MIC2027/2077 Micrel
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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 shutdown 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).
Features
• 140mΩ 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
Typical Application
5V ± 3%
MIC5203-3.3
LDO Regulator
IN OUT
4.7
µF
GND
Bold lines indicate
0.1" wide, 1-oz. copper
high-current traces.
* 33µF, 16V tantalum or 100µF, 10V electrolytic per port
1µF
10k
V+
D+
D–
ON/OFF
OVERCURRENT
GND
MIC20273.3V USB Controller
ENA
FLGA IN
ENB OUTA
FLGB
ENC
END
FLGD GND
IN
OUTB
OUTC
OUTDFLGC
GND
4-Port Self-Powered Hub
33µF*
0.1
µF
33µF*
33µF*
33µF*
Ferrite
Bead
0.01µF
0.01µF
0.01µF
0.01µF
V
BUS
D+
D–
GND
V
BUS
D+
D–
GND
V
BUS
D+
D–
GND
V
BUS
D+
D–
GND
Downstream
USB
Port 1
500mA max.
Downstream
USB
Port 2
500mA max.
Downstream
USB
Port 3
500mA max.
Downstream
USB
Port 4
500mA max.
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
June 2000 1 MIC2027/2077
MIC2027/2077 Micrel
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
FLGA
OUTA
IN(C/D)
OUTC
FLGC
1
ENA
2
3
GND
4
5
6
ENC
7
8
16-Lead SOP (M)
16-Lead Wide SOP (WM)
16
15
14
13
12
11
10
9
FLGB
ENB
OUTB
IN(A/B)
GND
OUTD
END
FLGD
ENA 2
FLGA 1
ENB 15
FLGB 16
ENC 7
FLGC 8
END 10
FLGD 9
Functional Pinout
LOGIC,
CHARGE
PUMP
LOGIC,
CHARGE
PUMP
LOGIC,
CHARGE
PUMP
LOGIC,
CHARGE
PUMP
3 OUTA
13 IN(A/B)
14 OUTB
6 OUTC
5 IN(C/D)
11 OUTD
124 GND
MIC2027/2077 2 June 2000
MIC2027/2077 Micrel
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 tD 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)
Absolute Maximum Ratings (Note 1)
Supply Voltage (VIN) ...................................... –0.3V to +6V
Fault Flag Voltage (V
Fault Flag Current (I
Output Voltage (V
Output Current (I
OUT
Enable Input (IEN).................................... –0.3V to VIN + 3V
Storage Temperature (TS) ...................... –65°C to +150 °C
)..............................................+6V
FLG
) ............................................25mA
FLG
) ..................................................+6V
OUT
)...............................Internally Limited
Operating Ratings (Note 2)
Supply Voltage (VIN) ................................... +2.7V to +5.5V
Ambient Temperature (TA).........................–40°C to +85°C
Junction Temperature Range (TJ) ........... Internally Limited
Thermal Resistance
[300 mil] Wide SOP (θJA) ..................................120°C/W
[150 mil] SOP (θJA) ...........................................112°C/W
DIP(θJA).............................................................130°C/W
Lead Temperature (soldering 5 sec.) ........................ 260°C
ESD Rating, Note 3 ......................................................1kV
June 2000 3 MIC2027/2077
MIC2027/2077 Micrel
Electrical Characteristics
VIN = +5V; TA = 25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted
Symbol Parameter Condition Min Typ Max Units
I
DD
V
EN
I
EN
R
DS(on)
t
ON
t
R
t
OFF
t
F
I
LIMIT
t
D
Supply Current MIC20x7-1, V
(switch off), OUT = open
MIC20x7-2, V
(switch off), OUT = open
MIC20x7-1, V
(switch on), OUT = open
MIC20x7-2, V
