MICREL MIC2580A

MIC2580A
Micrel, Inc.
MIC2580A
Hot-Swap PCI Power Controller
General Description
Features
The MIC2580A is a hot-swap controller that provides for safe
and orderly insertion and removal of PCI based adapter cards
from a PCI hot-plug compliant system backplane or
CompactPCI™ system.
The MIC2580A incorporates a circuit breaker function that
protects all four supplies (+12V, +5V, +3.3V, and –12V) upon
an overcurrent fault condition. Current foldback limiting prevents large transient currents caused by plugging adapter
cards into live backplanes, such as in a CompactPCI system.
A programmable slew-rate control limits high inrush currents
to all loads that occur when power is applied to large capacitive loads.
Voltage supervisory functions for all four power supplies are
provided by “power good” (/PWRGD) and “overcurrent fault”
(/FAULT) diagnostic outputs. Power good and overcurrent
fault include deglitch filters to prevent nuisance tripping.
Power good is active when all four supplies are within
tolerance. Fault (/FAULT) goes active upon overcurrent or
overtemperature conditions. The on-off control input (/ON) is
used to cycle power to the adapter card.
•
•
•
•
•
•
•
•
•
•
PCI hot-plug and CompactPCI™ hot-swap support
+12V, +5V, +3.3V, and –12V power supply control
Circuit breaker function to protect system
Programmable slew rate control for all supplies
Foldback current-limiting
+5V and +3.3V programmable current-limit thresholds
Undervoltage and overcurrent diagnostic outputs
Deglitch filters on diagnostic fault outputs
Integrated +12V and –12V MOSFET switches
Integrated high-side drivers for 3.3V and 5V external
switches
• Precharge supply for CompatPCI™ I/O termination
Applications
• PCI hot-plug systems
• CompactPCI™ hot-swap systems
Typical Application
10mΩ
+12V
+5V/8A
+5V
12VIN
GND
–12V/1A
–12V
5VGATE
3VSENSE
1µF
3VGATE
/BD_SEL
/HEALTHY
VPCHG
1.2k
/POR
/ON
CSLEW
VIO
VPCH = +1V ±20%
(PRECHARGE SUPPLY)
CRST
/PCIRST
/ON
+3.3V
3VOUT
3VIN
1µF
/PCIRST
+5V
5VOUT
5VIN
VIO
VIO
+12V
12VOUT
5VSENSE
+3.3V
GND
/PCI_RST
IRF7413
IRF7413
MIC2580A
+12V/1A
+3.3V/8A
10mΩ
Adapter
Platform
1µF
Overcurrent
Fault
/LPCIRST
/FAULT
/EPWRGD CSTART
/PGD
GND
/PWRGD
M12VIN M12VOUT
–12V
1µF
/LPCIRST
Data Bus
D0
D0
PCI
D1 Controller D1
D2
D2
Dn
Dn
Data Bus
/ENUM
CompactPCI™ Adapter with Early Power
CompactPCI is a trademark of the PCI Industrial Computer Manufacturer’s Group.
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
February 2005
1
MIC2580A
MIC2580A
Micrel, Inc.
Ordering Information
Part Number
Pb-Free
Standard
Precharge
Voltage
Temperature
Range
Package
MIC2580A-1.0BTS
MIC2580A-1.0YTS
1V
–40°C to +85°C
24-lead TSSOP
MIC2580A-1.6BTS
MIC2580A-1.6YTS
1.6V
–40°C to +85°C
24-lead TSSOP
Pin Configuration
12VOUT 1
24 12VIN
3VGATE 2
23 5VGATE
3VOUT 3
22 5VOUT
3VSENSE 4
21 5VSENSE
3VIN 5
20 5VIN
/PCIRST 6
19 /FAULT
/LPCIRST 7
18 CSTART
/EPWRGD 8
17 CSLEW
/PWRGD 9
16 /POR
VPCHG 10
15 CRST
GND 11
14 /ON
M12VIN 12
13 M12VOUT
24-lead TSSOP (TS)
Pin Description
Pin Number
Pin Name
1
12VOUT
+12V Switched Supply (Output): Load carrying output.
