MIC2583 [MICREL]
Single Channel Hot Swap Controllers; 单通道热插拔控制器
| 型号： | MIC2583 |
| 厂家： | 
MICREL SEMICONDUCTOR |
| 描述： | Single Channel Hot Swap Controllers |
| 文件： | 总22页 (文件大小：191K) |
| 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
Final
General Description
Features
The MIC2582 and MIC2583 are single channel positive
voltage hot swap controllers designed to allow the safe
insertionofboardsintolivesystembackplanes.TheMIC2582
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
thresholdisexceededforadeterminedperiod.TheMIC2583R
option includes an auto-restart function upon detecting an
overcurrent 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
• Dual-level overcurrent fault sensing eliminates false
tripping
• Fast response to short circuit conditions (<1µs)
• Programmable output undervoltage detection
• Undervoltage Lockout (UVLO) protection
• Auto-restart function (MIC2583R)
• Power-On Reset and Power-Good status outputs
(Power-Good for the MIC2583 and MIC2583R only)
• /FAULT status output (MIC2583 and MIC2583R)
Applications
• RAID systems
• Base stations
• PC board hot swap insertion and removal
• Hot swap CompactPCI cards
• Network switches
Typical Application
RSENSE
0.006Ω
2%
Q1
Si7892DP
(PowerPAK™ SO-8)
BACKPLANE PCB EDGE
CONNECTOR CONNECTOR
Long Pin
VIN
12V
1
2
VOUT
12V@6A
R1
3
4
3.3Ω
**D1
(18V)
CLOAD
500µF
C1
1µF
16
15
VCC
SENSE
14
13
R5
GATE
DIS
Short Pin
93.1kΩ
1%
3
ON
C2
0.01µF
R2
76.8kΩ
VIN
VIN
1%
9.76kΩ
DOWNSTREAM
CONTROLLER
R3
R4
47kΩ
R7
47kΩ
R8
47kΩ
MIC2583/83R
1%
2
PWRGD
/POR
FB
EN
Power-Good Output
/FAULT
Signal
11
1
FAULT
/RESET
Power-On Reset Output
Medium
(or Short) Pin
12
CPOR
GND
CFILTER
R6
12.4kΩ
1%
4
7, 8
5
C3
0.1µF
C4
8200pF
Long Pin
GND
*Undervoltage (Input) = 10.5V
*Undervoltage (Output) &
Power-Good (Output) = 11.0V
*START-UP Delay = 12ms
*/POR Delay = 50ms
*Circuit Breaker Response Time = 1.5ms
**D1 is BZX84C18
*(See Functional Description and Applications Information)
Figure 1. MIC2583/83R Typical Application Circuit
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
April 2003
1
MIC2582/MIC2583
MIC2582/MIC2583
Micrel
Ordering Information
Fast Circuit
Part Number
MIC2582-JBM
MIC2583-xBQS
Breaker Threshold
Circuit Breaker
Latched off
Package
8-pin SOIC
16-pin QSOP
100mV
x = J, 100mV
x = K, 150mV
x = L, 200mV
x = M, Off
Latched off
MIC2583R-xBQS
x = J, 100mV
x = K*, 150mV
x = L*, 200mV
x = M*, Off
Auto-retry
16-pin QSOP
* Contact factory for availability.
Pin Configuration
/POR
PWRGD
ON
1
2
3
4
5
6
7
8
16 VCC
15 SENSE
14 GATE
13 DIS
/POR
ON
1
2
3
4
8
7
6
5
VCC
SENSE
GATE
FB
CPOR
CFILTER
NC
CPOR
GND
12 FB
11 /FAULT
10 NC
GND
8-Pin SOIC (M)
GND
9 NC
16-Pin QSOP (QS)
MIC2582/MIC2583
2
April 2003
MIC2582/MIC2583
Micrel
Pin Description
Pin Name
8-pin SOIC
16-pin QSOP
Pin Function
/POR
1
1
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.
ON
2
3
ON Input: Active High. The ON pin, an input to a Schmitt-triggered compara-
tor 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.
CPOR
3
4
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 = 0, then tSTART defaults to 20µs.
GND
FB
4
5
7,8
12
Ground connection: Tie to analog ground.
Power-Good Threshold Input (Undervoltage 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 undervoltage 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.
GATE
6
7
14
15
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
undervoltage 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.
VCC
8
16
Positive Supply Input: 2.3V to 13.2V. The GATE pin is held low by an
internal undervoltage 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.
April 2003
3
MIC2582/MIC2583
MIC2582/MIC2583
Micrel
Pin Name
8-pin SOIC
16-pin QSOP
Pin Function
PWRGD
N/A
N/A
N/A
2
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.
CFILTER
/FAULT
5
Current Limit Response Timer: A capacitor connected to this pin defines the
period of time (tOCSLOW) in which an overcurrent 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
overcurrent condition or when an undervoltage lockout condition exists. The
/FAULT pin requires a pull-up resistor (10kΩ minimum) to VCC.
DIS
NC
N/A
N/A
13
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.
MIC2582/MIC2583
4
April 2003
MIC2582/MIC2583
Micrel
Absolute Maximum Ratings (Note 1)
All voltages are referred to GND
Operating Ratings (Note 2)
Supply Voltage (V )................................... 2.3V to 13.2V
CC
Supply Voltage (V ).................................... –0.3V to 20V
/POR, /FAULT, PWRGD pins ....................... –0.3V to 15V
Thermal Resistance (R
)
CC
θ(J-A)
8-pin SOIC ........................................................163°C/W
16-pin QSOP .................................................... 112°C/W
Operating Temperature Range ................. –40°C to +85°C
SENSE pin ...........................................–0.3V to V +0.3V
CC
ON pin..................................................–0.3V to V +0.3V
CC
GATE pin ...................................................... –0.3V to 20V
FB input pins ................................................... –0.3V to 6V
Junction Temperature .............................................. 125°C
ESD Rating ........................................................................
Human body model ............................................... 2kV
Machine model ....................................................100V
Electrical Characteristics (Note 3)
VCC = 5.0V, TA = 25°C unless otherwise noted. Bold values indicate –40°C ≤ TA ≤ +85°C.
