MIC2590A Micrel MIC2590A Dual-Slot PCI Hot-Plug Controller Preliminary Information General Description Features The MIC2590A is a power controller supporting power distribution requirements for Peripheral Component Interconnect (PCI) Hot-Plug compliant systems incorporating the Intelligent Platform Management Interface (IPMI). The MIC2590A provides complete power control support for two PCI slots including the 3.3VAUX defined by the PCI 2.2 specification. Support for +5V, +3.3V, +12V and -12V supplies is provided including programmable constant-current inrush limiting, voltage supervision, programmable current-limit, fault reporting and circuit breaker functions which provide fault isolation. The MIC2590A also incorporates a SMBus interface in which complete status and control of power within each slot is provided. Data such as voltage and current from each supply of each slot can be obtained for IPMI sensor records in addition to power status of each slot. * Supports two independent PCI 2.2 slots * SMBus interface for slot power control and status * +5V, +3.3V, +12V, -12V, +3.3VAUX supplies supported per PCI specification 2.2 * Programmable inrush current-limiting * Active current regulation controls inrush current * Electronic circuit breaker * Dual level fault detection for quick fault response without nuisance tripping * Thermal isolation between circuitry for slot A and slot B Applications * PCI hot-plug power distribution Ordering Information 5V & 3V Fast-trip Threshold +12V & -12V Fast-trip Threshold Operating Temp. Range Package MIC2590A-2BTQ 100mV 1.5A/0.4A 0C to +70C 48-Pin TQFP MIC2590A-3BTQ 150mV* 1.5A/0.4A 0C to +70C 48-Pin TQFP MIC2590A-4BTQ 200mV* 1.5A/0.4A 0C to +70C 48-Pin TQFP MIC2590A-5BTQ Disabled* 1.5A/0.4A 0C to +70C 48-Pin TQFP Part Number *Contact factory for availability. Micrel, Inc. * 1849 Fortune Drive * San Jose, CA 95131 * USA * tel + 1 (408) 944-0800 * fax + 1 (408) 944-0970 * http://www.micrel.com March 2002 1 MIC2590A MIC2590A Micrel Typical Application Power Supply +12V -12V +5.0V +3.3V 1A Schotty Diode (Clamp) PCI Connector VSTBY 12VIN1 12VIN2 12MVIN1 12MVIN2 VSTBY1 PCI Bus VAUXA VSTBY2 3.3VAUXA 5VINA RSENSE 5VSENA 12SLEWA R5VGATEA 12SLEWB 5VGATEA 5VOUTA 5V, 5A CGATE CFILTERA 3VINA 20k 1% RSENSE 3VSENA IREF CFILTERB CGATE R3VGATEA 3VGATEA 3VOUTA 3.3V, 7.6A 12V, 0.5A 12VOUTA -12V, 0.1A 12MVOUTA 5VINB MIC2590 GND ONA/ONB 2 AUXENA/AUXENB 2 /FAULTA, /FAULTB 2 Hot-Plug Controller ONA/ONB 4.7F 4.7F RSENSE PCI Bus 5VSENB AUXENA/AUXENB 5VGATEB /FAULTA, /FAULTB 5VOUTB R5VGATEB 5V, 5A CGATE A0 3VINB A1 3VSENB RSENSE CGATE R3VGATEB A2 3VGATEB /INT 3VOUTB 3.3V, 7.6A SCL 12VOUTB 12V, 0.5A SDA 12MVOUTB -12V, 0.1A 3.3VAUXB VAUXB 4.7F 4.7F SMBus I/O SDA MIC2590A SDA SCL SCL /INT /INT Bus Switch Management Controller A 2 /OE B March 2002 MIC2590A Micrel SDA SCL GND AUXENA ONA ONB AUXENB A0 A1 A2 GPIB /INT Pin Configuration 1 2 3 4 5 6 7 8 9 10 11 12 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 13 14 15 16 17 18 19 20 21 22 23 24 /FAULTB CFILTERB 12VSLEWB IREF 12VIN 5VINB 5VSENSEB 5VGATEB 5VOUTB 12VOUTB VSTBY 3VINB 3VSENSEA 3VGATEA VAUXA 3VOUTA 12VMIN 12VMIN 12MVOUTA 12MVOUTB 3VOUTB VAUXB 3VGATEB 3VSENSEB /FAULTA CFILTERA 12VSLEWA GPIA 12VIN 5VINA 