LM3526
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
overcurrent reporting caused by in-rush currents during hot-
plug events.
The dual stage thermal protection circuit in the LM3526
provides individual protection to each switch and the entire
device. In a short-circuit/over-current event, the switch dis-
sipating 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 R
ON
, 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
nCompatible with USB1.1 and USB 2.0
n1 ms fault flag delay filters Hot-Plug events
nSmooth turn-on eliminates in-rush induced voltage drop
nUL recognized component: REF# 205202
n1A nominal short circuit output current protects PC
power supplies
nThermal shutdown protects device in direct short
condition
n500mA minimum continuous load current
nSmall SO-8 package minimizes board space
n2.7V to 5.5V input voltage range
n140 mΩMax. switch resistance
n1 µA Max. standby current
n200 µA Max. operating current
nUnder-voltage lockout (UVLO)
Applications
nUniversal Serial Bus (USB) Root Hubs including
Desktop and Notebook PC
nUSB Monitor Hubs
nOther Self-Powered USB Hub Devices
nHigh Power USB Devices Requiring In-rush Limiting
nGeneral Purpose High Side Switch Applications
Typical Operating Circuit and Connection Diagram
10109701
10109702
LM3526-H
10109740
10109728
LM3526-L
March 2005
LM3526 Dual Port USB Power Switch and Over-Current Protection
© 2005 National Semiconductor Corporation DS101097 www.national.com
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
LM3526
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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 (T
A
= 25˚C)
(Note 2) 700 mW
T
JMAX
(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 T
J
= 25˚C, and limits in boldface type apply over the full operating temperature range. Un-
less otherwise specified: V
IN
= 5.0V, V
EN
= 0V (LM3526-L) or V
EN
=V
IN
(LM3526-H).
Symbol Parameter Conditions Min Typ Max Units
R
ON
On Resistance V
IN
= 5V, I
OUT
= 500mA, each switch 100 140 mΩ
V
IN
= 2.7V, I
OUT
= 500mA, each switch 110 180
I
OUT
OUT pins continuous
output current
Each Output 0.5 A
I
SC
Short Circuit Output
Current
Each Output (enable into Load) (Note 4)
V
OUT
= 4.0V
V
OUT
= 0.1V
0.5 1.2
1
1.9
1.5
A
OC
THRESH
Over-current Threshold 2.2 3.2 A
I
LEAK
OUT pins Output Leakage
Current
V
EN
=V
IN
(LM3526-L)
V
EN
= 0V (LM3526-H)
0.01 10 µA
R
FO
FLAG Output Voltage
I
FO
= 10 mA, V
IN
= 5.0V 10 25
ΩI
FO
= 10 mA, V
IN
= 3.3V 11 35
I
FO
= 10 mA, V
IN
= 2.7V 12 40
I
EN
EN/EN Leakage Current V
EN
/V
EN
=0VorV
EN
/V
EN
=V
IN
−0.5 0.5 µA
V
IH
EN/EN Input Logic High (Note 5) 2.4 1.9 V
V
IL
EN/EN Input Logic Low (Note 5) 1.7 0.8 V
V
UVLO
Under-Voltage Lockout
Threshold
1.8 V
I
DDOFF
Supply Current Switch-Off
−40˚C ≤T
J
≤85˚C
0.2 1
2
µA
I
DDON
Supply Current Switch-On 115 200 µA
Th
SD
Over-temperature
Shutdown Threshold
T
J
Increasing, with no shorted output
T
J
Increasing, with shorted output (s)
T
J
Decreasing (Note 4)
150
145
135
˚C
I
FH
Error Flag Leakage
Current
V
flag
= 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 =(T
JMAX −T
A)/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 kΩresistor 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.
LM3526
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AC Electrical Characteristics
Limits in standard typeface are for T
J
= 25˚C, and limits in boldface type apply over the full operating temperature range. Un-
less otherwise specified: V
IN
= 5.0V.
Symbol Parameter Conditions Min Typ Max Units
t
r
OUT Rise Time R
L
=10Ω100 µs
t
f
OUT Fall Time R
L
=10Ω5µs
t
ON
Turn on Delay, EN to OUT R
L
=10Ω150 µs
t
OFF
Turn off Delay, EN to OUT R
L
=10Ω5µs
t
OC
Over Current Flag Delay R
L
=0 1 ms
Pin Description
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
LM3526
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Typical Performance Characteristics
V
IN
= 5.0V, I
L
= 500 mA, T
A
= 25˚C unless otherwise
specified.
