MIC2545A/2549A
Programmable Current-Limit
High-Side Switch
General Description
Features
The MIC2545A and MIC2549A are integrated high-side
power switches optimized for low-loss DC power switching
and other power-management applications, including
advanced configuration and power interface (ACPI). The
MIC2545A/49A is a cost-effective, highly-integrated
solution that requires few external components to satisfy
USB and ACPI requirements.
Load current management features include a precision,
resistor-programmable output current-limit and a soft-start
circuit, which minimizes inrush current when the switch is
enabled. Thermal shutdown, along with adjustable currentlimit, protects the switch and the attached device.
The MIC2545A/49A’s open-drain flag output is used to
indicate current-limiting or thermal shutdown to a local
controller. The MIC2549A has an additional internal latch
which turns the output off upon thermal shutdown,
providing robust fault control. The enable signal is
compatible with both 3V and 5V logic, and is also used as
the thermal shutdown latch reset for the MIC2549A.
The MIC2545A and MIC2549A are available in active-high
and active-low enable versions in 8-pin DIP, SOIC, and
TSSOP packages.
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
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•
•
•
•
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2.7V to 5.5V input
Adjustable current-limit up to 3A
Reverse current flow blocking
90µA typical on-state supply current
1µA typical off-state supply current
50mΩ maximum on-resistance
Open-drain fault flag
Thermal shutdown
Thermal-shutdown output latch (MIC2549A)
2ms (slow) soft-start turn-on, fast turnoff
Available with active-high or active-low enable
Applications
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USB power distribution
PCI Bus Power Switching
Notebook PC
ACPI power distribution
PC card hot swap applications
Inrush current-limiting
_________________________________________________________________________________________________________________________
Typical Application
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
June 2011
M9999-062711-A
Micrel, Inc.
MIC2545A/2549A
Ordering Information
Part Number
Enable
Temperature Range
Latch
Pb-Free
Package
MIC2545A-1BM
Active HIGH
–40°C to +85°C
No
No
8-Pin SOP
MIC2545A-1BN
Active HIGH
–40°C to +85°C
No
No
8-Pin DIP
MIC2545A-1BTS
Active HIGH
–40°C to +85°C
No
No
14-Pin TSSOP
MIC2545A-2BM
Active LOW
–40°C to +85°C
No
No
8-Pin SOP
MIC2545A-2BN
Active LOW
–40°C to +85°C
No
No
8-Pin DIP
MIC2545A-2BTS
Active LOW
–40°C to +85°C
No
No
14-Pin TSSOP
MIC2545A-1YM
Active HIGH
–40°C to +85°C
No
Yes
8-Pin SOP
MIC2545A-1YN
Active HIGH
–40°C to +85°C
No
Yes
8-Pin DIP
MIC2545A-1YTS
Active HIGH
–40°C to +85°C
No
Yes
14-Pin TSSOP
MIC2545A-2YM
Active LOW
–40°C to +85°C
No
Yes
8-Pin SOP
MIC2545A-2YN
Active LOW
–40°C to +85°C
No
Yes
8-Pin DIP
MIC2545A-2YTS
Active LOW
–40°C to +85°C
No
Yes
14-Pin TSSOP
MIC2549A-1BM
Active HIGH
–40°C to +85°C
Yes
No
8-Pin SOP
MIC2549A-1BN
Active HIGH
–40°C to +85°C
Yes
No
8-Pin DIP
MIC2549A-1BTS
Active HIGH
–40°C to +85°C
Yes
No
14-Pin TSSOP
MIC2549A-2BM
Active LOW
–40°C to +85°C
Yes
No
8-Pin SOP
MIC2549A-2BN
Active LOW
–40°C to +85°C
Yes
No
8-Pin DIP
MIC2549A-2BTS
Active LOW
–40°C to +85°C
Yes
No
14-Pin TSSOP
MIC2549A-1YM
Active HIGH
–40°C to +85°C
Yes
Yes
8-Pin SOP
MIC2549A-1YN
Active HIGH
–40°C to +85°C
Yes
Yes
8-Pin DIP
MIC2549A-1YTS
Active HIGH
–40°C to +85°C
Yes
Yes
14-Pin TSSOP
MIC2549A-2YM
Active LOW
–40°C to +85°C
Yes
Yes
8-Pin SOP
MIC2549A-2YN
Active LOW
–40°C to +85°C
Yes
Yes
8-Pin DIP
MIC2549A-2YTS
Active LOW
–40°C to +85°C
Yes
Yes
14-Pin TSSOP
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MIC2545A/2549A
Pin Configuration
8-Pin SOP (M)
8-Pin DIP (N)
14-Pin TSSOP (TS)
Pin Description
Pin Number
SOP, DIP
Pin Number
TSSOP
Pin Name
1
1
EN
Enable (Input): Logic-compatible enable input (−1 version is active high, −2
version is active low). High input >1.8V typical; low input VIN) when the switch is disabled. In this
situation, the MIC2545A/49A avoids undesirable current
flow from OUT to IN. Both IN pins must be connected
together, and both OUT pins must be connected
together.
