MIC2582-JBMTR [MICROCHIP]
Power Supply Management Circuit, Adjustable, 1 Channel, PDSO8, SOIC-8;
| 型号： | MIC2582-JBMTR |
| 厂家： | 
MICROCHIP |
| 描述： | Power Supply Management Circuit, Adjustable, 1 Channel, PDSO8, SOIC-8 光电二极管 |
| 文件： | 总25页 (文件大小：826K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MIC2582/MIC2583
Single Channel Hot Swap Controllers
General Description
Features
The MIC2582 and MIC2583 are single channel positive
voltage hot swap controllers designed to allow the safe
insertion of boards into live system backplanes. The
MIC2582 and MIC2583 are available in 8-pin SOIC and
16-pin QSOP packages, respectively. Using a few external
components and by controlling the gate drive of an
external N-Channel MOSFET device, the MIC2582/83
provide inrush current limiting and output voltage slew rate
control in harsh, critical power supply environments.
Additionally, a circuit breaker function will latch the output
MOSFET off if the current limit threshold is exceeded for a
determined period. The MIC2583R option includes an
auto-restart function upon detecting an over current
condition.
• MIC2582:
Pin-for-pin functional equivalent to the LTC1422
• 2.3V to 13.2V supply voltage operation
• Surge voltage protection up to 20V
• Current regulation limits inrush current regardless of load
capacitance
• Programmable inrush current limiting
• Electronic circuit breaker
• Optional dual-level overcurrent threshold detects
excessive load faults
• Fast response to short circuit conditions (<1µs)
• Programmable output under-voltage detection
• Under-voltage Lockout (UVLO) protection
• Auto-restart function (MIC2583R)
• Power-On Reset and Power-Good status outputs
(Power-Good for the MIC2583 and MIC2583R only)
Datasheets and support documentation can be found on
Micrel’s web site at www.micrel.com.
• /FAULT status output (MIC2583 and MIC2583R)
Applications
• RAID systems
• Base stations
• PC board hot swap insertion and removal
• +12V backplanes
• Network switches
___________________________________________________________________________________________________________
Typical Applications
Figure 1. MIC2583/83R Typical Application Circuit
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
M9999-043009-C
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Micrel, Inc.
MIC2582/MIC2583
Ordering Information
Part Number
Standard
Fast Circuit Breaker Threshold
Circuit Breaker
Package
Pb-Free
MIC2582-JBM
MIC2582-xYM
x = J, 100mV
x = J1, Off
Latched off
8-Pin SOIC
x = M, Off
MIC2583-xBQS
MIC2583-xYQS
x = J, 100mV
x = K*, 150mV
x = L*, 200mV
x = M*, Off
Latched off
Auto-retry
16-pin QSOP
16-pin QSOP
MIC2583R-xBQS
MIC2583R-xYQS
x = J, 100mV
x = K*, 150mV
x = L*, 200mV
x = M*, Off
Note:
* Contact factory for availability.
Pin Configuration
8-Pin SOIC (M)
16-Pin QSOP (QS)
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Micrel, Inc.
MIC2582/MIC2583
Pin Description
Pin Number
8-Pin SOIC
Pin Number
16-Pin QSOP
Pin Name
Pin Name
1
1
/POR
Power-On Reset Output: Open drain N-channel device, Active Low. This pin
remains asserted during start-up until a time period (tPOR) after the FB pin
voltage rises above the power-good threshold (VFB). The timing capacitor CPOR
determines tPOR. When the output voltage monitored at the FB pin falls below
VFB, /POR is asserted for a minimum of one timing cycle (tPOR). The /POR pin
requires a pull-up resistor (10kΩ minimum) to VCC.
2
3
4
ON
ON Input: Active High. The ON pin, an input to a Schmitt-triggered comparator
used to enable/disable the controller, is compared to a 1.24V reference with
50mV of hysteresis. When a logic high is applied to the ON pin (VON > 1.24V), a
start-up sequence begins when the GATE pin starts ramping up towards its final
operating voltage. When the ON pin receives a logic low signal (VON < 1.19V),
the GATE pin is grounded and /FAULT remains high if VCC is above the UVLO
threshold. ON must be low for 20µs in order to initiate a start-up sequence.
Additionally, toggling the ON pin LOW to HIGH resets the circuit breaker.
3
CPOR
Power-On Reset Timer: A capacitor connected between this pin and ground sets
the supply contact start-up delay (tSTART) and the power-on reset interval (tPOR).
When VCC rises above the UVLO threshold, the capacitor connected to CPOR
begins to charge. When the voltage at CPOR crosses 0.3V, the start-up
threshold (VSTART), a start cycle is initiated if ON is asserted while capacitor CPOR
is immediately discharged to ground. When the voltage at FB rises above VFB,
capacitor CPOR begins to charge again. When the voltage at CPOR rises above
the power-on reset delay threshold (VTH), the timer resets by pulling CPOR to
ground, and /POR is de-asserted. If CPOR is left open, then tSTART defaults to
20µs.
4
5
7, 8
12
GND
FB
Ground Connection: Tie to analog ground.
Power-Good Threshold Input (Under-voltage Detect): This input is internally
compared to a 1.24V reference with 30mV of hysteresis. An external resistive
divider may be used to set the voltage at this pin. If this input momentarily goes
below 1.24V, then /POR is activated for one timing cycle, tPOR, indicating an
output under-voltage condition. The /POR signal de-asserts one timing cycle
after the FB pin exceeds the power-good threshold by 30mV. A 5µs filter on this
pin prevents glitches from inadvertently activating this signal.
6
7
14
15
GATE
Gate Drive Output: Connects to the gate of an external N-channel MOSFET. An
internal clamp ensures that no more than 9V is applied between the GATE pin
and the source of the external MOSFET. The GATE pin is immediately brought
low when either the circuit breaker trips or an under-voltage lockout condition
occurs.
