MICREL MIC2026

MIC2026/2076
Micrel
MIC2026/2076
Dual-Channel Power Distribution Switch
Preliminary Information
General Description
Features
The MIC2026 and MIC2076 are high-side MOSFET switches
optimized for general-purpose power distribution requiring
circuit protection.
The MIC2026/76 are internally current limited and have
thermal shutdown that protects the device and load.
The MIC2076 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 faults are internally
filtered.
The MIC2026/76 are available in 8-pin DIP or 8-lead SOP.
•
•
•
•
•
•
•
•
•
•
•
•
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 (MIC2076)
Logic-compatible inputs
Soft-start circuit
Low quiescent current
Pin-compatible with MIC2526
Applications
•
•
•
•
•
•
USB peripherals
General purpose power switching
ACPI power distribution
Notebook PCs
PDAs
PC card hot swap
Typical Application
VCC
2.7V to 5.5V
VCONT.
10k
10k
Logic Controller
VIN
MIC2026-2
ON/OFF
ENA
OUTA
OVERCURRENT
FLGA
IN
OVERCURRENT
FLGB
GND
ENB
OUTB
ON/OFF
Load
0.1µF
Load
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
March 2000
1
MIC2026/2076
MIC2026/2076
Micrel
Ordering Information
Part Number
Enable
Temperature Range
Package
MIC2026-1BM
Active High
–40°C to +85°C
8-lead SOP
MIC2026-2BM
Active Low
–40°C to +85°C
8-lead SOP
MIC2026-1BN
Active High
–40°C to +85°C
8-pin DIP
MIC2026-2BN
Active Low
–40°C to +85°C
8-pin DIP
MIC2076-1BM
Active High
–40°C to +85°C
8-lead SOP
MIC2076-2BM
Active Low
–40°C to +85°C
8-lead SOP
MIC2076-1BN
Active High
–40°C to +85°C
8-pin DIP
MIC2076-2BN
Active Low
–40°C to +85°C
8-pin DIP
Pin Configuration
MIC2026/76
ENA
1
8
OUTA
FLGA
2
7
IN
FLGB
3
6
GND
ENB
4
5
OUTB
8-Lead SOP (BM)
8-Pin DIP (BN)
Pin Description
Pin Number
Pin Name
1
ENA
Switch A Enable (Input): Logic-compatible enable input. Active high (-1) or
active low (-2).
2
FLGA
Fault Flag A (Output): Active-low, open-drain output. Indicates overcurrent
or thermal shutdown conditions. Overcurrent conditions must last longer
than tD in order to assert FLGA.
3
FLGB
Fault Flag B (Output): Active-low, open-drain output. Low indicates
overcurrent or thermal shutdown conditions.Overcurrent conditions must last
longer than tD in order to assert FLGB.
4
ENB
Switch B Enable (Input): Logic-compatible enable input. Active-high (-1) or
active-low (-2).
5
OUTB
Switch B (Output)
6
GND
Ground
7
IN
8
OUTA
MIC2026/2076
Pin Function
Input: Switch and logic supply input.
Switch A (Output)
2
March 2000
MIC2026/2076
Micrel
Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
Supply Voltage (VIN) ...................................... –0.3V to +6V
Fault Flag Voltage (VFLG) .............................................. +6V
Fault Flag Current (IFLG) ............................................ 25mA
Output Voltage (VOUT) .................................................. +6V
Output Current (IOUT) ............................... Internally Limited
Enable Input (IEN) .................................... –0.3V to VIN + 3V
Storage Temperature (TS) ...................... –65°C to +150 °C
ESD Rating, Note 3
Supply Voltage (VIN) ................................... +2.7V to +5.5V
Ambient Temperature (TA) ......................... –40°C to +85°C
Junction Temperature Range (TJ) ........... Internally Limited
Thermal Resistance
SOP (θJA) .......................................................... 160°C/W
