Page 1
MIC2536 Micrel
MIC2536
Dual USB Power Distribution Switch
Preliminary Information
General Description
The MIC2536 is a cost-effective high-side power switch, with
two independently controlled channels, optimized for buspowered Universal Serial Bus (USB) applications. Few external components are necessary to satisfy USB requirements.
Each switch channel of the MIC2536 will supply up to 100mA
as required for USB bus-powered downstream devices. Fault
current is limited to typically 275mA by fast-acting currentlimit circuitry which minimizes voltage droop on the upstream
port during fault conditions. A flag output with transient filter
indicates fault conditions to the local USB controller but will
ignore short flag signals resulting from inrush current during
hot plug-in events.
Soft start eliminates the momentary voltage droop on other
ports that may occur when the switch is enabled in buspowered applications. Additional features include thermal
shutdown to prevent catastrophic switch failure from highcurrent loads and 3.3V and 5V logic compatible enable
inputs.
The MIC2536 is available in active-high and active-low versions in 8-lead SOP and MSOP.
Features
• Compliant to USB specifications
• 2.7V to 5.5V operating range
• 150mA minimum continuous load current per channel
• 400mΩ typical on-resistance
• Fast-acting short circuit protection with
thermal shutdown
• Integrated filter eliminates
false overcurrent flag assertions
• Individual open-drain fault flag pins with transient filter
• 3V/5V-compatible enable inputs
• Active-high (-1) and active-low (-2) versions
• Reverse-current blocking in off mode (no “body diode”)
• Soft-start circuit
• 100µA maximum on-state supply current
• <1µA typical off-state supply current
•–40°C to 85°C operation
Applications
• USB keyboard bus-powered hubs
• USB bus-powered docking stations
• Note Book PCs
• PDAs
• General purpose power distribution applications
• PC board hot swap
• Inrush current-limiting
Typical Application
4.50V to 5.25V
Upstream V
100mA max.
BUS
V
BUS
D+
D–
GND
4.7µF
Data
1.5k
MIC5207-3.3
IN OUT
GND
10k
10k
MIC2536-23.3V USB Controller
VIN
OVERCURRENT
1µF
OVERCURRENT
ON/OFF
ON/OFF
ENA OUTA
FLGA IN
FLGB GND
ENB OUTB
Typical Two-Port Bus-Powered Hub
0.1µF
63µF
63µF
Ferrite
Beads
Data
(Two Pair)
to USB
Controller
.01µF
.01µF
V
BUS
D+
D–
GND
V
BUS
D+
D–
GND
USB
Port 1
USB
Port 2
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
March 2000 1 MIC2536
Page 2
MIC2536 Micrel
Ordering Information
Part Number Enable Temperature Range Package
MIC2536-1BM Active High –40°C to +85°C 8-Lead SOP
MIC2536-2BM Active Low –40°C to +85°C 8-Lead SOP
MIC2536-1BMM Active High –40°C to +85°C 8-Lead MSOP
MIC2536-2BMM Active Low –40°C to +85°C 8-Lead MSOP
Pin Configuration
MIC2536-x
ENA
FLGA
1
2
8
7
OUTA
IN
FLGB
ENB
Pin Description
Pin Number Pin Name Pin Function
1 ENA Enable A (Input): Channel A control input. Active high (–1) or active low (–2)
2 FLGA Flag A: (Output): Channel A open-drain fault flag output. Indicates
3 FLGB Flag B (Output): Channel B open-drain fault flag output. Indicates overcur-
4 ENB Enable B (Input): Channel B control input. Active high (–1) or active low (–2)
5 OUTB Output B: Channel B switch output.
6 GND Ground
7 IN Positive Switch and Logic Supply Input
8 OUTA Output A: Channel A switch output.
GND
3
4
6
5
OUTB
8-Lead SOP (M)
8-Lead MSOP (MM)
input.
overcurrent or thermal shutdown conditions. Overcurrent conditions must
last longer than tD in order to assert FLG.
rent or thermal shutdown conditions. Overcurrent conditions must last
longer than tD in order to assert FLG.
input.