SENSE
Circuit Breaker Sense Input: A resistor between this pin and VCC sets the
current limit threshold. Whenever the voltage across the sense resistor exceeds
the slow trip current limit threshold (VTRIPSLOW), the GATE voltage is adjusted to
ensure a constant load current. If VTRIPSLOW (50mV) is exceeded for longer than
time period tOCSLOW, then the circuit breaker is tripped and the GATE pin is
immediately pulled low. If the voltage across the sense resistor exceeds the fast
trip circuit breaker threshold, VTRIPFAST, at any point due to fast, high amplitude
power supply faults, then the GATE pin is immediately brought low without delay.
To disable the circuit breaker, the SENSE and VCC pins can be tied together.
The default VTRIPFAST for either device is 100mV. Other fast trip thresholds are
available: 150mV, 200mV, or OFF (VTRIPFAST disabled). Please contact factory for
availability of other options.
8
16
VCC
Positive Supply Input: 2.3V to 13.2V. The GATE pin is held low by an internal
under-voltage lockout circuit until VCC exceeds a threshold of 2.2V. If VCC
exceeds 13.2V, an internal shunt regulator protects the chip from transient
voltages up to 20V at the VCC and SENSE pins.
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Micrel, Inc.
MIC2582/MIC2583
Pin Number
8-Pin SOIC
Pin Number
16-Pin QSOP
Pin Name
Pin Name
n/a
n/a
n/a
2
PWRGD
Power-Good Output: Open drain N-channel device, Active High. When the
voltage at the FB pin is lower than 1.24V, PWRGD output is held low. When the
voltage at the FB pin exceeds 1.24V, then PWRGD is asserted immediately. The
PWRGD pin requires a pull-up resistor (10kΩ minimum) to VCC.
5
CFILTER
/FAULT
Current Limit Response Timer: A capacitor connected to this pin defines the
period of time (tOCSLOW) in which an over current event must last to signal a fault
condition and trip the circuit breaker. If no capacitor is connected, then tOCSLOW
defaults to 5µs.
11
Circuit Breaker Fault Status Output: Open drain N-channel device, Active Low.
The /FAULT pin is asserted when the circuit breaker trips due to an over current
condition or when an under-voltage lockout condition exists. The/FAULT pin
requires a pull-up resistor (10kΩ minimum) to VCC.
n/a
n/a
13
DIS
NC
Discharge Output: When the MIC2583/83R is turned off, a 500Ω internal resistor
at this output allows the discharging of any load capacitance to ground.
6, 9, 10
No internal connection.
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Micrel, Inc.
MIC2582/MIC2583
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage (VCC)....................................... –0.3V to 20V
/POR, /FAULT, PWRGD pins.......................... –0.3V to 15V
SENSE pin ............................................ –0.3V to VCC+0.3V
Supply Voltage (VCC).................................. +2.3V to +13.2V
Ambient Temperature (TA) ..........................–40°C to +85°C
Junction Thermal Resistance
ON pin
............................................ –0.3V to VCC+0.3V
SOIC (θJA)........................................................163°C/W
QSOP (θJA) ......................................................112°C/W
GATE pin ..................................................... –0.3V to 20V
FB Input pins..................................................... –0.3V to 6V
Junction Temperature ..............................................+125°C
Lead Temperature
Standard Package (-JBM and –xBQS)
(IR Reflow, Peak Temperature) ..240°C + 0°C/-5°C
Pb-Free Package (-xYM or –xYQS)
(IR Reflow, Peak Temperature) ..260°C + 0°C/-5°C
EDS Rating
Human body model..................................................2kV
Machine model ......................................................100V
Electrical Characteristics(3)
VCC = 5.0V, TA = 25°C unless noted. Bold values indicate –40°C ≤ TA ≤ +85°C.
Symbol Parameter
Condition
Min
2.3
Typ
Max
13.2
2.5
Units
V
VCC
ICC
Supply Voltage
Supply Current
VON = 2V
1.5
50
mA
VTRIP
Circuit Breaker Trip Voltage
(Current Limit Threshold)
VTRIP = VCC − VSENSE VTRIPSLOW
42
59
VTRIPFAST
(MIC2582-Jxx)
100
mV
VTRIPFAST
(MIC2583/83R) X = J
85
130
175
100
150
200
110
170
225
mV
mV
mV
X = K
X = L
VGS
External Gate Drive
VGATE − VCC
VCC > 3V
7
8
9
V
V
CC = 2.3V
Start Cycle, VGATE = 0V, VCC = 13.2V
CC = 2.3V
3.5
−30
−26
4.8
17
6.5
−8
−8
V
IGATE
GATE Pin Pull-Up Current
GATE Pink Sink Current
µA
µA
µA
µA
µA
V
17
IGATEOFF
VGATE > 1V
VCC = 13.2V, Note 4
VCC = 2.3V, Note 4
Turn Off
100
50
/FAULT = 0
(MIC2583/83R only)
110
ITIMER
Current Limit/Overcurrent Timer
(CFILTER) Current
(MIC2583/83R)
VCC − VSENSE > VTRIPSLOW (timer on)
CC − VSENSE > VTRIPSLOW (timer off)
−8.5
−6.5
−4.5
µA
µA
V
4.5
6.5
8.5
ICPOR
Power-On-Reset Timer Current
Timer on
Timer off
−3.5
2.5
1.3
−1.5
µA
0.5
mA
VTH
VUV
POR Delay and Overcurrent
Timer (CFILTER) Threshold
V
CPOR rising
VCFILTER rising (MIC2583/83R only)
1.19
2.1
1.245
2.2
1.30
2.3
V
V
Undervoltage Lockout Threshold
VCC rising
CC falling
V
1.90
2.05
150
1.24
1.19
50
2.20
V
VUVHYS
VON
Undervoltage Lockout Hysteresis
ON Pin Threshold Voltage
mV
V
2.3V ≤ VCC ≤ 13.2V
ON rising
ON falling
1.19
1.14
1.29
1.24
V
VONHYS
ON Pin Hysteresis
mV
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Micrel, Inc.
