LM3526MX-L [NSC]
Dual Port USB Power Switch and Over-Current Protection; 双端口USB电源开关和过流保护
| 型号： | LM3526MX-L |
| 厂家： | 
National Semiconductor |
| 描述： | Dual Port USB Power Switch and Over-Current Protection |
| 文件： | 总11页 (文件大小：326K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
February 2000
LM3526
Dual Port USB Power Switch and Over-Current
Protection
General Description
Features
n 1 ms fault flag delay filters Hot-Plug events
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.
n Smooth turn-on eliminates in-rush induced voltage drop
n UL recognized component: REF 205202
n 1A nominal short circuit output current protects PC
power supplies
n Thermal shutdown protects device in direct short
condition
#
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 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.
n 500mA minimum continuous load current
n Small SO-8 package minimizes board space
n 2.7V to 5.5V input voltage range
n 140 mΩ Max. switch resistance
n 1 µA Max. standby current
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.
n 200 µA Max. operating current
n Under-voltage lockout (UVLO)
Applications
n Universal Serial Bus (USB) Root Hubs including
Desktop and Notebook PC
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 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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Ordering Information
Part Number
Enable, Delivery Option
Active High Enable, 95 units per rail
Active Low Enable, 95 units per rail
Package Type
LM3526M-H
LM3526M-L
LM3526MX-H
LM3526MX-L
SO-8,
NS Package
Number M08A
Active High Enable, 2500 units per reel
Active Low Enable, 2500 units per reel
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2
Absolute Maximum Ratings (Note 1)
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
Operating Junction Temperature
Range
Supply Voltage
−0.3V to 6V
−0.3V to 6V
−40˚C to 125˚C
−65˚C to +150˚C
Output Voltage
Storage Temperature Range
Voltage at All Other Pins
−0.3V to 5.5V
Lead Temperature
Power Dissipation (TA = 25˚C)
(Note 2)
(Soldering, 5 seconds)
260˚C
700 mW
160˚C
ESD Rating (Note 3)
ESD Rating Output Only
2kV
8kV
TJMAX (Note 2)
DC Electrical Characteristics
=
Limits in standard typeface are for TJ 25˚C, and limits in boldface type apply over the full operating temperature range. Un-
=
=
=
less otherwise specified: VIN 5.0V, VEN 0V (LM3526-L) or VEN VIN (LM3526-H).
Symbol Parameter Conditions
Min
Typ
100
110
Max
140
180
Units
mΩ
A
=
=
VIN 5V, IOUT 500mA, each switch
RON
IOUT
ISC
On Resistance
=
=
VIN 2.7V, IOUT 500mA, each switch
OUT pins continuous
output current
Each Output
0.5
Short Circuit Output
Current
Each Output (enable into Load) (Note 4)
VOUT 4.0V
A
=
0.5
1.2
1
1.9
1.5
=
VOUT 0.1V
OCTHRESH Over-current Threshold
2.2
3.2
10
A
ILEAK
OUT pins Output
Leakage Current
VEN = VIN (LM3526-L)
VEN = 0V (LM3526-H)
0.01
µA
=
IFO = 10 mA, VIN 5.0V
10
11
12
25
35
40
0.5
=
RFO
FLAG Output Voltage
IFO = 10 mA, VIN 3.3V
Ω
=
IFO = 10 mA, VIN 2.7V
IEN
EN/EN Leakage Current
EN/EN Input Logic High
EN/EN Input Logic Low
VEN/VEN = 0V or VEN/VEN = VIN
−0.5
µA
V
VIH
(Note 5)
(Note 5)
2.4
1.9
1.7
1.8
VIL
0.8
V
VUVLO
Under-Voltage Lockout
Threshold
V
IDDOFF
Supply Current
Switch-Off
0.2
1
µA
−40˚C ≤ TJ ≤ 85˚C
2
IDDON
ThSD
Supply Current
Switch-On
115
200
µA
˚C
Over-temperature
Shutdown Threshold
TJ Increasing, with no shorted output
TJ Increasing, with shorted output (s)
TJ Decreasing (Note 4)
150
145
135
=
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 T
(Maximum junction temperature), θ (junction to am-
JA
JMAX
=
bient thermal resistance), and T (ambient temperature). The maximum allowable power dissipation at any temperature is P
(T
− T )/θ or the number
A
DMAX
JMAX A JA
=
given in the Absolute Maximum Ratings, which ever is lower. θ
150˚C/W.