MIC2536 2 March 2000
Page 3
MIC2536 Micrel
Absolute Maximum Ratings (Note 1)
Supply Voltage (V
Fault Flag Voltage (V
Fault Flag Current (I
Output Voltage (V
Output Current (I
Control Input (V
) .....................................................+6V
IN
)..............................................+6V
FLG
) ............................................25mA
FLG
) ..................................................+6V
OUT
)...............................Internally Limited
OUT
)................................... –0.3V to VIN +2V
EN
Operating Ratings (Note 2)
Supply Voltage (V
Ambient Operating Temperature (T
Thermal Resistance
SOP (θ
) ..........................................................160°C/W
JA
MSOP (θJA) .......................................................206°C/W
) ................................... +2.7V to +5.5V
IN
) ........ –40°C to +85°C
A
Storage Temperature (TS) ....................... –65°C to +150°C
Lead Temperature (Soldering 5 sec.) ....................... 260°C
ESD Rating, Note 3 ......................................................1kV
Electrical Characteristics
VIN = +5V; TA = 25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted
Parameter Condition Min Typ Max Units
Supply Current both switches off, OUTA–B = open, Note 4 0.75 5 µA
both switches on, OUTA–B = open, Note 4 60 100 µA
Enable Input Threshold low-to-high transition, Note 4 1.7 2.4 V
high-to-low transition, Note 4 0.8 1.5 V
Enable Input Current VEN = 0V to 5.5V 0.01 1 µA
Enable Input Capacitance Note 5 1pF
Switch Resistance single switch, I
Output Turn-On Delay, t
ON
Output Turn-On Rise Time, t
Output Turnoff Delay, t
Output Turnoff Fall Time, t
OFF
F
R
RL = 50Ω, CL = 1µF 1.5 ms
RL = 50Ω, CL = 1µF 1.4 ms
RL = 50Ω, CL = 1µF130µs
RL = 50Ω, CL = 1µF115µs
Output Leakage Current each output (switch off) 1 10 µA
Current Limit Threshold ramped load applied to enable output 500 mA
Short Circuit Current Limit each output (enabled into load), V
Current Limit Response V
Flag Response Delay, t
D
= 0V to I
OUT
VIN = 5V, apply V
VIN = 3.3V, apply V
Overtemperature Shutdown TJ increasing, Note 5 135 °C
Threshold TJ decreasing, Note 5 125 °C
Error Flag Output Resistance VIN = 5V, IL = 10mA 10 20 Ω
VIN = 3.3V, IL = 10mA 15 30 Ω
Error Flag Off Current V
Note 1. Exceeding the absolute maximum rating may damage the device.
Note 2. The device is not guaranteed to function outside its operating rating.
Note 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF.
Note 4. Off is ≤ 0.8V and on is ≥ 2.4V for the MIC2536-1. Off is ≥ 2.4V and on is ≤ 0.8V for the MIC2536-2. The enable input has approximately
200mV of hysteresis.
Note 5. Guaranteed by design. Not production tested.