Symbol
VCC
Parameter
Condition
Min
2.3
Typ
Max
13.2
2.5
Units
V
Supply Voltage
Supply Current
ICC
VON = 2V
1.5
50
mA
mV
mV
VTRIP
Circuit Breaker Trip Voltage
(Current Limit Threshold)
VTRIP = VCC – VSENSE VTRIPSLOW
42
59
VTRIPFAST (MIC2582)
100
VTRIPFAST x = J
(MIC2583/83R) x = K
x = L
85
130
175
100
150
200
110
170
225
mV
mV
mV
VGS
External Gate Drive
VGATE – VCC
VCC > 3V
7
8
9
V
VCC = 2.3V
3.5
–30
–26
4.8
17
6.5
–8
–8
V
IGATE
GATE Pin Pull-Up Current
GATE Pin Sink Current
Start Cycle, VGATE = 0V, VCC =13.2V
VCC = 2.3V
µA
µA
mA
mA
17
IGATEOFF
VGATE >1V
VCC = 13.2V, Note 4
100
50
VCC = 2.3V, Note 4
/FAULT = 0
(MIC2583/83R only)
Turn off
110
–6.5
6.5
µA
µA
µA
µA
mA
Current Limit/Overcurrent Timer
(CFILTER) Current
ITIMER
VCC – VSENSE > VTRIPSLOW (timer on)
VCC – VSENSE < VTRIPSLOW (timer off)
timer on
–8.5
4.5
–4.5
8.5
(MIC2583/83R)
ICPOR
Power-On-Reset Timer Current
–3.5
0.5
2.5
–1.5
timer off
1.3
VTH
POR Delay and Overcurrent
Timer (CFILTER) Threshold
VCPOR rising
VCFILTER rising (MIC2583/83R only)
1.19
2.1
1.245
2.2
1.30
2.3
V
V
VUV
Undervoltage Lockout Threshold
VCC rising
VCC falling
1.90
2.05
150
1.24
1.19
50
2.20
V
VUVHYS
VON
Undervoltage Lockout Hysteresis
ON Pin Threshold Voltage
mV
V
ON rising
ON falling
1.19
1.14
1.29
1.24
V
VONHYS
ION
ON Pin Hysteresis
mV
µA
V
ON Pin Input Current
VON = VCC
–0.5
VSTART
Start-Up Delay Timer
Threshold
VCPOR rising
0.26
0.31
0.36
VAUTO
Auto-Restart Threshold Voltage
(MIC2583R only)
upper threshold
lower threshold
charge current
discharge current
1.19
0.26
10
1.24
0.31
13
1.30
0.36
16
V
V
IAUTO
Auto-Restart Current
(MIC2583R only)
µA
µA
1.4
2
April 2003
5
MIC2582/MIC2583
MIC2582/MIC2583
Micrel
Symbol
Parameter
Condition
FB rising
FB falling
Min
1.19
1.15
Typ
1.24
1.20
40
Max
1.29
1.25
Unit
V
VFB
Power-Good Threshold Voltage
V
VFBHYS
VOL
FB Hysteresis
mV
V
/POR, /FAULT, PWRGD
Output Voltage
IOUT = 1mA
0.4
(/FAULT, PWRGD MIC2583/83R only)
RDIS
Output Discharge Resistance
(MIC2583/83R only)
500
1
1000
Ω
AC Parameters (Note 4)
tOCFAST Fast Overcurrent SENSE to GATE
VCC = 5V
µs
Low Trip Time
VCC – VSENSE = 100mV
CGATE = 10nF
Figure 2
tOCSLOW
Slow Overcurrent SENSE to GATE
Low Trip Time
VCC = 5V, VCC – VSENSE = 50mV
CFILTER = 0
5
µs
Figure 2
tONDLY
tFBDLY
ON Delay Filter
FB Delay Filter
20
20
µs
µs
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. Specification for packaged product only.
Note 4. Not a tested parameter, guaranteed by design.
Timing Diagrams
VTRIPFAST
50mV
(VCC – VSENSE
)
tOCFAST
tOCSLOW
GATE
1V
1V
Figure 2. Current Limit Response
1.2V
FB
tPOR
1.5V
/POR
1.5V
/PWRGD
Figure 3. Power-On Reset Response
VUVLO
VCC
tSTART
1V
VGATE
Figure 4. Power-On Start-Up Delay Timing
MIC2582/MIC2583
6
April 2003
MIC2582/MIC2583
Micrel
Typical Characteristics
Voltage Threshold (V
vs. Temperature
)
ON Pin Threshold vs. Temperature
TH
ON Pin Threshold vs. Temperature
(Lower Threshold)
(Upper Threshold)
1.240
1.300
1.290
1.280
1.270
1.260
1.250
1.240
1.230
1.220
1.210
1.200
1.300
1.290
1.280
1.270
1.260
1.230
VCC = 5.0V
1.220
1.210
1.200
1.190
1.180
VCC = 2.3V
VCC = 13.2
VCC = 13.2
1.250
1.240
VCC = 13.2V
1.230
VCC = 2.3
VCC = 5.0
VCC = 2.3
1.220
1.210
1.200
VCC = 5.0
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
Power-Good Threshold
vs. Temperature
(Increasing)
I
I
GATE(OFF)
GATE(ON)
vs. Temperature
vs. Temperature
1.300
1.275
1.250
1.225
1.200
1.175
1.150
1.125
1.100
150
140
130
120
110
100
90
-30
-25
-20
-15
-10
-5
VCC = 13.2V
VCC = 13.2V
VCC = 13.2V
