June 2000
1
MIC2544/2548
MIC2544/2548
Micrel
MIC2544/2548
Programmable Current Limit High-Side Switch
Preliminary Information
General Description
The MIC2544 and MIC2548 are integrated high-side power
switches optimized for low loss dc power switching and other
power management applications, including Advanced Con-
figuration and Power Interface (ACPI). The MIC2544/48 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 resis-
tor-programmable output current-limit and a soft-start circuit
which minimizes inrush current when the switch is enabled.
Thermal shutdown, along with current-limit, protects the
switch and the attached device.
The MIC2544/48's open-drain flag output is used to indicate
current-limiting or thermal shutdown to a local controller. The
MIC2548 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 MIC2548.
The MIC2544 and MIC2548 are available in active-high and
active-low enable versions in the 8-pin SOP (small-outline
package) and 8-pin MSOP (micro-small-outline package).
Typical Application
EN
FLG
GND
ILIM
OUT
IN
OUT
NC
MIC2544-xBM
On/Off
Peripheral
0.1F
R
SET
+5V
R
FLG
33F
SOP pinout shown
Typical Advanced Configuration and Power Interface (ACPI) Application
Features
2.7V to 5.5V input
Adjustable current-limit up to 1.5A
Reverse current flow blocking (no "body diode")
75
A typical on-state supply current
1
A typical off-state supply current
120m
maximum on-resistance
Open-drain fault flag
Thermal shutdown
Thermal shutdown output latch (MIC2548)
2ms (slow) turn-on and fast turnoff
Available with active-high or active-low enable
Applications
USB power distribution
PCI Bus Power Switching
Notebook PC
ACPI power distribution
PC card hot swap applications
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
MIC2544/2548
Micrel
MIC2544/2548
2
June 2000
Pin Configuration
1
2
3
4
8
7
6
5
OUT
IN
OUT
NC
EN
FLG
GND
ILIM
MIC2544/2548
8-Pin SOP (M)
Ordering Information
Part Number
Enable
Latch*
Temperature Range
Package
MIC2544-1BM
Active High
40
C to +85C
8-pin SOP
MIC2544-1BMM
Active High
40
C to +85C
8-pin MSOP
MIC2544-2BM
Active Low
40
C to +85C
8-pin SOP
MIC2544-2BMM
Active Low
40
C to +85C
8-pin MSOP
MIC2548-1BM
Active High
40
C to +85C
8-pin SOP
MIC2548-1BMM
Active High
40
C to +85C
8-pin MSOP
MIC2548-2BM
Active Low
40
C to +85C
8-pin SOP
MIC2548-2BMM
Active Low
40
C to +85C
8-pin MSOP
* Thermal Shutdown Latch
Pin Description
Pin Number
Pin Number
Pin Name
Pin Function
MSOP-8
SOP-8
1
1
EN
Enable (Input): Logic-compatible enable input. Active-high (-1) or active-low
(-2). High input >1.7V typical; low input <1.5V typical. Do not float.
MIC2548 only: Also resets thermal shutdown latch.
2
2
FLG
Fault Flag (Output): Active-low, open-drain output. Indicates overcurrent or
thermal shutdown conditions.
MIC2548 only: latched low on thermal shutdown.
3
3
GND
Ground
5
4
ILIM
Current Limit: Sets current-limit threshold using an external resistor, R
SET
,
connected to ground. 154
< R
SET
< 2.29k
.
7
7
IN
Input: Output MOSFET drain. Also powers internal circuitry.
6,8
6,8
OUT
Switch (Output): Output MOSFET source. Pins 6 and 8 must be externally
connected.
4
5
NC
Not internally connected
1
2
3
4
8
7
6
5
OUT
IN
OUT
ILIM
EN
FLG
GND
NC
MIC2544/2548
8-Pin MSOP (MM)
LOGIC,
CHARGE
PUMP
(OUT)
(IN)
(EN)
(FLG)
(GND)
(ILIM)
MIC2544/2548
NOTE: PINS 4 AND 5
FOR SOIC AND MSOP
ARE DIFFERENT.