= 5V 0.01 1 µA
FLAG
= 100mA 400 700 mΩ
OUT
= 0V 150 275 400 mA
OUT
OUT
= I
OUT
(short applied to output), Note 5 10 µs
LIMIT
= 0V until FLG low 5 13 20 ms
= 0V until FLG low 13 ms
OUT
March 2000 3 MIC2536
Page 4
MIC2536 Micrel
Test Circuit
V
Device
Under
Test
OUT
C
R
L
L
OUT
Functional Characteristics Test Circuit
Timing Diagrams
t
r
V
OUT
90%
10%
90%
10%
t
f
Output Rise and Fall Times
V
EN
V
OUT
50%
t
ON
90%
t
OFF
10%
Active-High Switch Delay Times (MIC2536-1)
V
EN
50%
t
OFF
t
ON
V
OUT
90%
10%
Active-Low Switch Delay Times (MIC2536-2)
MIC2536 4 March 2000
Page 5
MIC2536 Micrel
Functional Characteristics
EN
V
(10V/div)
FLG
V
(5V/div)
OUT
V
(5V/div)
OUT
I
(100mA/div)
EN
V
(10V/div)
FLG
V
(5V/div)
OUT
V
(5V/div)
Turn-On / Turnoff
(MIC2536-1)
VIN = 5V
= 4.7µF
C
IN
R
C
Time (1ms/div)
Turnoff
(MIC2536-1)
= 50Ω
L
= 1µF
L
VIN = 5V
= 4.7µF
C
IN
R
L
C
L
= 35Ω
= 10µF
EN
V
(10V/div)
FLG
V
(5V/div)
OUT
V
(5V/div)
OUT
I
(100mA/div)
EN
V
(10V/div)
FLG
V
(5V/div)
OUT
V
(5V/div)
Turn-On
(MIC2536-1)
VIN = 5V
C
Time (1ms/div)
Turn-On
(MIC2536-1)
= 35Ω
VIN = 5V
= 4.7µF
C
IN
(output current limited)
R
L
= 47µF || 10µF
C
L
= 4.7µF
IN
= 35Ω
R
L
= 10µF
C
L
OUT
I
(100mA/div)
EN
V
(10V/div)
FLG
V
(5V/div)
OUT
V
(5V/div)
OUT
I
(100mA/div)
Time (1ms/div)
(MIC2536-1)
VIN = 5V
= 4.7µF
C
IN
Time (5µs/div)
Turnoff
= 35Ω
R
L
= 47µF || 10µF
C
L
OUT
I
(100mA/div)
EN
V
(10V/div)
FLG
V
(5V/div)
OUT
V
(5V/div)
OUT
I
(200mA/div)
Time (1ms/div)
Enabled Into Short Circuit
(MIC2536-1)
t
D
VIN = 5V
= 4.7µF
C
IN
OUT = GND
C
L
Time (10ms/div)
= 0
March 2000 5 MIC2536
March 2000 5 MIC2536
Page 6
MIC2536 Micrel
EN
V
(10V/div)
FLG
V
(5V/div)
OUT
V
(5V/div)
OUT
I
(200mA/div)
Ramped Into Short Circuit
(MIC2536-1)
VIN = 5V
= 4.7µF
C
IN
= 0Ω
R
L
Thermal Shutdown
Time (100ms/div)
Current-Loop Response
(MIC2536-1)
output = open
EN
V
(10V/div)
FLG
V
(5V/div)
OUT
I
(100mA/div)
Inrush Current
= 10
C
L
(MIC2536-1)
C
= 110µF
L
= 210µF
C
L
= 310µF
C
L
= 410µF
C
L
Time (5µs/div)
VIN = 5V
= 4.7µF
C
IN
= 35Ω
R
L
OUT
V
OUT
I
(5V/div)
(1A/div)
VEN = 5V
= 5V
V
IN
= 4700µF
C
IN
= 47µF
C
L
Time (5µs/div)
output = ground
MIC2536 6 March 2000
Page 7
MIC2536 Micrel
Block Diagram
FLGA
ENA
ENB
MIC2536
CHARGE
PUMP
OSC.
CHARGE
PUMP
THERMAL
SHUTDOWN
GND
GATE
CONTROL
REFERENCE
GATE
CONTROL
1.2V
DELAY
CURRENT
LIMIT
CURRENT
LIMIT
DELAY
OUTA
IN
OUTB
FLGB
March 2000 7 MIC2536
Page 8
MIC2536 Micrel
Functional Description
The MIC2536-1 and MIC2536-2 are dual high-side switches
with active-high and active-low enable inputs, respectively.
Fault conditions turn off or inhibit turn-on of one or more of the
output transistors, depending upon the type of fault, and
activate the open-drain error flag transistors making them
sink current to ground.
