June 2000
1
MIC2027/2077
MIC2027/2077
Micrel
MIC2027/2077
Quad USB Power Distribution Switch
Preliminary Information
General Description
The MIC2027 and MIC2077 are quad high-side MOSFET
switches optimized for general-purpose power distribution
requiring circuit protection. The MIC2027/77 are internally
current limited and have thermal shutdown that protects the
device and load.
The MIC2077 offers "smart" thermal shutdown that reduces
current consumption in fault modes. When a thermal shut-
down fault occurs, the output is latched off until the faulty load
is removed. Removing the load or toggling the enable input
will reset the device output.
Both devices employ soft-start circuitry that minimizes inrush
current in applications where highly capacitive loads are
employed.
A fault status output flag is asserted during overcurrent and
thermal shutdown conditions. Transient current limit faults
are internally filtered.
The MIC2027/77 is available in narrow (150 mil) and wide
(300 mil) SOP (small outline packages).
Typical Application
ON/OFF
OVERCURRENT
MIC2027
3.3V USB Controller
V
BUS
D+
D
GND
V
BUS
D+
D
GND
MIC5203-3.3
LDO Regulator
IN
OUT
GND
33
F*
Ferrite
Bead
D+
D
V+
ENA
IN
FLGA
IN
ENB
OUTA
FLGB
OUTB
Bold lines indicate
0.1" wide, 1-oz. copper
high-current traces.
Downstream
USB
Port 1
500mA max.
Downstream
USB
Port 2
500mA max.
33
F*
0.1
F
V
BUS
D+
D
GND
V
BUS
D+
D
GND
33
F*
ENC
OUTD
FLGC
END
GND
FLGD
GND
Downstream
USB
Port 3
500mA max.
Downstream
USB
Port 4
500mA max.
33
F*
0.01
F
0.01
F
0.01
F
0.01
F
4.7
F
1
F
GND
5V
3%
* 33
F, 16V tantalum or 100
F, 10V electrolytic per port
OUTC
10k
4-Port Self-Powered Hub
Features
140m
maximum on-resistance per channel
2.7V to 5.5V operating range
500mA minimum continuous current per channel
Short-circuit protection with thermal shutdown
Thermally isolated channels
Fault status flag with 3ms filter
eliminates false assertions
Undervoltage lockout
Reverse current flow blocking (no "body diode")
Circuit breaker mode (MIC2077)
reduces power consumption
Logic-compatible inputs
Soft-start circuit
Low quiescent current
Pin-compatible with MIC2524 and MIC2527
Applications
USB peripherals
General purpose power switching
ACPI power distribution
Notebook PCs
PDAs
PC card hot swap
Micrel, Inc. 1849 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 944-0970 http://www.micrel.com
MIC2027/2077
Micrel
MIC2027/2077
2
June 2000
Ordering Information
Part Number
Enable
Temperature Range
Package
MIC2027-1BWM
Active High
40
C to +85
C
16-lead wide SOP
MIC2027-1BM
Active High
40
C to +85
C
16-lead SOP
MIC2027-2BWM
Active Low
40
C to +85
C
16-lead wide SOP
MIC2027-2BM
Active Low
40
C to +85
C
16-lead SOP
MIC2077-1BWM
Active High
40
C to +85
C
16-lead wide SOP
MIC2077-1BM
Active High
40
C to +85
C
16-lead SOP
MIC2077-2BWM
Active Low
40
C to +85
C
16-lead wide SOP
MIC2077-2BM
Active Low
40
C to +85
C
16-lead SOP
Pin Configuration
1
2
3
4
16
15
14
13
FLGB
ENB
OUTB
IN(A/B)
FLGA
ENA
OUTA
GND
5
6
7
8
12
11
10
9
GND
OUTD
END
FLGD
IN(C/D)
OUTC
ENC
FLGC
16-Lead SOP (M)
16-Lead Wide SOP (WM)
LOGIC,
CHARGE
PUMP
LOGIC,
CHARGE
PUMP
3 OUTA
14 OUTB
13 IN(A/B)
ENA 2
FLGA 1
ENB 15
FLGB 16
LOGIC,
CHARGE
PUMP
LOGIC,
CHARGE
PUMP
6 OUTC
11 OUTD
5 IN(C/D)
ENC 7
FLGC 8
END 10
FLGD 9
12
4 GND
Functional Pinout
June 2000
3
MIC2027/2077
MIC2027/2077
Micrel
Absolute Maximum Ratings
(Note 1)
Supply Voltage (V
IN
) ...................................... 0.3V to +6V
Fault Flag Voltage (V
FLG
) .............................................. +6V
Fault Flag Current (I
FLG
) ............................................ 25mA
Output Voltage (V
OUT
) .................................................. +6V
Output Current (I
OUT
) ............................... Internally Limited
Enable Input (I
EN
) .................................... 0.3V to V
IN
+ 3V
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 Temperature (T
A
) ......................... 40
C to +85
C
Junction Temperature Range (T
J
) ........... Internally Limited
Thermal Resistance
[300 mil] Wide SOP (
JA
) .................................. 120
C/W
[150 mil] SOP (
JA
) ........................................... 112
C/W
DIP(
JA
) ............................................................. 130
C/W
Pin Description
Pin Number
Pin Name
Pin Function
1
FLGA
Fault Flag A: (Output): Active-low, open-drain output. Low indicates
overcurrent or thermal shutdown conditions. Overcurrent conditions must
last longer than t
D
to assert flag.
