January 2005 1 MIC2044/2045
MIC2044/2045 Micrel
MIC2044/2045
Single Channel, High Current, Low Voltage,
Protected Power Distribution Switch
General Description
The MIC2044 and MIC2045 are high-side MOSFET switches
optimized for general purpose power distribution applications
that require circuit protection. These devices switch up to
5.5V and as low as 0.8V while offering both programmable
current limiting and thermal shutdown to protect the device
and the load. A fault status output is provided to indicate
overcurrent and thermal shutdown fault conditions. Both
devices employ soft-start circuitry to minimize the inrush
current in applications that employ highly capacitive loads.
Additionally, for tighter control over inrush current during start
up, the output slew-rate may be adjusted by an external
capacitor.
The MIC2045 features a auto-reset circuit breaker that latches
the output OFF upon detecting an overcurrent condition
lasting more than 32ms. The output is reset by removing or
reducing the load.
Data sheets and support documentation can be found on
Micrel’s web site at www.micrel.com.
Typical Application
7, 11,
13, 16
8
2
3
6
4
15
9,12,14
1
5
R
SET
100
W
Note:
All V
IN
pins (7, 11, 13, 16) must be externally tied together.
All V
OUT
pins (9, 12, 14) must be externally tied together.
I
LIMIT
= 4A.
Output Power-Good = 3.0V.
*C4 is optional. See
"Applications Information."
C4*
0.022
m
F
C1
0.1
m
F
Logic
Controller
ON/OFF
OVERCURRENT
IN
10
MIC2044-1BTS
MIC39100-2.5BS
VBIAS
VIN
EN
/FAULT
ILIM
SLEW 2.5V
VOUT
PGREF
PWRGD
UVLOIN
GND
R1
20k
W
R2
294k
W
1%
R3
24.3k
W
1%
EN
IN
GND
OUT
C
LOAD
33
m
F
V
OUT
3.3V@ 3.5A
R4
20k
W
(OPEN)
+3.3V
Power
Supply
OUT1 OUT2
C3
4.7
m
F
C2
0.1
m
F
Features
• 30mΩ maximum on-resistance
•0.8V to 5.5V operating range
•Adjustable current limit
•Up to 6A continuous output current
•Short circuit protection
•Very fast reaction to short circuits
•Thermal shutdown
•Adjustable slew-rate control
•Circuit breaker mode (MIC2045)
•Fault status flag
•Power-Good detection
•Undervoltage lockout
•No reverse current flow through the switching MOSFET
when OFF or disabled
•Low quiescent current
Applications
•Docking stations
•LAN servers
•WAN switches
•Hot swap board insertions
•Notebook PCs
•PDAs
•Base stations
•RAID controllers
•USB hosts
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
MIC2044/2045 Micrel
MIC2044/2045 2 January 2005
Pin Configuration
1PWRGD
EN
/FAULT
SLEW
UVLOIN
ILIM
VIN
VBIAS
16 VIN
PGREF
VOUT
VIN
VOUT
VIN
GND
VOUT
15
14
13
12
11
10
9
2
3
4
5
6
7
8
MIC2044/MIC2045
16-Pin TSSOP (TS)
Ordering Information
Part Number
Standard Pb-Free Enable Circuit Breaker Package
MIC2044-1BTS MIC2044-1YTS Active-High 16-Pin TSSOP
MIC2044-2BTS MIC2044-2YTS Active-Low 16-Pin TSSOP
MIC2045-1BTS MIC2045-1YTS Active-High X 16-Pin TSSOP
MIC2045-2BTS MIC2045-2YTS Active-Low X 16-Pin TSSOP
January 2005 3 MIC2044/2045
MIC2044/2045 Micrel
Pin Description
Pin Number Pin Name Pin Function
1PWRGD Power-Good (Output): Open drain N-Channel device, active high. This pin
asserts high when the voltage at PGREF exceeds its threshold.
2ENSwitch Enable (Input): Gate control pin of the output MOSFET available as
an active high (–1) or active low (–2) input signal.
3/FAULT Fault Status (Output): Open drain N-Channel device, active low. This pin
indicates an overcurrent or thermal shutdown condition. For an overcurrent
event, /FAULT is asserted if the duration of the overcurrent condition lasts
longer than 32ms.