Thermal Shutdown
Thermal shutdown shuts off the output MOSFET and
signals the fault flag 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 the
switch is enabled.
The MIC2549A features an internal latch which causes
the part to remain off after thermal shutdown until a reset
pulse is provided via the enable pin (pin1).While in
current-limit, the thermal shutdown latch prevents on/off
cycling of the output. Refer to Figure 2 for timing
diagram. The flag remains low until reset.
The nominal current-limit value, ILIMIT, is set with an
external resistor between ILIM (Pin 4) and GND (Pin 3).
For a desired current-limit, the value of the external set
resistor is given by:
⎛ 230
R SET = ⎜⎜
⎝ ILIMIT
where:
76.8Ω < RSET < 459Ω
Enable Input
EN must be driven logic high or logic low, or be pulled
high or 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.
Refer to the “Typical Characteristics: Current-Limit vs
RSET” graph for more details.
Current through RSET increases with output current. The
voltage across RSET could be monitored with a highimpedance comparator to provide an indication of output
current. RSET should be between 76.8Ω and 459Ω (1%
resister value).
Current-Limit Operation
The current limit is user adjustable with an external set
resistor. Current limiting in the range of 500mA to 3A is
available with a set point accuracy of better than ±30%
(±20% for ISET 1 to 2.5A). The current-limit circuit
prevents damage to the output MOSFET and external
load.
June 2011
⎞
⎟⎟
⎠
Fault Flag
FLG is an N-channel, open-drain MOSFET output. The
fault-flag is active (low) for current-limit or thermal
shutdown conditions. The flag output MOSFET is
capable of sinking a 10mA load to typically 100mV
above ground. For applications with VIN = 3.6V, it is
recommended that flag current be limited to 5mA or less.
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MIC2545A/2549A
To relate this to junction temperature, the following
equation can be used:
Application Information
Supply Filtering
A 0.1µF to 1µF bypass capacitor from IN to GND,
located near the MIC2545A and MIC2549A, 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 transients must not exceed the absolute maximum
supply voltage (VIN (max) = 6V) even for a short
duration.
TJ = PD × θJA + TA
where:
TJ = Junction temperature
TA = Ambient temperature
θJA = The thermal resistance of the package
Transient Overcurrent Filter
The inrush current from the connection of a heavy
capacitive load may cause the fault flag to fall for 10µs to
200µs while the switch is in a constant-current mode,
charging the capacitance. Adding an optional series
resistor-capacitor (RSET2) in parallel with RSET, as
shown in Figure 4, allows the transient current-limit to be
set to a different value than steady state. A typical USB
hot-plug inrush is 2A to 3A for 10µs to 20µs. If RSET is
435Ω (530mA), an RSET2 of 88Ω (2.5A) and CSET of 1µF
(RC ≈ 90µs) allows transient surge of 3A to pass for
90µs without tripping the overcurrent flag (FLG).
USB Power Dissipations
The MIC2545A is ideal for meeting USB power
distribution requirements. Figure 7 depicts a USB Host
application. RSET should be set to a value providing a
current-limit >500mA. The accurate current-limit of the
MIC2545A will reduce power supply current
requirements. Also, fast reaction to short-circuit faults
prevent voltage droop in mobile PC applications.
Figure 3. Supply Bypassing
Power Dissipation
The device's junction temperature 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 junction
temperature are found below.
Calculation of power dissipation can be accomplished by
the following equation:
Printed Circuit Board Hot-Plug
The MIC2545A/49A is an ideal inrush current-limiter
suitable for hot-plug applications. Due to the integrated
charge pump, the MIC2545A/49A 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 during hot-plug events.
Figure 5 shows how the MIC2545A may be used in a
hot-plug application.
PD = RDS(ON) × (IOUT)2
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MIC2545A/2549A
Figure 4. USB Host Application
Figure 5. Hot-Plug Application
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MIC2545A/2549A
Package Information
8-Pin DIP (N)
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MIC2545A/2549A
Package Information (Continued)
8-Pin SOIC (M)
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MIC2545A/2549A
Package Information (Continued)
14-Pin TSSOP (TS)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This
information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry,
specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual
property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability
whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2004 Micrel, Incorporated.
June 2011
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