2
ENA
Switch A Enable (Input): Logic-compatible enable input. Active high (-1) or
active low (-2).
3
OUTA
Switch A Output
4, 12
GND
Ground
5
IN(C/D)
Input: Channel C and D switch and logic supply input.
6
OUTC
Switch C Output
7
ENC
Switch C Enable (Input)
8
FLGC
Fault Flag C (Output)
9
FLGD
Fault Flag D (Output)
10
END
Switch D Enable (Input)
11
OUTD
Switch D Output
13
IN(A/B)
Supply Input: Channel A and B switch and logic supply input.
14
OUTB
Switch B Output
15
ENB
Switch B Enable (Input)
16
FLGB
Fault Flag B (Output)
MIC2027/2077
Micrel
MIC2027/2077
4
June 2000
Electrical Characteristics
V
IN
= +5V; T
A
= 25
C, bold values indicate 40
C
T
A
+85
C; unless noted
Symbol
Parameter
Condition
Min
Typ
Max
Units
I
DD
Supply Current
MIC20x7-1, V
ENAD
0.8V
1.5
10
A
(switch off), OUT = open
MIC20x7-2, V
ENAD
2.4V
1.5
10
A
(switch off), OUT = open
MIC20x7-1, V
ENAD
2.4V
200
320
A
(switch on), OUT = open
MIC20x7-2, V
ENAD
0.8V
200
320
A
(switch on), OUT = open
V
EN
Enable Input Threshold
low-to-high transition
1.7
2.4
V
high-to-low transition
0.8
1.45
V
Enable Input Hysteresis
250
mV
I
EN
Enable Input Current
V
EN
= 0V to 5.5V
1
0.01
1
A
Enable Input Capacitance
1
pF
R
DS(on)
Switch Resistance
V
IN
= 5V, I
OUT
= 500mA
100
150
m
V
IN
= 3.3V, I
OUT
= 500mA
110
170
m
Output Leakage Current
MIC20x7-1, V
ENx
0.8V;
10
A
MIC20x7-2, V
ENx
2.4V, (output off)
Output Current in
MIC2077 (per Latch Output)
50
A
Latched Thermal Shutdown
(during thermal shutdown state)
t
ON
Output Turn-On Delay
R
L
= 10
, C
L
= 1
F, see "Timing Diagrams"
1.3
5
ms
t
R
Output Turn-On Rise Time
R
L
= 10
, C
L
= 1
F, see "Timing Diagrams"
1.15
4.9
ms
t
OFF
Output Turnoff Delay
R
L
= 10
, C
L
= 1
F, see "Timing Diagrams"
35
100
s
t
F
Output Turnoff Fall Time
R
L
= 10
, C
L
= 1
F, see "Timing Diagrams"
32
100
s
I
LIMIT
Short-Circuit Output Current
V
OUT
= 0V, enabled into short-circuit
0.5
0.9
1.25
A
Current-Limit Threshold
ramped load applied to output
1.0
1.25
A
Short-Circuit Response Time
V
OUT
= 0V to I
OUT
= I
LIMIT
20
s
(short applied to output)
t
D
Overcurrent Flag Response
V
IN
= 5V, apply V
OUT
= 0V until FLG low
1.5
3
7
ms
Delay
V
IN
= 3.3V, apply V
OUT
= 0V until FLG low
3
ms
Undervoltage Lockout
V
IN
rising
2.2
2.4
2.7
V
Threshold
V
IN
falling
2.0
2.15
2.5
V
Error Flag Output
I
L
= 10mA, V
IN
= 5V
10
25
Resistance
I
L
= 10mA, V
IN
= 3.3V
15
40
Error Flag Off Current
V
FLAG
= 5V
10
A
Overtemperature Threshold
T
J
increasing, each switch
140
C
Note 4
T
J
decreasing, each switch
120
C
T
J
increasing, both switches
160
C
T
J
decreasing, both switches
150
C
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.