2
3VGATE
3.3V Gate Drive (Output): Drives gate of external N-channel MOSFET +3V
switch. Adding capacitance will slow the slew rate of the external MOSFET
switch turn-on. (The external MOSFET’s gate is charged by an internal
current source.)
3
3VOUT
+3.3V Output Voltage Sense (Input): Connect to source of external
N-channel MOSFET (+3V switched output) to monitor for output undervoltage conditions.
4
3VSENSE
5
3VIN
6
/PCIRST
MIC2580A
Pin Function
+3.3V Current Sense (Input): Measures voltage drop across an external
sense resistor with respect to 3VIN for overcurrent detection through the
+3.3V switch.
3V Supply (Input): +3.3V-supply input for current monitoring (reference input
for 3VSENSE). Not a load-current carrying input.
PCI-Bus Reset (Input): Input from PCI bus that resets the internal logic.
2
February 2005
MIC2580A
Micrel, Inc.
Pin Number
Pin Name
Pin Function
7
/LPCIRST
Local PCI Reset (Open-Drain Output): Local PCI reset output to PCI
controller. Compliant to CompactPCI specification for LOCAL_PCI_RESET.
8
/EPWRGD
Early Power Good (Open-Drain Output): This signal goes active should
/FAULT or /PWRGD go active. No deglitch filtering is provided. This signal
satisfies PCI /RST timing for TFAIL per PCI Local Bus Specification, version 2.1.
9
/PWRGD
Power Good (Open-Drain Output): Active-low output goes active when all
supplies are within tolerance. (A 20µs delay is inserted prior to activation to
reduce nuisance tripping.)
10
VPCHG
Precharge Supply (Output): (MIC2580A-1.0) +1V ±20% supply used for
precharge bias for I/O terminations (CompactPCI only).
11
GND
12
M12VIN
13
M12VOUT
14
/ON
On-Off Control (Input): Logic low turns on all switches; logic high turns off all
switches. Also used to reset the device from a circuit breaker condition. The
/ON pin is edge-triggered and requires a high-to-low transition once all four
supplies are above their respective thresholds.
15
CRST
Reset Delay (External Component): Connect to external capactior (CRST) to
increase power-on reset delay.
16
/POR
Reset (Open-Drain Output): Active-low signal remains active for a time
determined by CRST after all supplies are within tolerance; i.e., /PWRGD is
active. This signal may be used as a reset for logic controllers.
17
CSLEW
Slew (External Component): Connect to external capacitor (CSLEW) to
program the output slew rate of 3VGATE, 5VGATE, 12VGATE (internal) and
M12VGATE (internal).
18
CSTART
Start-Up Timer (External Component): Connect to external capacitor
(CSTART) to increase the filter delay used to gate the /FAULT output upon
start-up. Used to prevent nuisance tripping during turn-on of supplies.
19
/FAULT
Fault (Open-Drain Output/Input): This active-low output signal activated
upon overcurrent or thermal shutdown. Includes 20µs deglitch filter. Fault is
reset using /ON.
Forcing pin low turns off all switches but does not activate the circuit breaker
function.
20
5VIN
21
5VSENSE
+5V Current Sense (Input): Measures voltage drop across an external
sense resistor with respect to 5VIN for overcurrent detection through the +5V
switch.
22
5VOUT
+5V Output Voltage Sense (Input): Connect to source of external N-channel
MOSFET (+5V switched output) to monitor for output undervoltage conditions.
23
5VGATE
24
12VIN
February 2005
Ground
–12V Supply (Input): Input for internal –12V switch.
–12V Switched Supply (Output): Switched –12V supply to PCI Hot Plug
compliant socket. Load carrying output.
5V Supply (Input): +5V-supply input for current monitoring (reference
voltage for 5VSENSE). Not a load-current carrying input.
5V Gate Drive (Output): Drives gate of external N-channel MOSFET +5V
switch. Adding capacitance will slow the slew rate of the external MOSFET
switch turn-on. (The external MOSFET’s gate is charged by an internal
current source.)
12V Supply (Input): MIC2580A power supply and input for internal +12
switch. Supplies power for internal circuitry.
3
MIC2580A
MIC2580A
Micrel, Inc.
Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
Supply Voltages
+12V Input (V12VIN) ................................................. +14V
+5V Input (V5VIN) ....................................................... +7V
+3.3V Input (V3VIN) .................................................... +7V
–12V Input (VM12VIN) ............................................... –14V
/PWRGD, /FAULT, /POR, /EPWRGD, and /PCIRST
Output Current ........................................................... 10mA
Lead Temperature (Soldering)
Standard Package (-x.xBTS)
IR Reflow ......................................... 240°C + 0ºC/-5ºC
Lead-free Package (-x.xYTS)
IR Reflow ......................................... 260ºC + 0ºC/-5ºC
ESD Rating, Note 3
Human body model ................................................... 2kV
Supply Voltages
+12V Input (V12VIN) ............................. +11.4V to +12.6V
–12V Input (VM12VIN) ........................... –11.4V to –12.6V
+5V Input (V5VIN) ................................... +4.75V to +5.25
+3.3V Input (V3VIN) .............................. +3.125V to +3.5V
Temperature Range (TA) ........................... –40°C to +85°C
Junction Temperature (TJ) ........................................ 150°C
Package Thermal Resistance (θJA)
24-Lead TSSOP .................................................. 83°C/W
Electrical Characteristics
V12VIN = 12V, V5VIN = 5V, V3VIN = 3.3V, VM12VIN = –12V; TA = 25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted
Symbol
Parameter
Condition
I12IN
Supply Current
/ON > VIH
Min
Typ
Max
Units
2.2
3
mA
I5IN
4
6
mA
I3IN
0.23
0.4
mA
3
5
mA
9.8
V
I12MIN
VUVLO
Undervoltage Lockout
V12VIN increasing
8.9
V12VIN UVLO hysteresis
VM12VIN decreasing
300
-10.5
VM12VIN UVLO hysteresis
V5VIN increasing
-8.3
100
2.1
V5VIN UVLO hysteresis
V3VIN increasing
mV
mV
3.1
20
2.4
V3VIN UVLO hysteresis
V
V
mV
2.6
V
60
mV
V5VGATE
5VGATE Voltage
10.5
11
V
V3VGATE
3VGATE Voltage
10.5
11
V
I5VGATE
5VGATE Output Current
–40
µA
6
mA
–40
µA
6
mA
during start-up, V5VGATE = 5V
during turnoff; /FAULT = 0
I3VGATE
3VGATE Output Current
during start-up, V5VGATE = 5V
during turnoff; /FAULT = 0
VPGTH
Power Good Threshold Voltage
V12VOUT increasing
11
V12VOUT Power-Good hysteresis
VM12VOUT decreasing
200
–11.2
VM12VOUT Power-Good hysteresis
V5VOUT increasing
Input Voltage Level (/ON)
VIH
IIL
MIC2580A
4.7
2.90
3.10
2.0
Input Leakage Currnet (/ON)
–1
4
V
mV
0.8
logic high
V
mV
60
logic low
V
mV
100
V3VOUT Power-Good hysteresis
VIL
–10
4.45
V
mV
50
V5VOUT Power-Good hysteresis
V3VOUT increasing
11.4
V
V
1
µA
February 2005
MIC2580A
Micrel, Inc.
