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MIC2580A
Micrel, Inc.
MIC2580A
Hot-Swap PCI Power Controller
General Description
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 CompactPCITM 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.
Features
* * * * * * * * * * PCI hot-plug and CompactPCITM 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 CompatPCITM I/O termination
Applications
* PCI hot-plug systems * CompactPCITM hot-swap systems
Typical Application
10m 1F 10m IRF7413
Platform
Adapter
IRF7413
MIC2580A +12V +5V +3.3V GND -12V 1F 5VIN 12VIN 12VOUT 5VSENSE 5VGATE 5VOUT 3VSENSE 3VGATE 3VIN 1F 1.2k /PCIRST /ON CSLEW 3VOUT VPCHG /POR CRST /LPCIRST Overcurrent Fault VIO VPCH = +1V 20%
(PRECHARGE SUPPLY)
+12V/1A +5V/8A +3.3V/8A GND -12V/1A
+12V
+5V
VIO
VIO
+3.3V
/PCI_RST /BD_SEL
/PCIRST /ON
/HEALTHY
/PGD
/FAULT /EPWRGD CSTART GND /PWRGD M12VIN M12VOUT 1F -12V /LPCIRST
/ENUM D0 D0 PCI D1 Controller D1 D2 D2 Dn Dn
Data Bus
CompactPCITM 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
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Data Bus
MIC2580A
MIC2580A
Micrel, Inc.
Ordering Information
Standard Part Number Pb-Free MIC2580A-1.0YTS MIC2580A-1.6YTS Precharge Voltage 1V 1.6V Temperature Range -40C to +85C -40C to +85C Package 24-lead TSSOP 24-lead TSSOP
MIC2580A-1.0BTS MIC2580A-1.6BTS
Pin Configuration
12VOUT 1 3VGATE 2 3VOUT 3 3VSENSE 4 3VIN 5 /PCIRST 6 /LPCIRST 7 /EPWRGD 8 /PWRGD 9 VPCHG 10 GND 11 M12VIN 12 24 12VIN 23 5VGATE 22 5VOUT 21 5VSENSE 20 5VIN 19 /FAULT 18 CSTART 17 CSLEW 16 /POR 15 CRST 14 /ON 13 M12VOUT
24-lead TSSOP (TS)
Pin Description
Pin Number 1 2 Pin Name 12VOUT 3VGATE Pin Function +12V Switched Supply (Output): Load carrying output. 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.) +3.3V Output Voltage Sense (Input): Connect to source of external N-channel MOSFET (+3V switched output) to monitor for output undervoltage conditions. +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.
3
3VOUT
4
3VSENSE
5 6
3VIN /PCIRST
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MIC2580A
Pin Number 7 8 Pin Name /LPCIRST /EPWRGD Pin Function
Micrel, Inc.
Local PCI Reset (Open-Drain Output): Local PCI reset output to PCI controller. Compliant to CompactPCI specification for LOCAL_PCI_RESET. 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. Power Good (Open-Drain Output): Active-low output goes active when all supplies are within tolerance. (A 20s delay is inserted prior to activation to reduce nuisance tripping.) Precharge Supply (Output): (MIC2580A-1.0) +1V 20% supply used for precharge bias for I/O terminations (CompactPCI only). 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. 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. Reset Delay (External Component): Connect to external capactior (CRST) to increase power-on reset delay. 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. Slew (External Component): Connect to external capacitor (CSLEW) to program the output slew rate of 3VGATE, 5VGATE, 12VGATE (internal) and M12VGATE (internal). 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. Fault (Open-Drain Output/Input): This active-low output signal activated upon overcurrent or thermal shutdown. Includes 20s deglitch filter. Fault is reset using /ON. Forcing pin low turns off all switches but does not activate the circuit breaker function. 5V Supply (Input): +5V-supply input for current monitoring (reference voltage for 5VSENSE). Not a load-current carrying input. +5V Current Sense (Input): Measures voltage drop across an external sense resistor with respect to 5VIN for overcurrent detection through the +5V switch. +5V Output Voltage Sense (Input): Connect to source of external N-channel MOSFET (+5V switched output) to monitor for output undervoltage conditions. 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.
9
/PWRGD
10 11 12 13 14
VPCHG GND M12VIN M12VOUT /ON
15 16
CRST /POR
17
CSLEW
18
CSTART
19
/FAULT
20 21
5VIN 5VSENSE
22
5VOUT
23
5VGATE
24
12VIN
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MIC2580A
MIC2580A
Micrel, Inc.