10 GND Ground connection: Tie to analog ground.
4SLEW Slew-Rate Control (Input): A capacitor connected between this pin and
ground will reduce (slow) the output slew-rate. The output turn-on time must
be less than the nominal flag delay of 32ms in order to avoid nuisance
tripping of the /FAULT output since VOUT must be “fully on” (i.e., within
200mV of the voltage at the input) before the /FAULT signal delay elapses.
The slew-rate limiting capacitor requires a 16V rating or greater, 25V is
recommended. See “Applications Information: Output Slew-Rate Adjust-
ment” for further details.
6ILIM Current Limit (Input): A resistor (RSET) connected from this pin to ground
sets the current limit threshold as ILIMIT = CLF/RSET. CLF is the current limit
factor specified in the “Electrical Characteristics” table. For the MIC2044/45,
the continuous output current range is 1A to 6A.
5UVLOIN
Undervoltage Lockout Adjust
(Input):
With this pin left open, the UVLO
threshold is internally set to 1.45V. When the switching voltage (V
IN
) is at or
below 1.5V, connecting an external resistive divider to this input will lower the
UVLO threshold. The total resistance of the divider must be less than 200kΩ.
To disable the UVLO, tie this pin to VIN. See “Applications Information” for
further detail.
7,11,13,16 VIN Switch Supply (Input): Connected to the drain of the output MOSFET. The
range of input for the switch is 0.8V to 5.5V. These pins must be externally
connected together to achieve rated performance.
9,12,14 VOUT Switch (Output): Connected to the source of the output MOSFET. These
pins must be externally connected together to achieve rated performance.
8VBIAS Bias Supply (Input): This input pin supplies power to operate the switch and
internal circuitry. The input range for VBIAS is 1.6V to 5.5V. When switched
voltage (VIN) is between 1.6V to 5.5V and the use of a single supply is
desired, connect VBIAS to VIN externally.
15 PGREF Power-Good Threshold (Input): Analog reference used to specify the
PWRGD threshold. When the voltage at this pin exceeds its threshold, VTH,
PWRGD is asserted high. An external resistive divider network is used to
determine the output voltage level at which VTH is exceeded. See the
“Functional Description” for further detail. When the PWRGD signal is not
utilized, this input should be tied to VOUT.
MIC2044/2045 Micrel
MIC2044/2045 4 January 2005
Absolute Maximum Ratings (Note 1)
VIN and VBIAS .................................................................................. 6V
/FAULT, PWRGD Output Voltage ................................... 6V
/FAULT, PWRGD Output Current .............................. 25mA
ESD Rating, Note 3
Human Body Model ................................................... 2kV
Machine Model ........................................................200V
Operating Ratings (Note 2)
Supply Voltage
VIN ............................................................... 0.8V to 5.5V
VBIAS ........................................................... 1.6V to 5.5V
Continuous Output Current ................................... 1A to 6A
Ambient Temperature (TA) ........................... –40°C to 85°C
Package Thermal Resistance (Rθ(J-A))
TSSOP ................................................................ 85°C/W
Electrical Characteristics (Note 4)
VIN = VBIAS = 5V, TA = 25°C unless specified otherwise. Bold indicates –40°C to +85°C.