(switch on), OUT = open
≤ 0.8V 1.5 10 µA
ENA–D
≥ 2.4V 1.5 10 µA
ENA–D
≥ 2.4V 200 320 µA
ENA–D
≤ 0.8V 200 320 µA
ENA–D
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
Enable Input Current V
= 0V to 5.5V –1 0.01 1 µA
EN
Enable Input Capacitance 1 pF
Switch Resistance VIN = 5V, I
VIN = 3.3V, I
Output Leakage Current MIC20x7-1, V
MIC20x7-2, V
= 500mA 100 150 mΩ
OUT
= 500mA 110 170 mΩ
OUT
≤ 0.8V; 10 µA
ENx
≥ 2.4V, (output off)
ENx
Output Current in MIC2077 (per Latch Output) 50 µA
Latched Thermal Shutdown (during thermal shutdown state)
Output Turn-On Delay RL = 10Ω, CL = 1µF, see “Timing Diagrams” 1.3 5 ms
Output Turn-On Rise Time RL = 10Ω, CL = 1µF, see “Timing Diagrams” 1.15 4.9 ms
Output Turnoff Delay RL = 10Ω, CL = 1µF, see “Timing Diagrams” 35 100 µs
Output Turnoff Fall Time RL = 10Ω, CL = 1µF, see “Timing Diagrams” 32 100 µs
Short-Circuit Output Current V
= 0V, enabled into short-circuit 0.5 0.9 1.25 A
OUT
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 µs
(short applied to output)
Overcurrent Flag Response VIN = 5V, apply V
Delay
VIN = 3.3V, apply V
= 0V until FLG low 1.5 3 7 ms
OUT
= 0V until FLG low 3 ms
OUT
Undervoltage Lockout VIN rising 2.2 2.4 2.7 V
Threshold
VIN falling 2.0 2.15 2.5 V
Error Flag Output IL = 10mA, VIN = 5V 10 25 Ω
Resistance
Error Flag Off Current V
Overtemperature Threshold T
Note 4
IL = 10mA, VIN = 3.3V 15 40 Ω
= 5V 10 µA
FLAG
increasing, each switch 140 °C
J
TJ decreasing, each switch 120 °C
T
increasing, both switches 160 °C
J
TJ 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.
MIC2027/2077 4 June 2000
MIC2027/2077 Micrel
Test Circuit
V
Device
Under
Test
OUT
C
R
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 (MIC20x7-2)
V
EN
V
OUT
50%
t
OFF
t
ON
90%
10%
Active-High Switch Delay Times (MIC20x7-1)
June 2000 5 MIC2027/2077
MIC2027/2077 Micrel
Supply On-Current
vs. Temperature
5V
3.3V
50
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
CURRENT (µA)
350
300
250
200
150
100
Supply On-Current
vs. Input Voltage
-40°C
+25°C
+85°C
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
CURRENT (µA)
400
300
200
100
On-Resistance
160
140
120
100
ON-RESISTANCE (mΩ)
vs. Temperature
3.3V
I
OUT
5V
= 500mA
80
60
40
20
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
On-Resistance
200
150
100
RESISTANCE (mΩ)
vs. Input Voltage
+85°C
+25°C
50
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
-40°C
I
= 500mA
OUT
INPUT VOLTAGE (V)
Turn-On Rise Time
vs. Temperature
5
4
3
2
VIN = 3.3V
RISE TIME (ms)
1
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
RL=10Ω
C
VIN = 5V
=1µF
L
Turn-Off Rise Time
vs. Input Voltage
2.5
2.0
1.5
1.0
RISE TIME (ms)
0.5
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
+85°C
+25°C
-40°C
INPUT VOLTAGE (V)
RL=10Ω
C
=1µF
L
Short-Circuit Current-Limit
1000
800
600
400
200
CURRENT LIMIT (mA)
vs. Temperature
VIN = 3.3V
VIN = 5V
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
Short-Circuit Current-Limit
800
700
600
500
400
300
200
CURRENT LIMIT (mA)
100
vs. Input Voltage
+25°C
+85°C
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
-40°C
Current-Limit Threshold
1200
1000
800