If there is an output current limit fault on one channel, that channel will shut down when the die reaches approximately 140
C. If the die
reaches approximately 160
C, the other channel driven by the same input will shut down, even if neither channel is in current limit.
June 2000
5
MIC2027/2077
MIC2027/2077
Micrel
Test Circuit
Device
Under
Test
C
L
OUT
R
L
V
OUT
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-Low Switch Delay Times (MIC20x7-2)
V
EN
50%
90%
V
OUT
10%
t
OFF
t
ON
Active-High Switch Delay Times (MIC20x7-1)
MIC2027/2077
Micrel
MIC2027/2077
6
June 2000
0
50
100
150
200
250
300
350
-40 -20
0
20
40
60
80 100
CURRENT (
A)
TEMPERATURE (
C)
Supply On-Current
vs. Temperature
5V
3.3V
0
20
40
60
80
100
120
140
160
-40 -20
0
20
40
60
80 100
ON-RESISTANCE (m
)
TEMPERATURE (
C)
On-Resistance
vs. Temperature
5V
3.3V
I
OUT
= 500mA
0
1
2
3
4
5
-40 -20
0
20
40
60
80 100
RISE TIME (ms)
TEMPERATURE (
C)
Turn-On Rise Time
vs. Temperature
R
L
=10
C
L
=1
F
V
IN
= 5V
V
IN
= 3.3V
0
100
200
300
400
2.5
3.0
3.5
4.0
4.5
5.0
5.5
CURRENT (
A)
INPUT VOLTAGE (V)
Supply On-Current
vs. Input Voltage
+85
C
+25
C
-40
C
0
50
100
150
200
2.5
3.0
3.5
4.0
4.5
5.0
5.5
RESISTANCE (m
)
INPUT VOLTAGE (V)
On-Resistance
vs. Input Voltage
I
OUT
= 500mA
+85
C
+25
C
-40
C
0
0.5
1.0
1.5
2.0
2.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
RISE TIME (ms)
INPUT VOLTAGE (V)
Turn-Off Rise Time
vs. Input Voltage
R
L
=10
C
L
=1
F
+85
C
+25
C
-40
C
0
200
400
600
800
1000
-40 -20
0
20
40
60
80 100
CURRENT LIMIT (mA)
TEMPERATURE (
C)
Short-Circuit Current-Limit
vs. Temperature
V
IN
= 3.3V
V
IN
= 5V
0
200
400
600
800
1000
1200
-40 -20
0
20
40
60
80 100
CURRENT LIMIT THRESHOLD (mA)
TEMPERATURE (
C)
Current-Limit Threshold
vs. Temperature
V
IN
= 3.3V
V
IN
= 5V
0
100
200
300
400
-40 -20
0
20
40
60
80 100
FALL TIME (
s)
TEMPERATURE (
C)
Fall Time
vs. Temperature
R
L
=10
C
L
=1
F
V
IN
= 3.3V
0
100
200
300
400
500
600
700
800
2.5
3.0
3.5
4.0
4.5
5.0
5.5
CURRENT LIMIT (mA)
INPUT VOLTAGE (V)
Short-Circuit Current-Limit
vs. Input Voltage
+85
C
+25
C
-40
C
0
200
400
600
800
1000
1200
2.5
3.0
3.5
4.0
4.5
5.0
5.5
CURRENT LIMIT THRESHOLD (mA)
INPUT VOLTAGE (V)
Current-Limit Threshold
vs. Input Voltage
+85
C
+25
C
-40
C
0
50
100
150
200
250