Symbol Parameter Condition Min Typ Max Units
VIN Switch Input Voltage VIN ≤ VBIAS 0.8 5.5 V
VBIAS Bias Supply Voltage 1.6 5.5 V
IBIAS VBIAS Supply Current - Switch OFF No load 0.1 5µA
VBIAS Supply Current - Switch ON No load 300 400 µA
Note 5
VEN Enable Input Voltage VIL(max) 2.4 1.5 V
VIH(min) 3.5 2.5 V
VENHYST Enable Input Threshold Hysteresis 100 mV
IEN Enable Input Current VEN = 0V to 5.5V –1 .01 1µA
RDS(ON) Switch Resistance VIN = VBIAS = 3V, 5V 20 30 mΩ
IOUT = 500mA
ILEAK Output Leakage Current Output off 10 µA
CLF Current Limit Factor VIN = 3V, 5V, 0.5V ≤ VOUT < 0.5VIN 300 380 460 A•Ω
Note 6 1A ≤ IOUT ≤ 6A
VTH PGREF Threshold VIN = VBIAS = 1.6V to 5.5V 215 230 245 mV
VLATCH Output Reset Threshold VIN = 0.8V to 5.5V VIN–.0.2 V
VOUT rising (MIC2045)
ILATCH Latched Output Off Current Output latched off (MIC2045) 1 3 5 mA
VOL Output Low Voltage IOL (/FAULT) = 15mA 0.4 V
(/FAULT, PWRGD) IOL (PWRGD) = 5mA
IOFF /FAULT, PWRGD Off Current VFAULT = VPWRGD = 5V 1µA
VUV Undervoltage Lockout Threshold VIN rising 1.30 1.45 1.58 V
VIN falling 1.20 1.35 1.50 V
VUVHYST Undervoltage Lockout 100 mV
Threshold Hysteresis
VUVINTH UVLO Adjust Pin Threshold Voltage VIN rising 200 230 260 mV
VIN falling 185 215 245 mV
VUVINHYST UVLO Adjust Pin Threshold Hysteresis 15 mV
Overtemperature Threshold TJ increasing 140 °C
TJ decreasing 120 °C
January 2005 5 MIC2044/2045
MIC2044/2045 Micrel
Symbol Parameter Condition Min Typ Max Units
tFLAG Flag Response Delay VIN = VBIAS = 3V, 5V 25 32 40 ms
tON Output Turn-on Delay RLOAD = 10Ω, CLOAD = 1µF0.75 1 1.25 ms
tROutput Turn-on Rise Time RLOAD = 10Ω, CLOAD = 1µF1.5 2.5 3.5 ms
tOFF Output Turn-off Delay RLOAD = 10Ω, CLOAD = 1µF15µs
tFOutput Turn-off Fall Time RLOAD = 10Ω, CLOAD = 1µF24µs
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: 1.5kΩ in series with 100pF.
Note 4. Specification for packaged product only.
Note 5. OFF is VEN < 1.0V for MIC2044/MIC2045–1 and VEN > 4.0V for MIC2044/MIC2045 –2. ON is VEN > 4.0V for MIC2044/MIC2045–1 and
VEN < 1.0V for MIC2044/MIC2045 –2.
Note 6. The current limit is determined as follows: ILIM = CLF/RSET.
Timing Diagrams
50%
(a) MIC2044/45-1
(b) MIC2044/45-2
10%
90%
0
VEN
tON
tOFF
0
VOUT
50%
10%
90%
0
VEN
tON tOFF
0
VOUT
Figure 1. Turn-On/Turn-Off Delay
0
VEN
ILIMIT
0
VOUT
0
IOUT
0
/FAULT
tFLAG
VIN 0.2V
Increase the load
Figure 2. Overcurrent Fault Response — MIC2044-2
MIC2044/2045 Micrel
MIC2044/2045 6 January 2005
Test Circuit
7, 11,
13, 16
8
2
3
5
4
15
9,12,14
1
6
*R
SET
*R
SET
and C
SLEW
use multiple values
(See specific response plots)
*C
SLEW
C2
0.1µF
10
MIC2044/45-xBTS
VBIAS
VIN
EN
/FAULT
UVLOIN
SLEW
VOUT
PGREF
PWRGD
ILIM
GND
R2
20kΩ
R1
20kΩR5
260kΩ
R6
24kΩ
C
LOAD
47µF
V
OUT
I
LOAD
R7
20kΩ
C3
10µF
C1
0.1µF
V
IN
V
DD
R3
75kΩ
R4
68kΩ
January 2005 7 MIC2044/2045
MIC2044/2045 Micrel
100
125
150
175
200
225
250
275
300