Input and Output
IN (input) is the power supply connection to the logic circuitry
and the drain of each output MOSFET. OUTx (output) is the
source of each respective MOSFET. In a typical circuit,
current flows through the switch from IN to OUTx toward the
load. If V
to IN during an on-condition since the MOSFET is bidirectional when enabled.
The output MOSFET and driver circuitry are also designed to
allow the MOSFET source to be externally forced to a higher
voltage than the drain (V
disabled. In this situation, the MIC2536 prevents reverse
current flow.
Thermal Shutdown
Each output MOSFET has its own thermal sensor. If either or
both channels reach 135°C, affected channel(s) will be shut
down and flag(s) asserted. 10°C of hysteresis prevents the
switches from turning on until the die temperature drops to
125°C. Overtemperature detection functions only when at
least one switch is enabled.
The MIC2536 will automatically reset its output when the die
temperature cools to approximately 125°C. The MIC2536
output and FLG signal will continue to cycle on and off until the
device is disabled or the fault is removed.
Depending on PCB layout, package, ambient temperature,
etc., it may take several hundred milliseconds from the
occurrence of the fault to the output MOSFET being shut off.
Delay to reach thermal shutdown will be shortest with a dead
short on the output.
Current-Limit Induced Thermal Shutdown
Internal circuitry increases the output MOSFET on-resistance until the series combination of the MOSFET on-resistance and the load impedance limits output current to approximately 275mA. The resulting increase in power dissipation may cause the shorted channel to go into thermal
shutdown. In addition, even though individual channels are
thermally isolated, it is possible they may shut down when an
adjacent channel is shorted. When this is undesirable, thermal shutdown can be avoided by externally responding to the
fault and disabling the current-limited channel before the
shutdown temperature is reached. The delay between the
flag indication of a current-limit fault and thermal shutdown
will vary with ambient temperature, board layout, and load
impedance, but is typically several seconds. The USB controller must therefore recognize a fault and disable the
appropriate channel within this time.
Power Dissipation
Power dissipation depends on several factors such as the
load, PCB layout, ambient temperature and package type.
is greater than VIN, current will flow from OUT
OUT
> VIN) when the output is
OUTx
Equations that can be used to calculate power dissipation
and die temperature are found below:
Calculation of power dissipated by each channel can be
accomplished by the following equation:
= R
P
D
DS(on)
× (I
OUT
2
)
Total power dissipation of the device will be the summation
of PD for both channels. To relate this to junction
temperature, the following equation can be used:
T
= PD × θJA + T
j
A
where:
Tj = junction temperature
TA = ambient temperature
θ
= is the thermal resistance of the package
JA
Current Sensing and Limiting
The current-limit threshold is preset internally. The preset
level prevents damage to the output MOSFET and external
load but allows a minimum current of 150mA through the
output MOSFET of each channel.
The current-limit circuit senses a portion of the output FET
switch current. The current sense resistor shown in the block
diagram is virtual and has no voltage drop. The reaction to an
overcurrent condition varies with the following three scenarios:
Switch Enabled into Short Circuit
If a switch is enabled into a heavy load or short circuit, the
switch immediately goes into a constant-current mode, reducing the output voltage. The FLG is asserted indicating an
overcurrent condition.
Short Circuit Applied to Output
When a heavy load or short circuit is applied to an enabled
switch, a large transient current may flow until the currentlimit circuitry responds. Once this occurs, the device limits
current to less than the maximum short-circuit current-limit
specification.
Current-Limit Response Ramped Load
The MIC2536 current-limit profile exhibits a small foldback
effect of approximately 100mA. Once this current-limit threshold is exceeded the device enters constant-current mode.
This constant current is specified as the short-circuit currentlimit in the “Electrical Characteristics” table. It is important to
note that the MIC2536 will deliver load current up to the
current-limit threshold before entering current-limited operation.