MIC2582/MIC2583
Symbol Parameter
Condition
Min
Typ
Max
Units
mV
µA
V
ON Pin Threshold Line Regulation 2.3V ≤ VCC ≤ 13.2V
2
ΔVON
ION
ON Pin Input Current
VON = VCC
−0.5
0.36
1.30
0.36
16
VSTART
VAUTO
Start-Up Delay Timer Threshold
VCPOR rising
0.26
0.19
0.26
10
0.31
1.24
0.31
13
Auto-Restart Threshold Voltage
(MIC2583R only)
Upper threshold
Lower threshold
Charge current
Discharge current
2.3V = VCC = 13.2V
V
V
IAUTO
Auto-Restart Current
(MIC2583R only)
µA
µA
V
1.4
2
VFB
Power-Good Threshold Voltage
FB rising
FB falling
1.19
1.15
1.24
1.20
40
1.29
1.25
V
VFBHYS
IFBLKG
VOL
FB Hysteresis
mV
µA
V
FB Pin Leakage Current
2.3V = VCC = 13.2V, VFB = 1.3V
IOUT = 1mA
1.5
0.4
/POR, /FAULT, PWRGD
Output Voltage
(/FAULT, PWRGD MIC2583/83R only)
RDIS
Output Discharge Resistance
(MIC2583/83R only)
500
1000
Ω
AC Parameters(4)
tOCFAST
Fast Overcurrent SENSE to GATE
Low Trip Time
V
CC = 5V, VCC − VSENSE = 100mV
1
5
µs
µs
CGATE = 10nF, Figure 2
tOCSLOW
Slow Overcurrent SENSE to GATE
Low Trip Time
V
C
CC = 5V, VCC − VSENSE = 50mV
FILTER = 0, Figure 2
tONDLY
tFBDLY
ON Delay Filter
FB Delay Filter
20
20
µs
µs
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Specification for packaged product only.
4. Not a tested parameter, guaranteed by design.
Timing Diagrams
Figure 2. Current-Limit Response
Figure 3. Power-On Reset Response
Figure 4. Power-On Start-Up Delay Timing
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Micrel, Inc.
MIC2582/MIC2583
Test Circuit
Figure 5. Applications Test Circuit
(not all pins shown for simplicity)
M9999-043009-C
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Micrel, Inc.
MIC2582/MIC2583
Typical Characteristics
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Micrel, Inc.
MIC2582/MIC2583
M9999-043009-C
April 2009
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Micrel, Inc.
MIC2582/MIC2583
Functional Characteristics (See Figure 5, Applications Test Circuit)
M9999-043009-C
April 2009
10
Micrel, Inc.
MIC2582/MIC2583
Functional Characteristics (See Figure 5, Applications Test Circuit)
M9999-043009-C
April 2009
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Micrel, Inc.
MIC2582/MIC2583
Functional Diagram
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Micrel, Inc.
MIC2582/MIC2583
Functional Description
delays using several standard value capacitors. As the
GATE voltage continues ramping toward its final value
(VCC + VGS) at a defined slew rate (See Load
Capacitance/Gate Capacitance Dominated Startup
sections), a second CPOR timing cycle begins if:
1)/FAULT is high and 2)CFILTER is low (i.e., not an
overvoltage, undervoltage lockout, or overcurrent state).
This second timing cycle (tPOR) begins when the voltage
at the FB pin exceeds its threshold (VFB). This condition
indicates that the output voltage is valid. See Figure 3 in
the Timing Diagrams. When the power supply is already
present (i.e., not a “hot swapping” condition) and the
MIC2582/83 device is enabled by applying a logic high
signal at the ON pin, the GATE output begins ramping
immediately as the first CPOR timing cycle is bypassed.
Active current regulation is employed to limit the inrush
current transient response during start-up by regulating
the load current at the programmed current limit value
(See Current Limiting and Dual-Level Circuit Breaker
section). The following equation is used to determine the
nominal current limit value:
Hot Swap Insertion
When circuit boards are inserted into live system
backplanes and supply voltages, high inrush currents
can result due to the charging of bulk capacitance that
resides across the supply pins of the circuit board. This
inrush current, although transient in nature, may be high
enough to cause permanent damage to on board
components or may cause the system’s supply voltages
to go out of regulation during the transient period which
may result in system failures. The MIC2582 and
MIC2583 act as a controller for external N-Channel
MOSFET devices in which the gate drive is controlled to
provide inrush current limiting and output voltage slew
rate control during hot plug insertions.
Power Supply
VCC is the supply input to the MIC2582/83 controller
with a voltage range of 2.3V to 13.2V. The VCC input
can withstand transient spikes up to 20V. In order to
ensure stability of the supply voltage, a minimum 0.47µF
capacitor from VCC to ground is recommended.
Alternatively, a low pass filter, shown in the typical
application circuit (see Figure 1), can be used to
eliminate high frequency oscillations as well as help
suppress transient spikes.
VTRIPSLOW
50mV
(2)
ILIM
=
=
RSENSE
RSENSE
where VTRIPSLOW is the current limit slow trip threshold
found in the electrical table and RSENSE is the selected
value that will set the desired current limit. There are two
basic start-up modes for the MIC2582/83: 1) Start-up
dominated by load capacitance and 2) start-up
dominated by total gate capacitance. The magnitude of
the inrush current delivered to the load will determine the
dominant mode. If the inrush current is greater than the
programmed current limit (ILIM), then load capacitance is
dominant. Otherwise, gate capacitance is dominant. The
expected inrush current may be calculated using the
following equation:
Also, due to the existence of an undetermined amount of
parasitic inductance in the absence of bulk capacitance
along the supply path, placing a Zener diode at the VCC
of the controller to ground in order to provide external
supply transient protection is strongly recommended for
relatively high current applications (≥3A). See Figure 1.