-40 -20 0 20 40 60 80 100
SUPPLY CURRENT (µA)
TEMPERATURE (°C)
Supply Current
vs. Temperature
VIN =V
BIAS =1.6V
VIN =V
BIAS = 5.5V
VIN =V
BIAS = 3V
0
1
2
3
4
5
-40 -20 0 20 40 60 80 100
V
EN
(V)
TEMPERATURE (°C)
Enable Input Threshold
(Rising)
vs. Temperature
V
BIAS
= 5.5V
V
BIAS
= 3V
V
BIAS
= 1.6V
0
1
2
3
4
5
-40 -20 0 20 40 60 80 100
V EN (V)
TEMPERATURE (°C)
Enable Input Threshold
(Falling)
vs. Temperature
V
BIAS
= 5.5V
V
BIAS
= 3V
V
BIAS
= 1.6V
0
250
500
750
1000
1250
1500
1750
2000
2250
2500
-40 -20 0 20 40 60 80 100
OUTPUT LEAKAGE (nA)
TEMPERATURE (°C)
Output Leakage Current
vs. Temperature
VBIAS = 5.5V
VBIAS = 3V
VBIAS = 1.6V
0
5
10
15
20
25
30
35
40
-40 -20 0 20 40 60 80 100
ON RESISTANCE (mΩ)
TEMPERATURE (°C)
ON Resistance
vs. Temperature
V
IN
= V
BIAS
= 1.6V
V
IN
= V
BIAS
= 3V
V
IN
= V
BIAS
= 5.5V
20
25
30
35
40
45
50
-40 -20 0 20 40 60 80 100
T
FLAG
(ms)
TEMPERATURE (°C)
Flag Response Delay
vs. Temperature
T
FLAG
= 3V
T
FLAG
= 5V
200
400
600
800
1000
1200
1400
1600
-40 -20 0 20 40 60 80 100
TURN ON DELAY (µs)
TEMPERATURE (°C)
Turn On Delay
vs. Temperature
V
IN
=V
BIAS
= 5.5V
V
IN
=V
BIAS
= 3V
V
IN
=V
BIAS
= 1.6V
0
5
10
15
20
25
0123456
I
R
(mA)
V
OUT
–V
BIAS
(V)
V
BIAS
Reverse Current Flow
vs. Output Voltage
V
IN
= GND
V
BIAS
= 1.6V
Typical Characteristics
0
0.5
1
1.5
2
2.5
3
-40 -20 0 20 40 60 80 100
UVLO THRESHOLD (V)
TEMPERATURE (°C)
UVLO Threshold
vs. Temperature
UVLO+
UVLO–
0
50
100
150
200
250
300
350
400
-40 -20 0 20 40 60 80 100
UVLOIN THRESHOLD (mV)
TEMPERATURE (°C)
UVLO Adjust Pin Threshold
vs. Temperature
UVLOIN+
UVLOIN–
0
5
10
15
20
25
-40 -20 0 20 40 60 80 100
SLEW PIN VOLTAGE (V)
TEMPERATURE (°C)
SLEW Voltage
vs. Temperature
VIN = VBIAS = 1.6V
VIN = VBIAS = 5V
VIN = VBIAS = 3V
210
215
220
225
230
-40 -20 0 20 40 60 80 100
V
TH
(mV)
TEMPERATURE (°C)
Power-Good Reference
Threshold
vs. Temperature
V
TH
@ 1.6V to 5.5V
MIC2044/2045 Micrel
MIC2044/2045 8 January 2005
Functional Characteristics
W
m
!
W
5V Turn-On
" #$%&
m
!
W
5V Turn-Off
" #
m
$%
I
OUT
2A/div
V
OUT
5V/div
/FAULT
5V/div
EN
5V/div
V
IN
= V
BIAS
=
5.0V
R
LOAD
=
1.8Ω
C
LOAD
=
47µF
R
SET
=
220Ω
Latched Output
MIC2045
TIME (5ms/div.)
V
OUT
2V/div
/FAULT
5V/div
EN
5V/div
V
IN
= V
BIAS
=
5.0V
R
LOAD
toggles from 2Ω to OPEN
C
LOAD
=
47µF
R
SET
=
220Ω
4.82V
Latched Output Reset
MIC2045
TIME (50ms/div.)
I
OUT
200mA/div
V
IN
1V/div
V
OUT
1V/div
V
IN
ramps 0V to 1.8V
R
LOAD
=
5Ω
C
LOAD
=
47µF
R
SET
=
220Ω
UVLO Response
TIME (2.5ms/div.)
1.45V
I
OUT
2A/div
/FAULT
5V/div
EN
5V/div
V
OUT
2V/div
V
IN
= V
BIAS
=
5.0V
R
LOAD
=
1.2Ω
C
LOAD
=
47µF
R
SET
=
100Ω
Current Limit Response
TIME (5ms/div.)
January 2005 9 MIC2044/2045
MIC2044/2045 Micrel
Functional Characteristics (continued)
V
OUT
1V/div
/FAULT
5V/div
EN
5V/div
I
OUT
500mA/div
V
IN
= 5.0V
R
LOAD
=
5Ω
C
LOAD
=
47µF
C
SLEW
=
0.033µF
R
SET
=
220Ω
Output Slew Response
TIME (2.5ms/div.)