600
400
200
CURRENT LIMIT THRESHOLD (mA)
vs. Temperature
VIN = 5V
VIN = 3.3V
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
Current-Limit Threshold
1200
1000
800
600
400
200
CURRENT LIMIT THRESHOLD (mA)
vs. Input Voltage
+25°C
+85°C
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
-40°C
Fall Time
vs. Temperature
VIN = 3.3V
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
RL=10Ω
C
=1µF
L
FALL TIME (µs)
400
300
200
100
Fall Time
vs. Input Voltage
TA = 25°C
C
= 1µF
50
L
R
= 10Ω
L
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
RISE TIME (µs)
300
250
200
150
100
MIC2027/2077 6 June 2000
MIC2027/2077 Micrel
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 (µA)
TEMPERATURE (°C)
Supply Off Current
vs. Temperature
5V
3.3V
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 (µA)
VOLTAGE (V)
Supply Off Current
vs. Input Voltage
+85°C
+25°C
-40°C
Enable Threshold
2.5
2.0
1.5
1.0
0.5
ENABLE THRESHOLD (V)
vs. Temperature
VEN RISING
VEN FALLING
VIN = 5V
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
Enable Threshold
vs. Input Voltage
2.5
2.0
1.5
1.0
0.5
ENABLE THRESHOLD (V)
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VEN RISING
VEN FALLING
TA = 25°C
INPUT VOLTAGE (V)
Flag Delay
vs. Temperature
5
4
3
2
DELAY TIME (ms)
1
0
-40 -20 0 20 40 60 80 100
VIN = 3.3V
VIN = 5V
TEMPERATURE (°C)
Flag Delay
vs. Input Voltage
5
+85°C
4
3
2
DELAY TIME (ms)
1
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
+25°C
-40°C
INPUT VOLTAGE (V)
June 2000 7 MIC2027/2077
UVLO Threshold
vs. Temperature
3.0
2.5
2.0
1.5
1.0
0.5
UVLO THRESHOLD (V)
0
-40 -20 0 20 40 60 80 100
VIN RISING
VIN FALLING
TEMPERATURE (°C)
MIC2027/2077 Micrel
Functional Characteristics
V
V
V
I
V
V
V
I
IN
FLG
OUT
OUT
EN
FLG
OUT
OUT
UVLO—VIN Rising
(MIC2027-1)
IN
V
2.4V
(2V/div.)
(2V/div.)
FLG
V
(2V/div.)
UVLO—VIN Falling
(MIC2027-1)
2.2V
(2V/div.)
VEN = V
IN
(2V/div.)
CL = 57µF
= 35Ω
R
L
V
I
OUT
OUT
(5V/div.)
VEN = V
IN
CL = 57µF
= 35Ω
R
L
(100mA/div.)
(100mA/div.)
TIME (10ms/div.)
Turn-On/Turnoff
(MIC2027-1)
EN
V
V
V
I
(10V/div.)
FLG
(5V/div.)
OUT
(5V/div.)
OUT
(200mA/div.)
(10V/div.)
(5V/div.)
(5V/div.)
712mA
(Inrush Current)
VIN = 5V
= 147µF
C
L
= 35Ω
R
L
140mA
(200mA/div.)
TIME (100ms/div.)
Turn-On
(MIC2027-1)
VIN = 5V
= 147µF
C
L
= 35Ω
R
L
140mA
V
V
V
I
EN
FLG
OUT
OUT
TIME (10ms/div.)
Turnoff
(MIC2027-1)
EN
(10V/div.)
(5V/div.)
(5V/div.)
VIN = 5V
= 147µF
C
L
= 35Ω
R
140mA
L
V
V
V
I
(10V/div.)
FLG
(5V/div.)
OUT
(5V/div.)
OUT
TIME (500µs/div.)
Enabled Into Short
(MIC2027-1)
3.1ms (tD)
700mA
VIN = 5V
(500mA/div.)
(200mA/div.)
TIME (5ms/div.)
TIME (500µs/div.)
MIC2027/2077 8 June 2000
MIC2027/2077 Micrel
Current-Limit Response
(Ramped Load–MIC2027-1)
TIME (100ms/div.)
I
OUT
(500mA/div.)
V
IN
(10V/div.)
V
OUT
(5V/div.)
V
FLG
(10V/div.)
VIN = 5V
C
L
= 47µF
Current-Limit
Threshold
(1A)
Thermal Shutdown
Thermal
Shutdown
Hysteresis
Short
Removed
Short-Circuit
Current (800mA)
Current-Limit Response
(MIC2027-1)
TIME (50µs/div.)
I
OUT
(5A/div.)
V
OUT
(5V/div.)
VIN = 5V
C
L
= 0
R
L
= stepped short
Short-Circuit (800mA)
Independent Thermal Shutdown
(MIC2027-1)
TIME (100ms/div.)
