Page 1
MIC2537 Micrel
MIC2537
Quad Power Distribution Switch
Preliminary Information
General Description
The MIC2537 is a cost-effective high-side power switch with
four independently controlled channels, optimized for buspowered Universal Serial Bus (USB) applications. Few external components are necessary to satisfy USB requirements.
The MIC2537 satisfies the following USB requirements: each
switch channel supplies up to 100mA as required by USB
bus-powered downstream devices; fault current is limited to
typically 250mA, well below the UL 25VA safety requirements; and a flag output is available to indicate fault conditions to the local USB controller. Soft start eliminates the
momentary voltage drop on the upstream port 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 MIC2537 is available in active-high and active-low versions in a 16-lead SOP package.
Features
• Compliant to USB specifications
• 3V to 5.5V input
• 100mA minimum continuous load current per port
• 425mΩ typical on-resistance
• < 400mA current limit
• Individual open-drain fault flag leads
• 3V/5V-compatible enable inputs
• Active-high (-1) and active-low (-2) versions
• 100µA max. on-state supply current
• <1µA typical off-state supply current
• 16-lead SOP package
•–40°C to 85°C operation
Applications
• USB keyboards
• USB bus-powered docking stations
• Notebook docking stations
• Notebook PCs
• PDA
• General power distribution
Typical Application
Upstream V
4.75V to 5.25V
500mA max.
4.7
µF
BUS
MIC5207-3.3
LDO Regulator
IN OUT
GND
Bold lines indicate
0.1" wide, 1-oz. copper
high-current traces.
* 33µF, 16V tantalum or 100µF, 10V electrolytic per port
1µF
10k
3.3V USB Controller
GND
EN
OC
EN
OC
EN
OC
EN
OC
V+
D+
D–
10k 10k 10k
MIC2537
ENA
FLGA NC
ENB OUTA
FLGB
OUTB
ENC
OUTC
OUTDFLGC
END
FLGD
NC
GND
Ferrite
Bead
V
BUS
33µF*
IN
0.1
µF
33µF*
33µF*
33µF*
0.01µF
0.01µF
0.01µF
0.01µF
D+
D–
GND
V
BUS
D+
D–
GND
V
BUS
D+
D–
GND
V
BUS
D+
D–
GND
Downstream
USB
Port 1
100mA max.
Downstream
USB
Port 2
100mA max.
Downstream
USB
Port 3
100mA max.
Downstream
USB
Port 4
100mA max.
Typical Bus-Powered Hub
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
December 1999 1 MIC2537
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MIC2537 Micrel
Ordering Information
Part Number Enable Temperature Range Package
MIC2537-1BM Active High –40°C to +85°C 16-Lead SOP
MIC2537-2BM Active Low –40°C to +85°C 16-Lead SOP
Pin Configuration
MIC2537-x
FLGA
ENA
1
2
16
15
FLGD
END
OUTA
GND
NC
OUTB
ENB
FLGB
Pin Description
Pin Number Pin Name Pin Function
1 FLGA Flag A: (Output): Channel A open-drain fault flag output.
2 ENA Enable A (Input): Channel A control input.
3 OUTA Output A: Channel A switch output.
4 GND Ground: Supply return. Connect both leads to ground.
5, 12 NC Not internally connected
6 OUTB Output B: Channel B switch output.
7 ENB Enable B (Input): Channel B control input.
8 FLGB Flag B (Output): Channel B open-drain fault flag output.
9 FLGC Flag C (Output): Channel C open-drain fault flag output.
10 ENC Enable C (Input): Channel C control input.
11 OUTC Output C: Channel C switch output.
13 IN Positive Supply Input
14 OUTD Output D: Channel D switch output.
15 END Enable D (Input): Channel D control input.
16 FLGD Flag D (Output): Channel D open-drain fault flag output.
3
4
5
6
7
8
16-Lead SOP (M)
14
13
12
11
10
9
OUTD
IN
NC
OUTC
ENC
FLGC
December 1999 2 MIC2537
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MIC2537 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 12V
EN
Operating Ratings (Note 2)
Supply Voltage (V
Ambient Operating Temperature (T
Thermal Resistance
SOP (θ
) ..........................................................120°C/W
JA
) ...................................... +3V 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....................................................... 2kV
Electrical Characteristics
VIN = +5V; TA = 25°C; unless noted.