DIP(θJA) ............................................................. 105°C/W
Electrical Characteristics
VIN = +5V; TA = 25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted
Symbol
Parameter
Condition
IDD
Supply Current
VEN
Enable Input Threshold
Min
Typ
Max
Units
MIC20x6-1, VENA = VENB ≤ 0.8V
(switch off), OUT = open
0.75
5
µA
MIC20x6-2, VENA = VENB ≥ 2.4V
(switch off), OUT = open
0.75
5
µA
MIC20x6-1, VENA = VENB ≥ 2.4V
(switch on), OUT = open
100
160
µA
MIC20x6-2, VENA = VENB ≤ 0.8V
(switch on), OUT = open
100
160
µA
low-to-high transition
1.7
2.4
V
high-to-low transition
0.8
Enable Input Hysteresis
IEN
Enable Input Current
VEN = 0V to 5.5V
–1
Enable Input Capacitance
RDS(on)
Switch Resistance
1.45
V
250
mV
0.01
1
1
µA
pF
VIN = 5V, IOUT = 500mA
90
140
mΩ
VIN = 3.3V, IOUT = 500mA
100
160
mΩ
10
µA
Output Leakage Current
MIC20x6-1, VENx ≤ 0.8V;
MIC20x6-1, VENx ≥ 2.4V, (output off)
OFF Current in
Latched Thermal Shutdown
MIC2076
(during thermal shutdown state)
50
tON
Output Turn-On Delay
RL = 10Ω, CL = 1µF, see “Timing Diagrams”
1.3
5
ms
tR
Output Turn-On Rise Time
RL = 10Ω, CL = 1µF, see “Timing Diagrams”
1.15
4.9
ms
tOFF
Output Turnoff Delay
RL = 10Ω, CL = 1µF, see “Timing Diagrams”
35
100
µs
tF
Output Turnoff Fall Time
RL = 10Ω, CL = 1µF, see “Timing Diagrams”
32
100
µs
ILIMIT
Short-Circuit Output Current
VOUT = 0V, enabled into short-circuit
0.9
1.25
A
Current-Limit Threshold
ramped load applied to output
1.0
1.25
A
Short-Circuit Response Time
VOUT = 0V to IOUT = ILIMIT
(short applied to output)
20
Overcurrent Flag Response
Delay
VIN = 5V, apply VOUT = 0V until FLG low
tD
Undervoltage Lockout
Threshold
March 2000
0.5
µA
µs
1.5
3
TBD
3
VIN rising
2.2
2.4
2.7
V
VIN falling
2.0
2.15
2.5
V
VIN = 3.3V, apply VOUT = 0V until FLG low
3
7
ms
ms
MIC2026/2076
MIC2026/2076
Symbol
Micrel
Parameter
Condition
Error Flag Output
Resistance
Error Flag Off Current
Min
Typ
Max
Units
IL = 10mA, VIN = 5V
10
25
Ω
IL = 10mA, VIN = 3.3V
15
40
Ω
10
µA
VFLAG = 5V
Overtemperature Threshold
Note 4
TJ increasing, each switch
140
°C
TJ decreasing, each switch
120
°C
TJ increasing, both switches
160
°C
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.
Note 4.
If there is a fault on one channel, that channel will shut down when the die reaches approximately 140°C. If the die reaches approximately
160°C, both channels will shut down, even if neither channel is in current limit.
Test Circuit
VOUT
Device
Under OUT
Test
RL
CL
Timing Diagrams
tR
tF
90%
VOUT
90%
10%
10%
Output Rise and Fall Times
VEN
50%
tOFF
tON
90%
VOUT
10%
Active-Low Switch Delay Times (MIC20x6-2)
VEN
50%
tOFF
tON
VOUT
90%
10%
Active-High Switch Delay Times (MIC20x6-1)
MIC2026/2076
4
March 2000
MIC2026/2076
Micrel
Supply On-Current
vs. Temperature
140
5V
120
100
80
3.3V
60
40
20
5
3.3V
120
4
100
5V
80
60
IOUT = 500mA
40
RL=10Ω
CL=1µF
3
2
VIN = 3.3V
1
20
VIN = 5V
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
Supply On-Current
vs. Input Voltage
On-Resistance
vs. Input Voltage
Turn-On Rise Time
vs. Input Voltage
200
-40°C
100
+25°C
+85°C
50
2.5
2.0
150
RISE TIME (ms)
150
RESISTANCE (mΩ)
200
CURRENT (µA)
Turn-On Rise Time
vs. Temperature
RISE TIME (ms)
160
160
ON-RESISTANCE (mΩ)
180
140
CURRENT (µA)
On-Resistance
vs. Temperature
+85°C
+25°C
100
-40°C
50
+85°C
1.5
1.0
+25°C
-40°C
0.5
RL=10Ω
CL=1µF
IOUT = 500mA