Absolute Maximum Ratings (Note 1)
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 ......................................... 240C + 0C/-5C Lead-free Package (-x.xYTS) IR Reflow ......................................... 260C + 0C/-5C ESD Rating, Note 3 Human body model ................................................... 2kV
Operating Ratings (Note 2)
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) ........................... -40C to +85C Junction Temperature (TJ) ........................................ 150C Package Thermal Resistance (JA) 24-Lead TSSOP .................................................. 83C/W
Electrical Characteristics
V12VIN = 12V, V5VIN = 5V, V3VIN = 3.3V, VM12VIN = -12V; TA = 25C, bold values indicate -40C TA +85C; unless noted Symbol I12IN I5IN I3IN I12MIN VUVLO Undervoltage Lockout V12VIN increasing V12VIN UVLO hysteresis VM12VIN decreasing VM12VIN UVLO hysteresis V5VIN increasing V5VIN UVLO hysteresis V3VIN increasing V3VIN UVLO hysteresis V5VGATE V3VGATE I5VGATE I3VGATE VPGTH 5VGATE Voltage 3VGATE Voltage 5VGATE Output Current during start-up, V5VGATE = 5V during turnoff; /FAULT = 0 3VGATE Output Current during start-up, V5VGATE = 5V during turnoff; /FAULT = 0 Power Good Threshold Voltage V12VOUT increasing V12VOUT Power-Good hysteresis VM12VOUT decreasing VM12VOUT Power-Good hysteresis V5VOUT increasing V5VOUT Power-Good hysteresis V3VOUT increasing V3VOUT Power-Good hysteresis VIL VIH IIL Input Leakage Currnet (/ON) Input Voltage Level (/ON) logic low logic high 2.0 -1 1 2.90 60 0.8 4.45 100 3.10 -11.2 50 4.7 11 200 -10 10.5 10.5 2.4 60 11 11 -40 6 -40 6 11.4 2.1 20 2.6 -10.5 100 3.1 8.9 300 -8.3 Parameter Supply Current Condition /ON > VIH Min Typ 2.2 4 0.23 3 Max 3 6 0.4 5 9.8 Units mA mA mA mA V mV V mV V mV V mV V V A mA A mA V mV V mV V mV V mV V V A
MIC2580A
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Symbol VOL Parameter Output-Low Voltage (/PWRGD, /FAULT, /POR, EPWRGD, /LPCIRST) Overtemperature Shutdown Threshold CRST Charge Current CSTART Charge Current CSLEW Charge Current Output MOSFET Resistance Condition IOL = 2mA Min Typ
Micrel, Inc.
Max 0.4 Units V
TOV ICRST ICSTART ICSLEW RDS(on)12 RDS(on)M12
TJ increasing TJ decreasing during turn-on during turn-on during turn-on +12V internal MOSFET, IDS = 500mA -12V internal MOSFET, IDS = 200mA +12V internal MOSFET -12V internal MOSFET -100 0 45 45 1.0 -0.4 -9 -9 -30
170 160 -11.5 -11.5 -39 450 430 -45 600 600 100 300 56 55 1.3 -0.5 140 -170 2.4 67 67 1.5 -0.7
C C A A A m m A A mV mV A A mA mA V 1.2 1.92 V V V
Output MOSFET Leakage
VCLTH ILIM12 ILIM12M
Current Limit Threshold Voltage
V5VIN - V5VSENSE V3VIN - V3VSENSE +12V internal MOSFET, ramped load -12V internal MOSFET, ramped load +12V internal MOSFET, VOUT = 0V -12V internal MOSFET, VOUT = 0V MIC2580A-1.0, IPCH = 10mA MIC2580A-1.6, IPCH = 10mA
Current-Limit Threshold Short-Circuit Current
VPOR(thr) VPCH VSTART tGOOD t/GOOD
Power-On Reset Threshold Voltage Precharge Bias Supply 0.8 1.28
1.0 1.6 2.4
Start-up Threshold Voltage
AC Parameters Early Power-Good Response Low Early Power-Good Response High Undervoltage to Power-Good Delay Current-limit to Fault Delay +5V Current-Limit-to-Off Delay Note 4 +3.3V Current-Limit-to-Off Delay Note 4 +12V Current-Limit-to-Off Delay Note 4 -12V Current-Limit-to-Off Delay Note 4
Note 1. Note 2. Note 3. Note 4.
See Figure 4 See Figure 4
200 100 20 20
ns ns s s s s s s
VSENSE = 10m VSENSE = 10m +12V -12V
7 7 25 25
Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating rating. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. Off refers to the condition in which the circuit breaker turns all outputs off.
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MIC2580A
MIC2580A
Micrel, Inc.