300
2.5
3.0
3.5
4.0
4.5
5.0
5.5
RISE TIME (
s)
INPUT VOLTAGE (V)
Fall Time
vs. Input Voltage
T
A
= 25
C
C
L
= 1
F
R
L
= 10
June 2000
7
MIC2027/2077
MIC2027/2077
Micrel
0
0.5
1.0
1.5
2.0
2.5
-40 -20
0
20
40
60
80 100
ENABLE THRESHOLD (V)
TEMPERATURE (
C)
Enable Threshold
vs. Temperature
V
IN
= 5V
V
EN
RISING
V
EN
FALLING
0
1
2
3
4
5
-40 -20
0
20
40
60
80 100
DELAY TIME (ms)
TEMPERATURE (
C)
Flag Delay
vs. Temperature
V
IN
= 3.3V
V
IN
= 5V
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
-40 -20
0
20
40
60
80 100
SUPPLY CURRENT (
A)
TEMPERATURE (
C)
Supply Off Current
vs. Temperature
5V
3.3V
0
0.5
1.0
1.5
2.0
2.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
ENABLE THRESHOLD (V)
INPUT VOLTAGE (V)
Enable Threshold
vs. Input Voltage
T
A
= 25
C
V
EN
FALLING
V
EN
RISING
0
1
2
3
4
5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
DELAY TIME (ms)
INPUT VOLTAGE (V)
Flag Delay
vs. Input Voltage
+85
C
+25
C
-40
C
0
0.05
0.10
0.15
0.20
0.25
0.30
0.35
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY CURRENT (
A)
VOLTAGE (V)
Supply Off Current
vs. Input Voltage
+85
C
+25
C
-40
C
0
0.5
1.0
1.5
2.0
2.5
3.0
-40 -20
0
20
40
60
80 100
UVLO THRESHOLD (V)
TEMPERATURE (
C)
UVLO Threshold
vs. Temperature
V
IN
RISING
V
IN
FALLING
MIC2027/2077
Micrel
MIC2027/2077
8
June 2000
Functional Characteristics
UVLO--V
IN
Rising
(MIC2027-1)
TIME (10ms/div.)
I
OUT
(100mA/div
.
)
V
IN
(2V/div
.
)
V
OUT
(2V/div
.
)
V
FLG
(2V/div
.
)
V
EN
= V
IN
C
L
= 57
F
R
L
= 35
2.4V
UVLO--V
IN
Falling
(MIC2027-1)
TIME (100ms/div.)
I
OUT
(100mA/div
.
)
V
IN
(2V/div
.
)
V
OUT
(5V/div
.
)
V
FLG
(2V/div
.
)
V
EN
= V
IN
C
L
= 57
F
R
L
= 35
2.2V
Turn-On/Turnoff
(MIC2027-1)
TIME (10ms/div.)
I
OUT
(200mA/div
.
)
V
EN
(10V/div
.
)
V
OUT
(5V/div
.
)
V
FLG
(5V/div
.
)
V
IN
= 5V
C
L
= 147
F
R
L
= 35
712mA
(Inrush Current)
140mA
Turn-On
(MIC2027-1)
TIME (500
s/div.)
I
OUT
(200mA/div
.
)
V
EN
(10V/div
.
)
V
OUT
(5V/div
.
)
V
FLG
(5V/div
.
)
V
IN
= 5V
C
L
= 147
F
R
L
= 35
140mA
Turnoff
(MIC2027-1)
TIME (5ms/div.)
I
OUT
(200mA/div
.
)
V
EN
(10V/div
.
)
V
OUT
(5V/div
.
)
V
FLG
(5V/div
.
)
V
IN
= 5V
C
L
= 147
F
R
L
= 35
140mA
Enabled Into Short
(MIC2027-1)
TIME (500
s/div.)
I
OUT
(500mA/div
.)
V
EN
(10V/div
.)
V
OUT
(5V/div
.)
V
FLG
(5V/div
.)