I
OUTA
(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
Inrush Current Response
(MIC2027-1)
EN
V
(10V/div.)
FLG
V
(5V/div.)
I
V
V
V
I
OUT
EN
FLG
OUT
OUT
CL = 110µF
CL = 210µF
CL = 310µF
VIN = 5V
= 31Ω
R
L
(200mA/div.)
= 10µF
C
L
TIME (1ms/div.)
Current-Limit Response
(Stepped Short—MIC2027-1)
(10V/div.)
(5V/div.)
(5V/div.)
(2A/div.)
800mA
VIN = 5V
= 47µF
C
L
= stepped short
R
L
TIME (1ms/div.)
Independent Thermal Shutdown
(MIC2027-1)
ENB
V
(10V/div.)
FLGA
V
(5V/div.)
FLGB
V
(5V/div.)
OUTB
I
(500mA/div.)
June 2000 9 MIC2027/2077
V
= No Load
OUTA
(No Thermal Shutdown)
Thermal Shutdown
TIME (100ms/div.)
= 5V
V
ENA
= 5V
V
ENB
= 0V
V
ENC
= 0V
V
END
MIC2027/2077 Micrel
Thermal Shutdown
(MIC2077-2—Output Latched Off)
Thermal
Shutdown
TIME (2.5s/div.)
Load Removed
Output
Reset
VIN = 5V
C
V
FLG
V
OUT
V
OUTB
I
RL = 0
(10V/div.)
(5V/div.)
(500mV/div.)
Thermal Shutdown
(Output Reset by Removing Load—MIC2077-2)
EN
V
(10V/div.)
V
V
I
FLG
(5V/div.)
OUT
(5V/div.)
OUT
(500mA/div.)
Output
Latched Off
Ramp Load
to Short
Thermal
Shutdown
VIN = 5V
C
No Load
= 47µF
L
= 0V
ENB
Load Removed
(Output Reset)
= 47µF
L
(Output Reset by Toggling Enable—MIC2077-2)
Thermal Shutdown
EN
V
(10V/div.)
FLG
V
V
I
(5V/div.)
OUT
(5V/div.)
OUT
= 57µF
C
L
= 35Ω
R
L
Ramp Load
to Short
Thermal
Shutdown
VIN = 5V
(500mA/div.)
TIME (100ms/div.)
Independent Thermal Shutdown
(MIC2077-2)
R
= 0
FLGB
V
FLGA
V
OUTA
I
L
No Thermal Shutdown on Channel B
(5V/div.)
(5V/div.)
Thermal
Shutdown
(500mA/div.)
Load
Removed
Output Reset
VIN = 5V
C
V
V
V
V
Enable
Reset
Output
Reset
No
Load
= 47µF
L
= 0V
ENB
= 0V
ENA
= 5V
ENC
= 5V
END
TIME (100ms/div.)
FLGB
V
FLGA
V
I
OUTB
TIME (2.5s/div.)
Independent Thermal Shutdown
(MIC2077-2)
Load
RL = 0
Removed
(10V/div.)
No Thermal Shutdown on Channel A
(5V/div.)
Thermal
Shutdown
(500mA/div.)
TIME (2.5s/div.)
No
Load
Output Reset
VIN = 5V
C
V
V
V
V
= 47µF
L
= 0V
ENB
= 0V
ENA
= 5V
ENC
= 5V
END
MIC2027/2077 10 June 2000
MIC2027/2077 Micrel
Block Diagram
ENB
ENC
RESET
(MIC2077 ONLY)
CHARGE
PUMP
OSC.
CHARGE
PUMP
RESET
(MIC2077 ONLY)
RESET
(MIC2077 ONLY)
CHARGE
PUMP
THERMAL
SHUTDOWN
LATCH
THERMAL
SHUTDOWN
THERMAL
SHUTDOWN
LATCH
THERMAL
SHUTDOWN
LATCH
UVLO
GATE
CONTROL
GATE
CONTROL
GATE
CONTROL
DELAY
1.2V
REFERENCE
DELAY
DELAY
FLAG
CURRENT
LIMIT
CURRENT
LIMIT
FLAG
FLAG
CURRENT
LIMIT
FLGA
OUTA
IN (A/B)
OUTB
FLGB
FLGC
OUTC
END
MIC2027
OSC.