5VSENSEA 5VGATEA 5VOUTA 12VOUTA VSTBY 3VINA 48-Pin TQFP (BTQ) March 2002 3 MIC2590A MIC2590A Micrel Pin Description Pin Number Pin Name 6, 31 5VINA, 5VINB 5V Supply Power and Sense Inputs [A/B]: Two pins are provided for Kelvin connection (one for each slot). Pin 6 is the Kelvin-sense connection to the supply side of the sense resistor for 5V Slot A. Pin 31 is the Kelvin-sense connection to the supply side of the sense resistor for 5V Slot B. These two pins must ultimately connect to each other within 10cm. An undervoltage lockout circuit (UVLO) prevents the switches from turning on while this input is less than its lockout threshold. 12, 25 3VINA, 3VINB 3.3V Supply Power and Sense Inputs [A/B]: Two pins are provided for Kelvin connection (one for each slot). Pin 12 is the Kelvin-sense connection to the supply side of the sense resistor for 3V Slot A. Pin 25 is the Kelvin-sense connection to the supply side of the sense resistor for 3V Slot B. These two pins must ultimately connect to each other within 10cm. An undervoltage lockout circuit (UVLO) prevents the switches from turning on while this input is less than its lockout threshold. 5, 32 12VIN - 2 pins +12V Supply Input: An undervoltage lockout circuit prevents the switches from turning on while this input is less than its lockout threshold. Both pins must be tied together at the chip. 17,18 12VMIN - 2 pins -12V Supply Input: An undervoltage lockout circuit prevents the switches from turning on while this input is less than its lockout threshold. Both pins must be tied together at the chip. 10, 27 12VOUTA, 12VOUTB 12V output [A/B] 19, 20 12MVOUTA, 12MVOUTB -12V output [A/B] 3, 34 12VSLEWA, 12VSLEWB 12V Slew Rate Control [A/B]: Connect capacitors between these pins and ground to set output slew rates of the +12V and -12V supplies. 45, 42 AUXENA, AUXENB AUX Enable Inputs [A/B]: Rising-edge sensitive enable inputs for VAUXA and VAUXB outputs. Taking AUXENA/AUXENB low after a fault resets the respective slot's Aux Output Fault Latch. Tie these pins to ground if using SMBus-mode power control. 16, 21 3VOUTA, 3VOUTB 3.3V Power-Good Sense Inputs: Connect to 3.3V[A/B] outputs. Used to monitor the 3.3V output voltages for Power-Good status. 9, 28 5VOUTA, 5VOUTB 5V Power-Good Sense Inputs: Connect to 5V[A/B] outputs. Used to monitor the 5V output voltages for Power-Good status. 33 IREF 7, 30 5VSENSEA, 5VSENSEB 5V Circuit Breaker Sense Input [A/B]: The current-limit thresholds are set by connecting sense resistors between these pins and 5VIN[A/B]. When the current-limit threshold of IR = 50mV is reached, the 5VGATE[A/B] pin is modulated to maintain a constant voltage across the sense resistor and therefore a constant current into the load. If the 50mV threshold is exceeded for tFLT, the circuit breaker is tripped and the GATE pin for the affected slot is immediately pulled low. 13, 24 3VSENSEA, 3VSENSEB 3V Circuit Breaker Sense Input [A/B]: The current-limit thresholds are set by connecting sense resistors between these pins and 3VIN[A/B]. When the current-limit threshold of IR = 50mV is reached, the 3VGATE[A/B] pin is modulated to maintain a constant voltage across the sense resistor and therefore a constant current into the load. If the 50mV threshold is exceeded for tFLT, the circuit breaker is tripped and the GATE pin for the affected slot is immediately pulled low. MIC2590A Pin Function A resistor connected between this pin and ground sets the ADC current measurement gain. This resistor must be 20k 1%. 