VIN = 3.3V
600
VIN = 5V
400
200
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
Short-Circuit Current-Limit
vs. Input Voltage
800
CURRENT LIMIT (mA)
700
600
500 +85°C
+25°C
-40°C
400
300
200
100
0
2.5
March 2000
3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
5.5
0
2.5
5.5
Current-Limit Threshold
vs. Temperature
1200
1200
3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
5.5
Fall Time
vs. Temperature
400
VIN = 5V
1000
800
FALL TIME (µs)
CURRENT LIMIT (mA)
1000
3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
VIN = 3.3V
600
400
300
VIN = 3.3V
200
RL=10Ω
CL=1µF
100
200
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
Current-Limit Threshold
vs. Input Voltage
Fall Time
vs. Input Voltage
300
1000
800
250
+85°C
+25°C
RISE TIME (µs)
Short-Circuit Current-Limit
vs. Temperature
800
0
2.5
5.5
CURRENT LIMIT THRESHOLD (mA)
3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
CURRENT LIMIT THRESHOLD (mA)
0
2.5
-40°C
600
400
200
0
2.5
200
150
100
50
3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
5
5.5
0
2.5
TA = 25°C
CL = 1µF
RL = 10Ω
3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
5.5
MIC2026/2076
MIC2026/2076
Micrel
Enable Threshold
vs. Temperature
Flag Delay
vs. Temperature
0.16
DELAY TIME (ms)
VEN RISING
2.0
1.5
VEN FALLING
1.0
0.5
SUPPLY CURRENT (µA)
VIN = 3.3V
4
VIN = 5V
3
2
1
VIN = 5V
0.14
5V
0.12
0.1
0.08
0.06
3.3V
0.04
0.02
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
Enable Threshold
vs. Input Voltage
Flag Delay
vs. Input Voltage
Supply Off Current
vs. Input Voltage
2.0
5
VEN RISING
1.5
VEN FALLING
1.0
0.5
4
3
0.18
+85°C
SUPPLY CURRENT (µA)
2.5
ENABLE THRESHOLD (V)
5
DELAY TIME (ms)
ENABLE THRESHOLD (V)
2.5
Supply Off Current
vs. Temperature
+25°C
-40°C
2
1
TA = 25°C
0
2.5
3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
0
2.5
5.5
3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
5.5
0.16
0.14
+85°C
0.12
0.10
0.08
0.06
0.04
+25°C
-40°C
0.02
0
2.5
3.0
3.5 4.0 4.5
VOLTAGE (V)
5.0
5.5
UVLO Threshold
vs. Temperature
UVLO THRESHOLD (V)
3.0
2.5
V IN RISING
2.0
V IN FALLING
1.5
1.0
0.5
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
MIC2026/2076
6
March 2000
MIC2026/2076
Micrel
Functional Characteristics
UVLO—VIN Falling
(MIC2026-1)
VFLG
VIN
(2V/div.) (2V/div.)
VIN
VFLG
(2V/div.) (2V/div.)
UVLO—VIN Rising
(MIC2026-1)
TIME (100ms/div.)
Turn-On/Turnoff
(MIC2026-1)
Turn-On
(MIC2026-1)
712mA
(Inrush Current)
VIN = 5V
CL = 147µF
RL = 35Ω
IOUT
(200mA/div.)
VIN = 5V
CL = 147µF
RL = 35Ω
IOUT
(200mA/div.)
VEN = VIN
CL = 57µF
RL = 35Ω
TIME (10ms/div.)
VOUT
VFLG
VEN
(5V/div.) (5V/div.) (10V/div.)
VEN
VOUT
VFLG
(5V/div.) (5V/div.) (10V/div.)
IOUT
(100mA/div.)
VEN = VIN
CL = 57µF
RL = 35Ω
140mA
140mA
TIME (10ms/div.)
TIME (500µs/div.)
Turnoff
(MIC2026-1)
Enabled Into Short
(MIC2026-1)
VEN
VOUT
VFLG
(5V/div.) (5V/div.) (10V/div.)
VEN
VOUT
VFLG
(5V/div.) (5V/div.) (10V/div.)
2.2V
VOUT
IOUT
(100mA/div.) (5V/div.)
VOUT
(2V/div.)
2.4V
3.1ms (tD)
IOUT
(500mA/div.)
IOUT
(200mA/div.)
700mA
VIN = 5V
CL = 147µF
RL = 35Ω
140mA
TIME (500µs/div.)
TIME (5ms/div.)
March 2000
VIN = 5V
7
MIC2026/2076
MIC2026/2076
Micrel
Current-Limit Response
(Ramped Load–MIC2026-1)
CL = 110µF
IOUT
(200mA/div.)
CL = 210µF
VOUT
(5V/div.)
VFLG
VIN
(10V/div.) (10V/div.)
VEN
VFLG
(5V/div.) (10V/div.)
Inrush Current Response
(MIC2026-1)
VIN = 5V
RL = 31Ω
IOUT
(500mA/div.)