CHARGE
PUMP
RESET
(MIC2077 ONLY)
THERMAL
SHUTDOWN
THERMAL
SHUTDOWN
LATCH
GND
UVLO
GATE
CONTROL
1.2V
REFERENCE
DELAY
CURRENT
LIMIT
FLAG
IN (C/D)
OUTD
FLGD
June 2000 11 MIC2027/2077
MIC2027/2077 Micrel
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
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
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 factors 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.
PD = R
DS(on)
Total power dissipation of the device will be the summation of
PD for all channels. To relate this to junction temperature, the
following equation can be used:
TJ = PD × θJA + T
is greater than VIN, current will flow
OUT
> VIN) when the
OUT
OUT
A
2
× I
where:
TJ = junction temperature
TA = ambient temperature
θJA = 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 MOSFET 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 indicating 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 currentlimit 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 overcurrent condition, FLG will be asserted only after the flag
response delay time, tD, 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 threshold. The FLG response delay time tD is typically 3ms.
Undervoltage Lockout
Undervoltage lockout (UVLO) prevents the output MOSFET
from turning on until VIN exceeds approximately 2.5V. Undervoltage detection functions only when the switch is enabled.
MIC2027/2077 12 June 2000
MIC2027/2077 Micrel
Load and Fault Removed
(Output Reset)
V
V
OUT
I
LIMIT
I
LOAD
I
OUT
EN
Short-Circuit Fault
Thermal
Shutdown
Reached
V
FLG
3ms typ.
delay
Figure 1. MIC2077-2 Fault Timing: Output Reset by Removing Load
V
V
OUT
I
LIMIT
I
LOAD
I
OUT
V
FLG
EN
Short-Circuit Fault
Load/Fault
Removed
Thermal
Shutdown
Reached
3ms typ.
delay
Figure 2. MIC2027-2 Fault Timing
June 2000 13 MIC2027/2077
MIC2027/2077 Micrel
Applications Information
Supply Filtering
A 0.1µF to 1µF bypass capacitor positioned close to VIN 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 inductance) 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 capacitive loads by reducing inrush current.
In cases of extremely large capacitive loads (>400µF), 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 external 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
of the MIC2027/77.
t
D(min)
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 buspowered (that is, powered from the bus). The requirement for
USB self-powered hubs is that the port must supply a minimum 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
120µF 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.
Logic Controller
OVERCURRENT
10k
R
C
Figure 3. Transient Filter
V+
MIC2027
116
FLGA FLGB
215
ENA
314
OUTA OUTB
413
GND IN(A/B)
512
IN(C/D) GND
611
OUTC OUTD
710
ENC END
89
FLGC FLGD
ENB
MIC2027/2077 14 June 2000
MIC2027/2077 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)
0.301 (7.645)
0.297 (7.544)
0.027 (0.686)
0.031 (0.787)
0.094 (2.388)
0.090 (2.286)
0.050 (1.27)
BSC
0.050 (1.270)
TYP
0.409 (10.389)
0.405 (10.287)
0.020 (0.51)
0.013 (0.33)
0.394 (10.00)
0.386 (9.80)
16-Lead SOP (M)
0.016 (0.046)
TYP
PIN 1
0.103 (2.616)
0.099 (2.515)
SEATING
PLANE
0.0098 (0.249)
0.0040 (0.102)
SEATING
PLANE
7°
TYP
0.015
R
(0.381)
0.015
(0.381)
MIN
DIMENSIONS:
INCHES (MM)
0.050 (1.27)
0.016 (0.40)
0.244 (6.20)
0.228 (5.79)
DIMENSIONS:
INCHES (MM)
0.297 (7.544)
0.293 (7.442)
0.330 (8.382)
0.326 (8.280)
0.032 (0.813) TYP
0.408 (10.363)
0.404 (10.262)
45°
0°–8°
0.022 (0.559)
0.018 (0.457)
10° TYP
5°
TYP
16-Lead Wide SOP (WM)
June 2000 15 MIC2027/2077
MIC2027/2077 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.
© 2000 Micrel Incorporated
MIC2027/2077 16 June 2000
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