Symbol
Parameter
Condition
VOL
Output-Low Voltage
(/PWRGD, /FAULT, /POR,
EPWRGD, /LPCIRST)
IOL = 2mA
TOV
Overtemperature Shutdown
Threshold
TJ increasing
170
˚C
TJ decreasing
160
˚C
ICRST
CRST Charge Current
during turn-on
–9
–11.5
µA
ICSTART
CSTART Charge Current
during turn-on
–9
–11.5
µA
ICSLEW
CSLEW Charge Current
during turn-on
–30
–39
–45
µA
RDS(on)12
Output MOSFET Resistance
+12V internal MOSFET, IDS = 500mA
450
600
mΩ
–12V internal MOSFET, IDS = 200mA
430
600
mΩ
RDS(on)M12
Output MOSFET Leakage
VCLTH
ILIM12
ILIM12M
Typ
Max
Units
0.4
V
+12V internal MOSFET
–100
100
µA
–12V internal MOSFET
0
300
µA
V5VIN – V5VSENSE
45
56
67
mV
V3VIN – V3VSENSE
45
55
67
mV
Current-Limit
Threshold
+12V internal MOSFET, ramped load
1.0
1.3
1.5
A
–12V internal MOSFET, ramped load
–0.4
–0.5
–0.7
A
Short-Circuit Current
+12V internal MOSFET, VOUT = 0V
–12V internal MOSFET, VOUT = 0V
Current Limit Threshold Voltage
VPOR(thr)
Power-On Reset Threshold Voltage
VPCH
Precharge Bias Supply
VSTART
Min
140
–170
mA
mA
2.4
V
MIC2580A-1.0, IPCH = 10mA
0.8
1.0
1.2
V
MIC2580A-1.6, IPCH = 10mA
1.28
1.6
1.92
V
Start-up Threshold Voltage
2.4
V
AC Parameters
tGOOD
Early Power-Good
Response Low
See Figure 4
200
ns
t/GOOD
Early Power-Good
Response High
See Figure 4
100
ns
Undervoltage to Power-Good Delay
20
µs
Current-limit to Fault Delay
20
µs
+5V Current-Limit-to-Off Delay
Note 4
VSENSE = 10mΩ
7
µs
+3.3V Current-Limit-to-Off Delay
Note 4
VSENSE = 10mΩ
7
µs
+12V Current-Limit-to-Off Delay
Note 4
+12V
25
µs
–12V Current-Limit-to-Off Delay
Note 4
–12V
25
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.
Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
Note 4.
Off refers to the condition in which the circuit breaker turns all outputs off.
February 2005
5
MIC2580A
MIC2580A
Micrel, Inc.
Timing Diagrams
/ON
/ON
+5V
+5V
5VOUT
Short Circuit
5VOUT
0V
0V
+3.3V
+3.3V
3VOUT
3VOUT
0V
0V
+12V
+12V
12VOUT
12VOUT
0V
0V
0V
0V
M12VOUT
M12VOUT
–12V
–12V
/PWRGD
/PWRGD
/FAULT
/FAULT
tSTART
tRESET
/POR
/POR
Figure 1. Controller Timing: Normal Cycle
Figure 2. Controller Timing: Enable Into Short
Circuit Breaker
Reset
/ON
+5V
Fault
5VOUT
0V
+3.3V
3VOUT
0V
+12V
12VOUT
0V
0V
VIN
M12VOUT
VPGTH
}1V
–12V
t/good
tgood
+5V
/PWRGD
/EPWRGD
0V
/FAULT
Figure 4. Early Power Good Response Time
Figure 3. Controller Timing: Short on 5V
MIC2580A
6
February 2005
MIC2580A
Micrel, Inc.
Typical Characteristics
-3
Power-On
Reset Time
-3
100x10
Output Rise Time vs.
Slew-Rate Capacitance
-3
100x10
Start-Up
Time
100x10
10x10-3
TIME (s)
TIME (s)
10x10-3
TIME (s)
10x10-3
1x10-3
1x10-3
1x10-3
100x10-6
100x10-6
0.001
February 2005
0.01
CPOR (µF)
0.1
100x10-6
0.0001
0.001
0.01
CSLEW (µF)
7
0.1
10x10-6
0.0001
0.001
0.01
C START (µF)
0.1
MIC2580A
MIC2580A
Micrel, Inc.
Functional Characteristics
10mΩ
IRF7413
10mΩ IRF7413
MIC2580A
+12V
12VIN
12VOUT
+5V
5VSENSE
+3.3V
5VGATE
C12L
R12L
C5L
R5L
C3L
R3L
CM12L
RM12L
5VOUT
5VIN
3VSENSE
3VGATE
3VOUT
3VIN
+5V
VPCHG
2.2k 2.2k
/POR CRST
/PCIRST
CSLEW
/ON
2.2k 2.2k
CRST
/LPCIRST
CSLEW
/FAULT
CSTART
/EPWRGD CSTART
/PWRGD
–12V
M12VIN
GND
M12VOUT
Functional Test Circuit
MIC2580A
8
February 2005
MIC2580A
Micrel, Inc.
