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 16 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 17 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 19 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 20 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 21 MIC2580A