4 March 2002 MIC2590A Micrel Pin Description Pin Number Pin Name 8, 29 5VGATEA, 5VGATEB Pin Function 5V Gate Drive Outputs [A/B]: Each connects to the gate of an external NChannel MOSFET. During power-up the CGATE and the gate of the MOSFETs are charged by a 20A current source. This controls the value of dv/dt seen at the source of the MOSFETs, and hence the current flowing into the load capacitance. During current-limit events, the voltage at this pin is adjusted to maintain constant current through the switch for a period of tFLT. Whenever an overcurrent, thermal shutdown or input undervoltage fault condition occurs the GATE pin for the affected slot is immediately brought low. During power-down these pins are discharged by an internal current source. 14, 23 3VGATEA, 3VGATEB 3V Gate Drive Outputs [A/B]: Each connects to the gate of an external NChannel MOSFET. During power-up the CGATE and the gate of the MOSFETs are charged by a 20A current source. This controls the value of dv/dt seen at the source of the MOSFETs, and hence the current flowing into the load capacitance. During current-limit events, the voltage at this pin is adjusted to maintain constant current through the switch for a period of tFLT. Whenever an overcurrent, thermal shutdown or input undervoltage fault condition occurs the GATE pin for the affected slot is immediately brought low. During power-down these pins are discharged by an internal current source. 11, 26 VSTBY - 2 pins 3.3V Standby input voltage required to support PCI 2.2 VAUX input: SMBus, internal registers and A/D converter run off of VSTBY to ensure chip access during standby modes. A UVLO circuit prevents turn-on of this supply until VSTBY rises above its UVLO threshold. Both pins must be tied together at the chip. 15, 22 VAUXA, VAUXB VAUX[A/B] output voltages to PCI card slots: These outputs connect the VAUX pin of the PCI 2.2 Connectors to VSTBY via internal 400m MOSFETs which are current-limited and protected against short-circuit faults. 44, 43 ONA, ONB Enable input for MAIN outputs: Rising-edge sensitive. Used to enable or disable MAIN (5V, 3.3V, +12V, -12V) outputs. Taking ONA/ONB low after a fault resets the respective slot's Main Output Fault Latch. Tie these pins to ground if using SMBus-mode power control. 1, 36 /FAULTA, /FAULTB Open Drain, Active-Low: Asserted whenever the circuit breaker trips due to a fault condition. /FAULT[A/B] is reset by bringing the faulted slot's ON pin low if /FAULT was asserted in response to a fault condition on one of the slot's MAIN outputs (+12V, +5V, +3.3V, or -12V). /FAULT[A/B] is reset by bringing the faulted slot's AUXEN pin low if /FAULT was asserted in response to a fault condition on the slot's VAUX output. If a fault condition occurred on both the MAIN and AUX outputs of the same slot, then both ON and AUXEN must be brought low to de-assert the /FAULT output. 