V
OUT
2V/div
/FAULT
5V/div
EN
5V/div
I
OUT
1A/div
V
IN
= V
BIAS
5.0V
R
LOAD
=
2Ω
C
LOAD
=
47µF
R
SET
=
220Ω
Thermal Shutdown Response
TIME (100ms/div.)
MIC2044/2045 Micrel
MIC2044/2045 10 January 2005
Functional Diagram
MIC2044/45
Bandgap
Reference
OSC
UVLO
5.3x
1x
V
REF
= 230mV
Current
Limit
Replica
Amp
++
V
IN
ILIM
6
VOUT
9,12,14
VBIAS
8
VIN
7,11,13,16
/FAULT
3
GND
10
+
Gate
Control
UVLOIN
5
SLEW
4
EN
2
PGREF
15
Open
Load
Detect
I
LIM
Delay
(32ms)
PWRGD
1
+
Error
Flag
Logic
Power-On
Reset
Input
Logic Latch
(MIC2045)
Charge
Pump
Thermal
Shutdown
Power-Off
Reset
January 2005 11 MIC2044/2045
MIC2044/2045 Micrel
Functional Description
The MIC2044 and MIC2045 are high-side N-Channel switches
equipped with programmable current limit up to 6A for use in
general purpose power distribution applications. The switches,
available with active-high or active-low enable inputs, provide
output slew-rate control and circuit protection via thermal
shutdown and an optional output latch during overcurrent
conditions.
Input and Output
VBIAS supplies power to the internal circuitry of the switch
and must be present for the switch to operate. VIN is con-
nected to the drain of the output MOSFET and sources power
to the switched load. VIN must be less than or equal to VBIAS.
VOUT is the source terminal of the output MOSFET and
attaches to the load. In a typical circuit, current flows from VIN
to VOUT toward the load. If VOUT is greater than VIN, current
will flow from VOUT to VIN since the switch is bi-directional
when the device is enabled. When disabled (OFF), the switch
will block current flow from either direction.
Enable Input
Enable, the ON/OFF control for the output switch, is a digital
input available as an active-high (–1) or active-low (–2)
signal. The EN pin, referenced to approximately 0.5 × VBIAS,
must be driven to a clearly defined logic high or logic low.
Failure to observe this requirement, or allowing EN to float,
will cause the MIC2044/45 to exhibit unpredictable behavior.
EN should not be allowed to go negative with respect to
ground, nor allowed to exceed VBIAS. Failure to adhere to
these conditions may result in damage to the device.
Undervoltage Lockout
When the switch is enabled, undervoltage lockout (UVLO)
monitors the input voltage, VIN, and prevents the output
MOSFET from turning on until VIN exceeds a predetermined
level, nominally set at 1.45V. The UVLO threshold is adjust-
able and can be varied by applying an external resistor divider
to the UVLOIN pin from VIN to GND. The resistive divider
network is required when the input voltage is below 1.5V. The
UVLO threshold is internally preset to 1.45V if the UVLOIN
pin is left open. See “Applications Information.”
Programmable Current Limit
The MIC2044/45 is designed to prevent damage to the
external load by limiting the maximum amount of current it
can draw. The current limit is programmed by an external
resistor (RSET) connected from ILIM (Pin 6) to ground and
becomes active when the output voltage is at least 200mV
below the voltage at the input to the device. The limiting
current value is defined by the current limit factor (CLF)
divided by RSET, and the MIC2044/45 will limit from 1A to 6A
with a set point accuracy of ±21%. In programming the
nominal current limit, the value of RSET is determined using
the following equation:
RCLF
I
380A
I
SET LIMIT LIMIT
== ×Ω
()
(1)
And given the ±21% tolerance of the current limit factor (CLF),
the external resistor is bound by:
50Ω ≤ RSET ≤ 460Ω (2)
The graphs below (Figure 3) display the current limit factor
characteristic over the full temperature range at the indicated
voltage. These curves can be used as a point of reference in
determining the maximum variation in the device’s current
limit over the full temperature range. For example: With VIN
= VBIAS = 3.0V and a nominal 4A current limit (RSET = 95Ω),
the low and high current limit settings for the MIC2044/45
would be 3.15A and 4.85A, respectively, as shown on the 3V
graph using the 95Ω reference point.