VCC = 5.0V
VCC = 5.0V
VCC = 2.3V
VCC = 5.0V
VCC = 2.3V
VCC = 2.3V
80
70
60
50
0
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
Auto-Restart Threshold Voltage
vs. Temperature (Lower)
MIC2583R
Auto-Restart Threshold Voltage
vs. Temperature (Upper)
MIC2583R
Power-Good Threshold
vs. Temperature
(Decreasing)
1.300
1.280
1.260
1.240
1.220
1.200
1.180
1.160
1.140
1.120
1.100
0.500
1.400
0.450
0.400
0.350
0.300
0.250
0.200
1.350
1.300
1.250
1.200
1.150
1.100
VCC = 13.2V
VCC = 2.3V
VCC = 13.2V
VCC = 5.0V
VCC = 13.2V
VCC = 2.3V
VCC = 5.0V
VCC = 2.3V
VCC = 5.0V
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
Gate Voltage
vs. Temperature
Current-Limit Timer Current
vs. Temperature
UVLO Threshold
vs. Temperature
20
18
16
14
12
10
8
2.50
2.40
2.30
2.20
2.10
2.00
1.90
1.80
1.70
1.60
1.50
-8.0
VCC = 12.0V
UVLO+
-7.5
-7.0
-6.5
-6.0
-5.5
-5.0
VCC = 13.2V
VCC = 5.0V
VCC = 2.3V
UVLO–
VCC = 5.0V
VCC = 2.3V
6
4
2
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
April 2003
7
MIC2582/MIC2583
MIC2582/MIC2583
Micrel
Circuit Breaker Fast (V
vs. Temperature
)
Circuit Breaker Slow (V
)
TRIP
TRIP
Power-On Reset Timer Current
vs. Temperature
vs. Temperature
120
55
54
53
52
51
50
49
48
47
46
45
4.0
VCC = 2.3V
110
100
90
80
70
60
50
40
30
20
3.5
VCC = 5.0V
VCC = 13.2V
VCC = 2.3V
3.0
2.5
2.0
1.5
1.0
VCC = 2.3V
VCC = 5.0V
VCC = 13.2V
VCC = 13.2V
VCC = 5.0V
-40 -20
0
20 40 60 80 100
TEMPERATURE (°C)
-40 -20
0
20 40 60 80 100
-40 -20
0
20 40 60 80 100
TEMPERATURE (°C)
TEMPERATURE (°C)
Gate Current
vs. Gate Voltage @ 85°C
Gate Current
vs. Gate Voltage @ –40°C
Gate Current
vs. Gate Voltage @ 25°C
20
18
16
14
12
10
8
18
16
14
12
10
8
16
14
12
10
8
VCC = 13.2V
VCC = 13.2V
VCC = 13.2V
VCC = 5.0V
VCC = 2.3V
6
6
6
4
4
VCC = 2.3V
VCC = 5.0V
4
2
2
VCC = 2.3V
2
VCC = 5.0V
0
0
0
0
2
4
6
8
10 12 14 16 18 20
0
2
4
6
8
10 12 14 16 18 20
0
2
4
6
8
10 12 14 16 18 20
VOLTAGE (V)
VOLTAGE (V)
VOLTAGE (V)
MIC2582/MIC2583
8
April 2003
MIC2582/MIC2583
Micrel
Test Circuit
RSENSE
IRF7413
or equivalent
IIN
IOUT
0.025Ω
1
2
+
+
3
4
CLOAD
VOUT
CIN
100kΩ
RLOAD
VIN
VCC
ON
SENSE
GATE
–
CGATE
DUT
R1
–
FB
12.4kΩ
1%
Figure 5. Applications Test Circuit
(not all pins shown for simplicity)
April 2003
9
MIC2582/MIC2583
MIC2582/MIC2583
Micrel
Functional Characteristics (See Figure 5, Applications Test Circuit)
Turn On - VOUT = 12V
Turn Off - VOUT = 12V
CIN = 4.7µF
CIN = 4.7µF
CLOAD = 100µF
CGATE = 47nF
RLOAD = 12Ω
R1 = 100kΩ
CLOAD = 100µF
CGATE = 47nF
RLOAD = 12Ω
R1 = 100kΩ
TIME (10ms/div.)
TIME (1ms/div.)
Turn On - VOUT = 5V
Turn Off - VOUT = 5V
CIN = 4.7µF
CIN = 4.7µF
CLOAD = 100µF
CGATE = 47nF
RLOAD = 5Ω
R1 = 33kΩ
CLOAD = 100µF
CGATE = 47nF
RLOAD = 5Ω
R1 = 33kΩ
TIME (5ms/div.)
TIME (1ms/div.)
Turn On (CGATE = 0) - VOUT = 5V
(MIC2583)
Inrush Current Response - VOUT = 5V
CIN = 4.7µF
CGATE = 0
CLOAD = 10µF
RLOAD = 5Ω
R1 = 33kΩ
CIN = 0.1µF
CLOAD = 100µF
CGATE = 10nF
RLOAD = 5Ω
R1 = 33kΩ
TIME (250µs/div.)
TIME (2.5ms/div.)
MIC2582/MIC2583
10
April 2003
MIC2582/MIC2583
Micrel
Functional Characteristics (See Figure 5, Applications Test Circuit)
Turn On Into Heavy Load - VOUT = 12V
Turn On Into Short Circuit - VOUT = 5V
1.85A
CIN = 4.7µF
CGATE = 0
CLOAD = 100µF
CFILTER = 100nF
RLOAD = 6Ω
ILIM = 1.7A
CGATE = CLOAD = 0
CFILTER = 100nF
CIN = 4.7µF
ILIM = 1.7A
R1 = 33kΩ
R1 = 100kΩ
TIME (20ms/div.)
TIME (2.5ms/div.)
Shutdown by Short Circuit - VOUT = 5V
(MIC2583)
CGATE = 0
CIN = 4.7µF
CLOAD = 10µF
RLOAD = 5Ω
ILIM = 3.3A
R1 = 33kΩ
TIME (100µs/div.)
