March 2000
1
MIC2536
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 bus-
powered Universal Serial Bus (USB) applications. Few exter-
nal 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 current-
limit 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 bus-
powered applications. Additional features include thermal
shutdown to prevent catastrophic switch failure from high-
current loads and 3.3V and 5V logic compatible enable
inputs.
The MIC2536 is available in active-high and active-low ver-
sions in 8-lead SOP and MSOP.
Typical Application
ENA
OUTA
FLGA
IN
FLGB
GND
ENB
OUTB
MIC2536-2
3.3V USB Controller
0.1F
V
BUS
D+
D
GND
Data
(Two Pair)
V
BUS
D+
D
GND
USB
Port 2
USB
Port 1
MIC5207-3.3
63F
63F
Ferrite
Beads
4.50V to 5.25V
Upstream V
BUS
100mA max.
V
BUS
D+
D
GND
Data
4.7F
1F
to USB
Controller
1.5k
ON/OFF
OVERCURRENT
OVERCURRENT
ON/OFF
VIN
10k
IN
OUT
GND
.01F
.01F
10k
Typical Two-Port Bus-Powered Hub
Features
Compliant to USB specifications
2.7V to 5.5V operating range
150mA minimum continuous load current per channel
400m
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
100
A maximum on-state supply current
<1
A 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
Micrel, Inc. 1849 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 944-0970 http://www.micrel.com
MIC2536
2
March 2000
MIC2536
Micrel
Pin Description
Pin Number
Pin Name
Pin Function
1
ENA
Enable A (Input): Channel A control input. Active high (1) or active low (2)
input.
2
FLGA
Flag A: (Output): Channel A open-drain fault flag output. Indicates
overcurrent or thermal shutdown conditions. Overcurrent conditions must
last longer than t
D
in order to assert FLG.
3
FLGB
Flag B (Output): Channel B open-drain fault flag output. Indicates overcur-
rent or thermal shutdown conditions. Overcurrent conditions must last
longer than t
D
in order to assert FLG.
4
ENB
Enable B (Input): Channel B control input. Active high (1) or active low (2)
input.
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.
Pin Configuration
1
2
3
4
8
7
6
5
OUTA
IN
GND
OUTB
ENA
FLGA
FLGB
ENB
MIC2536-x
8-Lead SOP (M)
8-Lead MSOP (MM)
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
March 2000
3
MIC2536
MIC2536
Micrel
Electrical Characteristics
V
IN
= +5V; T
A
= 25
C, bold values indicate 40
C
T
A
+85
C; unless noted
Parameter
Condition
Min
Typ
Max
Units
Supply Current
both switches off, OUTAB = open, Note 4
0.75
5
A
both switches on, OUTAB = open, Note 4
60
100
A
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
V
EN
= 0V to 5.5V
0.01
1
A
Enable Input Capacitance
Note 5
1
pF
Switch Resistance
single switch, I
OUT
= 100mA
400
700
m
Output Turn-On Delay, t
ON
R
L
= 50
, C
L
= 1
F
1.5
ms
Output Turn-On Rise Time, t
R
R
L
= 50
, C
L
= 1
F
1.4
ms
Output Turnoff Delay, t
OFF
R
L
= 50
, C
L
= 1
F
130
s
Output Turnoff Fall Time, t
F
R
L
= 50
, C
L
= 1
F
115
s
Output Leakage Current
each output (switch off)
1
10
A
Current Limit Threshold
ramped load applied to enable output
500
mA
Short Circuit Current Limit
each output (enabled into load), V
OUT
= 0V
150
275
400
mA
Current Limit Response
V
OUT
= 0V to I
OUT
= I
LIMIT
(short applied to output), Note 5
10
s
Flag Response Delay, t
D
V
IN
= 5V, apply V
OUT
= 0V until FLG low
5
13
20
ms
V
IN
= 3.3V, apply V
OUT
= 0V until FLG low
13
ms
Overtemperature Shutdown
T
J
increasing, Note 5
135
C
Threshold
T
J
decreasing, Note 5
125
C
Error Flag Output Resistance
V
IN
= 5V, I
L
= 10mA
10
20
V
IN
= 3.3V, I
L
= 10mA
15
30
Error Flag Off Current
V
FLAG
= 5V
0.01
1
A
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, 1.5k
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.
