MIC2526
Micrel
MIC2526
Dual USB Power Control Switch
Not Recommended for New Designs
Refer to MIC2026
General Description
Features
The MIC2526 is a dual integrated high-side power switch with
independent enable and flag functions, optimized for selfpowered and bus-powered Universal Serial Bus (USB) applications. Few external components are necessary to satisfy
USB requirements.
The MIC2526 satisfies the following USB requirements: each
switch channel supplies up to 500mA as required by USB
downstream devices; the switch’s low on-resistance meets
USB voltage drop requirements; fault current is limited to
typically 750mA, 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.
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Additional features include thermal shutdown to prevent
catastrophic switch failure from high-current loads,
undervoltage lockout (UVLO) to ensure that the device remains off unless there is a valid input voltage present, and
3.3V and 5V logic compatible enable inputs.
The MIC2526 is available in active-high and active-low versions in 8-pin DIP and SOIC packages.
Compliant to USB specifications
UL Recognized Component
2 independent switches
3V to 5.5V input
500mA minimum continuous load current per port
140mΩ maximum on-resistance
1.25A maximum short circuit current limit
Individual open-drain fault flag pins
110µA typical on-state supply current
1µA typical off-state supply current
Output can be forced higher than input (off-state)
Thermal shutdown
2.4V typical undervoltage lockout (UVLO)
1ms turn-on (soft-start) and fast turnoff
Active-high or active-low enable versions
8-pin SOIC and DIP packages
Applications
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USB host and self-powered hubs
USB bus-powered hubs
Hot plug-in power supplies
Battery-charger circuits
Typical Application
VCC
5.0V
4.50V to 5.25V
Upstream VBUS
100mA max.
VBUS
10k
100k
10k
100k
3.3V USB Controller
MIC2526-2
Ferrite
Beads
VBUS
D+
MIC5207-3.3
IN
D+
1µF
D–
GND
VIN
OUT
GND
1µF
ENA
ON/OFF
OUTA
OVERCURRENT
FLGA
IN
OVERCURRENT
FLGB
GND
ENB
OUTB
ON/OFF
D–
47µF
USB
Port 1
GND
0.1µF
VBUS
D+
D–
47µF
USB
Port 2
GND
Data
Data
(Two Pair)
to USB
Controller
2-Port USB Self-Powered Hub
UL Recognized Component
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
February 2000
1
MIC2526
MIC2526
Micrel
Ordering Information
Part Number
Enable
Temperature Range
Package
MIC2526-1BM
Active High
–40°C to +85°C
8-Pin SOIC
MIC2526-2BM
Active Low
–40°C to +85°C
8-Pin SOIC
MIC2526-1BN
Active High
–40°C to +85°C
8-pin DIP
MIC2526-2BN
Active Low
–40°C to +85°C
8-pin DIP
Pin Configuration
MIC2526
ENA
1
8
OUTA
FLGA
2
7
IN
FLGB
3
6
GND
ENB
4
5
OUTB
8-Pin SOIC (M)
8-Pin DIP (N)
MIC2526
(ENA) 1
(FLGA) 2
LOGIC,
CHARGE
PUMP
(FLGB) 3
(ENB) 4
LOGIC,
CHARGE
PUMP
8 (OUTA)
7 (IN)
5 (OUTB)
6 (GND)
Pin Description
Pin Number
Pin Name
1/4
EN(A/B)
Enable (Input): Logic-compatible enable input. High input > 2.1V typical.
Low input VIN) when the output is off. In
this situation, the MIC2526 avoids undesirable current flow
from OUT to IN. If VIN < 2.5V, UVLO disables both switches.
Thermal Shutdown
Thermal shutdown shuts off the affected output MOSFETs
and signals all 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 limit current to typically 850mA.
The increase in power dissipation, in most cases, will cause
the MIC2526 to go into thermal shutdown, disabling affected
channels. 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 hundred milliseconds. The USB controller must therefore recognize a fault and disable the appropriate channel
within this time. If the fault is not removed or the switch is not
disabled within this time, then the device will enter into a
thermal oscillation of about 2Hz. This does not cause any
damage to the device. Refer to “Functional Characteristics:
Thermal Shutdown Response.”
MIC2526
Switch Enabled into Short Circuit
If a switch is powered on or enabled into a heavy load or shortcircuit, the switch immediately goes into a constant-current
mode, reducing the output voltage. The fault flag goes low
until the load is reduced. See the “Functional Characteristics:
Short Circuit Response, Enabled into Short Circuit” photo.