Start-Up Cycle
Supply Contact Delay
During a hot insert of a PC board into a backplane or
when the supply (VCC) is powered up, as the voltage at
the ON pin rises above its threshold (1.24V typical), the
MIC2582/83 first checks that both supply voltages are
above their respective UVLO thresholds. If so, the
device is enabled and an internal 2.5µA current source
begins charging capacitor CPOR to 0.3V to initiate a start-
up sequence. Once the start-up delay (tSTART) elapses,
the CPOR pin is pulled immediately to ground and a
17µA current source begins charging the GATE output
CLOAD
CGATE
CLOAD
CGATE
(3)
INRUSH ≅ IGATE
x
= 17μA x
where IGATE is the GATE pin pull-up current, CLOAD is the
load capacitance, and CGATE is the total GATE
capacitance (CISS of the external MOSFET and any
external capacitor connected from the MIC2582/83
GATE pin to ground).
Load Capacitance Dominated Start-Up
to drive the external MOSFET that switches VIN to VOUT
.
In this case, the load capacitance (CLOAD) is large
enough to cause the inrush current to exceed the
programmed current limit but is less than the fast-trip
threshold (or the fast-trip threshold is disabled, ‘M’
option). During start-up under this condition, the load
current is regulated at the programmed current limit
value (ILIM) and held constant until the output voltage
rises to its final value. The output slew rate and
equivalent GATE voltage slew rate is computed by the
The programmed contact start-up delay is calculated
using the following equation:
⎡
⎤
VSTART
(1)
tSTART = CPOR
≅ 0.12xCPOR
(
μF
)
⎢
⎥
ICPOR
⎣
⎦
Where the start-up delay timer threshold (VSTART) is 0.3V,
and the Power-On Reset timer current (ICPOR) is 2.5µA.
See Table 2 for some typical supply contact start-up
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MIC2582/MIC2583
following equation:
Current Limiting and Dual-Level Circuit Breaker
Many applications will require that the inrush and steady
state supply current be limited at a specific value in order
to protect critical components within the system.
Connecting a sense resistor between the VCC and
SENSE pins sets the nominal current limit value of the
MIC2582/83 and the current limit is calculated using
Equation 2.
ILIM
Output Voltage Slew Rate, dVOUT/dt =
(4)
CLOAD
where ILIM is the programmed current limit value.
Consequently, the value of CFILTER must be selected to
ensure that the overcurrent response time, tOCSLOW
exceeds the time needed for the output to reach its final
value. For example, given a MOSFET with an input
capacitance CISS = CGATE = 4700pF, CLOAD is 2200µF,
and ILIM is set to 6A with a 12V input, then the load
capacitance dominates as determined by the calculated
,
The MIC2582/83 also features a dual-level circuit
breaker triggered via 50mV and 100mV current-limit
thresholds sensed across the VCC and SENSE pins.
The first level of the circuit breaker functions as follows.
For the MIC2583/83R, once the voltage sensed across
these two pins exceeds 50mV, the overcurrent timer, its
duration set by capacitor CFILTER, starts to ramp the
voltage at CFILTER using a 6.5µA constant current source.
If the voltage at CFILTER reaches the overcurrent timer
threshold (VTH) of 1.24V, then CFILTER immediately
returns to ground as the circuit breaker trips and the
GATE output is immediately shut down. The default
overcurrent time period for the MIC2582/83 is 5µs. For
the second level, if the voltage sensed across VCC and
SENSE exceeds 100mV at any time, the circuit breaker
trips and the GATE shuts down immediately, bypassing
the overcurrent time period. The MIC2582-MYM option
is equipped with only a single circuit breaker threshold
(50mV). To disable current limit and circuit breaker
operation, tie the SENSE and VCC pins together and the
CFILTER (MIC2583/83R) pin to ground.
INRUSH > ILIM. Therefore, the output voltage slew rate
determined from Equation 4 is:
6A
V
Output Voltage Slew Rate, dVOUT/dt =
= 2.73
2200μF
ms
and the resulting tOCSLOW needed to achieve a 12V
output is approximately 4.5ms. (See Power-On Reset
and Overcurrent Timer Delays section to calculate
tOCSLOW).
GATE Capacitance Dominated Start-Up
In this case, the value of the load capacitance relative to
the GATE capacitance is small enough such that the
load current during start-up never exceeds the current
limit threshold as determined by Equation 3. The
minimum value of CGATE that will ensure that the current
limit is never exceeded is given by the equation below:
Output Undervoltage Detection
IGATE
(5)
CGATE (min) =
× CLOAD
The MIC2582/83 employ output undervoltage detection
by monitoring the output voltage through a resistive
divider connected at the FB pin. During turn on, while the
voltage at the FB pin is below the threshold (VFB), the
/POR pin is asserted low.
ILIM
where CGATE is the summation of the MOSFET input
capacitance (CISS) and the value of the external
capacitor connected to the GATE pin of the MIC2582/83
to ground. Once CGATE is determined, use the following
equation to determine the output slew rate for gate
capacitance dominated start-up.
Once the FB pin voltage crosses VFB, a 2.5µA current
source charges capacitor CPOR. Once the CPOR pin
voltage reaches 1.24V, the time period tPOR elapses as
the CPOR pin is pulled to ground and the /POR pin goes
HIGH. If the voltage at FB drops below VFB for more than
10µs, the /POR pin resets for at least one timing cycle
defined by tPOR (See Applications Information for an
example).
IGATE
dVOUT/dt =
(6)
CGATE
Table 1 depicts the output slew rate for various values of
CGATE
.
IGATE = 17µA
Power-On Reset and Overcurrent Timer Delays
CGATE
0.001µF
0.01µF
0.1µF
dVOUT/dt
17V/ms
The Power-On Reset delay, tPOR, is the time period for
the /POR pin to go HIGH once the voltage at the FB pin
exceeds the power-good threshold (VFB). A capacitor
connected to CPOR sets the interval and is determined
by using Equation 1 with VTH substituted for VSTART. The
resulting equation becomes:
1.7V/ms
0.17V/ms
0.017V/ms
1µF
VTH
Table 1. Output Slew Rate Selection for GATE
Capacitance Dominated Start-Up
(7)
tPOR = CPOR
×
≅ 0.5× CPOR
(
μF
)
ICPOR
where the Power-On Reset threshold (VTH) and timer
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Micrel, Inc.
MIC2582/MIC2583
current (ICPOR
respectively.
