USB Power Switch and Over-Current Protection
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