CL = 310µF
CL = 10µF
Short
Removed
Thermal
Shutdown
Hysteresis
Current-Limit Response
(MIC2026-1)
VEN
VFLG
(5V/div.) (10V/div.)
Current-Limit Response
(Stepped Short—MIC2026-1)
VOUT
(5V/div.)
VIN = 5V
CL = 47µF
RL = stepped short
IOUT
(5A/div.)
VOUT
(5V/div.)
800mA
VIN = 5V
CL = 0
RL = stepped short
Short-Circuit (800mA)
TIME (1ms/div.)
TIME (50µs/div.)
Independent Thermal Shutdown
(MIC2026-1)
Independent Thermal Shutdown
(MIC2026-1)
VENA
VFLGB VFLGA
(5V/div.) (5V/div.) (10V/div.)
IOUT
(2A/div.)
VFLGA
VENB
(5V/div.) (10V/div.)
Short-Circuit
Current (800mA)
Thermal Shutdown
TIME (100ms/div.)
VOUTA = No Load
(No Thermal Shutdown)
IOUTA
(500mA/div.)
VFLGB
(5V/div.)
IOUTB
(500mA/div.)
Current-Limit
Threshold
(1A)
TIME (1ms/div.)
Thermal Shutdown
TIME (100ms/div.)
MIC2026/2076
VIN = 5V
CL = 47µF
VOUTB = No Load
(No Thermal Shutdown)
Thermal Shutdown
TIME (100ms/div.)
8
March 2000
MIC2026/2076
Micrel
No Load
Load Removed
Enable
Reset
VFLG
(5V/div.)
VOUT
VFLG
(5V/div.) (10V/div.)
RL = 0
IOUTB
(500mV/div.)
VOUT
(5V/div.)
VIN = 5V
CL = 47µF
VENB = 0V
Output
Reset
Ramp Load
to Short
CL = 57µF
RL = 35Ω
IOUT
(500mA/div.)
Output
Reset
Thermal
Shutdown
Thermal
Shutdown
VIN = 5V
TIME (2.5s/div.)
TIME (100ms/div.)
Thermal Shutdown
(Output Reset by Removing Load—MIC2076-2)
Independent Thermal Shutdown
(MIC2076-2)
Output
Latched Off
VFLGB
VFLGA
(5V/div.) (5V/div.)
RL = 0
Load Removed
(Output Reset)
Ramp Load
to Short
Load
Removed
Output Reset
Thermal
Shutdown
Thermal
Shutdown
VIN = 5V
CL = 47µF
No
Load
No Thermal Shutdown on Channel B
IOUTA
(500mA/div.)
IOUT
(500mA/div.)
VOUT
(5V/div.)
VEN
VFLG
(5V/div.) (10V/div.)
Thermal Shutdown
(Output Reset by Toggling Enable—MIC2076-2)
VEN
(10V/div.)
Thermal Shutdown
(MIC2076-2—Output Latched Off)
TIME (100ms/div.)
VIN = 5V
CL = 47µF
VENB = 0V
VENA = 0V
TIME (2.5s/div.)
Independent Thermal Shutdown
(MIC2076-2)
IOUTB
(500mA/div.)
VFLGA VFLGB
(5V/div.) (10V/div.)
RL = 0
Load
Removed
No
Load
Output Reset
No Thermal Shutdown on Channel A
Thermal
Shutdown
VIN = 5V
CL = 47µF
VENB = 0V
VENA = 0V
TIME (2.5s/div.)
March 2000
9
MIC2026/2076
MIC2026/2076
Micrel
Block Diagram
FLGA
FLAG
RESPONSE
DELAY
OUTA
ENA
CHARGE
PUMP
GATE
CONTROL
CURRENT
LIMIT
OSC.
THERMAL
SHUTDOWN
UVLO
1.2V
REFERENCE
CHARGE
PUMP
GATE
CONTROL
IN
CURRENT
LIMIT
ENB
FLAG
RESPONSE
DELAY
OUTB
FLGB
MIC2026/2076
GND
The MIC2026 will automatically reset its output when the die
temperature cools down to 120°C. The MIC2026 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 = RDS(on) × IOUT2
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 VOUT is greater than VIN, 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 (VOUT > VIN) when the
switch is disabled. In this situation, the MIC2026/76 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 channel is not effected. If however, the die temperature exceeds 160°C, both channels will be shut off. Upon
determining a thermal shutdown condition, the MIC2076 will
latch the output off. In this case, a pull-up current source is
activated. This allows the output latch to automatically reset
when the load (such as a USB device) is removed. The output
can also be reset by toggling EN. Refer to Figure 1 for timing
details.