April 2003
11
MIC2582/MIC2583
MIC2582/MIC2583
Micrel
Functional Diagram
MIC2583/83R
15(7)
SENSE
16(8)
VCC
14(6)
13
Charge
Pump
+
–
GATE
DIS
9V
21V
50mV
500Ω
+
–
Circuit Breaker
Trips
or UVLO
UVLO
2.2V
VCC
100mV
ITIMER
6.5µA
11
/FAULT
/POR
5
CFILTER
+
–
VREF
Logic
6.5µA
1(1)
7,8(4)
12(5)
GND
FB
2
+
–
Glitch
Filter
PWRGD
VREF
VCC
2.5µA
ICPOR
0.3V
4 (3)
3(2)
+
–
CPOR
ON
+
–
Glitch
Filter
VREF
+
–
1.24V
Reference
VREF
Pin numbers for MIC2582 are in parenthesis ( ) where applicable
MIC2582/MIC2583
12
April 2003
MIC2582/MIC2583
Micrel
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 immedi-
ately 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
programmedcurrentlimitvalue(SeeCurrentLimitingandDual-
Level Circuit Breaker section). The following equation is used
to determine the nominal current limit value:
Functional Description
Hot Swap Insertion
When circuit boards are inserted into live system backplanes
and supply voltages, high inrush currents can result due to the
chargingofbulkcapacitancethatresidesacrossthesupplypins
of the circuit board. This inrush current, although transient in
nature, maybehighenoughtocausepermanentdamagetoon
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
controllerforexternalN-ChannelMOSFETdevicesinwhichthe
gate drive is controlled to provide inrush current limiting and
output voltage slew rate control during hot plug insertions.
V
50mV
TRIPSLOW
I
=
=
LIM
(2)
R
R
SENSE
SENSE
where V
in the electrical table and R
is the current limit slow trip threshold found
TRIPSLOW
is the selected value that will
SENSE
Power Supply
setthedesiredcurrentlimit.Therearetwobasicstart-upmodes
fortheMIC2582/83:1)Start-updominatedbyloadcapacitance
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
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.
thantheprogrammedcurrentlimit(I ), thenloadcapacitance
LIM
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
controllertogroundinordertoprovideexternalsupplytransient
protection is strongly recommended for relatively high current
applications (≥3A). See Figure 1.
CLOAD
CGATE
CLOAD
CGATE
INRUSH IGATE
where I
×
17µA ×
(3)
is the GATE pin pull-up current, C
is the load
GATE
LOAD
capacitance, andC
isthetotalGATEcapacitance(C of
the external MOSFET and any external capacitor connected
from the MIC2582/83 GATE pin to ground).
GATE
ISS
Start-Up Cycle
Supply Contact Delay
Load Capacitance Dominated Start-Up
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
aboveitsthreshold(1.24Vtypical),theMIC2582/83firstchecks
that both supply voltages are above their respective UVLO
thresholds. If so, the device is enabled and an internal 2.5µA
In this case, the load capacitance (C
) is large enough to
LOAD
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 source begins charging capacitor C
to 0.3V to
current limit value (I ) and held constant until the output
POR
LIM
initiate a start-up sequence. Once the start-up delay (t
elapses, the CPOR pin is pulled immediately to ground and a
17µA current source begins charging the GATE output to drive
)
voltage rises to its final value. The output slew rate and
equivalentGATEvoltageslewrateiscomputedbythefollowing
equation:
START
the external MOSFET that switches V to V
grammed contact start-up delay is calculated using the follow-
ing equation:
. The pro-
IN
OUT
ILIM
Output Voltage Slew Rate, dVOUT/dt =
(4)
CLOAD
where I
quently, the value of C
the overcurrent response time, t
neededfortheoutputtoreachitsfinalvalue.Forexample,given
a MOSFET with an input capacitance C = C = 4700pF,
is the programmed current limit value. Conse-
V
LIM
START
t
= C
×
0.12 × C
(µF)
must be selected to ensure that
START
POR
POR
(1)
) is 0.3V, and
FILTER
I
CPOR
, exceeds the time
OCSLOW
where the start-up delay timer threshold (V
the Power-On Reset timer current (I
START
) is 2.5µA. See Table
CPOR
ISS
GATE
2 for some typical supply contact start-up delays using several
standard value capacitors. As the GATE voltage continues
rampingtowarditsfinalvalue(V +V )atadefinedslewrate
C
is2200µF, andI issetto6Awitha12Vinput, thenthe
LOAD LIM
load capacitance dominates as determined by the calculated
INRUSH > I . Therefore, the output voltage slew rate deter-
CC
GS
LIM
(See Load Capacitance/Gate Capacitance Dominated Start-
up 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
mined from Equation 4 is:
6A
V
Output Voltage Slew Rate, dV
/dt =
= 2.73
OUT
2200µF
ms
cycle (t
) begins when the voltage at the FB pin exceeds its
and the resulting t
approximately 4.5ms. (See Power-On Reset and Overcurrent
Timer Delays section to calculate t
needed to achieve a 12V output is
POR
OCSLOW
threshold(V ). Thisconditionindicatesthattheoutputvoltage
is valid. See Figure 3 in the Timing Diagrams. When the power
FB
)
OCSLOW
April 2003
13
MIC2582/MIC2583
MIC2582/MIC2583
Micrel
GATE Capacitance Dominated Start-Up
charges capacitor C
. Once the CPOR pin voltage reaches
POR
1.24V, the time period t
to ground and the /POR pin goes HIGH. If the voltage at FB
elapses as the CPOR pin is pulled
In this case, the value of the load capacitance relative to the
GATEcapacitanceissmallenoughsuchthattheloadcurrent
during start-up never exceeds the current limit threshold as
POR
drops below V for more than 10µs, the /POR pin resets for at
FB
least one timing cycle defined by t
Information for an example).
(See Applications
determined by Equation 3. The minimum value of C
will ensure that the current limit is never exceeded is given by
the equation below:
that
POR
GATE
Power-On Reset and Overcurrent Timer Delays
The Power-On Reset delay, t , is the time period for the
IGATE
POR
CGATE(min) =
× CLOAD
(5)
/PORpintogoHIGHoncethevoltageattheFBpinexceedsthe
ILIM
power-good threshold (V ). A capacitor connected to CPOR
FB
where C
is the summation of the MOSFET input
GATE
setstheintervalandisdeterminedbyusingEquation1withV
TH
capacitance (C ) and the value of the external capacitor
ISS
substituted for V
. The resulting equation becomes:
START
connectedtotheGATEpinoftheMIC2582/83toground. Once
VTH
C
is determined, use the following equation to determine
tPOR = CPOR
×
0.5 × CPOR µF
(
)
GATE
(7)
ICPOR
the output slew rate for gate capacitance dominated start-up.
where the Power-On Reset threshold (V ) and timer current
I
TH
GATE
dV
/dt =
(I
) are typically 1.24V and 2.5µA, respectively.