V
IN
= 5V
3.1ms (t
D
)
700mA
June 2000
9
MIC2027/2077
MIC2027/2077
Micrel
Inrush Current Response
(MIC2027-1)
TIME (1ms/div.)
I
OUT
(200mA/div
.
)
V
EN
(10V/div
.
)
V
FLG
(5V/div
.
)
V
IN
= 5V
R
L
= 31
C
L
= 10
F
C
L
= 110
F
C
L
= 210
F
C
L
= 310
F
Current-Limit Response
(Ramped LoadMIC2027-1)
TIME (100ms/div.)
I
OUT
(500mA/div
.
)
V
IN
(10V/div
.
)
V
OUT
(5V/div
.
)
V
FLG
(10V/div
.
)
V
IN
= 5V
C
L
= 47
F
Current-Limit
Threshold
(1A)
Thermal Shutdown
Thermal
Shutdown
Hysteresis
Short
Removed
Short-Circuit
Current (800mA)
Current-Limit Response
(Stepped Short--MIC2027-1)
TIME (1ms/div.)
I
OUT
(2A/div
.
)
V
EN
(10V/div
.
)
V
OUT
(5V/div
.
)
V
FLG
(5V/div
.
)
V
IN
= 5V
C
L
= 47
F
R
L
= stepped short
800mA
Current-Limit Response
(MIC2027-1)
TIME (50
s/div.)
I
OUT
(5A/div
.
)
V
OUT
(5V/div
.
)
V
IN
= 5V
C
L
= 0
R
L
= stepped short
Short-Circuit (800mA)
Independent Thermal Shutdown
(MIC2027-1)
TIME (100ms/div.)
I
OUTB
(500mA/div
.
)
V
ENB
(10V/div
.
)
V
FLGB
(5V/div
.
)
V
FLGA
(5V/div
.
)
V
OUTA
= No Load
(No Thermal Shutdown)
Thermal Shutdown
V
ENA
= 5V
V
ENB
= 5V
V
ENC
= 0V
V
END
= 0V
Independent Thermal Shutdown
(MIC2027-1)
TIME (100ms/div.)
I
OUT
A
(500mA/div
.
)
V
ENA
(10V/div
.
)
V
FLGB
(5V/div
.
)
V
FLGA
(5V/div
.
)
V
OUTB
= No Load
(No Thermal Shutdown)
Thermal Shutdown
V
ENA
= 5V
V
ENB
= 5V
V
ENC
= 0V
V
END
= 0V
MIC2027/2077
Micrel
MIC2027/2077
10
June 2000
Thermal Shutdown
(MIC2077-2--Output Latched Off)
No Load
TIME (2.5s/div.)
I
OUTB
(500mV/div
.
)
V
OUT
(5V/div
.
)
V
FLG
(10V/div
.
)
V
IN
= 5V
C
L
= 47
F
V
ENB
= 0V
Thermal
Shutdown
Load Removed
Output
Reset
R
L
= 0
Thermal Shutdown
(Output Reset by Toggling Enable--MIC2077-2)
TIME (100ms/div.)
I
OUT
(500mA/div
.
)
V
EN
(10V/div
.
)
V
OUT
(5V/div
.
)
V
FLG
(5V/div
.
)
V
IN
= 5V
Enable
Reset
Thermal
Shutdown
Output
Reset
Ramp Load
to Short
C
L
= 57
F
R
L
= 35
Thermal Shutdown
(Output Reset by Removing Load--MIC2077-2)
TIME (100ms/div.)
I
OUT
(500mA/div
.
)
V
EN
(10V/div
.
)
V
OUT
(5V/div
.
)
V
FLG
(5V/div
.
)
V
IN
= 5V
C
L
= 47
F
Load Removed
(Output Reset)
Output
Latched Off
Thermal
Shutdown
Ramp Load
to Short
Independent Thermal Shutdown
(MIC2077-2)
TIME (2.5s/div.)
I
OUT
A
(500mA/div
.
)
V
FLGA
(5V/div
.
)
V
FLGB
(5V/div
.
)
V
IN
= 5V
C
L
= 47
F
V
ENB
= 0V
V
ENA
= 0V
V
ENC
= 5V
V
END
= 5V
Output Reset
Load
Removed
No Thermal Shutdown on Channel B
Thermal
Shutdown
R
L
= 0
No
Load
Independent Thermal Shutdown
(MIC2077-2)
TIME (2.5s/div.)