3V and 5V
Gate-Voltage Response
CRST = 0.01µF
CSLEW = 0.03µF
CSTART = 0.01µF
V/ON
(5V/div)
VCSLEW
(5V/div)
V3VGATE
(5V/div)
V5VGATE
(5V/div)
Time (2.5ms/div)
Power-On
Reset Response
CRST = 0.01µF
V/ON
(10V/div)
V/PWRGD
(5V/div)
VCRST
(2V/div)
V/POR
(5V/div)
tRESET = 2.6ms
Time (1ms/div)
Power-Good
Response
V/EPWRGD
(5V/div)
V/PWRGD
(5V/div)
Time (10µs/div)
February 2005
9
MIC2580A
MIC2580A
Micrel, Inc.
CRST = 0.01µF
Fault Response
V/ON
(10V/div)
V/FAULT
(10V/div)
V3VOUT
(5V/div)
Pull /FAULT Low
V5VOUT
(5V/div)
V12VOUT
(10V/div)
VM12VOUT
(10V/div)
Time (10ms/div)
MIC2580A
10
February 2005
MIC2580A
Micrel, Inc.
Turn-On and Turn-off
CSTART = 0.01µF
CSLEW = 0.03µF
CRST = 0.01µF
V/ON
(10V/div)
V3VOUT
(5V/div)
V5VOUT
(5V/div)
V12VOUT
(10V/div)
VM12VOUT
(10V/div)
V/PWRGD
(5V/div)
V/POR
(5V/div)
V/FAULT
(5V/div)
Time (2.5ms/div)
-12V Turn-On
CSTART = 0.01µF
CSLEW = 0.07µF
CRST = 0.01µF
CM12L = 1µF
RM12L = 80Ω
V/ON
(10V/div)
VCSTART
(5V/div)
VM12VOUT
(10V/div)
IM12VIN
(100mA/div)
150mA
V/PWRGD
(5V/div)
V/POR
(5V/div)
V/FAULT
(5V/div)
Time (2.5ms/div)
February 2005
11
MIC2580A
MIC2580A
Micrel, Inc.
3V Turn-On
CSTART = 0.01µF
CSLEW = 0.03µF
CRST = 0.01µF
C3L = 100µF
R3L = 2.2Ω
V/ON
(10V/div)
VCSTART
(5V/div)
V3VOUT
(2V/div)
I3VIN
(1A/div)
1.5A
0.6A/ms
V/PWRGD
(5V/div)
V/POR
(5V/div)
V/FAULT
(5V/div)
Time (2.5ms/div)
5V Turn-On
CSTART = 0.01µF
CSLEW = 0.03µF
CRST = 0.01µF
C5L = 100µF
R5L = 3.3Ω
V/ON
(10V/div)
VCSTART
(5V/div)
V5VOUT
(5V/div)
I5VIN
(1A/div)
1.5A
0.375A/ms
V/PWRGD
(5V/div)
V/POR
(5V/div)
V/FAULT
(5V/diV)
Time (2.5ms/div)
MIC2580A
12
February 2005
MIC2580A
Micrel, Inc.
12V Turn-On
CSTART = 0.01µF
CSLEW = 0.04µF
CRST = 0.01µF
C12L = 1µF
R12L = 80Ω
V/ON
(10V/div)
VCSTART
(5V/div)
V12VOUT
(10V/div)
150mA
I12VIN
(100mA/div)
V/PWRGD
(5V/div)
V/POR
(5V/div)
V/FAULT
(5V/div)
Time (1ms/div)
Enable Into
-12V Output Short Circuit
CSTART = 0.01µF
CSLEW = 0.01µF
CRST = 0.01µF
R12L = 100Ω
C12L = 1µF
M12VOUT = GND
V/ON
(10V/div)
VCSTART
(5V/div)
V3VOUT
(5V/div)
V5VOUT
(5V/div)
V12VOUT
(10/div)
VM12VOUT
(10V/div)
IM12VIN
(200mA/div)
V/PWRGD
(5V/div)
V/POR
(5V/div)
V/FAULT
(5V/div)
Time (1ms/div)
February 2005
13
MIC2580A
MIC2580A
Micrel, Inc.