OUT
(6)
CPOR
C
GATE
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
Table1depictstheoutputslewrateforvariousvaluesofC
.
GATE
IGATE = 17µA
CGATE
0.001µF
0.01µF
0.1µF
1µF
dVOUT/dt
17V/ms
(t
), determined by C
. When no capacitor is
OCSLOW
FILTER
1.7V/ms
connectedtoCFILTERandfortheMIC2582, t
defaults
OCSLOW
0.17V/ms
0.017V/ms
to 5µs. If t
elapses, then the circuit breaker is activated
OCSLOW
and the GATE output is immediately pulled to ground. For the
MIC2583/83R, the following equation is used to determine the
Table 1. Output Slew Rate Selection for GATE
Capacitance Dominated Start-Up
overcurrent timer period, t
.
OCSLOW
VTH
Current Limiting and Dual-Level Circuit Breaker
tOCSLOW = CFILTER
×
0.19 × CFILTER(µF)
(8)
ITIMER
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.
where V , the CFILTER timer threshold, is 1.24V and I
,
TH
TIMER
the overcurrent timer current, is 6.5µA. Tables 2 and 3 provide
a quick reference for several timer calculations using select
standard value capacitors.
C
POR
t
t
POR
START
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
0.01µF
0.02µF
0.033µF
0.05µF
0.1µF
1.2ms
2.4ms
4ms
5ms
10ms
16.5ms
25ms
6ms
overcurrent timer, its duration set by capacitor C
, starts
FILTER
12ms
40ms
56ms
120ms
50ms
torampthevoltageatCFILTERusinga6.5µAconstantcurrent
source.IfthevoltageatCFILTERreachestheovercurrenttimer
0.33µF
0.47µF
1µF
165ms
235ms
500ms
threshold(V )of1.24V, thenCFILTERimmediatelyreturnsto
TH
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,
thecircuitbreakertripsandtheGATEshutsdownimmediately,
bypassing the overcurrent time period. To disable current limit
and circuit breaker operation, tie the SENSE and VCC pins
together and the CFILTER (MIC2583/83R) pin to ground.
Table 2. Selected Power-On Reset and Start-Up Delays
C
FILTER
t
OCSLOW
680pF
2200pF
4700pF
8200pF
0.033µF
0.1µF
130µs
420µs
900µs
1.5ms
6ms
Output Undervoltage Detection
The MIC2582/83 employ output undervoltage detection by
monitoring the output voltage through a resistive divider con-
nected at the FB pin. During turn on, while the voltage at the FB
19ms
42ms
90ms
0.22µF
0.47µF
pin is below the threshold (V ), the /POR pin is asserted low.
FB
Once the FB pin voltage crosses V , a 2.5µA current source
FB
Table 3. Selected Overcurrent Timer Delays
MIC2582/MIC2583
14
April 2003
MIC2582/MIC2583
Micrel
Applications Information
Output Undervoltage Detection
VOUT(Good)
R5 = R6
where V
–1
(9.1)
= 11V, and R6 is
OUT(Good)
VFB(MAX)
Foroutputundervoltagedetection,thefirstconsiderationisto
establish the output voltage level that indicates “power is
good.” For this example, the output value for which a 12V
supplywillsignal“good”is11V. Next, considerthetolerances
= 1.29V, V
FB(MAX)
12.4kΩ. Substituting these values into Equation 9.1 now
yields R5 = 93.33kΩ. A standard 93.1kΩ ± 1% is selected.
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
of the input supply and FB threshold (V ). For this example,
FB
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
theresistivedividernetwork(R5andR6)attheFBpin, shown
in the typical application circuit on page 1, use the following
iterative design procedure.
sensed at the FB pin exceeds V
, thus the /POR and
FB(MAX)
PWRGD (MIC2583/83R) signals will transition from LOW to
HIGH, indicating “power is good” given the worse case
tolerances of this example.
PCB Connection Sense
1) Choose R6 so as to limit the current through the
ThereareseveralconfigurationoptionsfortheMIC2582/83’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,
theresistornetworkispulleduptotheinputsupply,12Vinthis
divider to approximately 100µA or less.
VFB(MAX)
1.29V
R6
12.9kΩ
.
100µA
100µA
R6 is chosen as 12.4kΩ ± 1%.
2) Next, determine R5 using the output “good”
voltage of 11V and the following equation:
R5 +R6
(
)
example, and the ON pin voltage exceeds its threshold (V
)
ON
VOUT(Good) = VFB
(9)
R6
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
Using some basic algebra and simplifying Equation 9 to
isolate R5, yields:
RSENSE
0.010Ω
Q1
Si7860DP
(PowerPAK“ SO-8)
Backplane PCB Edge
Long
Connector Connector
Pin
5%
VIN
5V
1
2
VOUT
5V@3A
3
4
C1
1 F
CLOAD
220 F
**R8
10Ω
16
15
R5
20kΩ
R4
20kΩ
VCC
SENSE
14
GATE
R6
3
ON
27.4kΩ
1%
R1
R2
33kΩ
C2
0.01 F
33kΩ
*Q2
R3
100Ω
/ON_OFF
13
12
MIC2583
DIS
FB
PCB Connection Sense
VIN
Short
Pin
R7
10.5kΩ
1%
R9
20Ω
11
/FAULT
GND
/FAULT
1
/POR
CPOR
GND
7,8
Downstream
Signal
Medium or
Short Pin
4
C3
0.05 F
Long
Pin
Undervoltage (Output) = 4.45V
/POR Delay = 25ms
START-UP Delay = 6ms
*Q2 is TN0201T (SOT-23)
**R8 is optional for noise filtering
Additional pins omitted for clarity.