I
OUTB
(500mA/div
.
)
V
FLGA
(5V/div
.
)
V
FLGB
(10V/div
.
)
V
IN
= 5V
C
L
= 47
F
V
ENB
= 0V
V
ENA
= 0V
V
ENC
= 5V
V
END
= 5V
Output Reset
Load
Removed
No Thermal Shutdown on Channel A
Thermal
Shutdown
R
L
= 0
No
Load
June 2000
11
MIC2027/2077
MIC2027/2077
Micrel
Block Diagram
1.2V
REFERENCE
THERMAL
SHUTDOWN
CHARGE
PUMP
OUTB
UVLO
GATE
CONTROL
IN (A/B)
RESET
(MIC2077 ONLY)
(MIC2077 ONLY)
(MIC2077 ONLY)
(MIC2077 ONLY)
RESET
RESET
RESET
GATE
CONTROL
OUTA
FLGB
CHARGE
PUMP
ENB
OSC.
FLGA
CURRENT
LIMIT
CURRENT
LIMIT
1.2V
REFERENCE
THERMAL
SHUTDOWN
CHARGE
PUMP
OUTD
UVLO
GATE
CONTROL
IN (C/D)
ENC
GATE
CONTROL
OUTC
FLGD
CHARGE
PUMP
END
OSC.
FLGC
CURRENT
LIMIT
CURRENT
LIMIT
GND
MIC2027
FLAG
DELAY
FLAG
DELAY
FLAG
DELAY
FLAG
DELAY
THERMAL
SHUTDOWN
LATCH
THERMAL
SHUTDOWN
LATCH
THERMAL
SHUTDOWN
LATCH
THERMAL
SHUTDOWN
LATCH
MIC2027/2077
Micrel
MIC2027/2077
12
June 2000
Functional Description
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
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
OUT
> V
IN
) when the
switch is disabled. In this situation, the MIC2027/77 prevents
undesirable current flow from OUT to IN.
Thermal Shutdown
Thermal shutdown is employed to protect the device from
damage should the die temperature exceed safe margins
due mainly to short circuit faults. Each channel employs its
own thermal sensor. Thermal shutdown shuts off the output
MOSFET and asserts the FLG output if the die temperature
reaches 140
C and the overheated channel is in current limit.
The other channels are not effected. If however, the die
temperature exceeds 160
C, all channels will be shut off.
Upon determining a thermal shutdown condition, the MIC2077
will latch the output off and activate a pull-up current source.
When the load is removed, this current source will pull the
output up and reset the latch. Toggling EN will also reset the
latch.
The MIC2027 will automatically reset its output when the die
temperature cools down to 120
C. The MIC2027 output and
FLG signal will continue to cycle on and off until the device is
disabled or the fault is removed. Figure 2 depicts typical
timing.
Depending on PCB layout, package, ambient temperature,
etc., it may take several hundred milliseconds from the
incidence of the fault to the output MOSFET being shut off.
This time will be shortest in the case of a dead short on the
output.
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 of each channel and junction temperature are
found below.
P
D
= R
DS(on)
I
OUT
2
Total power dissipation of the device will be the summation of
P
D
for all 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 device and external load but still
allows a minimum current of 500mA to be delivered to the
load.
The current-limit circuit senses a portion of the output MOS-
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 three scenarios:
Switch Enabled into Short-Circuit
If a switch is enabled into a heavy load or short-circuit, the
switch immediately enters into a constant-current mode,
limiting the output voltage. The FLG signal is asserted indicat-
ing an overcurrent condition.
Short-Circuit Applied to Enabled 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 short-circuit current limit specification.
Current-Limit Response--Ramped Load
The MIC2027/77 current-limit profile exhibits a small foldback
effect of about 100mA. Once this current-limit threshold is
exceeded the device switches into a constant current mode.
It is important to note that the device will supply current up to
the current-limit threshold.
Fault Flag
The FLG signal is an N-channel open-drain MOSFET output.
FLG is asserted (active-low) when either an overcurrent or
thermal shutdown condition occurs. In the case of an overcur-
rent condition, 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. For example, 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 thresh-
old. The FLG response delay time t
D
is typically 3ms.
