NSC LM3526MX-L

LM3526
Dual Port USB Power Switch and Over-Current
Protection
General Description
Features
The LM3526 provides Universal Serial Bus standard power
switch and over-current protection for all host port applications. 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 dissipating 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.
n
n
n
n
n
n
n
n
n
n
n
n
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
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 In-rush Limiting
n General Purpose High Side Switch Applications
Typical Operating Circuit and Connection Diagram
DS101097-2
LM3526-H
DS101097-1
DS101097-40
DS101097-28
LM3526-L
© 2000 National Semiconductor Corporation
DS101097
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LM3526 Dual Port USB Power Switch and Over-Current Protection
February 2000
LM3526
Ordering Information
Part Number
Enable, Delivery Option
LM3526M-H
Active High Enable, 95 units per rail
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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2
Package Type
SO-8,
NS Package
Number M08A
Operating Ratings
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage Range
2.7V to 5.5V
Operating Ambient Range
−40˚C to 85˚C
Supply Voltage
−0.3V to 6V
Operating Junction Temperature
Range
Output Voltage
−0.3V to 6V
Storage Temperature Range
Voltage at All Other Pins
−0.3V to 5.5V
Power Dissipation (TA = 25˚C)
(Note 2)
700 mW
TJMAX (Note 2)
160˚C
−40˚C to 125˚C
−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
VIN = 5V, IOUT = 500mA, each switch
VIN = 2.7V, IOUT = 500mA, each switch
Min
RON
On Resistance
IOUT
OUT pins continuous
output current
Each Output
0.5
ISC
Short Circuit Output
Current
Each Output (enable into Load) (Note 4)
VOUT = 4.0V
VOUT = 0.1V
0.5
OCTHRESH
Over-current Threshold
ILEAK
OUT pins Output
Leakage Current
RFO
FLAG Output Voltage
IFO = 10 mA, VIN
= 3.3V
= 2.7V
IEN
EN/EN Leakage Current
VEN/VEN = 0V or VEN/VEN = VIN
−0.5
VIH
EN/EN Input Logic High
(Note 5)
2.4
(Note 5)
VIL
EN/EN Input Logic Low
VUVLO
Under-Voltage Lockout
Threshold
IDDOFF
Supply Current
Max
100
140
110
180
Units
mΩ
A
A
VEN = VIN (LM3526-L)
VEN = 0V (LM3526-H)
IFO = 10 mA, VIN = 5.0V
IFO = 10 mA, VIN
Typ
1.2
1
1.9
1.5
2.2
3.2
A
0.01
10
µA
10
25
11
35
12
40
0.5
1.9
1.7
µA
V
0.8
1.8
Switch-Off
−40˚C ≤ TJ ≤ 85˚C
Ω
V
V
0.2
1
2
µA
200
µA
IDDON
Supply Current
Switch-On
115
ThSD
Over-temperature
Shutdown Threshold
150
145
135
IFH
Error Flag Leakage
Current
TJ Increasing, with no shorted output
TJ Increasing, with shorted output (s)
TJ Decreasing (Note 4)
Vflag = 5V
0.01
˚C
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
Absolute Maximum Ratings (Note 1)
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
tr
OUT Rise Time
RL = 10Ω
100
µs
tf
OUT 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 Description
Pin Number
Pin Name
1, 4
ENA, ENB
(LM3526-L)
ENA, ENB
(LM3526-H)
2, 3
FLAG A
FLAG B
6
GND
7
IN
8, 5
OUT A
OUT B
Pin Function
Enable (Input): Logic-compatible enable inputs.
Fault Flag (Output): Active-low, open-drain outputs. Indicates overcurrent, UVLO or thermal
shutdown. *See application section for more information.
Ground
Supply Input: This pin is the input to the power switch and the supply voltage for the IC.
Switch Output: These pins are the outputs of the high side switch.
Typical Application Circuit
DS101097-3
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VIN = 5.0V, IL = 500 mA, TA = 25˚C unless otherwise specified.
RON vs Temperature
RON vs Temperature
DS101097-5
DS101097-4
Quiescent Current vs Input Voltage
Quiescent Current vs Temperature
DS101097-6
Current Limit vs Output Voltage
DS101097-7
OC Threshold vs Temperature
DS101097-8
DS101097-9
5
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LM3526
Typical Performance Characteristics
LM3526
Typical Performance Characteristics
VIN = 5.0V, IL = 500 mA, TA = 25˚C unless otherwise
specified. (Continued)
Fault Flag Delay vs Temperature
Fault Flag Delay vs Temperature
DS101097-35
Under Voltage Lockout (UVLO)
DS101097-36
Under Voltage Lockout Threshold vs Temperature
DS101097-34
DS101097-37
Over Current/Current Limit Response*
Short Circuit Response with
Thermal Cycling*
DS101097-10
DS101097-11
* Output is shorted to Ground through a 100 mΩ resistor
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VIN = 5.0V, IL = 500 mA, TA = 25˚C unless otherwise
specified. (Continued)
Turn-ON/OFF Response with
47Ω/10µF Load
Turn-ON/OFF Response with
47Ω/150µF Load
DS101097-12
Thermal Shutdown Response
(Port A output shorted*)
DS101097-13
Thermal Shutdown Response (See Notes)
DS101097-29
DS101097-14
* Port A is shorted to GND through a 100 mΩ resistor
Enable into a short
DS101097-30
7
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LM3526
Typical Performance Characteristics
LM3526
Functional Description
Application Information
The LM3526-H and LM3526-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.
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 capacitance 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.
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 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 ensures 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 removed.
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.
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 functions only when device is enabled.
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 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.
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 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.
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DS101097-24
FIGURE 1.
8
(Continued)
•
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.
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 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.
DS101097-23
FIGURE 2. Self-Powered Hub Per-Port Voltage Drop
9
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LM3526
Application Information
LM3526
Typical Applications
DS101097-25
FIGURE 3. Dual-Port USB Self-Powered Hub
DS101097-26
FIGURE 4. Soft-Start Application (Single port shown)
DS101097-27
FIGURE 5. In-rush Current-limit Application
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LM3526 Dual Port USB Power Switch and Over-Current Protection
Physical Dimensions
inches (millimeters) unless otherwise noted
See Order Information Table
NS Package Number M08A
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