Figure 6. PCB Connection Sense with ON/OFF Control
April 2003
15
MIC2582/MIC2583
MIC2582/MIC2583
Micrel
controlfromtheprocessororothersignalcontrollertoshutoff
5V Switch with 3.3V Supply Generation
the output of the MIC2582/83. R4 pulls the GATE of Q2 to V
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
exceededwhichtriggersthepower-onresetcomparator.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
powerdissipationcapabilityoftheselectedMOSFETas1.5V
to 2V will drop across the device during normal operation in
this application. Therefore, the device is susceptible to over-
heating dependent upon the current requirements for the
regulatedoutput. Inthisexample, thepowerdissipatedbyQ2
is approximately ≤1W. However, a substantial amount of
power will be generated with higher current requirements
and/orconditions. Asageneralguideline, expecttheambient
temperature within the power supply box to exceed the
maximum operating ambient temperature of the system
environment by approximately 20°C. Given the MOSFET’s
IN
andtheONpinisheldlowuntiltheconnectorsarefullymated.
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 V exceeds 2.2V. If VCC falls
CC
below2.1V, theUVLOcircuitpullstheGATEoutputtoground
and clears the overvoltage and/or current limit faults. 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
R1
1+
×1.24V
. The GATE
to remain off until V exceeds
IN
R2
drive output will be shut down when V falls below
IN
R1
1+
×1.19V
. In the example circuit (Figure 7), the rising
R2
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
R
and the expected power dissipated by the MOSFET,
θ(J-A)
an approximation for the junction temperature at which the
device will operate is obtained as follows:
exceeds its threshold (V ) and after the start-up timer
ON
T = (P x R
) + T '
(10)
J
D
θ(J-A)
A
elapses.
where T '=T
+ 20°C. As a precaution, the
A
A(MAX OPERATING)
implementation of additional copper heat sinking is highly
recommended for the area under/around the MOSFET.
For additional information on MOSFET thermal consider-
ations, please see MOSFET Selection text and subsequent
sections.
RSENSE
0.010Ω
Q1
IRF7822
5%
(SO-8)
VIN
12V
1
2
VOUT
12V@4A
CLOAD
3
4
C1
1µF
D1
(18V)
220µF
R4
R3
R1
332kΩ
1%
8
7
10Ω
133kΩ
1%
VCC
SENSE
6
5
GATE
FB
C2
0.01µF
2
ON
MIC2582
R2
49.9kΩ
1%
R5
16.2kΩ
1%
GND
4
Undervoltage Lockout Threshold (rising) = 9.5V
Undervoltage Lockout Threshold (falling) = 9.1V
Undervoltage (Output) = 11.4V
Additional pins omitted for clarity.
Figure 7. Higher UVLO Setting
MIC2582/MIC2583
16
April 2003
MIC2582/MIC2583
Micrel
Q2
Si4876DY
(SO-8)
VOUT
3.3V@0.5A
C6
100 F
Q1
Si4876DY
(SO-8)
Backplane PCB Edge
Connector Connector
Long
Pin
VIN
5V
1
2
VOUT
5V@3.5A
3
4
RSENSE
0.010Ω
2%
D1
(9V)
C1
0.47 F
C5
330 F
R3
10Ω
R2
10Ω
8
7
R4
1.2MΩ
VCC
SENSE
R1
47kΩ
6
GATE
2
ON
C2
0.022 F
C3
4700pF
R5
510kΩ
VIN
MIC2582
R8
20kΩ
R9
750Ω
R6
20kΩ
1%
C4
0.1 F
1
5
Q3
PN2222
/POR
FB
3
Open
Circuit
CPOR
Short
Pin
GND
R7
11.8kΩ
4
1%
GND
Long
Pin
Undervoltage (Output) = 3.3V
All resistors 5% unless specified otherwise
Figure 8. 5V Switch/3.3V LDO Application
Auto-Restart - MIC2583R
The MIC2583R provides an auto-restart function. Upon an
overcurrent fault condition such as a short circuit, the
MIC2583RinitiallyshutsofftheGATEoutput.TheMIC2583R
attemptstorestartwitha12µAchargecurrentatapreset10%
duty cycle until the fault condition is removed. The interval
Once the value of R
it is good practice to check the maximum I
the circuit may let through in the case of tolerance buildup in
the opposite direction. Here, the worst-case maximum cur-
rent is found using a 59mV trip voltage and a sense resistor
that is 3% low in value. The resulting equation is:
has been chosen in this manner,
SENSE
which
LOAD(CONT)
between auto-retry attempts is set by capacitor C
.
FILTER
Sense Resistor Selection
59mV
0.97 R
60.8mV
ILOAD(CONT,MAX)
=
=
(12)
TheMIC2582andMIC2583usealow-valuesenseresistorto
measure the current flowing through the MOSFET switch
(and therefore the load). This sense resistor is nominally set
RSENSE(NOM)
(
)
SENSE(NOM)
As an example, if an output must carry a continuous 2A
without nuisance trips occurring, Equation 11
at 50mV/I
. To accommodate worst-case toler-
LOAD(CONT)
ances 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.
40.8mV
RSENSE(MAX)
=
= 20.4mΩ
. The next lowest
yields:
2A
standard value is 20mΩ At the other set of tolerance ex-
.
tremes for the output in question,
The current limit threshold voltage (i.e., the “trip point”) for the
MIC2582/83 may be as low as 42mV, which would equate to
60.8mV
ILOAD(CONT,MAX)
=
= 3.04A
, approximately 3A.
20.0mΩ
Knowing this final datum, we can determine the necessary
wattage of the sense resistor using P = I R, where
a sense resistor value of 42mV/I
. Carrying the
LOAD(CONT)
numbers through for the case where the value of the sense
resistor is 3% high yields:
2
I will be
I
, and R will be (0.97)(R
).
These
SENSE(NOM)
LOAD(CONT, MAX)
42mV
40.8mV
2
numbersyieldthefollowing:P
=(3A) (19.4mΩ)
= 0.175W.
RSENSE(MAX)
=
=
MAX
(11)
1
ILOAD(CONT)
1.03 I
In this example, a / W sense resistor is sufficient.
(
)
(
)
LOAD(CONT)
4
April 2003
17
MIC2582/MIC2583
MIC2582/MIC2583
Micrel
MOSFET Selection
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 MOSFET (again, assuming 12V opera-
tion). 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
beusedtopreventbreakdownoftheexternalMOSFETwhen
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.
As a general tip, choose surface-mount devices with a drain-
source rating of 30V as a starting point.