Timing Diagrams
/ON
+5V
/ON
+5V
5VOUT
0V +3.3V
5VOUT
0V +3.3V
Short Circuit
3VOUT
0V +12V
3VOUT
0V +12V
12VOUT
0V 0V
12VOUT
0V 0V
M12VOUT
-12V
M12VOUT
-12V
/PWRGD /FAULT tRESET /POR
/PWRGD tSTART /FAULT /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
M12VOUT
-12V
VIN
}1V
t/good
+5V
VPGTH tgood
/PWRGD /FAULT
/EPWRGD
0V
Figure 3. Controller Timing: Short on 5V
Figure 4. Early Power Good Response Time
MIC2580A
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MIC2580A
Micrel, Inc.
Typical Characteristics
Power-On Reset Time Output Rise Time vs. Slew-Rate Capacitance Start-Up Time
100x10
-3
100x10
-3
100x10
-3
10x10-3 TIME (s)
TIME (s) TIME (s)
10x10-3
10x10-3
1x10-3
1x10-3
1x10-3 100x10-6
100x10-6 0.001
0.01 CPOR (F)
0.1
100x10-6 0.0001
0.001 0.01 CSLEW (F)
0.1
10x10-6 0.0001
0.001 0.01 C START (F)
0.1
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MIC2580A
MIC2580A
Micrel, Inc.
Functional Characteristics
10m 10m IRF7413
IRF7413
MIC2580A +12V +5V +3.3V 5VIN 12VIN 12VOUT 5VSENSE 5VGATE 5VOUT 3VSENSE 3VGATE +5V 2.2k 2.2k /PCIRST 3VIN 3VOUT VPCHG /POR CRST CRST /LPCIRST /FAULT 2.2k 2.2k /ON CSLEW /PWRGD -12V M12VIN
C12L
R12L
C5L
R5L
C3L
R3L
CSLEW
/EPWRGD CSTART GND M12VOUT
CSTART
CM12L
RM12L
Functional Test Circuit
MIC2580A
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February 2005
MIC2580A
Micrel, Inc.
3V and 5V Gate-Voltage Response
V/ON (5V/div)
CRST = 0.01F CSLEW = 0.03F CSTART = 0.01F
VCSLEW (5V/div) V3VGATE (5V/div) V5VGATE (5V/div) Time (2.5ms/div)
Power-On Reset Response
V/ON (10V/div)
CRST = 0.01F
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 (10s/div)
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MIC2580A
MIC2580A
Micrel, Inc.
CRST = 0.01F
Fault Response
V/ON (10V/div) V/FAULT (10V/div) V3VOUT (5V/div) V5VOUT (5V/div) V12VOUT (10V/div) VM12VOUT (10V/div)
Pull /FAULT Low
Time (10ms/div)
MIC2580A
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MIC2580A
Micrel, Inc.
Turn-On and Turn-off
V/ON (10V/div)
CSTART = 0.01F CSLEW = 0.03F CRST = 0.01F
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
V/ON (10V/div) VCSTART (5V/div)
CSTART = 0.01F CSLEW = 0.07F CRST = 0.01F CM12L = 1F RM12L = 80
VM12VOUT (10V/div)
IM12VIN (100mA/div)
150mA
V/PWRGD (5V/div)
V/POR (5V/div)
V/FAULT (5V/div)
Time (2.5ms/div)
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MIC2580A
MIC2580A
Micrel, Inc.
3V Turn-On
V/ON (10V/div)
VCSTART (5V/div)
CSTART = 0.01F CSLEW = 0.03F CRST = 0.01F C3L = 100F R3L = 2.2
V3VOUT (2V/div)
1.5A
I3VIN (1A/div)
0.6A/ms
V/PWRGD (5V/div)
V/POR (5V/div)
V/FAULT (5V/div)
Time (2.5ms/div)
5V Turn-On
V/ON (10V/div)
VCSTART (5V/div)
CSTART = 0.01F CSLEW = 0.03F CRST = 0.01F C5L = 100F R5L = 3.3
V5VOUT (5V/div)
1.5A
I5VIN (1A/div)
0.375A/ms
V/PWRGD (5V/div)
V/POR (5V/div)
V/FAULT (5V/diV)
Time (2.5ms/div)
MIC2580A
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MIC2580A
Micrel, Inc.
12V Turn-On
V/ON (10V/div)
VCSTART (5V/div)
CSTART = 0.01F CSLEW = 0.04F CRST = 0.01F C12L = 1F R12L = 80
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
V/ON (10V/div)
VCSTART (5V/div) V3VOUT (5V/div) V5VOUT (5V/div) V12VOUT (10/div) VM12VOUT (10V/div)
CSTART = 0.01F CSLEW = 0.01F CRST = 0.01F R12L = 100 C12L = 1F M12VOUT = GND
IM12VIN (200mA/div)
V/PWRGD (5V/div) V/POR (5V/div)
V/FAULT (5V/div)
Time (1ms/div)
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MIC2580A
MIC2580A
Micrel, Inc.
