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LM3525
Single Port USB Power Switch and Over-Current
Protection
LM3525 Single Port USB Power Switch and Over-Current Protection
January 2000
General Description
The LM3525 provides Universal Serial Bus standard power
switch and over-current protection for all host port applications. The single port device is ideal for Notebook PC and
Handheld PC applications that supply power to one port.
A 1 ms delay on fault flag output prevents erroneous overcurrent reporting caused by inrush currents during the
hot-plug events.
The LM3525 accepts an input voltage between 2.7V and
5.5V allowing use as a device-based inrush current limiter
for 3.3V USB peripherals, as well as Root and Self-Powered
Hubs at 5.5V. The Enable input accepts both 3.3V and 5.0V
logic thresholds.
The small size, low R
LM3525 a good choice for root hubs as well as ganged
power control in space-critical self-powered hubs.
, and 1 ms fault flag delay make the
ON
Features
n 1 ms Fault Flag Delay During Hot-Plug Events
n Smooth Turn-On Eliminates Inrush Induced Voltage
Drop
n UL Recognized Component: REF
n 1A Nominal Short Circuit Output Current Protects
Notebook PC Power Supplies
n Thermal Shutdown Protects Device in Direct Short
Condition
n 500mA Minimum Continuous Load Current
n Small SO-8 Package Minimizes Board Space
n 2.7V to 5.5V Input Voltage Range
n Switch Resistance ≤ 120 mΩ Max. at V
n 1µA Max Standby Current
n 100 µA Max Operating Current
n Undervoltage Lockout (UVLO)
Applications
n Universal Serial Bus (USB) Root Hubs including
Desktop and Notebook PC
n USB Monitor Hubs
n Other Self-Powered USB Hub Devices
n High Power USB Devices Requiring Inrush Limiting
n General Purpose High Side Switch Applications
Typical Operating Circuit and Connection Diagram
#
205202
=
5V
IN
DS101055-2
LM3525M-L
DS101055-1
DS101055-31
DS101055-30
LM3525M-H
© 2000 National Semiconductor Corporation DS101055 www.national.com
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Ordering Information
LM3525
Part Number Enable, Delivery Option Package Type
LM3525M-H Active High Enable, 95 units per rail
LM3525M-L Active Low Enable, 95 units per rail
LM3525MX-H Active High Enable, 2500 units per reel
LM3525MX-L Active Low Enable, 2500 units per reel
SO-8,
NS Package
Number M08A
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LM3525
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National SemiconductorSalesOffice/
Distributors for availability and specifications.
Supply Voltage −0.3V to 6.0V
Output Voltage −0.3V to 6.0V
Voltage at All Other Pins −0.3V to 5.5V
Power Dissipation (T
(Note 2) 700 mW
T
(Note 2) 150˚C
JMAX
= 25˚C)
A
Operating Ratings
Supply Voltage Range 2.7 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) 2 kV
DC Electrical Characteristics
Limits in standard typeface are for T
less otherwise specified: V
=
IN
Symbol Parameter Conditions Min Typ Max Units
R
I
ON
OUT
On-Resistance
OUT pins continuous output
current
I
SC
I
LEAK
Short Circuit Output Current (Note 4) 0.5 1.0 1.5 A
OUT pins Output Leakage
Current
OC
R
FO
I
EN
V
IH
V
IL
V
UVLO
I
DDOFF
I
DDON
Th
THRESH
SD
Over-current Threshold 2.25 3.2 A
FLAG Output Resistance
EN/EN Leakage Current EN/EN = 0V or EN/EN = V
EN/EN Input Voltage (Note 5) 2.4 1.9 V
EN/EN Input Voltage (Note 5) 1.7 0.8 V
Under-Voltage Lockout V
Supply Current Switch OFF 0.05 1 µA
Supply Current Switch ON 65 100 µA
Overtemperature Shutdown
Threshold (Note 4)
I
FH
Error Flag Leakage Current V
=
25˚C, and limits in boldface type apply over the full operating temperature range. Un-
J
5.0V, EN=0V (LM3525-L) or EN=V
IN to Out pins
=
V
5V
IN
=
2.7V
V
IN
EN=VIN(LM3525-L) or
EN=GND (LM3525-H),
I
= 10 mA, V
FO
= 10 mA, V
I
FO
=
IN
=
V
IN
Increasing
Decreasing
IN
IN
TJIncreasing
Decreasing
T
J
=
5V 0.1 1 µA
FLAG
(LM3525-H).
IN
80
120
0.5 A
0.15 10 µA
=
5V 6 25
=
2.7V 8 40
IN
−0.5 0.5 µA
1.9
1.8
135
125
120
160
mΩ
Ω
V
˚C
˚C
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AC Electrical Characteristics
Limits in standard typeface are for T
LM3525
less otherwise specified: V
=
IN
Symbol Parameter Conditions Min Typ Max Units
t
r
t
f
t
ON
t
OFF
t
OC
Note 1: Absolute Maximum Ratings indicate limits beyondwhich damage to the device may occur. Electrical specifications do not apply when operating the device
beyond its rated operating conditions. Products are not tested under negative Absolute Maximum conditions.
Note 2: The maximum power dissipation must be derated at elevated temperatures and is dictated by T
bient thermal resistance), and T
given in the Absolute Maximum Ratings, which ever is lower. The thermal resistance θ
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.
Note 4: Thermal shutdown will protect the device from permanent damage.
Note 5: For the LM3525-L, OFF is EN ≥ 2.4V and ON is EN ≤ 0.8V. For the LM3525-H, OFF is EN ≤ 0.8V and ON is EN ≥ 2.4V
OUT Rise Time RL=10Ω 200 µs
OUT Fall Time RL=10Ω 20 µs
Turn on Delay, EN to OUT RL=10Ω 200 µs
Turn off Delay, EN to OUT RL=10Ω 20 µs
Over Current Flag Delay RL=0 1 ms
(ambient temperature). The maximum allowable power dissipation at any temperature is P
A
5.0V.