Short Circuit Applied to Output
When a heavy load is applied, a large transient current may
flow until the current limit circuitry will respond. Once this
occurs, the device limits current to less than the short-circuit
current limit specification. See the “Short Circuit Transient
Response, Short Applied to Output” graph.
Current-Limit Response
The MIC2526 current-limit profile exhibits a small foldback
effect of approximately 500mA. 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 MIC2526 will deliver load current up to the
current-limit threshold which is typically 1.6A. Refer to “Functional Characteristics: Current-Limit Response” photo for
details.
Fault Flag
FLG is an N-channel, open-drain MOSFET output. The faultflag is active (low) for one or more of the following conditions:
undervoltage (while 2V < VIN < 2.7), current limit, or thermal
shutdown. The flag output MOSFET is capable of sinking a
10mA load to typically 100mV above ground. Multiple FLG
pins may be “wire NORed” to a common pull-up resistor.
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February 2000
MIC2526
Micrel
Soft Start
The MIC2526 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 for bus-powered applications as shown in
Figure 2.
The soft start circuit shown in Figure 3 can be utilized to meet
USB transient regulation specifications with large load capacitances (CBULK > 10uF). The MIC2526 will provide inrush
current limiting for these applications.
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 (VIN max = 6V) even for a short
duration.
3.0V to 5.5V
Transient Overcurrent Filter
When the MIC2526 is enabled, large values of capacitance
at the output of the device will cause inrush current to exceed
the short circuit current-limit threshold of the device and
assert the flag. The duration of this time will depend on the
size of the output capacitance. Refer to the “Functional
Characteristics” turn-on and turnoff behaviors for details.
During the capacitance charging time, the device enters into
constant-current mode. As the capacitance is charged, the
current decreases below the short circuit current-limit threshold, and the flag will then be deasserted.
MIC2526
ENA
OUTA
FLGA
IN
FLGB
GND
ENB
OUTB
0.1µF to 1µF
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.
USB
Controller
MIC2526-xBM
VBUS
USB Host
4.7
µF
1
ENA
2
FLGA
IN
3
FLGB
GND
6
4
ENB
OUTB
5
OUTA
8
7
CBULK
0.1µF
Capacitive
Load
GND
Cable
Cable
Bus Powered Hub
Downstream USB Device
Figure 2. Soft Start (Single Channel)
USB
Controller
MIC2526-2BM
1
VBUS
4.7
µF
USB Hub
ENA
OUTA
USB
Function
8
2
7
FLGA
IN
3
FLGB
GND
6
4
ENB
OUTB
5
CBULK
USB
Function
CBULK
GND
Cable
USB Peripheral
Figure 3. Inrush Current-Limit Application
February 2000
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MIC2526
MIC2526
Micrel
In USB applications, it is required that output bulk capacitance is utilized to support hot-plug events. When the MIC2526
is enabled, the flag may go active for about 1ms due to inrush
current exceeding the current-limit setpoint. Additionally,
during hot-plug events, inrush currents may also cause the
flag to go active for 30µs. Since these conditions are not valid
overcurrent faults, the USB controller must ignore the flag
during these events. To prevent this erroneous overcurrent
reporting, a 1ms RC filter as shown in Figure 4 may be used.
Alternatively, a 1ms debounce routine may be programmed
into the USB logic controller, eliminating the need for the RC
filter.
MIC2526
V+
USB Controller
MIC2526
10k
1
10k
OVERCURRENT
0.1
µF
2
3
4
ENA
OUTA
FLGA
IN
FLGB
GND
ENB
OUTB
8
7
6
5
Figure 4. Transient Filter
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February 2000
MIC2526
Micrel
Package Information
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
DIMENSIONS:
INCHES (MM)
0.020 (0.51)
0.013 (0.33)
0.050 (1.27)
TYP
0.064 (1.63)
0.045 (1.14)
45°
0.0098 (0.249)
0.0040 (0.102)
0.197 (5.0)
0.189 (4.8)
0°–8°
0.010 (0.25)
0.007 (0.18)
0.050 (1.27)
0.016 (0.40)
SEATING
PLANE
0.244 (6.20)
0.228 (5.79)
8-Pin SOP (M)
PIN 1
DIMENSIONS:
INCH (MM)
0.380 (9.65)
0.370 (9.40)
0.255 (6.48)
0.245 (6.22)
0.135 (3.43)
0.125 (3.18)
0.300 (7.62)
0.013 (0.330)
0.010 (0.254)
0.018 (0.57)
0.100 (2.54)
0.130 (3.30)
0.380 (9.65)
0.320 (8.13)
0.0375 (0.952)
8-Pin Plastic DIP (N)
February 2000
11
MIC2526
MIC2526
Micrel
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
USA
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
MIC2526
12
February 2000