)
are typically 1.24V and 2.5µA,
CPOR
0.01µF
0.02µF
0.033µF
0.05µF
0.1µF
tSTART
1.2ms
2.4ms
4ms
tPOR
5ms
For the MIC2583/83R, a capacitor connected to
CFILTER is used to set the timer which activates the
circuit breaker during overcurrent conditions. When the
voltage across the sense resistor exceeds the slow trip
current limit threshold of 50mV, the overcurrent timer
begins to charge for a time period (tOCSLOW), determined
by CFILTER. When no capacitor is connected to CFILTER
and for the MIC2582, tOCSLOW defaults to 5µs. If tOCSLOW
elapses, then the circuit breaker is activated and the
GATE output is immediately pulled to ground. For the
MIC2583/83R, the following equation is used to
10ms
16.5ms
25ms
50ms
165ms
235ms
500ms
6ms
12ms
40ms
56ms
120ms
0.33µF
0.47µF
1µF
determine the overcurrent timer period, tOCSLOW
.
Table 2. Selected Power-On Reset and Start-Up Delays
VTH
(8)
≅ 0.19 × CFILTER (μF)
tOCSLOW = CFILTER
×
ITIMER
CFILTER
680pF
tOCSLOW
130µs
420µs
900µs
1.5ms
6ms
where VTH, the CFILTER timer threshold, is 1.24V and
ITIMER, the overcurrent timer current, is 6.5µA. Tables 2
and 3 provide a quick reference for several timer
calculations using select standard value capacitors.
2200pF
4700pF
8200pF
0.033µF
0.1µF
19ms
42ms
90ms
0.22µF
0.47µF
Table 3. Selected Overcurrent Timer Delays
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Micrel, Inc.
MIC2582/MIC2583
(9.1)
⎡
⎤
Application Information
⎛
⎜
⎜
⎝
⎞
⎟
⎟
⎠
VOUT(Good)
R5 = R6 ⎢
− 1⎥
VFB(MAX)
Design Consideration for Output Undervoltage
Detection
⎢
⎣
⎥
⎦
where VFB(MAX) = 1.29V, VOUT(Good) = 11V, and R6 is
12.4kΩ. Substituting these values into Equation 9.1 now
yields R5 = 93.33kΩ. A standard 93.1kΩ ±% is selected.
For output undervoltage detection, the first consideration
is to establish the output voltage level that indicates
“power is good.” For this example, the output value for
which a 12V supply will signal “good” is 11V. Next,
consider the tolerances of the input supply and FB
threshold (VFB). For this example, the 12V supply varies
±5%, thus the resulting output voltage may be as low as
11.4V and as high as 12.6V. Additionally, the FB
threshold has ±50mV tolerance and may be as low as
1.19V and as high as 1.29V. Thus, to determine the
values of the resistive divider network (R5 and R6) at the
FB pin, shown in the typical application circuit on page 1,
use the following iterative design procedure.
Now, consider the 11.4V minimum output voltage, the
lower tolerance for R6 and higher tolerance for R5,
12.28kΩ and 94.03kΩ, respectively. With only 11.4V
available, the voltage sensed at the FB pin exceeds
VFB(MAX), thus the /POR and PWRGD (MIC2583/83R)
signals will transition from LOW to HIGH, indicating
“power is good” given the worse case tolerances of this
example. Lastly, in giving consideration to the leakage
current associated with the FB input, it is recommended
to either: 1) provide ample design margin (20mV to
30mV) to allow for loss in the potential (∆V) at the FB
pin, or 2) allow >>100µA to flow in the FB resistor
network.
1) Choose R6 to allow 100µA or more in the FB
resistive divider branch.
VFB(MAX)
1.29V
R6 =
=
= 12.9kΩ
PCB Connection Sense
100μA
100μA
There are several configuration options for the
MIC2582/83’s ON pin to detect if the PCB has been fully
seated in the backplane before initiating a start-up cycle.
In the typical applications circuit, the MIC2582/83 is
mounted on the PCB with a resistive divider network
connected to the ON pin. R2 is connected to a short pin
on the PCB edge connector. Until the connectors mate,
the ON pin is held low which keeps the GATE output
charge pump off. Once the connectors mate, the resistor
network is pulled up to the input supply,
R6 is chosen as 12.4kΩ ±1%.
2) Next, determine R5 using the output “good”
voltage of 11V and the following equation:
(
R5 + R6
)
⎡
⎤
VOUT(Good) = VFB
(9)
⎢
⎥
R6
⎣
⎦
Using some basic algebra and simplifying Equation 9 to
isolate R5, yields:
Figure 6. PCB Connection Sense with ON/OFF Control
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Micrel, Inc.
MIC2582/MIC2583
5V Switch with 3.3V Supply Generation
12V in this example, and the ON pin voltage exceeds its
threshold (VON) of 1.24V and the MIC2582/83 initiates a
start-up cycle. In Figure 6, the connection sense consisting
of a discrete logic-level MOSFET and a few resistors allows
for interrupt control from the processor or other signal
controller to shut off the output of the MIC2582/83. R4 pulls
the GATE of Q2 to VIN and the ON pin is held low until the
connectors are fully mated.
The MIC2582/83 can be configured to switch a primary
supply while generating a secondary regulated voltage rail.
The circuit in Figure 8 enables the MIC2582 to switch a 5V
supply while also providing a 3.3V low dropout regulated
supply with only a few added external components. Upon
enabling the MIC2582, the GATE output voltage increases
and thus the 3.3V supply also begins to ramp. As the 3.3V
output supply crosses 3.3V, the FB pin threshold is also
exceeded which triggers the power-on reset comparator.