Enable Into
3V Output Short Circuit
CSTART = 0.01µF
CSLEW = 0.01µF
CRST = 0.01µF
3VOUT = GND
R12L = 100Ω
C12L = 1µF
RM12L = 100Ω
CM12L = 1µF
V/ON
(10V/div)
VCSTART
(5V/div)
V3VOUT
(5V/div)
I3VIN
(1A/div)
V5VOUT
(5V/div)
V12VOUT
(10V/div)
VM12VOUT
(10V/div)
V/PWRGD
(5V/div)
V/POR
(5V/div)
V/FAULT
(5V/div)
Time (1ms/div)
Enable Into
5V Output Short Circuit
CSTART = 0.01µF
CSLEW = 0.01µF
CRST = 0.01µF
R12L = 100Ω
C12L = 1µF
RM12L = 100Ω
CM12L = 1µF
5VOUT = GND
V/ON
(10V/div)
VCSTART
(5V/div)
V3VOUT
(5V/div)
V5VOUT
(5V/div)
I5VIN
(200mA/div)
V12VOUT
(10V/div)
VM12VOUT
(10V/div)
V/PWRGD
(5V/div)
V/POR (5V/div)
V/FAULT
(5V/div)
MIC2580A
Time (1ms/div)
14
February 2005
MIC2580A
Micrel, Inc.
Enable Into
12V Output Short Circuit
CSTART = 0.01µF
CSLEW = 0.01µF
CRST = 0.01µF
C12L = 1µF
RM12L = 100Ω
CM12L = 1µF
12VOUT = GND
V/ON
(10V/div)
VCSTART
(5V/div)
V3VOUT
(5V/div)
V5VOUT
(5V/div)
V12VOUT
(10V/div)
I12VIN
(500MA/div)
VM12VOUT
(10V/div)
V/PWRGD
(5V/div)
V/POR
(5V/div)
V/FAULT
(5V/div)
Time (1ms/div)
Start-up Blanking Response
CSTART = 0.01µF
CSLEW = 0.01µF
CRST = 0.01µF
V/ON
(10V/div)
VCSTART
(5V/div)
V5VOUT
(5V/div)
Short Removed
I5VIN
(200mA/div)
V/PWRGD
(5V/div)
V/POR
(5V/div)
V/FAULT
(5V/div)
Time (1ms/div)
February 2005
15
MIC2580A
MIC2580A
Micrel, Inc.
Circuit Breaker
Reset Response
New Start Cycle
ON#
(10V/div)
Circuit Breaker
CSTART = 0.01µF
CSLEW = 0.01µF
CRST = 0.01µF
3VOUT
(5V/div)
Short Circuit
5VOUT
(5V/div)
12VOUT
(10V/div)
M12VOUT
(10V/div)
PWRGD#
(5V/div)
FAULT#
(5V/div)
POR#
(5V/div)
Time (10ms/div)
MIC2580A
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February 2005
MIC2580A
Micrel, Inc.
Functional Diagram
12VIN
12V
Switch
5VIN
5VSENSE
5V
Switch
Control
3VIN
Precharge
Supply
CSLEW
5VGATE
R5SNS
Q5OUT
5VOUT
3VSENSE
3.3V
Switch
Control
CSLEW
12VOUT
3VGATE
R3SNS
Q3OUT
3VOUT
VPCHG
/POR
Slew
Control
Reset
CRST
CRST
Current
Limit
/ON
Thermal
Shutdown
/FAULT
Control Logic
and
Power Good
tD = 20µs
(delay)
CSTART
CSTART
/EPWRGD
tD = 20µs
(delay)
/PWRGD
/LPCIRST
/PCIRST
–12V
Switch
M12VIN
M12VOUT
MIC2580A
GND
February 2005
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MIC2580A
MIC2580A
Micrel, Inc.
Thermal Shutdown
The +12V and –12V internal MOSFET switches are protected
by current limit and overtemperature shutdown circuitry.