June 2000
3
MIC2544/2548
MIC2544/2548
Micrel
Electrical Characteristics
V
IN
= +5V; T
A
= 25
C, bold indicates 40C to +85C; unless noted
Symbol
Parameter
Condition
Min
Typ
Max
Units
Supply Current
switch off, OUT = open, Note 4
0.75
5
A
switch on, OUT = open, Note 4
75
160
A
V
EN
Enable Input Voltage
enable high, Note 4
2.4
1.7
V
enable low, Note 1
1.5
0.8
V
Enable Input Current
V
EN
= V
OH(min)
= 2.4V
0.01
1
A
V
EN
= V
OL(max)
= 0.8V
0.01
1
A
Enable Input Capacitance
Note 6
1
pF
R
DS(on)
Switch Resistance
I
OUT
= 500mA
80
120
m
Current Limit Factor
I
OUT
= 100mA to 1A, V
OUT
= 1V to 4V, Note 5
184
230
276
V
I
OUT
= 500mA to 1.5A, V
OUT
= 1V to 4V, Note 5
161
230
299
V
Output Leakage Current
switch off
1
10
A
t
ON
Output Turn-On Delay
R
L
= 10
, C
L
= 1
F, Figures 1a, 1b
1
2
5
ms
t
R
Output Turn-On Rise Time
R
L
= 10
, C
L
= 1
F, Figures 1a, 1b
1
2
5
ms
t
OFF
Output Turnoff Delay
R
L
= 10
, C
L
= 1
F, Figures 1a, 1b
22
s
t
F
Output Turnoff Fall Time
R
L
= 10
, C
L
= 1
F, Figures 1a, 1b
21
s
Overtemperature Threshold
T
J
increasing
140
C
Shutdown
T
J
decreasing
130
C
Error Flag Output Resistance
V
IN
= 5V, I
L
= 10
A
4
15
V
IN
= 3.3V, I
L
= 10
A
5
20
Error Flag Off Current
V
FLG
= 5V
0.01
1
A
EN Pulse Reset Width
MIC2548 thermal shutdown latch
5
s
V
IN
to EN Set-Up
MIC2548, Note 6
0
s
Current-Limit Response Time
V
OUT
= 0V, Note 6
25
s
Overcurrent Flag Response Time
V
OUT
= V
IN
/2 to FLG low
5
s
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 MIC2544-1 and MIC2548-1. Off is 2.4V and on is 0.8V for the MIC2544-2 and MIC2548-2. The
enable input has about 200mV of hysteresis.
Note 5.
Current limit threshold is determined by
I
R
LIMIT
SET
==
230V
, where R
SET
is in ohms.
Note 6.
Guaranteed by design but not production tested.
Absolute Maximum Ratings
(Note 1)
Supply Voltage (V
IN
) .................................................. +6.0V
Output Voltage (V
OUT
) ............................................... +6.0V
Output Current (I
OUT
) ............................... Internally Limited
Enable Input (V
EN
) ................................. 0.3V to V
IN
+0.3V
Fault Flag Voltage (V
FLG
) ........................................... +6.0V
Fault Flag Current (I
FLG
) ............................................ 50mA
Storage Temperature (T
S
) ....................... 65
C to +150C
Junction Temperature (T
J
) ....................... Internally Limited
Lead Temperature (soldering 5 sec.) ........................ 260
C
ESD Rating, Note 3 ...................................................... 2kV
Operating Ratings
(Note 2)
Supply Voltage (V
IN
) ................................... +2.7V to +5.5V
Current Limit Set Range .................................. 0.1A to 1.5A
Ambient Temperature Range (T
A
) ............. 40
C to +85C
Package Thermal Resistance
SOP
(
JA
) .......................................................... 160
C/W
MSOP
(
JA
) ....................................................... 206