The /POR pin goes HIGH, turning on transistor Q3 which
lowers the voltage on the gate of MOSFET Q2. The result is
a regulated 3.3V supply with the gate feedback loop of Q2
compensated by capacitor C3 and resistors R4 and R5. For
MOSFET Q2, special consideration must be given to the
power dissipation capability of the selected MOSFET as
1.5V to 2V will drop across the device during normal
operation in this application. Therefore, the device is
susceptible to overheating dependent upon the current
requirements for the regulated output. In this example, the
power dissipated by Q2 is approximately = 1W. However, a
substantial amount of power will be generated with higher
current requirements and/or conditions. As a general
guideline, expect the ambient temperature within the power
supply box to exceed the maximum operating ambient
temperature of the system environment by approximately
20ºC. Given the MOSFET’s Rθ(JA) and the expected power
dissipated by the MOSFET, an approximation for the
junction temperature at which the device will operate is
obtained as follows:
Once the connectors fully mate, a logic LOW at the
/ON_OFF signal turns Q2 off and allows the ON pin to pull
up above its threshold and initiate a start-up cycle. Applying
a logic HIGH at the /ON_OFF signal will turn Q2 on and
short the ON pin of the MIC2582/83 to ground which turns
off the GATE output charge pump.
Higher UVLO Setting
Once a PCB is inserted into a backplane (power supply), the
internal UVLO circuit of the MIC2582/83 holds the GATE
output charge pump off until VCC exceeds 2.2V. If VCC falls
below 2.1V, the UVLO circuit pulls the GATE output to
ground and clears the overvoltage and/or current limit faults.
A typical 12V application, for example, should implement a
higher UVLO than the internal 2.1V threshold of MIC2582 to
avoid delivering power to downstream modules/loads while
the input is below tolerance. For a higher UVLO threshold,
the circuit in Figure 7 can be used to delay the output
MOSFET from switching on until the desired input voltage is
achieved. The circuit allows the charge pump to remain off
R1
R2
⎛
⎞
⎟
until V exceeds 1+
× 1.24V. The GATE drive output
⎜
IN
⎝
⎠
TJ = (PD x Rθ(JA)) + TA
(10)
R1
R2
⎛
⎞
⎟
will be shut down when V falls below 1+
× 1.19V. In
⎜
IN
where TA = TA (MAX OPERATING) + 20ºC. As a precaution, the
implementation of additional copper heat sinking is highly
recommended for the area under/around the MOSFET.
⎝
⎠
the example circuit (Figure 7), the rising UVLO threshold is
set at approximately 9.5V and the falling UVLO threshold is
established as 9.1V. The circuit consists of an external
resistor divider at the ON pin that keeps the GATE output
charge pump off until the voltage at the ON pin exceeds its
threshold (VON) and after the start-up timer elapses.
Figure 7. Higher UVLO Setting
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Micrel, Inc.
MIC2582/MIC2583
For additional information on MOSFET thermal
considerations, please see MOSFET Selection text and
subsequent sections.
42mV
40.8mV
(11)
RSENSE(MAX )
=
=
(
1.03
)
(
ILOAD(CONT )
)
ILOAD(CONT )
Once the value of RSENSE has been chosen in this
manner, it is good practice to check the maximum
Auto-Restart - MIC2583R
I
LOAD(CONT) which the circuit may let through in the case of
The MIC2583R provides an auto-restart function. Upon
an overcurrent fault condition such as a short circuit, the
MIC2583R initially shuts off the GATE output. The
MIC2583R attempts to restart with a 12µA charge
current at a preset 10% duty cycle until the fault
condition is removed. The interval between auto-retry
tolerance buildup in the opposite direction. Here, the
worst-case maximum current is found using a 59mV trip
voltage and a sense resistor that is 3% low in value. The
resulting equation is:
59mV
60.8mV
ILOAD(CONT,MAX )
=
=
(12)
attempts is set by capacitor CFILTER
.
(0.97)
(
RSENSE(NOM)
)
RSENSE(NOM)
Sense Resistor Selection
As an example, if an output must carry a continuous 2A
without nuisance trips occurring, Equation 11
40.8mV
The MIC2582 and MIC2583 use a low-value sense
resistor to measure the current flowing through the
MOSFET switch (and therefore the load). This sense
yields: RSENSE(MAX )
=
= 20.4mΩ. The next
2A
resistor is nominally set at 50mV/ILOAD(CONT)
.
To
lowest standard value is 20mΩ. At the other set of
tolerance extremes for the output in question,
60.8mV
accommodate worst-case tolerances for both the sense
resistor (allow ±3% over time and temperature for a
resistor with ±1% initial tolerance) and still supply the
maximum required steady-state load current, a slightly
more detailed calculation must be used.
ILOAD(CONT,MAX )
=
= 3.04A, approximately 3A.
20.0mΩ
Knowing this final data, we can determine the necessary
wattage of the sense resistor using P = I2R, where I will
be ILOAD(CONT, MAX), and R will be (0.97)(RSENSE(NOM)).
These numbers yield the following: PMAX = (3A)2
(19.4mΩ) = 0.175W.
The current limit threshold voltage (i.e., the “trip point”)
for the MIC2582/83 may be as low as 42mV, which
would equate to
a
sense resistor value of
42mV/ILOAD(CONT). Carrying the numbers through for the
case where the value of the sense resistor is 3% high
yields:
In this example, a ¼W sense resistor is sufficient.
Figure 8. 5V Switch/3.3V LDO Application
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Micrel, Inc.
MIC2582/MIC2583
MOSFET (again, assuming 12V operation).
MOSFET Selection
Selecting the proper external MOSFET for use with the
MIC2582/83 involves three straightforward tasks:
At the same time, if the output of the external MOSFET
(its source) is suddenly subjected to a short, the gate-
source voltage will go to (19.5V – 0V) = 19.5V. This
means that the external MOSFET must be chosen to
have a gate-source breakdown voltage of 20V or more,
which is an available standard maximum value.
However, if operation is at or above 13V, the 20V gate-
source maximum will likely be exceeded. As a result, an
external Zener diode clamp should be used to prevent
breakdown of the external MOSFET when operating at
voltages above 8V. A Zener diode with 10V rating is
recommended as shown in Figure 9. At the present time,
most power MOSFETs with a 20V gate-source voltage
rating have a 30V drain-source breakdown rating or
higher.
•
•
•
Choice of a MOSFET which meets minimum voltage
requirements.
Selection of a device to handle the maximum
continuous current (steady-state thermal issues).