MIC2026/2076
Total power dissipation of the device will be the summation of
PD for both channels. To relate this to junction temperature,
the following equation can be used:
TJ = PD × θJA + TA
where:
TJ = junction temperature
TA = ambient temperature
θJA = is the thermal resistance of the package
10
March 2000
MIC2026/2076
Micrel
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:
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 for up to 1ms. 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.
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,
reducing 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 MIC2026/76 current-limit profile exhibits a small foldback
effect of about 200mA. 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.
Load and Fault Removed
(Output Reset)
Short-Circuit Fault
VEN
VOUT
ILIMIT
ILOAD
IOUT
VFLG
Thermal
Shutdown
Reached
3ms typ.
delay
Figure 1. MIC2076-2 Fault Timing: Output Reset by Removing Load
Short-Circuit Fault
VEN
Load/Fault
Removed
VOUT
ILIMIT
ILOAD
IOUT
VFLG
Thermal
Shutdown
Reached
3ms typ.
delay
Figure 2. MIC2026-2 Fault Timing
March 2000
11
MIC2026/2076
MIC2026/2076
Micrel
Universal Serial Bus (USB) Power Distribution
The MIC2026/76 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). Figure 5 shows a
typical USB Host application that may be suited for mobile PC
applications employing USB. The requirement for USB host
systems 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.
For bus-powered hubs, USB requires that each downstream
port be switched on or off under control by the host. Up to four
downstream ports each capable of supplying 100mA at 4.4V
minimum are allowed. In addition, to reduce voltage droop on
the upstream VBUS, soft-start is necessary. Although the hub
can consume up to 500mA from the upstream bus, the hub
must consume only 100mA max at start-up, until it enumerates with the host prior to requesting more power. The same
requirements apply for bus-powered peripherals that have no
downstream ports. Figure 6 shows a bus-powered hub.
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 MIC2026/76 are ideal inrush current-limiters for hot-plug
applications. Due to the integrated charge pump, the
MIC2026/76 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. Figure 3 shows how
the MIC2076 may be used in a card hot-plug application.
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 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 4, 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 tD(min) of the
MIC2026/76.
USB
Controller
MIC2026-2BM
1
VBUS
4.7
µF
to "Hot"
Receptacle
ENA
USB
Function
8
OUTA
2
7
FLGA
IN
3
FLGB
GND
6
4
ENB
OUTB
5
CBULK
USB
Function
CBULK
GND
USB Peripheral
Cable
Figure 3. Hot-Plug Application
V+
Logic Controller
OVERCURRENT
MIC2026
10k
1
R
C
2
3
4
EN
OUTA
FLGA
IN
FLGB
GND
ENB
OUTB
8
7
6
5
Figure 4. Transient Filter
MIC2026/2076
12
March 2000
MIC2026/2076
Micrel
VCC
5.0V
Ferrite
Beads
10k
4.50V to 5.25V
Upstream VBUS
100mA max.
VBUS
10k
VBUS
D+
3.3V USB Controller
MIC5207-3.3
IN
D+
1µF
D–
VIN
OUT
GND
1µF
GND
MIC2026-2
ON/OFF
ENA
OUTA
OVERCURRENT
FLGA
OVERCURRENT
FLGB
GND
ENB
OUTB
ON/OFF
IN
D–
47µF
USB
Port 1
GND
0.1µF
VBUS
D+
D–
47µF
USB
Port 2
GND
Data
Data
(Two Pair)
to USB
Controller
Figure 5. USB Two-Port Host Application
1.5k 2%
Ferrite
Beads
10k
10k
4.50V to 5.25V
Upstream VBUS
3.3V USB Controller
MIC5207-3.3
VBUS
IN
D+
1µF
D–
GND
VIN
OUT
GND
VBUS
1µF
D+
MIC2026-2
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
Figure 6. USB Two-Port Bus-Powered Hub
March 2000
13
MIC2026/2076
MIC2026/2076
Micrel
Package Information
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
DIMENSIONS:
INCHES (MM)
0.050 (1.27)
TYP
0.064 (1.63)
0.045 (1.14)
0.197 (5.0)
0.189 (4.8)
0.020 (0.51)
0.013 (0.33)
45°
0.0098 (0.249)
0.0040 (0.102)
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-Lead 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 DIP (N)
MIC2026/2076
14
March 2000
MIC2026/2076
March 2000
Micrel
15
MIC2026/2076
MIC2026/2076
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
MIC2026/2076
16
March 2000