C/W
MIC2544/2548
Micrel
MIC2544/2548
4
June 2000
Test Circuit
Device
Under
Test
C
L
OUT
R
L
V
OUT
I
OUT
90%
V
OUT
10%
90%
10%
t
r
t
f
Functional Characteristics Test Circuit
Timing Diagrams
V
EN
50%
90%
V
OUT
10%
t
OFF
t
ON
Figure 1a. MIC2544/48-1
V
EN
50%
90%
V
OUT
10%
t
OFF
t
ON
Figure 1b. MIC2544/48-2
June 2000
5
MIC2544/2548
MIC2544/2548
Micrel
EN
V
OUT
I
OUT
Short-Circuit Fault
Thermal Shutdown
Reached
Fault Removed
FLG
I
LIMIT
I
DC
Output Reset
Figure 2a. MIC2548-2 Timing: Output is reset by toggling EN
EN
V
OUT
I
OUT
Short-Circuit
Fault
Thermal Shutdown
Reached
Fault
Removed
FLG
I
LIMIT
I
DC
Figure 2b. MIC2544-2 Timing
MIC2544/2548
Micrel
MIC2544/2548
6
June 2000
50
60
70
80
90
100
2.5
3.0
3.5
4.0
4.5
5.0
5.5
ON-RESISTANCE (m
)
SUPPLY VOLTAGE (V)
Output On-Resistance
vs. Supply Voltage
T
A
= 27
C
40
60
80
100
120
-40 -20
0
20
40
60
80 100
ON-RESISTANCE (m
)
TEMPERATURE (
C)
Output On-Resistance
vs. Temperature
2.7V
3.3V
5.0V
0
20
40
60
80
100
120
140
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY CURRENT (mA)
SUPPLY VOLTAGE (V)
On-State Supply Current
vs. Supply Voltage
T
A
= 27
C
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY CURRENT (
A)
SUPPLY VOLTAGE (V)
Off-State Supply Current
vs. Supply Voltage
T
A
= 27
C
1.0
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
ENABLE THRESHOLD (V)
SUPPLY VOLTAGE (V)
Enable Threshold Voltage
vs. Supply Voltage
T
A
= 27
C
V
EN
RISING
V
EN
FALLING
0
20
40
60
80
100
120
140
-40 -20
0
20
40
60
80 100
SUPPLY CURRENT (
A)
TEMPERATURE (
C)
On-State Supply Current
vs. Temperature
2.7V
3.3V
5.0V
0
0.1
0.2
0.3
0.4
-40 -20
0
20
40
60
80 100
SUPPLY CURRENT (
A)
TEMPERATURE (
C)
Off-State Supply Current
vs. Temperature
2.7V
3.3V
5.0V
R
L
= 44
1.0
1.2
1.4
1.6
1.8
2.0
-40 -20
0
20
40
60
80 100
ENABLE THRESHOLD (V)
TEMPERATURE (
C)
Enable Threshold Voltage
vs. Temperature
V
EN
RISING
V
EN
FALLING
0
1
2
3
4
5
6
7
-40 -20
0
20
40
60
80 100
OUTPUT RISE TIME (ms)
TEMPERATURE (
C)
Rise Time
vs. Temperature
2.7V
3.3V
5.0V
R
L
= 44
0
0.5
1.0
1.5
2.0
2.5
-40 -20
0
20
40
60
80 100
OUTPUT FALL TIME (
s)
TEMPERATURE (
C)
Output Fall Time
vs. Temperature
2.7V
3.3V
R
L
= 44
5.0V
0
500
1000
1500
2000
100
1000
5000
CURRENT LIMIT (mA)
R
SET
(
)
Current Limit
vs. R
SET
I
TH
V
IN
= 5V
I
SET
I
SHORT
0
500
1000
1500
2000
0
1
2
3
4
5
6
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
Output Current
vs. Output Voltage
R
SET
= 150
V
IN
= 5V
R
SET
= 470
R
SET
= 2.3k
Typical Characteristics
June 2000
7
MIC2544/2548
MIC2544/2548
Micrel
600
700
800
900
1000
1100
-40 -20
0
20
40
60
80 100
OUTPUT CURRENT (mA)
TEMPERATURE (
C)
Current Limit
vs. Temperature
I
TH
I
SET
I
SHORT
V
IN
= 5V
R
SET
= 230
600
700
800
900
1000
1100
2.5
3.0
3.5
4.0
4.5
5.0
5.5
CURRENT LIMIT (mA)
SUPPLY VOLTAGE (V)
Current Limit
vs. Supply Voltage
I
TH
I
SET
I
SHORT
T
A
= 27
C
R
L
= 230
MIC2544/2548
Micrel
MIC2544/2548
8
June 2000
Functional Characteristics
Turn-On Response
TIME (500
s/div.)