Fault Flag
FLGx is an open-drain N-channel MOSFET output. Fault
flags are active (low) for current-limit or thermal shutdown. In
the case where an overcurrent condition occurs, FLG will be
asserted only after the flag response delay time, tD has
elapsed. This ensures that FLG is asserted only upon valid
overcurrent conditions and that erroneous error reporting is
eliminated. False overcurrent conditions can occur during
hot-plug events when a highly capacitive load is connected
and causes a high transient inrush current that exceeds the
current-limit threshold. The flag response delay time is typically 12ms.
MIC2536 8 March 2000
Page 9
MIC2536 Micrel
Applications Information
Supply Filtering
A 0.1µF to 1µF bypass capacitor from IN to GND, located at
the device, is strongly recommended to control supply transients. Without a bypass capacitor, an output short may
cause sufficient ringing on the input (from supply lead inductance) to damage internal control circuitry.
Input or output transients must not exceed the absolute
maximum supply voltage (V
duration.
2.7V to 5.5V
MIC2536
ENA OUTA
FLGA
FLGB GND
ENB OUTB
IN
Figure 1. Supply Bypassing
= 6V) even for a short
IN(max)
V
IN
0.1µF to 1µF
Enable Input
EN must be driven logic high or logic low for a clearly defined
input. Floating the input may cause unpredictable operation.
EN should not be allowed to go negative with respect to GND.
Printed Circuit Board Hot-Plug
The MIC2536 is an ideal inrush current-limiter for hot-plug
applications. Due to the integrated charge pump, the MIC2536
presents a high impedance when off and slowly becomes a
low impedance as it turns on. This “soft-start” feature effectively isolates power supplies from highly capacitive loads by
reducing inrush current. Figure 2 shows how the MIC2536
may be used in a hot-plug card application.
Overcurrent Transients
The MIC2536 incorporates an internal circuit designed to
prevent FLG from being asserted due to transient inrush
current. Overcurrent events <12ms (typ.) will not assert FLG.
In case of large capacitive loads (i.e., >430µF), the length of
the transient due to inrush current may exceed the delay
provided by the integrated filter. Since this inrush current
exceeds the current-limit delay specification, FLG will be
asserted during this time. To prevent the logic controller from
responding to FLG being asserted, an external RC filter, as
shown in Figure 3, can be used to filter out transient FLG
assertion. The value of the RC time constant should be
selected to match the length of the transient, minus flag tD.
V
CC
to "Hot"
Receptacle
GND
MIC2536-2
18
27
0.1
µF
36
4
OUTA
EN
FLGA
FLGB GND
OUTB
ENB
Adaptor Card
IN
5
Figure 2. Hot-Plug Card Application
V+
Logic Controller
OVERCURRENT
10k
R
C
MIC2536
18
EN OUTA
27
FLGA
36
FLGB GND
45
ENB OUTB
IN
Figure 3. Transient Filter
C
BULK
Backend
Function
March 2000 9 MIC2536
Page 10
MIC2536 Micrel
Universal Serial Bus (USB) Power Distribution
Applications
The MIC2536 is ideally suited for USB (Universal Serial Bus)
power distribution applications. For Bus-Powered hubs, USB
requires that each downstream port be switched on or off
under control by the host. Up to four downstream ports each
capable of supplying 100mA at 4.4V minimum are allowed. In
additon, to reduce voltage droop on the upstream bus the hub
must consume only 100mA max at start-up until it enumerates with the host prior to requesting more power. The same
requirements apply for bus-powered peripherals that have no
downstream ports. Figure 4 shows a two-port bus-powered
hub.
Bus-Powered Hub Port Switching
The USB Specification requires that bus-powered hubs implement port switching on either a ganged or individual basis.
The specific implementation must be reported via the Hub
Descriptor Status Register. Individual port switching has
advantages in that a fault on one port will not prevent the other
ports from operating correctly. In addition, a soft-start circuit
must be included in order to reduce inrush currents when the
switch is enabled. To meet this requirement, the MIC2536
has been designed to slowly ramp its output.