Selecting the proper external MOSFET for use with the
MIC2582/83 involves three straightforward tasks:
• 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 V
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.
. For instance, a 12V input may
IN(MAX)
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 avail-
able. Please see Table 4 MOSFET and Sense Resistor
Vendors for suggested manufacturers.
The second breakdown voltage criterion that must be met is
abitsubtlerthansimpledrain-sourcebreakdownvoltage, but
RSENSE
0.006Ω
Q1
IRF7822
(SO-8)
*D2
1N5240B
10V
5%
VIN
12V
1
2
VOUT
12V@6A
3
4
D1
(18V)
CLOAD
220µF
C1
1µF
R1
33kΩ
R4
100kΩ
1%
R3
10Ω
8
7
VCC
SENSE
6
GATE
C2
0.01µF
2
ON
5
1
MIC2582
FB
VIN
R5
13.3kΩ
1%
R2
33kΩ
R6
47kΩ
/POR
CPOR
GND
DOWNSTREAM
SIGNAL
3
4
C3
0.05µF
Undervoltage (Output) = 11.0V
/POR Delay = 25ms
START-UP Delay = 6ms
*Recommended for MOSFETs with gate-source
breakdown of 20V or less for catastrophic output
short circuit protection. (IRF7822 V (MAX) = 12V)
GS
Figure 9. Zener Clamped MOSFET Gate
MIC2582/MIC2583
18
April 2003
MIC2582/MIC2583
Micrel
current. The use of a thermocouple on the drain
MOSFET Steady-State Thermal Issues
leads, or infrared pyrometer on the package, will
then give a reasonable idea of the device’s
junction temperature.
TheselectionofaMOSFETtomeetthemaximumcontinuous
current is a fairly straightforward exercise. First, arm yourself
with the following data:
MOSFET Transient Thermal Issues
• The value of I
for the output in
LOAD(CONT, MAX.)
question (see Sense Resistor Selection).
Having chosen a MOSFET that will withstand the imposed
voltage stresses, and the worse case continuous I R power
2
• The manufacturer’s data sheet for the candidate
dissipation which it will see, it remains only to verify the
MOSFET’s ability to handle short-term overload power dissi-
pation without overheating. A MOSFET can handle a much
higher pulsed power without damage than its continuous
dissipationratingswouldimply.Thereasonforthisisthat,like
everything else, thermal devices (silicon die, lead frames,
etc.) have thermal inertia.
MOSFET.
• The maximum ambient temperature in which the
device will be required to operate.
• 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?).
In terms related directly to the specification and use of power
MOSFETs, this is known as “transient thermal impedance,”
The data sheet will almost always give a value of on resis-
tancegivenfortheMOSFETatagate-sourcevoltageof4.5V,
and another value at a gate-source voltage of 10V. As a first
approximation, addthetwovaluestogetheranddividebytwo
to get the on-resistance of the part with 8V of enhancement.
or Z
. Almost all power MOSFET data sheets give a
θ(J-A)
Transient Thermal Impedance Curve. For example, take the
followingcase:V =12V, t hasbeensetto100msec,
IN
OCSLOW
I
is 2.5A, the slow-trip threshold is 50mV
LOAD(CONT. MAX)
nominal, and the fast-trip threshold is 100mV. If the output is
accidentally connected to a 3Ω load, the output current from
the MOSFET will be regulated to 2.5A for 100ms (t
before the part trips. During that time, the dissipation in the
MOSFET is given by:
Call this value R . Since a heavily enhanced MOSFET acts
ON
as an ohmic (resistive) device, almost all that’s required to
)
OCSLOW
2
determine steady-state power dissipation is to calculate I R.
The one addendum to this is that MOSFETs have a slight
increase in R
with increasing die temperature. A good
ON
P = E x I E
= [12V-(2.5A)(3Ω)] = 4.5V
MOSFET
approximation for this value is 0.5% increase in R per °C
ON
P
= (4.5V x 2.5A) = 11.25W for 100msec.
MOSFET
riseinjunctiontemperatureabovethepointatwhichR was
ON
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.
Figure10showsthecurvefortheVishay(Siliconix)Si4410DY,
a commonly used SO-8 power MOSFET.
initially specified by the manufacturer. For instance, if the
selected MOSFET has a calculated R
of 10mΩ at a
ON
T = 25°C, and the actual junction temperature ends up
J
at 110°C, a good first cut at the operating value for R
ON
would be:
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“singlepulse”event,thatistosay,there’snosignificantduty
cycle. Then, reading up from the X-axis at the point where
“SquareWavePulseDuration”isequalto0.1sec(=100msec),
R
10mΩ[1 + (110 - 25)(0.005)] 14.3mΩ
ON
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 °C/W) as that with which the MOSFET’s
performance was specified by the manufacturer. Here are a
few practical tips:
1. The heat from a surface-mount device such as
an SO-8 MOSFET flows almost entirely out of
the drain leads. If the drain leads can be sol-
dered 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.
we see that the Z
of this MOSFET to a highly infrequent
θ(J-A)
event of this duration is only 8% of its continuous R
.
θ(J-A)
θ(J-A)
This particular part is specified as having an R
of
50°C/W for intervals of 10 seconds or less. Thus:
Assume T = 55°C maximum, 1 square inch of copper at the
A
drain leads, no airflow.
Recalling from our previous approximation hint, the part has
2. Airflow works. Even a few LFM (linear feet per
minute) of air will cool a MOSFET down sub-
stantially. If you can, position the MOSFET(s)
near the inlet of a power supply’s fan, or the
outlet of a processor’s cooling fan.
an R of (0.0335/2) = 17mΩ at 25°C.
ON
Assume it has been carrying just about 2.5A for some time.
When performing this calculation, be sure to use the highest
anticipated ambient temperature (T
) in which the
A(MAX)
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
MOSFET's temperature in the actual layout of
the expected final circuit, at full operating
MOSFET will be operating as the starting temperature, and
find the operating junction temperature increase (∆T ) from
J
thatpoint.Then,asshownnext,thefinaljunctiontemperature
isfoundbyaddingT
and∆T . Sincethisisnotaclosed-
A(MAX)
J
formequation, gettingacloseapproximationmaytakeoneor
April 2003
19 MIC2582/MIC2583
MIC2582/MIC2583
Micrel
two iterations, But it’s not a hard calculation to perform, and
So our original approximation of 61.1°C was very close to the
tends to converge quickly.
correct value. We will use T = 61°C.