MIC2544-1
I
OUT
(200mA/div
.)
V
OUT
(2V/div
.)
V
EN
(5V/div
.)
V
FLG
(10V/div
.)
V
IN
= 5V
C
IN
= 4.7
F
C
L
= 1
F
R
L
= 10
Turnoff Response
TIME (1ms/div.)
MIC2544-1
V
IN
= 5V
C
IN
= 4.7
F
C
L
= 1
F
R
L
= 10
I
OUT
(200mA/div
.)
V
OUT
(2V/div
.)
V
EN
(10V/div
.)
V
FLG
(5V/div
.)
Current-Limit Response
TIME (100ms/div.)
MIC2544-1
I
OUT
(500mA/div
.)
V
OUT
(5V/div
.)
V
EN
(10V/div
.)
V
FLG
(10V/div
.)
I
SET
= 1A
Thermal Shutdown
V
IN
= 5V
C
IN
= 4.7
F
R
L
= 1
Enable Into Heavy Load
TIME (100ms/div.)
MIC2544-1
I
OUT
(500mA/div
.)
V
OUT
(5V/div
.)
V
EN
(10V/div
.)
V
FLG
(10V/div
.)
V
IN
= 5V
C
IN
= 4.7
F
I
SET
= 1A
R
L
= 1
Inrush Current Response
TIME (500
s/div.)
MIC2544-1
V
IN
= 5V
C
IN
= 4.7
F
R
L
= 10
I
OUT
(500mA/div
.)
V
EN
(10V/div
.)
V
FLG
(5V/div
.)
C
L
= 10
F
C
L
= 60
F
C
L
= 110
F
Enable Into Heavy Load
TIME (500
s/div.)
MIC2548-1
V
IN
= 5V
C
IN
= 4.7
F
R
L
= 1
I
SET
= 1A
I
OUT
(1A/div
.)
V
EN
(10V/div
.)
V
FLG
(5V/div
.)
V
OUT
(5V/div
.)
Reset
Thermal Shutdown
Output Latched
June 2000
9
MIC2544/2548
MIC2544/2548
Micrel
Functional Description
The MIC2544 and MIC2548 are high-side N-channel switches
available with active-high or active-low enable inputs. Fault
conditions turn off or inhibit turn-on of the output transistor
and activate the open-drain error flag transistor making it sink
current to ground.
Input and Output
IN is the power supply connection to the logic circuitry and the
drain of the output MOSFET. OUT is the source of the output
MOSFET. In a typical circuit, current flows from IN to OUT
toward the load. If V
OUT
is greater than V
IN
, current will flow
from OUT to IN since the switch is bidirectional when en-
abled. 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
OUT
> V
IN
) when the
switch is disabled. In this situation, the MIC2544/48 avoids
undesirable current flow from OUT to IN. 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 140
C. 10C of
hysteresis prevents the switch from turning on until the die
temperature drops to 130
C. Overtemperature detection
functions only when the switch is enabled.
The MIC2548 features an internal latch which causes the part
to remain off after thermal shutdown until a reset pulse is
provided via the enable pin (pin 1). 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.
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, and V
EN
should be less than
or equal to V
IN
.
Adjustable Current-Limit
The short-circuit current-limit is user-adjustable with an exter-
nal set resistor. Current-limit in the range of 100mA to 1.5A is
available with a set point accuracy of better than
20%. The
current-limit circuit prevents damage to the output MOSFET
and external load.
The nominal current-limit value is set with an external resistor
between ILIM and GND. For a desired current-limit, the value
of the external set resistor is given by:
R
=
I
SET
LIMIT
230V
where:
154
< R
SET
< 2.29k
For example, to set a 1A nominal current-limit, R
SET
is
calculated as:
230V
1A
==
230
Current through R
SET
increases with OUT current. The
voltage across R
SET
could be monitored with a high imped-
ance comparator to provide an indication of output current.