Suspend Current
Universal Serial Bus Specification
places a maximum sus-
pend current requirement of 500µA on devices. For hubs,
Universal Serial Bus Specification Revision 1.1
clarifies this
issue. Revision 1.1, section 7.2.3, stipulates that the maximum suspend current for a configured hub is 2.5mA. This
number is derived by allocating 500µA for up to four downstream ports plus 500µA for the hub’s internal functions. A
nonconfigured hub is considered a low-power device and
may not consume more than 500µA. In a nonconfigured state
all downstream devices will be switched off. In most cases, a
nonconfigured hub is not a practical state for the system.
Therefore, the 2.5mA specification is the applicable target
specification for the suspend state. In a bus-powered hub
with less than 4 ports, the hub may use the additional current
for internal functions.
The 500µA worst case suspend current must be further
divided among the data port termination resistors and internal
functions. The termination resistors will consume
3.6V ÷ (16.5KΩ – 5%) = 230µA. This leaves only 270µA for
internal functions. Assuming 100µA as the maximum USB
controller suspend current, 170µA remains for the rest of the
system. The MIC2536 will consume 100µA maximum, leaving a margin of 70µA.
USB Voltage Regulation
USB specifications require a minimum downstream voltage
supply of 4.40V from a bus-powered hub port (See
tion Note 17
for details). The USB specification allows for a
Applica-
100mV drop across the hub, leaving 250mV for PCB, upstream cable, and connector resistance. Therefore, the onresistance of the switch for each port, not including PCB
resistance, must be <100mV ÷ 100mA = 1Ω. The MIC2536
has a maximum on-resistance of 700mΩ, which easily satisfies this requirement.
Overcurrent Indication
The USB Specification does not require bus-powered hubs to
report overcurrent conditions to the host, since the hub is
already current-limited at the upstream port. However, if it is
desired to report overcurrent, the Hub Descriptor Status
Register must be programmed to indicate this. The MIC2536
provides a flag output for this application.
Ferrite
Beads
Data
(Two Pair)
to USB
Controller
.01µF
.01µF
V
BUS
D+
D–
GND
V
BUS
D+
D–
GND
USB
Port 1
USB
Port 2
4.50V to 5.25V
Upstream V
100mA max.
BUS
V
D+
D–
GND
BUS
Data
4.7µF
1.5k
MIC5207-3.3
IN OUT
GND
VIN
1µF
10k
10k
ON/OFF
OVERCURRENT
OVERCURRENT
ON/OFF
MIC2536-23.3V USB Controller
ENA OUTA
FLGA IN
FLGB GND
ENB OUTB
63µF
0.1µF
63µF
Figure 4. USB Two-Port Bus-Powered Hub
MIC2536 10 March 2000
Page 11
MIC2536 Micrel
Package Information
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
0.064 (1.63)
0.045 (1.14)
0.122 (3.10)
0.112 (2.84)
0.036 (0.90)
0.032 (0.81)
0.050 (1.27)
TYP
0.197 (5.0)
0.189 (4.8)
0.020 (0.51)
0.013 (0.33)
0.0098 (0.249)
0.0040 (0.102)
SEATING
PLANE
8-Lead SOP (M)
0.199 (5.05)
0.187 (4.74)
0.120 (3.05)
0.116 (2.95)
0.043 (1.09)
0.038 (0.97)
DIMENSIONS:
INCHES (MM)
0°–8°
0.012 (0.30) R
45°
0.050 (1.27)
0.016 (0.40)
0.244 (6.20)
0.228 (5.79)
DIMENSIONS:
INCH (MM)
0.010 (0.25)
0.007 (0.18)
0.007 (0.18)
0.005 (0.13)
0.012 (0.03)
0.0256 (0.65) TYP
0.008 (0.20)
0.004 (0.10)
8-Lead MSOP (MM)
5° MAX
0° MIN
0.012 (0.03) R
0.039 (0.99)
0.035 (0.89)
0.021 (0.53)
March 2000 11 MIC2536
Page 12
MIC2536 Micrel
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com
This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or
other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.
© 2000 Micrel Incorporated
MIC2536 12 March 2000
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