=
25˚C, and limits in boldface type apply over the full operating temperature range. Un-
J
(maximum junction temperature), θJA(junction to am-
JMAX
of the LM3525 in the SO-8 package is 150˚C/W.
JA
DMAX
=
(T
JMAX−TA
)/θJAor the number
Pin Description
Pin Number Pin Name Pin Function
1EN
(LM3525-L)
EN
(LM3525-H)
2 FLG Fault Flag (Output): Active-low, open-drain output. Indicates overcurrent, UVLO and thermal
3 GND Ground
4, 5 NC Not internally connected.
7 IN Supply Input: This pin is the input to the power switch and the supply voltage for the IC.
6, 8 OUT Switch Output: This pin is the output of the high side switch. Pins6&8must be tied together.
Enable (Input): Logic-compatible enable input.
shutdown.
Typical Application Circuit
DS101055-3
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LM3525
Typical Performance Characteristics V
ON
vs V
IN
DS101055-4
RDS
Current Limit vs Temperature
=
5.0V, I
IN
=
500 mA, T
L
=
25˚C unless otherwise specified.
A
RDSONvs Temperature
Over Current Threshold vs Temperature
DS101055-5
Delay vs Temperature
DS101055-6
DS101055-8
DS101055-7
UVLO Threshold
DS101055-9
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Typical Performance Characteristics V
specified. (Continued)
LM3525
=
5.0V, I
IN
=
500 mA, T
L
=
25˚C unless otherwise
A
Short Circuit Response
Turn-ON/OFF Delay and Rise Time/Fall Time
DS101055-10
Under Voltage Lock Out (UVLO)
DS101055-11
Short Circuit Current
DS101055-12
DS101055-13
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Functional Description
The LM3525-H and LM3525-L are high side P-Channel
switches with active-high and active-low enable inputs, respectively. Fault conditions turn off and inhibit turn-on of the
output transistor and activate the open-drain error flag transistor 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 drain of the output MOSFET. In a typical
application circuit, current flows through the switch from IN to
OUT towards the load.
If V
is greater than VINwhen the switch is enabled, cur-
OUT
rent will flow from OUT to IN since the MOSFET is bidirectional.
THERMAL SHUTDOWN
LM3525 is internally protected against excessive power dissipation. In the event of a shorted output or heavy loads that
could elevate the die temperature to above approximately
135˚C, the thermal shutdown circuit of the LM3525 will be
activated and the power switch turned off.
The switch is turned on after die temperature drops by 10˚C.
This built-in temperature hysteresis prevents undesirable oscillation of the thermal protection circuit and allows the device to reset itself after it is cooled down.
UNDERVOLTAGE LOCKOUT
UVLO prevents the MOSFET switch from turning on until input voltage exceeds 1.9V.
UVLO shuts off the MOSFET switch and signals the fault flag
if input voltage drops below 1.8V. UVLO functions 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 limit the maximum current to 1.0A typical.
In selecting a ferrite bead, the DC resistance of the wire used
must be kept to minimum to reduce the voltage drop.
A 0.01 µF ceramic capacitor is recommended on each port
directly between the V
and ground pins to prevent EMI
bus
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 inrush current to the peripheral, charging its bulk capacitance to V
. This current is initially supplied by the in-
bus
put 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 inrush
current is internally limited to 1.0A.
TRANSIENT OVER-CURRENT DELAY
In USB applications, it is required that output bulk capacitance is utilized to support hot-plug events. During hot-plug
events, inrush currents may also cause the flag to go active.
Since these conditions are not valid over-current faults, the
USB controller must ignore the flag during these events.
High transient current is also generated when switch is enabled and large values of capacitance at the output have to
be rapidly charged. The inrush 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 LM3525. The duration of the inrush current depends
on the size of the output capacitance and load current. Since
this is not a valid fault condition, the LM3525 delays the generation of the fault flag for 1 ms. If condition persists due to
other causes such as a short, a fault flag is generated after
a 1 ms delay has elapsed.
The LM3525’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.
LM3525
FAULT FLAG
The fault flag is an open-drain output capable of sinking
10 mA load current to typically 60 mV above ground.
The fault flag is active (pulled low) when any of the following
conditions are present: undervoltage, current limit, or thermal shutdown.
A 1ms delay in reporting fault condition prevents erroneous
fault flags and eliminates the need for 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.
DS101055-24
FIGURE 1. Transient Fitter
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 as
shown in
Figure 2
. The PCB layout rules and guidelines
must be followed.
Place the switch as close to the USB connector as pos-
•
sible. Keep all V
least 50-mil, 1 ounce copper for all V
traces as short as possible and use at
bus
traces. Solder
bus
plating the traces will reduce the trace resistance.
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Application Information (Continued)
Avoid vias as much as possible. If vias are used, use mul-
•
LM3525
tiple 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.
FIGURE 2. Self-Powered Hub Per-Port Voltage Drop
If ferrite beads are used, use wires with minimum resis-
•
tance and large solder pads to minimize connection resistance.
DS101055-23
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Typical Applications
LM3525
DS101055-25
FIGURE 3. SIngle-Port USB Self-Powered Hub
FIGURE 4. Soft-Start Application
FIGURE 5. Inrush Current-limit Application
DS101055-26
DS101055-27
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Physical Dimensions inches (millimeters) unless otherwise noted
For Order Numbers , see Ordering Information Table
NS Package Number M08A
LM3525 Single Port USB Power Switch and Over-Current Protection
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