When current limiting occurs, the MIC2044 and MIC2045
respond differently. Upon first reaching the limiting current
both devices restrict current flow, allowing the load voltage to
drop below VIN. If the VIN to VOUT differential voltage exceeds
200mV, then a fault condition is declared and the fault delay
timer is started. If the fault condition persists longer than the
delay period, typically 32ms, then the /FAULT output asserts
low. At this point, the MIC2044 will continue to supply current
to the load at the limiting value (ILIMIT), whereas the MIC2045
will latch off its output.
0
1
2
3
4
5
6
7
8
050100 150 200 250 300 350 400 450
I LIMIT (A)
R SET (Ω)
Current Limit
vs. RSET
–40°C to +85°C
VIN =V
BIAS = 3V, 5V
CLF (LO)
CLF (HI)
0
1
2
3
4
5
6
7
8
050100 150 200 250 300 350 400 450
I LIMIT (A)
R SET (Ω)
Current Limit
vs. RSET
–40°C to +85°C
VIN =V
BIAS = 1.6V
CLF (LO)
CLF (HI)
Figure 3. Current Limit Factor
MIC2044/2045 Micrel
MIC2044/2045 12 January 2005
/FAULT
The /FAULT signal is an N-Channel, open-drain MOSFET
output. An external pull-up resistor tied to a maximum 6V rail
is required for the /FAULT pin. The /FAULT pin is asserted
(active-low) when either an overcurrent or thermal shutdown
condition occurs. During a hot insert of a PCB or when turning
on into a highly capacitive load, the resulting high transient
inrush current may exceed the current limit threshold of the
MIC2044/45. In the case where an overcurrent condition
occurs, /FAULT will assert only after the flag delay time has
elapsed, typically 32ms. This ensures that /FAULT is as-
serted only upon valid overcurrent conditions and that nui-
sance error reporting is prevented.
Thermal Shutdown
For the MIC2044, thermal shutdown is employed to protect
the device from damage should the die temperature exceed
safe margins due to a short circuit or an excessive load.
Thermal shutdown shuts off the output MOSFET and asserts
the /FAULT output if the die temperature exceeds 140°C.
The MIC2044 automatically resets its output and resumes
supplying current to the load when the die temperature drops
to 120°C. If the fault is still present, the MIC2044 will quickly
re-heat and shut down again. This process of turning
ON-OFF-ON is called thermal cycling and will continue as
long as the power switch is enabled while the fault or
excessive load is present.
Depending on PCB layout (including thermal considerations
such as heat sinking), package, and ambient temperature, it
may take several hundred milliseconds from the incidence of
the fault to the output MOSFET being shut off.
Circuit Breaker Function (MIC2045)
The MIC2045 is designed to shut off all power to the load
when a fault condition occurs, just as a circuit breaker would
do. In this case, a fault condition is deemed to be anytime the
output current exceeds the current limit for more than the flag
delay period, nominally 32ms. Once the output shuts off, it
remains off until either the fault load is removed from VOUT
or the EN input is cycled ON-OFF-ON. If the fault is still
present after EN has been cycled, the MIC2045 will again
shut off all power to the load after 32ms. Once the fault has
been removed, then normal operation will resume.
Open Load Detection
The MIC2045 will automatically reset its output when the fault
load is cleared. This is accomplished by applying a small
current to VOUT and watching for the voltage at VOUT to rise
to within 200mV of VIN. This current is supplied by an internal
resistor connected to VIN and is connected to VOUT when
MIC2045 latches off.
Power-Good Detection
The MIC2044/45 can detect when the output voltage is above
or below a preset threshold that is monitored by a comparator
at the PGREF input. The PWRGD signal is an N-Channel
open-drain MOSFET output and an external pull-up resistor
up to a 6V maximum rail is required for the PWRGD pin.
Whenever the voltage at the PGREF pin exceeds its thresh-
old (VTH), typically 230mV, the PWRGD output is asserted.
Using the typical applications circuit from page 1 that switches
3.3V as an example, the output voltage threshold determin-
ing “power is good” is calculated by the following equation:
VV1
R2
R3
OUT(GOOD) TH
=×+
(3)
In substituting the resistor values of the circuit and the typical
PGREF threshold, the resulting VOUT(GOOD) is calculated as
3.0V for this 3.3V switching application.