Absolute Maximum Ratings
(Note 1)
Supply Voltage (V
IN
) ..................................................... +6V
Fault Flag Voltage (V
FLG
) .............................................. +6V
Fault Flag Current (I
FLG
) ............................................ 25mA
Output Voltage (V
OUT
) .................................................. +6V
Output Current (I
OUT
) ............................... Internally Limited
Control Input (V
EN
) ................................... 0.3V to V
IN
+2V
Storage Temperature (T
S
) ....................... 65
C to +150
C
Lead Temperature (Soldering 5 sec.) ....................... 260
C
ESD Rating, Note 3 ...................................................... 1kV
Operating Ratings
(Note 2)
Supply Voltage (V
IN
) ................................... +2.7V to +5.5V
Ambient Operating Temperature (T
A
) ........ 40
C to +85
C
Thermal Resistance
SOP (
JA
) .......................................................... 160
C/W
MSOP (
JA
) ....................................................... 206
C/W
MIC2536
4
March 2000
MIC2536
Micrel
Test Circuit
Device
Under
Test
C
L
OUT
R
L
V
OUT
Functional Characteristics Test Circuit
Timing Diagrams
90%
V
OUT
10%
90%
10%
t
r
t
f
Output Rise and Fall Times
V
EN
50%
90%
V
OUT
10%
t
OFF
t
ON
Active-High Switch Delay Times (MIC2536-1)
V
EN
50%
90%
V
OUT
10%
t
OFF
t
ON
Active-Low Switch Delay Times (MIC2536-2)
March 2000
5
MIC2536
MIC2536
Micrel
March 2000
5
MIC2536
Functional Characteristics
Turn-On / Turnoff
(MIC2536-1)
I
OUT
(100mA/div)
V
EN
(10V/div)
V
OUT
(5V/div)
V
FLG
(5V/div)
V
IN
= 5V
C
IN
= 4.7
F
R
L
= 50
C
L
= 1
F
Time (1ms/div)
Turn-On
(MIC2536-1)
I
OUT
(100mA/div)
V
EN
(10V/div)
V
OUT
(5V/div)
V
FLG
(5V/div)
V
IN
= 5V
C
IN
= 4.7
F
R
L
= 35
C
L
= 10
F
Time (1ms/div)
Turnoff
(MIC2536-1)
I
OUT
(100mA/div)
V
EN
(10V/div)
V
OUT
(5V/div)
V
FLG
(5V/div)
V
IN
= 5V
C
IN
= 4.7
F
R
L
= 35
C
L
= 10
F
Time (1ms/div)
Turn-On
(MIC2536-1)
I
OUT
(100mA/div)
V
EN
(10V/div)
V
OUT
(5V/div)
V
FLG
(5V/div)
V
IN
= 5V
C
IN
= 4.7
F
(output current limited)
R
L
= 35
C
L
= 47
F || 10
F
Time (1ms/div)
Turnoff
(MIC2536-1)
I
OUT
(100mA/div)
V
EN
(10V/div)
V
OUT
(5V/div)
V
FLG
(5V/div)
V
IN
= 5V
C
IN
= 4.7
F
R
L
= 35
C
L
= 47
F || 10
F
Time (5
s/div)
Enabled Into Short Circuit
(MIC2536-1)
I
OUT
(200mA/div)
V
EN
(10V/div)
V
OUT
(5V/div)
V
FLG
(5V/div)
V
IN
= 5V
C
IN
= 4.7
F
OUT = GND
C
L
= 0
Time (10ms/div)
t
D
MIC2536
6
March 2000
MIC2536
Micrel
Ramped Into Short Circuit
(MIC2536-1)
I
OUT
(200mA/div)
V
EN
(10V/div)
V
OUT
(5V/div)
V
FLG
(5V/div)
V
IN
= 5V
C
IN
= 4.7
F
R
L
= 0
Thermal Shutdown
Time (100ms/div)
Inrush Current
(MIC2536-1)
I
OUT
(100mA/div)
V
EN
(10V/div)
V
FLG
(5V/div)
V
IN
= 5V
C
IN
= 4.7
F
R
L
= 35
C
L
= 410
F
C
L
= 310
F
C
L
= 210
F
C
L
= 110
F
C
L
= 10
Time (5
s/div)
Current-Loop Response
(MIC2536-1)
I
OUT
(1A/div)
V
OUT
(5V/div)
Time (5
s/div)
V
EN
= 5V
V
IN
= 5V
C
IN
= 4700
F
C
L
= 47
F
output = ground
output = open
March 2000
7
MIC2536
MIC2536
Micrel
Block Diagram
1.2V
REFERENCE
THERMAL
SHUTDOWN
CHARGE
PUMP
OUTB
GATE
CONTROL
IN
ENA
GATE
CONTROL
OUTA
FLGB
CHARGE
PUMP
ENB
OSC.
FLGA
CURRENT
LIMIT
CURRENT
LIMIT
GND
MIC2536
DELAY
DELAY
MIC2536
8
March 2000
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
OUT
is greater than V
IN
, current will flow from OUT
to IN during an on-condition since the MOSFET is bidirec-
tional 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
OUTx
> V
IN
) when the output is
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-resis-
tance until the series combination of the MOSFET on-resis-
tance and the load impedance limits output current to ap-
proximately 275mA. The resulting increase in power dissipa-
tion 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, ther-
mal 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 con-
troller 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.
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:
P
D
= R
DS(on)
(I
OUT
)
2
Total power dissipation of the device will be the summation
of P
D
for both channels. To relate this to junction
temperature, the following equation can be used:
T
j
= P
D
JA
+ T
A
where:
T
j
= junction temperature
T
A
= ambient temperature
JA
= is the thermal resistance of the package
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 sce-
narios:
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, re-
ducing 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 current-
limit 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 thresh-
old is exceeded the device enters constant-current mode.