R
ON
vs Temperature R
ON
vs Temperature
10109704 10109705
Quiescent Current vs Input Voltage Quiescent Current vs Temperature
10109706 10109707
Current Limit vs Output Voltage OC Threshold vs Temperature
10109708 10109709
LM3526
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Typical Performance Characteristics V
IN
= 5.0V, I
L
= 500 mA, T
A
= 25˚C unless otherwise
specified. (Continued)
Fault Flag Delay vs Temperature Fault Flag Delay vs Temperature
10109735 10109736
Under Voltage Lockout (UVLO) Under Voltage Lockout Threshold vs Temperature
10109734
10109737
Over Current/Current Limit Response*
Short Circuit Response with
Thermal Cycling*
10109710
* Output is shorted to Ground through a 100 mΩresistor
10109711
LM3526
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Typical Performance Characteristics V
IN
= 5.0V, I
L
= 500 mA, T
A
= 25˚C unless otherwise
specified. (Continued)
Turn-ON/OFF Response with
47Ω/10µF Load
Turn-ON/OFF Response with
47Ω/150µF Load
10109712 10109713
Thermal Shutdown Response
(Port A output shorted*) Thermal Shutdown Response (See Notes)
10109714
* Port A is shorted to GND through a 100 mΩresistor
10109729
Enable into a short
10109730
LM3526
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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
circuitry 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 V
OUT
is greater than V
IN
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 ther-
mal shutdown circuitry turns off any switch that is current
limited. Non-overloaded switches continue to function nor-
mally. If the die temperature rises above 150˚C, both
switches are turned off and both fault flag outputs are acti-
vated. Hysteresis ensures that a switch turned off by thermal
shutdown will not be turned on again until the die tempera-
ture 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 removed.
UNDERVOLTAGE LOCKOUT
UVLO prevents the MOSFET switch from turning on until
input 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 func-
tions only when device is enabled.
CURRENT LIMIT
The current limit circuit is designed to protect the system
supply, the MOSFET switches and the load from damage
caused by excessive currents. The current limit threshold is
set internally 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 V
IN
pin.
Pulling the flag pins to voltages higher than V
IN
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 V
IN
.
The fault flag is active (pulled low) when any of the following
conditions are present: under-voltage, current limit, or ther-
mal 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 recom-
mended 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 V
bus
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
capacitance to V
bus
. This current is initially supplied by the
input capacitor. A 33 µF 16V tantalum capacitor is recom-
mended.
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
exceed 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
aftera1msdelay 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.
LM3526
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Application Information (Continued)
PCB LAYOUT CONSIDERATIONS
In order to meet the USB requirements for voltage drop,
droop and EMI, each component used in this circuit must be
evaluated 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 pos-
sible. Keep all V
bus
traces as short as possible and use at
least 50-mil, 1 ounce copper for all V
bus
traces. Solder
plating the traces will reduce the trace resistance.
•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 resis-
tance and large solder pads to minimize connection
resistance.
10109723
FIGURE 2. Self-Powered Hub Per-Port Voltage Drop
LM3526
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Typical Applications
10109725
FIGURE 3. Dual-Port USB Self-Powered Hub
10109726
FIGURE 4. Soft-Start Application (Single port shown)
LM3526
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Typical Applications (Continued)
10109727
FIGURE 5. In-rush Current-limit Application
LM3526
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Physical Dimensions inches (millimeters) unless otherwise noted
See Order Information Table
NS Package Number M08A
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves
the right at any time without notice to change said circuitry and specifications.
For the most current product information visit us at www.national.com.
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WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR
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which, (a) are intended for surgical implant into the body, or
(b) support or sustain life, and whose failure to perform when
properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to result
in a significant injury to the user.
2. A critical component is any component of a life support
device or system whose failure to perform can be reasonably
expected to cause the failure of the life support device or
system, or to affect its safety or effectiveness.
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LM3526 Dual Port USB Power Switch and Over-Current Protection