Verify the selected part’s ability to withstand any peak
currents (transient thermal issues).
MOSFET Voltage Requirements
The first voltage requirement for the MOSFET is easily
stated: the drain-source breakdown voltage of the
MOSFET must be greater than VIN(MAX). For instance, a
12V input may reasonably be expected to see high-
frequency transients as high as 18V. Therefore, the
drain-source breakdown voltage of the MOSFET must
be at least 19V. For ample safety margin and standard
availability, the closest value will be 20V.
As a general tip, choose surface-mount devices with a
drain-source rating of 30V as a starting point.
Finally, the external gate drive of the MIC2582/83
requires a low-voltage logic level MOSFET when
operating at voltages lower than 3V. There are 2.5V
logic level MOSFETs available. Please see Table 4
“MOSFET and Sense Resistor Vendors” for
suggested manufacturers.
The second breakdown voltage criterion that must be
met is a bit subtler than simple drain-source breakdown
voltage, but is not hard to meet. In MIC2582/83
applications, the gate of the external MOSFET is driven
up to approximately 19.5V by the internal output
Figure 9. Zener Clamped MOSFET Gate
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Micrel, Inc.
MIC2582/MIC2583
MOSFET Steady-State Thermal Issues
processor’s cooling fan.
The selection of a MOSFET to meet the maximum
continuous current is a fairly straightforward exercise.
First, arm yourself with the following data:
3. The best test of a surface-mount MOSFET for
an application (assuming the above tips show
it to be a likely fit) is an empirical one. Check
the MOSFETs temperature in the actual layout
of the expected final circuit, at full operating
current. The use of a thermocouple on the
drain leads, or infrared pyrometer on the
package, will then give a reasonable idea of
the device’s junction temperature.
• The value of ILOAD(CONT, MAX.) for the output in
question (see Sense Resistor Selection).
• The manufacturer’s data sheet for the
candidate MOSFET.
• The maximum ambient temperature in which
the device will be required to operate.
MOSFET Transient Thermal Issues
• Any knowledge you can get about the heat
sinking available to the device (e.g., can heat
be dissipated into the ground plane or power
plane, if using a surface-mount part? Is any
airflow available?).
Having chosen a MOSFET that will withstand the
imposed voltage stresses, and the worse case
continuous I2R power dissipation which it will see, it
remains only to verify the MOSFETs ability to handle
short-term
overload
power
dissipation
without
The data sheet will almost always give a value of on
resistance given for the MOSFET at a gate-source
voltage of 4.5V, and another value at a gate-source
voltage of 10V. As a first approximation, add the two
values together and divide by two to get the on-
resistance of the part with 8V of enhancement.
overheating. A MOSFET can handle a much higher
pulsed power without damage than its continuous
dissipation ratings would imply. The reason for this is
that, like everything else, thermal devices (silicon die,
lead frames, etc.) have thermal inertia.
In terms related directly to the specification and use of
power MOSFETs, this is known as “transient thermal
impedance,” or Zθ(JA). Almost all power MOSFET data
sheets give a Transient Thermal Impedance Curve. For
example, take the following case: VIN = 12V, tOCSLOW has
been set to 100msec, ILOAD(CONT. MAX) is 2.5A, the slow-
trip threshold is 50mV nominal, and the fast-trip
threshold is 100mV. If the output is accidentally
connected to a 3Ω load, the output current from the
Call this value RON. Since a heavily enhanced MOSFET
acts as an ohmic (resistive) device, almost all that’s
required to determine steady-state power dissipation is
to calculate I2R.
The one addendum to this is that MOSFETs have a
slight increase in RON with increasing die temperature. A
good approximation for this value is 0.5% increase in
RON per ºC rise in junction temperature above the point
at which RON was initially specified by the manufacturer.
For instance, if the selected MOSFET has a calculated
RON of 10mΩ at a TJ = 25ºC, and the actual junction
temperature ends up at 110ºC, a good first cut at the
operating value for RON would be:
MOSFET will be regulated to 2.5A for 100ms (tOCSLOW
)
before the part trips. During that time, the dissipation in
the MOSFET is given by:
P = E x I; EMOSFET = [12V-(2.5A)(3Ω)] = 4.5V
PMOSFET = (4.5V x 2.5A) = 11.25W for 100msec.
RON ≅ 10mΩ
[
1+
(
110 − 25)(0.005
)
]
≅ 14.3mΩ
(13)
At first glance, it would appear that a really hefty
MOSFET is required to withstand this sort of fault
condition. This is where the transient thermal impedance
curves become very useful. Figure 10 shows the curve
for the Vishay (Siliconix) Si4410DY, a commonly used
SOIC-8 power MOSFET.
The final step is to make sure that the heat sinking
available to the MOSFET is capable of dissipating at
least as much power (rated in ºC/W) as that with which
the MOSFETs performance was specified by the
manufacturer. Here are a few practical tips:
Taking the simplest case first, we’ll assume that once a
fault event such as the one in question occurs, it will be
a long time– 10 minutes or more– before the fault is
isolated and the channel is reset. In such a case, we can
approximate this as a “single pulse” event, that is to say,
there’s no significant duty cycle. Then, reading up from
the X-axis at the point where “Square Wave Pulse
Duration” is equal to 0.1sec (=100msec), we see that the
Zθ(JA) of this MOSFET to a highly infrequent event of this
1. The heat from a surface-mount device such as
an SOIC-8 MOSFET flows almost entirely out
of the drain leads. If the drain leads can be
soldered down to one square inch or more, the
copper will act as the heat sink for the part.
This copper must be on the same layer of the
board as the MOSFET drain.
2. Airflow works. Even a few LFM (linear feet per
minute) of air will cool a MOSFET down
substantially.
duration is only 8% of its continuous Rθ(JA)
.
This particular part is specified as having an Rθ(JA) of
50°C/W for intervals of 10 seconds or less.
If you can, position the MOSFET(s) near the
inlet of a power supply’s fan, or the outlet of a
M9999-043009-C
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Micrel, Inc.