SLEW
The MIC2044/45’s output rise time is controlled at turn-on to
a minimum of 1.5ms and is controlled by an internal slew-rate
limiting circuit. A slew-rate adjustment control pin is available
for applications requiring slower rise times. By placing a
capacitor between SLEW and ground, longer rise times can
be achieved. For further detail, see the “Applications Informa-
tion” section.
January 2005 13 MIC2044/2045
MIC2044/2045 Micrel
Applications Information
Input and Output
Supply Bypass Filtering
The need for input supply bypass is brought about due to
several factors, most notably the input/output inductance
along the power path, operating current and current limit, and
output capacitance. A 0.1µF to 0.47µF bypass capacitor
positioned very close to the VIN pin to GND of the device is
strongly recommended to filter high frequency oscillations
due to inductance. Also, a sufficient bypass capacitor posi-
tioned close to the input source to the switch is strongly
advised in order to suppress supply transient spikes and to
limit input voltage droop. Inrush current increases with larger
output capacitance, thus the minimum value of this capacitor
will require experimental determination for the intended appli-
cation and design. A good starting point is a capacitor
between 4.7µF to 15µF. Without these bypass capacitors, an
extreme overload condition such as a short circuit, or a large
capacitive load, may cause either the input supply to exceed
the maximum rating of 6V and possibly cause damage to the
internal control circuitry or allow the input supply to droop and
fall out of regulation and/or below the minimum operating
voltage of the device.
Output Capacitance
When the MIC2044 die exceeds the overtemperature thresh-
old of approximately 140°C, the device can enter into a
thermal shutdown mode if the die temperature falls below
120°C and then rises above 140°C in a continuous cycle.
With VOUT cycling on and off, the MIC2044 will reset the
/FAULT while in an overtemperature fault condition if VOUT is
allowed to swing below ground. The inductance present at
the output must be neutralized by capacitance in order to
ensure that the output does not fall below ground. In order to
counter the board parasitic inductance and the inductance of
relatively short-length power cable (≤ 1ft., 16 - 20 gauge wire),
a minimum output capacitance of 22µF is strongly recom-
mended and should be placed close to the VOUT pin of the
MIC2044. For applications that use more than a foot of cable,
an additional 10µF/ft. is recommended.
Reverse Current Blocking
The MIC2044/45 provides reverse current flow blocking
through the output MOSFET if the voltage at VOUT is greater
than VIN when the device is disabled. The VBIAS supply has
a limited reverse current flow if the voltage at VOUT is pulled
above VBIAS when the device is disabled. A graph of the
VBIAS reverse current flow is shown in the “Functional
Characteristics” section. The reverse current for VBIAS can
be completely blocked by inserting a Schottky diode from the
VBIAS pin (cathode) to the supply (anode). However, the
minimum voltage of 1.6V must be supplied to VBIAS after
accounting for the voltage drop across the diode.
Output Slew-Rate Adjustment
The output slew-rate for the MIC2044/45 can be slowed down
by the use of a capacitor (16V rating, minimum; 25V sug-
gested) between SLEW and GND. The slew-rate control
circuitry is independent of the load capacitance and exhibits
a non-linear response. See the “Functional Characteristics”
section. Table 1 shows the rise time for various standard
capacitor values. Additionally, the output turn-on time must
be less than the nominal flag delay of 32ms in order to avoid
nuisance tripping of the /FAULT output. This limit is imposed
by the current limiting circuitry which monitors the
(VIN – VOUT) differential voltage and concludes a fault
condition is present if the differential voltage exceeds 200mV
for more than the flag delay period. For the MIC2045, the
/FAULT will assert and the output will latch off if the output is
not within 200mV of the input before the flag delay times out.
When using the active-low (–2) option with the EN input tied
to ground, slew control is functional during initial start-up but
does not function upon resetting the input power to the
device. In order for the SLEW control to operate during
consecutive system restarts, the EN pin must reset (toggle
OFF to ON).
UVLO Threshold Setting With Low Input Voltages
When the switching voltage is below 1.6V, the device’s
standard UVLO threshold (1.45V nominal) will hinder the
output MOSFET in switching VIN to VOUT. In this case, the
use of the UVLOIN pin is required to override the standard
UVLO threshold and set a new, lower threshold for the lower
input voltage. An external resistive divider network con-
nected at the UVLOIN pin is used to set the new threshold.