Undervoltage Lockout
Undervoltage lockout (UVLO) prevents the output MOSFET
from turning on until V
IN
exceeds approximately 2.5V. Under-
voltage detection functions only when the switch is enabled.
June 2000
13
MIC2027/2077
MIC2027/2077
Micrel
V
EN
V
OUT
I
OUT
Short-Circuit Fault
Thermal
Shutdown
Reached
Load and Fault Removed
(Output Reset)
V
FLG
I
LIMIT
I
LOAD
3ms typ.
delay
Figure 1. MIC2077-2 Fault Timing: Output Reset by Removing Load
V
EN
V
OUT
I
OUT
Short-Circuit Fault
Thermal
Shutdown
Reached
Load/Fault
Removed
V
FLG
I
LOAD
I
LIMIT
3ms typ.
delay
Figure 2. MIC2027-2 Fault Timing
MIC2027/2077
Micrel
MIC2027/2077
14
June 2000
Applications Information
Supply Filtering
A 0.1
F to 1
F bypass capacitor positioned close to V
IN
and
GND of 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 induc-
tance) to damage internal control circuitry.
Printed Circuit Board Hot-Plug
The MIC2027/77 are ideal inrush current-limiters for hot-plug
applications. Due to the integrated charge pump, the
MIC2027/77 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 ca-
pacitive loads by reducing inrush current.
In cases of extremely large capacitive loads (>400
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 flag delay specification,
FLG will be asserted during this time. To prevent the logic
controller from responding to FLG being asserted, an exter-
nal 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, less
t
D(min)
of the MIC2027/77.
Universal Serial Bus (USB) Power Distribution
The MIC2027/77 is ideally suited for USB (Universal Serial
Bus) power distribution applications. The USB specification
defines power distribution for USB host systems such as PCs
and USB hubs. Hubs can either be self-powered or bus-
powered (that is, powered from the bus). The requirement for
USB self-powered hubs is that the port must supply a mini-
mum of 500mA at an output voltage of 5V
5%. In addition,
the output power delivered must be limited to below 25VA.
Upon an overcurrent condition, the host must also be notified.
To support hot-plug events, the hub must have a minimum of
120
F of bulk capacitance, preferably low ESR electrolytic or
tantulum. Please refer to Application Note 17 for more details
on designing compliant USB hub and host systems.
10k
V+
MIC2027
FLGA
FLGB
ENA
OUTA OUTB
GND IN(A/B)
ENB
1
16
2
15
3
14
4
13
OVERCURRENT
Logic Controller
R
C
5
12
6
11
7
10
8
9
IN(C/D) GND
OUTC OUTD
ENC
END
FLGC
FLGD
Figure 3. Transient Filter
June 2000
15
MIC2027/2077
MIC2027/2077
Micrel
Package Information
45
0
8
0.244 (6.20)
0.228 (5.79)
0.394 (10.00)
0.386 (9.80)
SEATING
PLANE
0.020 (0.51)
REF
0.020 (0.51)
0.013 (0.33)
0.157 (3.99)
0.150 (3.81)
0.050 (1.27)
0.016 (0.40)
0.0648 (1.646)
0.0434 (1.102)
0.050 (1.27)
BSC
PIN 1
DIMENSIONS:
INCHES (MM)
0.0098 (0.249)
0.0040 (0.102)
16-Lead SOP (M)
0.022 (0.559)
0.018 (0.457)
5
TYP
0.408 (10.363)
0.404 (10.262)
0.409 (10.389)
0.405 (10.287)
0.103 (2.616)
0.099 (2.515)
SEATING
PLANE
0.027 (0.686)
0.031 (0.787)
0.016 (0.046)
TYP
0.301 (7.645)
0.297 (7.544)
0.094 (2.388)
0.090 (2.286)
0.297 (7.544)
0.293 (7.442)
10
TYP
0.032 (0.813) TYP
0.330 (8.382)
0.326 (8.280)
7
TYP
0.050 (1.270)
TYP
0.015
(0.381)
R
0.015
(0.381)
MIN
PIN 1
DIMENSIONS:
INCHES (MM)
16-Lead Wide SOP (WM)
MIC2027/2077
Micrel
MIC2027/2077
16
June 2000
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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