Enable Into 3V Output Short Circuit
V/ON (10V/div)
VCSTART (5V/div) V3VOUT (5V/div)
CSTART = 0.01F CSLEW = 0.01F CRST = 0.01F 3VOUT = GND R12L = 100 C12L = 1F RM12L = 100 CM12L = 1F
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
V/ON (10V/div) VCSTART (5V/div) V3VOUT (5V/div) V5VOUT (5V/div) I5VIN (200mA/div)
CSTART = 0.01F CSLEW = 0.01F CRST = 0.01F R12L = 100 C12L = 1F RM12L = 100 CM12L = 1F 5VOUT = GND
V12VOUT (10V/div) VM12VOUT (10V/div)
V/PWRGD (5V/div) V/POR (5V/div) V/FAULT (5V/div) Time (1ms/div)
MIC2580A
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MIC2580A
Micrel, Inc.
Enable Into 12V Output Short Circuit
V/ON (10V/div)
VCSTART (5V/div) V3VOUT (5V/div)
CSTART = 0.01F CSLEW = 0.01F CRST = 0.01F C12L = 1F RM12L = 100 CM12L = 1F 12VOUT = GND
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
V/ON (10V/div)
CSTART = 0.01F CSLEW = 0.01F CRST = 0.01F
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
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MIC2580A
MIC2580A
Micrel, Inc.
Circuit Breaker Reset Response
New Start Cycle ON# (10V/div) Circuit Breaker 3VOUT (5V/div) Short Circuit 5VOUT (5V/div)
CSTART = 0.01F CSLEW = 0.01F CRST = 0.01F
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 5V Switch Control 3VIN 3.3V Switch Control 12VOUT
5VSENSE 5VGATE 5VOUT 3VSENSE 3VGATE 3VOUT
R5SNS Q5OUT
R3SNS Q3OUT
Precharge Supply CSLEW CSLEW
VPCHG
Slew Control Reset
/POR CRST CRST
Current Limit
Thermal Shutdown
/ON
Control Logic and Power Good
/FAULT tD = 20s (delay) CSTART CSTART /EPWRGD
tD = 20s (delay)
/PWRGD
/PCIRST
/LPCIRST
M12VIN
-12V Switch
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 160C, /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) x IOUT2 PD(supplies) = VSUPPLY x ISUPPLY To relate this to operating junction temperature: TJ = PD x JA + TA where: TA = ambient temperature JA = 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.
+5V R
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 10s. 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-1.6 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.
MIC2580A
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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 x ZJA + TA where PDM is the power dissipated in the MOSFET usually computed as VIN x IDRAIN and ZJA 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.
Application Information
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
10m 10m Power Supply +12V +5V +3.3V GND -12V 3VIN +5V /PCIRST /ON CSLEW 5VIN MIC2580A 12VIN 12VOUT 5VSENSE 5VGATE 5VOUT 3VSENSE 3VGATE 3VOUT VPCHG /POR PCI Hot-Plug Controller CRST /LPCIRST IRF7413
IRF7413
Platform
Adapter
12V/500mA 5V/5A 3.3V/7.6A GND -12V /100mA /CIRST
12V
5V
3.3V
/FAULT /EPWDGD CSTART GND /PWDGD /CIRST BUS EN M12VIN M12VOUT
-12V /CIRST
Data Bus
Bus Switch
Dn Dn
Figure 6. Hot-Plug PCI Application
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Data Bus
D0 D1 D2
D0 D1 D2
MIC2580A
MIC2580A CompactPCITM 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.
Micrel, Inc. 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
VIO (3.3V or 5V)
MIC2580A /FAULT
2k 2k
/RESET /ON
to VIN pin
to SENSE pin
Figure 8. Layout Recommendation
1N914 10k 2N3904
50k 1.2k BD_SEL#
On PCB
3.3F
Figure 7. /ON Pin Assertion Delay Circuit
MIC2580A
20
February 2005
MIC2580A
Micrel, Inc.
Package Information
4.50 (0.177) 6.4 BSC (0.252) 4.30 (0.169)
DIMENSIONS: MM (INCH)
0.30 (0.012) 0.19 (0.007) 7.90 (0.311) 7.70 (0.303)
1.10 MAX (0.043)
0.20 (0.008) 0.09 (0.003)
0.65 BSC (0.026)
0.15 (0.006) 0.05 (0.002)
8 0
1.00 (0.039) REF 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. (c) 2001 Micrel Incorporated
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MIC2580A

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