Due to the ratio of the internal components, the total series
resistance of the external resistive divider should not exceed
200kΩ. The circuit shown in Figure 4 illustrates an application
that switches 0.8V while the device is powered from a
separate 2.5V power supply. The UVLO threshold is set by
the following equation.
V 0.23V 1 R2
R3
UVTH
=×+
(4)
In substituting the resistor values from Figure 4, the resulting
UVLO threshold (VUVTH) is calculated as 0.6V for this 0.8V
switching application. When using the UVLOIN pin to set a
new UVLO threshold, an optional 0.1µF to 1.0µF capacitor
from UVLOIN to GND may be used as a glitch filter in order
to avoid nuisance tripping of the UVLO threshold. If the
UVLOIN pin is not in use, this pin should be left open
(floating). The use of a pull-down resistor to ground will offset
the ratio of the internal resistive divider to this pin resulting in
a shift in the UVLO threshold. To bypass (disable) UVLO,
connect the UVLOIN pin directly to the VIN pin of the
MIC2044/45.
Conditions: VIN = VBIAS = 5V/3V
CLOAD = 47µF; ILOAD = 1A
CSLEW (µF) Rise Time (ms)
5V 3V
0.02 4.4 6.6
0.033 7.5 11.25
0.047 11 16
0.1 24 31.5
Table 1. Typical Output Rise Time for Various CSLEW
(VIN = 5V, 3V)
MIC2044/2045 Micrel
MIC2044/2045 14 January 2005
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Figure 4. Lower UVLO Setting
Power Dissipation
Power dissipation depends on several factors such as the
load, PCB layout, ambient temperature, and package type.
The following equations can be used to calculate power
dissipation and die temperature.
Calculation of power dissipation can be accomplished by the
following equation:
PD = RDS(on) × (IOUT)2 (5)
To relate this to junction temperature, the following equation
can be used:
TJ = PD × R(θJ-A) + TA (6)
where TJ = junction temperature, TA = ambient temperature
and Rθ(J-A) is the thermal resistance of the package.
Printed Circuit Board Hot Plug
The MIC2044/45 are ideal inrush current limiting power
switches suitable for hot plug applications. Due to the inte-
grated charge pump, the MIC2044/45 present a high imped-
ance when in the off state and the device slowly becomes a
low impedance as it turns on. This effectively isolates power
supplies from highly capacitive loads by reducing inrush
current during hot plug events. This same feature also can be
used for soft-start requirements.
PCB Layout Recommendations
The MIC2044 and MIC2045 have very low on-resistance,
typically 20mΩ, and the switches can provide up to 6A of
continuous output current. Under heavy loads, the switched
current may cause the devices to heat up considerably. The
following list contains some useful suggestions for PCB
layout design of the MIC2044/45 in order to prevent the die
from overheating under normal operating conditions. 1. Micrel Semiconductor does not assume responsibility for the use of
this program tool in the event that any PCB assembled, tested,
produced, and/or manufactured becomes damaged and/or causes any
degradation of system performance or damage to any system
components in which the aforementioned PCB is included.
1. Supply additional copper area under the device
to remove heat away from the IC.
See “Application Hint 17” for a general guideline
in calculating the suggested area.
2. Provide additional pad area on the corner pins of
the MIC2044/45 IC for heat distribution.
3. Tie the common power pins (VIN = pins 7, 11,
13, 16 and VOUT = pins 9, 12, 14) together in a
manner such that the traces entering and
leaving the device have a uniform width suffi-
cient for the application’s current requirements
plus added margin (25% minimum recom-
mended).
Ex: For 4A maximum current, design traces for
5A capability.
4. For PCB trace width calculation, there are
numerous calculator programs available on the
internet and elsewhere. As a general rule of
thumb, 15-20 mils width for every 1A of current
when using 1oz. copper. However, the trace
width calculators often take into account maxi-
mum temperature increase constraints, as well
as layer arrangement, in determining the PCB
trace widths. As a reference, the following link is
suggested for trial tests in PCB trace width
calculations.1
http://www.aracnet.com/cgi-usr/gpatrick/trace.pl
January 2005 15 MIC2044/2045
MIC2044/2045 Micrel
Package Information
Rev. 01
16-Pin TSSOP (TS)
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
The information furnished by Micrel in this datasheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use.
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
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 at Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2005 Micrel, Incorporated.