JA
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.
3
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AC Electrical Characteristics
=
Limits in standard typeface are for TJ 25˚C, and limits in boldface type apply over the full operating temperature range. Un-
=
less otherwise specified: VIN 5.0V.
Symbol Parameter
OUT Rise Time
Conditions
Min
Typ
100
5
Max
Units
µs
tr
tf
RL = 10Ω
RL = 10Ω
RL = 10Ω
RL = 10Ω
RL = 0
OUT Fall Time
µs
tON
tOFF
tOC
Turn on Delay, EN to OUT
Turn off Delay, EN to OUT
Over Current Flag Delay
150
5
µs
µs
1
ms
Pin Description
Pin Number
Pin Name
Pin Function
Enable (Input): Logic-compatible enable inputs.
1, 4
ENA, ENB
(LM3526-L)
ENA, ENB
(LM3526-H)
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
7
GND
IN
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.
8, 5
OUT A
OUT B
Typical Application Circuit
DS101097-3
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=
=
=
Typical Performance Characteristics VIN 5.0V, IL 500 mA, TA 25˚C unless otherwise specified.
RON vs Temperature
RON vs Temperature
DS101097-5
DS101097-7
DS101097-9
DS101097-4
DS101097-6
DS101097-8
Quiescent Current vs Input Voltage
Quiescent Current vs Temperature
Current Limit vs Output Voltage
OC Threshold vs Temperature
5
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=
=
=
Typical Performance Characteristics VIN 5.0V, IL 500 mA, TA 25˚C unless otherwise
specified. (Continued)
Fault Flag Delay vs Temperature
Under Voltage Lockout (UVLO)
Over Current/Current Limit Response
Fault Flag Delay vs Temperature
DS101097-35
DS101097-36
Under Voltage Lockout Threshold vs Temperature
DS101097-34
DS101097-37
*
Short Circuit Response with
*
Thermal Cycling
DS101097-10
DS101097-11
*
Output is shorted to Ground through a 100 mΩ resistor
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=
=
=
Typical Performance Characteristics 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
DS101097-13
Thermal Shutdown Response
Thermal Shutdown Response (See Notes)
*
(Port A output shorted )
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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Functional Description
Application Information
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.
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. Fer-
rite beads in series with all power and ground lines are rec-
ommended to eliminate or significantly reduce EMI.
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.
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.
If VOUT is greater than VIN when the switch is enabled, cur-
rent will flow from OUT to IN since the MOSFET is bidirec-
tional.
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 sup-
ply the in-rush current to the peripheral, charging its bulk ca-
pacitance to Vbus. This current is initially supplied by the in-
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 lim-
ited. 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. Hyster-
esis ensures that a switch turned off by thermal shutdown
will not be turned on again until the die temperature is re-
duced 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.
put capacitor.
recommended.
A 33 µF 16V tantalum capacitor is
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.
UNDERVOLTAGE LOCKOUT
UVLO prevents the MOSFET switch from turning on until in-
put voltage exceeds 1.8V (typical).
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 gen-
eration of the fault flag for 1 ms. If the condition persists due
to other causes such as a short, a fault flag is generated af-
ter a 1 ms delay has elapsed.
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.
The LM3526’s 1 ms delay in issuing the fault flag is adequate
for most applications. If longer delays are required, an RC fil-
ter as shown in Figure 1 may be used.
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 di-
ode drop above VIN
.
The fault flag is active (pulled low) when any of the following
conditions are present: under-voltage, current limit, or ther-
mal shutdown.
DS101097-24
A 1ms (typ.) delay in reporting the fault condition prevents er-
roneous fault flags and eliminates the need for an external
RC delay network.
FIGURE 1.
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8
•
Avoid vias as much as possible. If vias are used, use mul-
tiple vias in parallel and/or make them as large as pos-
sible.
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 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 re-
sistance.
•
Place the switch as close to the USB connector as pos-
sible. 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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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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10
Physical Dimensions inches (millimeters) unless otherwise noted
See Order Information Table
NS Package Number M08A
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DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:
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systems 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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