This constant current is specified as the short-circuit current-
limit 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 opera-
tion.
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, t
D
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 typi-
cally 12ms.
March 2000
9
MIC2536
MIC2536
Micrel
Applications Information
Supply Filtering
A 0.1
F to 1
F bypass capacitor from IN to GND, located at
the device, is strongly recommended to control supply tran-
sients. Without a bypass capacitor, an output short may
cause sufficient ringing on the input (from supply lead induc-
tance) to damage internal control circuitry.
Input or output transients must not exceed the absolute
maximum supply voltage (V
IN(max)
= 6V) even for a short
duration.
MIC2536
ENA
OUTA
FLGA
FLGB
GND
ENB
OUTB
IN
0.1F to 1F
V
IN
2.7V to 5.5V
Figure 1. Supply Bypassing
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 effec-
tively 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., >430
F), 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 t
D
.
MIC2536-2
EN
OUTA
FLGA
FLGB
GND
OUTB
IN
1
8
2
7
3
6
5
ENB
4
Adaptor Card
to "Hot"
Receptacle
C
BULK
GND
V
CC
0.1
F
Backend
Function
Figure 2. Hot-Plug Card Application
10k
V+
MIC2536
EN
OUTA
FLGA
FLGB
GND
ENB
OUTB
IN
1
8
2
7
3
6
4
5
OVERCURRENT
Logic Controller
R
C
Figure 3. Transient Filter
MIC2536
10
March 2000
MIC2536
Micrel
ENA
OUTA
FLGA
IN
FLGB
GND
ENB
OUTB
MIC2536-2
3.3V USB Controller
0.1F
V
BUS
D+
D
GND
Data
(Two Pair)
V
BUS
D+
D
GND
USB
Port 2
USB
Port 1
MIC5207-3.3
63F
63F
Ferrite
Beads
4.50V to 5.25V
Upstream V
BUS
100mA max.
V
BUS
D+
D
GND
Data
4.7F
1F
to USB
Controller
1.5k
ON/OFF
OVERCURRENT
OVERCURRENT
ON/OFF
VIN
10k
IN
OUT
GND
.01F
.01F
10k
Figure 4. USB Two-Port Bus-Powered Hub
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 enumer-
ates 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 imple-
ment 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 500
A on devices. For hubs,
Universal Serial Bus Specification Revision 1.1 clarifies this
issue. Revision 1.1, section 7.2.3, stipulates that the maxi-
mum suspend current for a configured hub is 2.5mA. This
number is derived by allocating 500
A for up to four down-
stream ports plus 500
A for the hub's internal functions. A
nonconfigured hub is considered a low-power device and
may not consume more than 500
A. 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 500
A worst case suspend current must be further
divided among the data port termination resistors and internal
functions. The termination resistors will consume
3.6V
(16.5K
5%) = 230
A. This leaves only 270
A for
internal functions. Assuming 100
A as the maximum USB
controller suspend current, 170
A remains for the rest of the
system. The MIC2536 will consume 100
A maximum, leav-
ing a margin of 70
A.
USB Voltage Regulation
USB specifications require a minimum downstream voltage
supply of 4.40V from a bus-powered hub port (See
Applica-
tion Note 17 for details). The USB specification allows for a
100mV drop across the hub, leaving 250mV for PCB, up-
stream cable, and connector resistance. Therefore, the on-
resistance of the switch for each port, not including PCB
resistance, must be <100mV
100mA = 1
. The MIC2536
has a maximum on-resistance of 700m
, which easily satis-
fies 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.
March 2000
11
MIC2536
MIC2536
Micrel
Package Information
45
0
8
0.244 (6.20)
0.228 (5.79)
0.197 (5.0)
0.189 (4.8)
SEATING
PLANE
0.026 (0.65)
MAX
)
0.010 (0.25)
0.007 (0.18)
0.064 (1.63)
0.045 (1.14)
0.0098 (0.249)
0.0040 (0.102)
0.020 (0.51)
0.013 (0.33)
0.157 (3.99)
0.150 (3.81)
0.050 (1.27)
TYP
PIN 1
DIMENSIONS:
INCHES (MM)
0.050 (1.27)
0.016 (0.40)
8-Lead SOP (M)
0.008 (0.20)
0.004 (0.10)
0.039 (0.99)
0.035 (0.89)
0.021 (0.53)
0.012 (0.03) R
0.0256 (0.65) TYP
0.012 (0.30) R
5
MAX
0
MIN
0.122 (3.10)
0.112 (2.84)
0.120 (3.05)
0.116 (2.95)
0.012 (0.03)
0.007 (0.18)
0.005 (0.13)
0.043 (1.09)
0.038 (0.97)
0.036 (0.90)
0.032 (0.81)
DIMENSIONS:
INCH (MM)
0.199 (5.05)
0.187 (4.74)
8-Lead MSOP (MM)
MIC2536
12
March 2000
MIC2536
Micrel
MICREL INC.
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USA
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
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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
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