When the die temperature exceeds 160°C, /FAULT is asserted and all supplies are shut off. The power dissipated in
the MIC2580A is primarily due to the sum of current flowing
through the internal MOSFET switches and, to a lesser
extent, power dissipated due to the supply current. To compute the total power dissipation of the MIC2580A the following equation is used:
PD(total) = PD(+12V switch) + PD(–12V switch) + PD(supplies)
where:
PD(switches) = RDS(on) × IOUT2
PD(supplies) = VSUPPLY × ISUPPLY
To relate this to operating junction temperature:
TJ = PD × θJA + TA
where:
TA = ambient temperature
θJA = package thermal resistance
Precharge Voltage
For CompactPCI applications, the MIC2580A-1.0BSM/BTS
integrates a 1V ±20% voltage source that satisfies
CompactPCI precharge requirements. The voltage source
can provide up to 10mA. For higher current, the MIC2580A1.6BSM/BTS integrates a 1.6V ±20% voltage source to bias
a NPN transistor.
Functional Description
Start-Up Sequence
The start-up sequence iniates after all four supplies are
connected to the inputs and then /ON is asserted by
transistioning from high to low. During the start-up sequence,
all four gates ramp up at a rate determined by CSLEW. During
this time /PWRGD is deasserted until all four supplies are
within specified levels. When /PWRGD is asserted the poweron-reset signal /POR timer begins. The time period is defined
by CRST. Refer to Figure 1 for a timing diagram of the signals
during the start-up sequence.
During the start-up sequence, a current source charges
CSTART at a constant rate until a threshold voltage of 2.4V is
reached. This period of time defines an interval during which
overcurrent events are ignored. This prevents high inrush
currents that normally occur when charging capacitance
erroneously asserting /FAULT. The magnitude of the startup time, tSTART is defined by CSTART.
The MIC2580A employs foldback current limiting that ensures the device starts up in current limit. This minimizes high
inrush currents due to ramping a voltage into capacitance
regardless of the size of the load capacitance.
Overcurrent Detection
The MIC2580A senses overcurrent via the use of external
sense resistors for the 5V and 3.3V supply rails. When the
sense voltage across these resistors is greater than or equal
to 50mV an overcurrent condition is detected. Therefore the
overcurrent set point is determined by ILIMIT = 50mV/RSENSE.
For the +12V and –12V supply rails overcurrent detection is
set internally at 1.3A and –0.5A respectively.
When an overcurrent condition is detected /FAULT is asserted only if the overcurrent condition lasts for a minimum
time period of 10µs. This delay prevents spurious noise from
the system erroneously tripping the circuit breaker and asserting /FAULT. Upon /FAULT being asserted an internal
latch is set that immediately turns off all four supplies to
prevent further damage to the system. Toggling /ON will reset
the latch and initiate another start-up sequence. Figures 2
and 3 depict the timing for two fault conditions.
MIC2580A
+5V
MIC2580A-1.6
R
VPCHG
I > 10mA
DATA
BUS
Figure 5. Voltage Source
Turnoff
Deasserting /ON will turn off all four supplies. Alternatively
driving /FAULT low will turn off all supplies but will not latch
the supplies off. Releasing /FAULT will initiate a new start
sequence.
18
February 2005
MIC2580A
Micrel, Inc.
must also be added to the dc voltage drop across the
MOSFET to compute total loss. In addition to meeting the
voltage regulation specifications, thermal specifications must
also be considered. During normal operation very little power
should be dissipated in the MOSFET. DC power dissipation
of the MOSFET is easily computed as I 2RDS where I is the
drain current and RDS is the specified on-resistance of the
MOSFET at the expected operating drain current. However,
during excessive drain current or short-circuit faults, the
power dissipation in the external MOSFET will increase
dramatically. To help compute the effective power dissipated
during such transients, MOSFET manufacturers provide
transient thermal impedance curves for each MOSFET.
These curves provide the effective thermal impedance of the
MOSFET under pulsed or repetitive conditions; for example,
as will be the case when enabling into a short circuit fault.
From these curves the effective rise in junction temperature
of the MOSFET for a given condition can be computed. The
equation is given as:
peak TJ = PDM × ZθJA + TA
where PDM is the power dissipated in the MOSFET usually
computed as VIN x IDRAIN and ZθJA is the thermal response
factor provided from the curves. Since the MIC2580A reduces the current to 30% of full scale even under severe faults
such as short-circuits the MOSFET power dissipation is held
to safe levels. This feature allows MOSFETs with smaller
packages to be used for a given application thereby reducing
cost and PCB real-estate requirements.