Parameter Condition Min Typ Max Units
Supply Current Note 4, switch off, OUTA–D = open 0.75 5 µA
Note 4, all switches on, OUTA–D = open 70 100 µA
Enable Input Threshold low-to-high transition 1.8 2.4 V
high-to-low transition, Note 4 0.8 1.6 V
Enable Input Current VEN = V
VEN = V
Enable Input Capacitance 1pF
Switch Resistance single switch, 100mA load 425 700 mΩ
Output Turn-On Delay RL = 50Ω, CL = 1µF, Note 5 0.51 ms
Output Turn-On Rise Time RL = 50Ω, CL = 1µF, Note 5 0.2 0.5 ms
Output Turnoff Delay RL = 50Ω, CL = 1µF, Note 5 150 300 µs
Output Turnoff Fall Time RL = 50Ω, CL = 1µF, Note 5 148 300 µs
Output Leakage Current each output (switch off) 1 10 µA
Current Limit Threshold ramped load applied to enable output, Note 6 300 500 mA
Continuous Load Current each output, FLG not active 100 mA
Short Circuit Current Limit each output (enabled into load), V
Overtemperature Shutdown TJ increasing 135 °C
Threshold TJ decreasing 125 °C
Error Flag Output Resistance VIN = 5V, IL = 10mA 10 Ω
VIN = 3.3V, IL = 10mA 12 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 MIC2537-1. Off is ≥ 2.4V and on is ≤ 0.8V for the MIC2537-2. The enable input has approximately
200mV of hysteresis. See control threshold charts.
Note 5. See “Timing Diagrams.”
Note 6. See “Functional Characteristics: Current-Limit Response” graph.
= 5V 0.01 1 µA
FLAG
= 2.4V 0.01 1 µA
OH(min)
= 0.8V 0.01 1 µA
OL(max)
= 4.0V 150 250 400 mA
OUT
December 1999 3 MIC2537
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MIC2537 Micrel
Typical Characteristics
Supply Current
vs. Supply Voltage
100
80
60
40
20
SUPPLY CURRENT (µA)
0
23456
SUPPLY VOLTAGE (V)
TA = 25°C
R
= ∞
L
Ouput On-Resistance
Variation vs. Temperature
500
400
300
200
100
ON RESISTANCE (mΩ)
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
VIN = 5V
I
= 100mA
L
Supply Current
100
SUPPLY CURRENT (µA)
vs. Temperature
80
60
40
20
0
-40 -20 0 20 40 60 80 100
VIN = 5V
VIN = 3.3V
RL = ∞
TEMPERATURE (°C)
Overcurrent Threshold and
Current Limit vs. Supply Voltage
300
250
200
150
100
CURRENT (mA)
50
0
23456
SUPPLY VOLTAGE (V)
I
THR
I
LIM
TA = 25°C
Ouput On-Resistance
Variation vs. Supply Voltage
500
400
300
200
100
ON-RESISTANCE (mΩ)
0
23456
SUPPLY VOLTAGE (V)
TA = 25°C
I
= 100mA
L
Overcurrent Threshold, and
Current Limit vs. Temperature
300
250
200
150
100
CURRENT (mA)
50
0
-40 -20 0 20 40 60 80 100
I
THR
I
LIM
VIN = 5V
TEMPERATURE (°C)
Control Threshold
vs. Supply Voltage
2.0
1.5
1.0
0.5
ENABLE VOLTAGE (V)
V
IH
V
IL
TA = 25°C
0
23456
SUPPLY VOLTAGE (V)
Output Fall Time
1.5
1.0
TIME (µs)
0.5
vs. Temperature
VIN = 5V
C
= 0.01µF
L
R
= 44Ω
L
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
Control Threshold
vs. Temperature
2.0
1.5
1.0
0.5
THRESHOLD VOLTAGE (V)
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
V
IH
V
IL
VIN = 5V
Output Rise Time
vs. Temperature
VIN = 5V
C
= 0.01µF
L
R
= 44Ω
L
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
TIME (µs)
500
400
300
200
100
December 1999 4 MIC2537
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MIC2537 Micrel
Functional Characteristics
Input V oltage Response
(Input Voltage Rising: MIC2537-2)
IN
V
(2V/div.)