R
SET
should be between 154
0.5% and 2.29k 0.5%.
Short-Circuit Protection
In the event of a short-circuit, the output current will fold back
to approximately 80% of the short-circuit current-limit.
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.
Block Diagram
1.2V
REFERENCE
THERMAL
SHUTDOWN
OSC.
CHARGE
PUMP
OUT
GATE
CONTROL
IN
FLG
EN
CURRENT
LIMIT
GND
ILIM
R
SET
THERMAL
SHUTDOWN
LATCH
(MIC2548)
RESET
MIC2544/2548
Micrel
MIC2544/2548
10
June 2000
Applications Information
Supply Filtering
A 0.1
F to 1F bypass capacitor from IN to GND, located near
the MIC2544 and MIC2548, 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 (V
IN max
= 6V) even for a short duration.
MIC2548-1BM
EN
OUT
FLG
GND
OUT
ILIM
NC
IN
1
8
2
7
3
6
4
5
0.1F to 1F
4.0V to 5.5V
R
SET
NOTE: MSOP PACKAGE OPTION USES PIN 5 FOR I
LIM
.
PIN 4 IS NOT CONNECTED (NC).
On/Off
On/Off
Power
Output
Figure 3. Supply Bypassing
Power Dissipation
The device's junction temperature depends on several fac-
tors 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:
P
D
= R
DS(on)
(I
OUT
)2
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
Transient Overcurrent Filter
The inrush current from the connection of a heavy capacitive
load may cause the fault flag to fall for 10
s to 200s while the
switch is in a constant-current mode, charging the capaci-
tance.
Adding an optional series resistor-capacitor (R
SET2
) in paral-
lel with R
SET
, 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 10
s to 20s. If
R
SET
is 435
(510mA), an R
SET2
of 88
(2.5A) and C
SET
of
1
F (RC = 100s) allows transient surge of 3A to pass for
100
s without tripping the overcurrent flag (FLG).
USB Power Distribution
The MIC2544 is ideal for meeting USB power distribution
requirements. Figure 4 depicts a USB Host application. R
SET
should be set to a value providing a current-limit >500mA.
The accurate current-limit of the MIC2544 will reduce power
supply current requirements. Also, fast reaction to short
circuit faults prevent voltage droop in mobile PC applications.
Printed Circuit Board Hot-Plug
The MIC2544/48 are ideal inrush current-limiters suitable for
hot-plug applications. Due to the integrated charge pump,
the MIC2544/48 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 MIC2544 may be used in a
hot-plug application.
ON/OFF
OVERCURRENT
MIC2544-2BM
3.3V USB Controller
V
BUS
D+
D
GND
10k
MIC5203-3.3
LDO Regulator
IN
OUT
GND
Ferrite
Bead
V
BUS
D+
D
GND
D+
D
V+
EN
OUT
FLG
IN
GND
OUT
ILIM
NC
Bold lines indicate
0.1" wide, 1-oz. copper
high-current traces.
Downstream
USB
Port 1
4.75V min.
500mA max.
120F
0.01F
1.0
F
GND
0.1F
5V
(+)
()
4.7F
NOTE: MSOP PACKAGE OPTION USES PIN 5 FOR I
LIM
.
PIN 4 IS NOT CONNECTED (NC).
R
SET
100k
R
SET(2)
(optional)
C
SET
1.5k 2%
Figure 4. USB Host Application
June 2000
11
MIC2544/2548
MIC2544/2548
Micrel
MIC2544-2BM
EN
OUT
FLG
GND
OUT
NC
IN
1
8
2
7
3
6
5
I
LIM
4
Adaptor Card
to "Hot"
Receptacle
C
BULK
GND
V
CC
0.1
F
Backend
Function
0.1F
NOTE: MSOP PACKAGE OPTION USES PIN 5 FOR I
LIM
AND PIN 4 IS NO CONNECT (NC).
Figure 5. Hot Plug Application
MIC2544/2548
Micrel
MIC2544/2548
12
June 2000
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-Pin 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-Pin MSOP (MM)
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
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