Thus:
MIC2582/MIC2583
x (2.5A)2 x (50ºC/W)
TJ ≅ (55ºC + (0.122W)(50ºC/W)
≅ 61.1ºC
Assume TA = 55°C maximum, 1 square inch of copper at
the drain leads, no airflow.
Recalling from our previous approximation hint, the part
has an RON of (0.0335/2) = 17mΩ at 25°C.
Assume it has been carrying just about 2.5A for some
time.
Iterate the calculation once to see if this value is within a
few percent of the expected final value. For this iteration
we will start with TJ equal to the already calculated value
of 61.1°C:
When performing this calculation, be sure to use the
highest anticipated ambient temperature (TA(MAX)) in
which the MOSFET will be operating as the starting
temperature, and find the operating junction temperature
increase (∆TJ) from that point. Then, as shown next, the
final junction temperature is found by adding TA(MAX) and
∆TJ. Since this is not a closed-form equation, getting a
close approximation may take one or two iterations, and
the calculation tends to converge quickly.
TJ ≅ TA + [17mΩ + (61.1ºC-25ºC)(0.005)(17mΩ)]
x (2.5A)2 x (50ºC/W)
TJ ≅ (55ºC + (0.125W)(50ºC/W) ≅ 61.27ºC
So our original approximation of 61.1ºC was very close
to the correct value. We will use TJ = 61ºC.
Finally, add the temperature increase due to the
maximum power dissipation calculated from a “single
event”, (11.25W)(50ºC/W)(0.08) = 45ºC to the steady-
Then the starting (steady-state) TJ is:
TJ ≅ TA(MAX) + ∆TJ
state TJ to get TJ(TRANSIENT
= 106ºC. This is an
MAX.)
acceptable maximum junction temperature for this part.
≅ TA(MAX) + [RON + TA(MAX) – TA)(0.005/ºC)(RON)]
x I2 x Rθ(JA)
TJ ≅ 55ºC + [17mΩ + (55ºC-25ºC)(0.005)(17mΩ)]
Figure 10. Transient Thermal Impedance
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Micrel, Inc.
MIC2582/MIC2583
PCB Layout Considerations
widths (W) need to be wide enough to allow the current
to flow while the rise in temperature for a given copper
plate (e.g., 1oz. or 2oz.) is kept to a maximum of
10ºC~25ºC. Also, these traces should be as short as
possible in order to minimize the IR drops between the
input and the load.
Because of the low values of the sense resistors used
with the MIC2582/83 controllers, special attention to the
layout must be used in order for the device’s circuit
breaker function to operate properly. Specifically, the
use of a 4-wire Kelvin connection to accurately measure
the voltage across RSENSE is highly recommended. Kelvin
sensing is simply a means of making sure that any
voltage drops in the power traces connecting to the
resistors does not get picked up by the traces
themselves. Additionally, these Kelvin connections
should be isolated from all other signal traces to avoid
introducing noise onto these sensitive nodes. Figure 11
illustrates a recommended, single layer layout for the
Finally, the use of plated-through vias will be needed to
make circuit connections to power and ground planes
when utilizing multi-layer PC boards.
MOSFET and Sense Resistor Vendors
Device types and manufacturer contact information for
power MOSFETs and sense resistors are provided in
Table 4. Some of the recommended MOSFETs include a
metal heat sink on the bottom side of the package. The
recommended trace for the MOSFET Gate of Figure 11
must be redirected when using MOSFETs packaged in
this style. Contact the device manufacturer for package
information.
R
SENSE, Power MOSFET, timer(s), and feedback network
connections. The feedback network resistor values are
selected for 12V application. Many hot swap
a
applications will require load currents of several
amperes. Therefore, the power (VCC and Return) trace
.
Figure 11. Recommended PCB Layout for Sense Resistor,
Power MOSFET, and Feedback Network
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Micrel, Inc.
MIC2582/MIC2583
MOSFET Vendor
Key MOSFET Type(s)
Applications(1)
OUT ≤ 10A
IOUT = 10-15A, VCC < 3V (203) 452-5664
OUT ≤ 5A, VCC ≤ 5V
IOUT ≤ 15A
OUT ≤ 10A
IOUT = 10-15A
OUT ≤ 5A, VCC ≤ 3V
Contact Information
www.siliconix.com
Vishay (Siliconix)
Si4420DY (SOIC-8) package
Si4442DY (SOIC-8) package
Si4876DY (SOIC-8) package
Si7892DY (PowerPAK™ SOIC-8)
I
I
International Rectifier
IRF7413 (SOIC-8 package)
IRF7457 (SOIC-8 package)
IRF7601 (SOIC-8 package)
I
www.irf.com
(310) 322-3331
I
Fairchild Semiconductor
FDS6680A (SOIC-8 package)
IOUT ≤ 10A
www.fairchildsemi.com
(207) 775-8100
Philips
Hitachi
PH3230 (SOT669-LFPAK)
HAT2099H (LFPAK)
IOUT ≥ 20A
IOUT ≥ 20A
www.philips.com
www.halsp.hitachi.com
(408) 433-1990
Note:
1. These devices are not limited to these conditions in many cases, but these conditions are provided as a helpful reference for customer applications.
Resistor Vendors
Sense Resistors
Contact Information
Vishay (Dale)
“WSL” Series
www.vishay.com/docswsl_30100.pdf
(203) 452-5664
IRC
“OARS” Series
”LR” Series
(second source to “WSL”)
www.irctt.com/pdf_files/OARS.pdf
www.irctt.com/pdf_files/LRC.pdf
(828) 264-8861
Table 4. MOSFET and Sense Resistor Vendors
M9999-043009-C
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Micrel, Inc.
MIC2582/MIC2583
Package Information
8-Pin SOIC (M)
M9999-043009-C
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Micrel, Inc.
MIC2582/MIC2583
16-Pin QSOP (QS)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
The information furnished by Micrel in this data sheet 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 a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2006 Micrel, Incorporated.
M9999-043009-C
April 2009
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相关型号：
MIC2583
The MIC2582 and MIC2583 are single-channel positive voltage hot swap controllers designed to allow
MICROCHIP
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