FLG
V
(2V/div.)
OUT
V
(2V/div.)
OUT
I
(100mA/div.)
TIME (25ms/div.)
Current Limit Transient Response
(Heavy Load Applied to Output: MIC2537-2)
EN
V
(5V/div.)
FLG
V
(10V/div.)
OUT
V
(5V/div.)
1V
EN = 0V
= 24Ω
R
L
VIN = 5V
IN
V
FLG
V
OUT
V
OUT
I
EN
V
FLG
V
OUT
V
Input V oltage Response
(Input Voltage Decreasing: MIC2537-2)
(2V/div.)
(2V/div.)
(2V/div.)
(100mA/div.)
TIME (25ms/div.)
EN = 0V
= 24Ω
R
L
Current Limit Response
(Ramped Load: MIC2537-2)
(5V/div.)
(10V/div.)
(5V/div.)
250mA
Current Limit
Threshold
1V
180mA
Short Circuit
Current Limit
OUT
I
(500mA/div.)
TIME (25µs/div.)
OUT
I
(100mA/div.)
TIME (5ms/div.)
VIN = 5V
December 1999 5 MIC2537
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MIC2537 Micrel
Test Circuit
V
Device
Under
Test
OUT
R
C
L
L
OUT
Timing Diagrams
t
R
V
OUT
90%
10%
90%
10%
t
F
Output Rise and Fall Times
V
EN
V
OUT
50%
t
OFF
t
ON
90%
10%
Active-Low Switch Delay Times (MIC2537-2)
V
EN
V
OUT
50%
t
ON
90%
t
OFF
10%
Active-Low Switch Delay Times (MIC2537-1)
December 1999 6 MIC2537
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MIC2537 Micrel
Functional Diagram
FLGA
OUTA
ENA
CHARGE
PUMP
GATE
CONTROL
CURRENT
LIMIT
FLG B
ENB
ENC
END
MIC2537
OSC.
CHARGE
PUMP
CHARGE
PUMP
CHARGE
PUMP
THERMAL
SHUTDOWN
GND
GATE
CONTROL
REFERENCE
GATE
CONTROL
GATE
CONTROL
1.2V
CURRENT
LIMIT
CURRENT
LIMIT
CURRENT
LIMIT
OUTB
IN
OUTC
FLGC
OUTD
FLGD
December 1999 7 MIC2537
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MIC2537 Micrel
Functional Description
The MIC2537-1 and MIC2537-2 are quad 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 since the MOSFET is bidirectional when on.
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
this situation, the MIC2537 prevents reverse current flow.
Thermal Shutdown
Thermal shutdown shuts off the affected output MOSFET
and signals the corresponding fault flags if the die temperature exceeds 135°C. 10°C of hysteresis prevents the switch
from turning on until the die temperature drops to 125°C.
Overtemperature detection functions only when at least one
switch is enabled.
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 200mA. 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, shutdown of the channels not shorted 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.
is greater than VIN, current will flow from OUT
OUT
> VIN) when the output is off. In
OUTx
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 0.15A 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 powered on or enabled into an excessive load or
short circuit, the switch immediately goes into a constantcurrent mode, slowly increasing the output voltage. The fault
flag goes low until the load is reduced.