J
Then the starting (steady-state)T is:
Finally, add (11.25W)(50°C/W)(0.08) = 45°C to the steady-
J
state T to get T
able maximum junction temperature for this part.
= 106°C. This is an accept-
J
J(TRANSIENT MAX.)
T
T
T
+ ∆T
J
J
A(MAX)
A(MAX)
+ [R + (T
– T )(0.005/°C)(R )]
A ON
ON
A(MAX)
PCB Layout Considerations
2
x I x R
θ(J-A)
Becauseofthelowvaluesofthesenseresistorsusedwiththe
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
T
T
55°C + [17mΩ + (55°C-25°C)(0.005)(17mΩ)]
J
2
x (2.5A) x (50°C/W)
(55°C + (0.122W)(50°C/W)
61.1°C
J
connectiontoaccuratelymeasurethevoltageacrossR
SENSE
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
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 T equal to the already calculated value of 61.1°C:
J
T
T + [17mΩ + (61.1°C-25°C)(0.005)(17mΩ)]
J
J
A
2
x (2.5A) x (50°C/W)
illustratesarecommended,singlelayerlayoutfortheR
,
T
( 55°C + (0.125W)(50°C/W) 61.27°C
SENSE
Normalized Thermal Transient Impedance, Junction-to-Ambient
2
1
Duty Cycle = 0.5
0.2
Notes:
0.1
P
DM
0.1
0.05
t
1
t
2
t
t
1
1. Duty Cycle, D =
2
0.02
2. Per Unit Base = R
= 50°C/W
thJA
(t)
3. T – T = P
JM
Z
A
DM thJA
Single Pulse
4. Surface Mounted
0.01
–4
–3
–2
–1
10
10
10
10
1
10
30
Square Wave Pulse Duration (sec)
Figure 10. Transient Thermal Impedance
Current Flow
to the Load
Current Flow
to the Load
*POWER MOSFET
(SO-8)
*SENSE RESISTOR
(2512)
D
G
D
D
S
S
W
W
D
S
**RGATE
93.1k
1%
8
7
6
5
12.4k
1%
**CGATE
1
2
3
4
**CPOR
Current Flow
to the Load
W
DRAWING IS NOT TO SCALE
*See Table 4 for part numbers and vendors.
**Optional components.
Trace width (W) guidelines given in "PCB Layout Recommendations" section of the datasheet.
Figure 11. Recommended PCB Layout for Sense Resistor, Power MOSFET, and Feedback Network
MIC2582/MIC2583 20 April 2003
MIC2582/MIC2583
Micrel
Power MOSFET, timer(s), and feedback network connec-
tions. The feedback network resistor values are selected for
a 12V application. Many hot swap applications will require
Finally, the use of plated-through vias will be needed to make
circuitconnectionstopowerandgroundplaneswhenutilizing
multi-layer PC boards.
load currents of several amperes. Therefore, the power (V
MOSFET and Sense Resistor Vendors
CC
andReturn)tracewidths(W)needtobewideenoughtoallow
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
10°C~25°C.Also,thesetracesshouldbeasshortaspossible
in order to minimize the IR drops between the input and the
load. For a starting point, there are many trace width calcu-
lation tools available on the web such as the following link:
Devicetypesandmanufacturercontactinformationforpower
MOSFETs and sense resistors is 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.
http://www.aracnet.com/cgi-usr/gpatrick/trace.pl
MOSFET Vendors
Key MOSFET Type(s)
Applications*
Contact Information
Vishay (Siliconix)
Si4420DY (SO-8 package)
Si4442DY (SO-8 package)
Si4876DY (SO-8 package)
Si7892DP (PowerPAK™ SO-8)
I
I
I
I
≤ 10A
= 10-15A, V < 3V
≤ 5A, V ≤ 5V
≤15A
www.siliconix.com
(203) 452-5664
OUT
OUT
OUT
OUT
CC
CC
International Rectifier
IRF7413 (SO-8 package)
IRF7457 (SO-8 package)
IRF7601 (SO-8 package)
I
I
I
≤ 10A
= 10-15A
≤ 5A, V < 3V
www.irf.com
(310) 322-3331
OUT
OUT
OUT
CC
Fairchild Semiconductor
FDS6680A (SO-8 package)
I
≤ 10A
www.fairchildsemi.com
(207) 775-8100
OUT
Philips
Hitachi
PH3230 (SOT669-LFPAK)
HAT2099H (LFPAK)
I
I
≥ 20A
≥ 20A
www.philips.com
OUT
OUT
www.halsp.hitachi.com
(408) 433-1990
* 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
April 2003
21
MIC2582/MIC2583
MIC2582/MIC2583
Micrel
Package Information
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
DIMENSIONS:
INCHES (MM)
0.020 (0.51)
0.013 (0.33)
0.050 (1.27)
TYP
45°
0.0098 (0.249)
0.0040 (0.102)
0.010 (0.25)
0.007 (0.18)
0°–8°
0.197 (5.0)
0.189 (4.8)
0.050 (1.27)
0.016 (0.40)
SEATING
PLANE
0.064 (1.63)
0.045 (1.14)
0.244 (6.20)
0.228 (5.79)
8-Pin SOP (M)
PIN 1
DIMENSIONS:
INCHES (MM)
0.157 (3.99)
0.150 (3.81)
0.009 (0.2286)
REF
0.012 (0.30)
0.008 (0.20)
0.025 (0.635)
BSC
45¡
0.0098 (0.249)
0.0075 (0.190)
0.0098 (0.249)
0.0040 (0.102)
8¡
0¡
0.196 (4.98)
0.050 (1.27)
0.189 (4.80)
0.016 (0.40)
SEATING 0.0688 (1.748)
PLANE
0.0532 (1.351)
0.244 (6.20)
0.229 (5.82)
Rev. 04
16-pin QSOP (QS)
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.
© 2003 Micrel, Incorporated.
MIC2582/MIC2583
22
April 2003
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