10mΩ
10mΩ
Power
Supply
+12V
IRF7413
MIC2580A
12VIN
12VOUT
12V
12V/500mA
5VSENSE
+5V
5VGATE
+3.3V
GND
IRF7413
Adapter
Whenever voltage is applied to a highly capacitive load, high
inrush currents may result in voltage droop that may bring the
supply voltage out of regulation for the duration of the
transient. The MIC2580A solves this problem by specifically
controlling the current and voltage supply ramps so that the
system supply voltages are not disturbed. Very large capacitive loads are easily supported with this device.
Figure 1 shows the timing during turn-on. When /ON is forced
low, all supplies are turned on at a slew rate determined by the
external capacitor, CSLEW.
Figure 2 shows the foldback characteristics for the supply
voltages. This foldback affect bounds the magnitude of the
current step when the supplies are turned on or shorted. This
specifies the compact PCI specification of 1.5A/ms, thereby
ensuring reliable operation. In discrete FET implementations, this magnitude can exceed several amps and may
cause the main supply to go out of regulation during this
transient event. This, in turn, could cause the system to
behave unpredictably. In addition, should a fault occur, the
MIC2580A will prevent system malfunctions by limiting the
current to within specifications.
MOSFET Selection
The external MOSFET should be selected to provide low
enough dc loss to satisfy the application’s voltage regulation
requirements. Note that the voltage across the sense resistor
Platform
Application Information
5VIN
5VOUT
5V
5V/5A
3VSENSE
–12V
3VGATE
3VIN
3VOUT
3.3V
3.3V/7.6A
VPCHG
+5V
/POR
PCI Hot-Plug
Controller
GND
CRST
/PCIRST
/LPCIRST
/ON
CSLEW
Data Bus
/CIRST
BUS EN
M12VIN
M12VOUT
–12V
/CIRST
D0
D1
D2
Bus
Switch
D0
D1
D2
Dn
–12V /100mA
/CIRST
Data Bus
/FAULT
/EPWDGD CSTART
GND
/PWDGD
Dn
Figure 6. Hot-Plug PCI Application
February 2005
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MIC2580A
MIC2580A
Micrel, Inc.
CompactPCI™ BD_SEL# Pin Tied to Ground
For applications that use system backplanes with the
BD_SEL# pin tied to ground, the MIC2580A /ON pin is edge
sensitive. Therefore, the /ON pin requires a delay circuit for
proper start-up when the board has already been inserted
into the backplane and the supplies are switched off, then
back on. The circuit, shown in the figure below, allows the
MIC2580A /ON pin to transition from high to low which is
necessary for start-up. The delay time may be increased or
decreased by changing the RC time constant in the circuit,
but the delay time must exceed the ramp time of all system
backplane supplies. The same circuit is functional for hot
swap insertion.
MIC2580A
PCB Layout Considerations
To achieve accurate current sensing Kelvin connections are
recommended between the supply pin and the respective
sense resistor as shown in Figure 8. PCB trace length should
be kept at a minimum. 0.02 inches per ampere is a minimum
width for 1 oz. copper to prevent damage to traces carrying
high current. Keep these high-current traces as short as
possible.
short-length, high-current
(wide) copper traces
sense resistor
from
supply
to
load
Kelvin
connections
2k
to
VIN
pin
VIO
(3.3V or 5V)
/FAULT
2k
/RESET
/ON
to
SENSE
pin
Figure 8. Layout Recommendation
1N914
50k
On PCB
10k
1.2k
2N3904
BD_SEL#
3.3µF
Figure 7. /ON Pin Assertion Delay Circuit
MIC2580A
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February 2005
MIC2580A
Micrel, Inc.
Package Information
DIMENSIONS:
MM (INCH)
4.50 (0.177)
6.4 BSC (0.252)
4.30 (0.169)
0.30 (0.012)
0.19 (0.007)
7.90 (0.311)
7.70 (0.303)
0.65 BSC
(0.026)
1.10 MAX (0.043)
0.20 (0.008)
0.09 (0.003)
1.00 (0.039) REF
8°
0°
0.15 (0.006)
0.05 (0.002)
0.70 (0.028)
0.50 (0.020)
24-Lead TSSOP (TS)
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
This 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.
© 2001 Micrel Incorporated
February 2005
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MIC2580A