2, 35 CFILTERA, CFILTERB 37 /INT March 2002 Filter Capacitor [A/B]: Capacitors connected between these pins and ground set the duration of tFLT. tFLT is the amount of time for which a slot remains in current-limit before its circuit breaker is tripped. Interrupt Output: Open Drain, Active-low. Asserted whenever a power fault is detected. Cleared by writing a logic 1 to the respective active bit into the Status Register. 5 MIC2590A MIC2590A Micrel Pin Description Pin Number Pin Name 48 SDA SMBus Data: Bidirectional SMBus data line. 47 SCL SMBus Clock: Input. 39, 40, 41 A2, A1, A0 SMBus Address Select pins: Connect to ground or leave open in order to program device SMBus base address. There is an internal pull-up to VSTBY on each of these inputs. 4, 38 GPIA, GPIB General Purpose Inputs: The state of these inputs are available by reading the Common Status Register. 46 GND MIC2590A Pin Function Ground. 6 March 2002 MIC2590A Micrel Absolute Maximum Ratings (Note 1) Operating Ratings (Note 2) Supply Voltage (12VIN) ..................................................................... +14V (12MVIN) .................................................................. -14V (5VIN) ......................................................................... +7V (3VIN), (VSTBY) .......................................................... +7V Any Logic Output Voltage ............ -0.5 (min.)/+5.5V (max.) Any Logic Input Voltage ............... -0.5 (min.)/+5.5V (max.) Output Current FAULT[A/B]#, (/INT, SDA) ................. 10mA Lead Temperature IR Reflow, Peak Temperature ..................... 235 +5/-0C Storage Temperature (TS) ....................... -65C to +150C ESD Rating, Note 3 ................................................... 1.5kV Supply Voltage (12VIN) ............................................... +11.65V to +12.6V (12MVIN) .............................................. -11.0V to -13.2V (5VIN) ................................................... +4.85V to +5.25V (3VIN) ....................................................... +3.1V to +3.6V (VSTBY) .................................................. +3.15V to +3.6V Ambient Temperature (TA) ............................. 0C to +70C Junction Temperature (TJ) ........................................ 125C Package Thermal Resistance TQFP (JA) ....................................................... 56.5C/W Electrical Characteristics 12VIN = 12V; 12MVIN = -12V; 5VIN = 5V; 3VIN = 3.3V; VSTBY = 3.3V; TA = 0C to 70C; unless noted. Power Control and Logic Sections Symbol Parameter Condition Min ICC12 ICC5 ICC33 ICC12M ICCVSBY Supply Current VUVLO Under-Voltage Lockout VHYSUV Under-Voltage Lockout Hysteresis 12VIN, 12MVIN, 5VIN, 3VIN 180 mV VHYSSTBY Under-voltage Lockout Hysteresis VSTBY 50 mV VUVTH VUVTH(12V) VUVTH(12MV) VUVTH(3V) VUVTH(5V) VUVTH(VAUX) Power Good Under-Voltage Thresholds 12VOUT[A/B] 12MVOUT[A/B] 3VOUT[A/B] 5VOUT[A/B] VAUX[A/B] VHYSPG Power-Good Detect Hysteresis VGATE 5VGATE/3VGATE Voltage 12VIN increasing 3VIN increasing 5VIN increasing 12MVIN decreasing VSTBY increasing 12VOUT[A/B] decreasing 12MVOUT[A/B] increasing 3VOUT[A/B] decreasing 5VOUT[A/B] decreasing VAUX[A/B] decreasing 10.2 -10.8 2.7 4.4 2.7 Max Units 0.6 1.2 0.5 -1.0 2.5 2.0 2.0 0.7 -2.0 5.0 mA mA mA mA mA 9 2.5 4.0 -9 2.9 10 2.75 