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 short circuit current-limit specification.
See the “Functional Characteristics: Current-Limit Transient
Response graph for details.
Current-Limit Response
The MIC2537 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 current
limit in the “Electrical Characteristics” table. It is important to
note that the MIC2537 will deliver load current up to the
current-limit threshold. See the “Functional Characteristics:
Current-Limit Response” graph for details.
Fault Flag
FLGx is an open-drain N-channel MOSFET output. Fault
flags are active (low) for current limit or thermal shutdown.
Each flag output MOSFET is capable of sinking a 10mA load
to approximately 200mV above ground. Several FLGx pins
may be wired-NOR connected to a common pull-up resistor.
December 1999 8 MIC2537
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MIC2537 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.
V
IN
3V to 5.5V
0.1µF to 1µF
MIC2537
FLGA FLGB
ENA
OUTA OUTB
GND IN
NC NC
OUTC
ENC END
FLGC FLGD
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.
Soft Start
The MIC2537 presents a high impedance when off and slowly
becomes a low impedance as it turns on. This reduces inrush
current and related voltage drop that results from charging a
capacitive load, satisfying the USB voltage droop requirements.
Transient Overcurrent Fault-Flag Filter
When the MIC2537 is enabled, large values of capacitance
at the output of the device will cause inrush currents to flow
that exceed the short circuit current-limit threshold of the
device and cause the flag to activate. The duration of this time
depends on the size of the output capacitance. See “Func-
tional Characteristics: Switch Turn-On and Turnoff
Charcteristics” for details. During the charging time, the
device enters into constant-current mode and the flag is
activated. As the capacitance is charged the current decreases below the short circuit current-limit threshold and the
flag will be deasserted.
= 6V) even for a short
IN(max)
ENB
OUTD
In USB applications it is required that output bulk capacitance
shown in “Typical Application” is utilized to meet transient
regulation requirements during hot-plug events. When the
MIC2537 is enabled, the flag will go active for about 5ms
depending on output capacitance. Additionally, during hotplug events, inrush currents may cause the flag to go active
for approximately 30µs. If these “false” overcurrent indications are a system problem, they can be masked by an RC
filter on the flag output (see Figure 2). Alternatively, a 15ms
debounce routine may be programmed into the USB logic
controller to eliminate the need for an RC filter.
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 MIC2537
has been designed to slowly ramp its output.
Suspend Current
For hubs,
Universal Serial Bus Specification 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 cannot 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 MIC2537 will consume 100µA maximum, leaving a margin of 70µA.
USB Controller
OVERCURRENT
10k
50k
0.3µF
FLGA
FLGB
FLGC
FLGD
Figure 2. Transient Filter
December 1999 9 MIC2537
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MIC2537 Micrel
USB Voltage Regulation
USB specifications require a minimum downstream voltage
supply of 4.40V from a bus-powered hub port (See
tion Note 17
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 about 100mV ÷ 100mA = 1Ω. The
MIC2537 has a maximum on-resistance of 700mΩ, which
easily satisfies this requirement.
for details). The USB specification allows for a
Applica-
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 MIC2537
provides a flag output for this application.
December 1999 10 MIC2537
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MIC2537 Micrel
Package Information
PIN 1
0.157 (3.99)
0.150 (3.81)
0.020 (0.51)
REF
0.0648 (1.646)
0.0434 (1.102)
0.050 (1.27)
BSC
0.394 (10.00)
0.386 (9.80)
0.020 (0.51)
0.013 (0.33)
0.0098 (0.249)
0.0040 (0.102)
SEATING
PLANE
16-Lead SOP (M)
DIMENSIONS:
INCHES (MM)
0.050 (1.27)
0.016 (0.40)
0.244 (6.20)
0.228 (5.79)
45°
0°–8°
December 1999 11 MIC2537
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MIC2537 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.
© 1999 Micrel Incorporated
December 1999 12 MIC2537
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