4.3 -8 3.0 V V V V V 10.5 -10.6 2.8 4.5 2.8 10.8 -10.2 2.9 4.7 2.9 30 12VIN-1.5 IGATE(SOURCE) 5VGATE/3VGATE Output Source Current start sycle IGATE(SINK) 5VGATE/3VGATE Output Sink Fault Current any fault condition, VGATE = 5V VFILTER CFILTER Threshold Voltage IFILTER CFILTER[A/B] Charge Current V[5/3]VIN - V[5/3]VSENSE > VTHILIMIT ISLEW 12VSLEW[A/B] Charge Current VTHILIMIT Current Limit Threshold Voltages 5V[A/B] Supplies 3.3V[A/B] Supplies VTHFAST 5VOUT[A/B] and 3VOUT[A/B] Fast-Trip Thresholds March 2002 8 2.2 3.7 -10 2.8 Typ 15 25 V V V V V mV 12VIN V 35 A 70 mA 1.20 1.25 1.30 V 1.80 2.5 5.0 A During Turn-On Only 13 22 35 A V5VIN - V5VSENSE V3VIN - V3VSENSE 35 35 50 50 65 65 mV mV MIC2590A-2 MIC2590A-3 MIC2590A-4 MIC2590A-5 90 113 150 200 Disabled 135 mV mV mV 7 MIC2590A MIC2590A Micrel Symbol Parameter Condition Min Typ VIL LOW-Level Input Voltage (SCL, SDA, ON[A/B], A[0-2],GPI[A/B]) VOL Output LOW Voltage /FAULT[A/B], /INT, SDA VIH HIGH-Level Input Voltage SCL, SDA, ON[A/B], A[0-2], AUXEN[A/B], GPI[A/B]) RPULL-UP Internal Pullups from A[0-2] to VSTBY IIL Input Leakage Current SCL, ON[A/B], AUXEN[A/B], GP[A/B]) 5 A ILKG(OFF) Off-State Leakage Current SDA, /FAULT[A/B], /INT 5 A TOV Overtemperature Shutdown & Reset Thresholds, with overcurrent on slot TJ Increasing, each slot, Note 5 TJ Decreasing, each slot, Note 5 140 130 C C Overtemperature Shutdown & Reset Thresholds, all other conditions (all outputs will latch OFF) TJ Increasing, both slots, Note 5 TJ Decreasing, both slots, Note 5 160 150 C C IOL = 3mA Max Units 0.8 V 0.4 V 2.1 V 40 ROUT(ON) RDS(12V) RDS(12VM) RDS(AUX) Output MOSFET Resistance 12V MOSFET -12V MOSFET VAUX MOSFET IDS = 500mA, TJ = 125C IDS = 100mA, TJ = 125C IDS = 375mA, TJ = 125C VOFF VOFF(+12V) VOFF(-12V) VOFF(VAUX) Off-State Output Offset Voltage 12VOUT[A/B] 12MVOUT[A/B] VAUX[A/B] 12VOUT[A/B] = Off, TJ = 125C 12MVOUT[A/B] = Off, TJ = 125C VAUX[A/B] = Off, TJ = 125C ITHSLOW ILIM(12) ILIM(12M) Current Limit Threshold 12V MOSFET -12V MOSFET 12VOUT[A/B] = 0V 12MVOUT[A/B] = 0V 0.52 -0.11 ITHFAST Fast-Trip Thresholds 12VOUT[A/B] (MIC2590A-2) 12MVOUT[A/B] (MIC2590A-2) 1.0 -0.20 IAUX(THRESH) Auxiliary Output Current Limit Threshold Current which must be drawn Figure 4 from VAUX to register as a fault ISC(TRAN) Maximum Transient Short Circuit Current ILIM(AUX) k 500 2 400 m m 50 50 mV mV mV 1.0 -0.2 1.5 -0.3 A A 2.15 -0.45 3.0 -0.6 A A -50 0.84 A VAUX Enabled, then Grounded IMAX = VSTBY / RDS(AUX) A Regulated Current after Transient From end of ISC(TRAN) to CFILTER Time-Out 0.375 A RDISCH R(12V) R(12MV) R(3V) R(5V) R(3VAUX) Output Discharge Resistance 12VOUT[A/B] 12MVOUT[A/B] 3VOUT[A/B] 5VOUT[A/B] 3VAUX[A/B] 12VOUT[A/B] = 6.0V 12MVOUT[A/B] = -6.0V 3VOUT[A/B] = 1.65V 5VOUT[A/B] = 2.5V 5VOUT[A/B] = 1.65V tOFF(3) tOFF(5) Current Limit Response Time for 3.3V and 5V Outputs, Figure 2 MIC2590A-2 with CGATE = 10nF, VIN - VSENSE = 200mV TSC(TRAN) 0.7 1.35 1600 600 150 150 430 1 s VAUX Current Limiter Response Time VAUX[A/B] = 0V, Note 5 Figure 5 33 s tOFF(12) 12V Current Limit Response Figure 3 12VOUT[A/B] = 0V, Note 5 1 s tOFF(12M) -12V Current Limit Response Figure 3 12MVOUT[A/B] = 0V, Note 5 1 s MIC2590A 8 March 2002 MIC2590A Symbol Micrel Parameter Condition Min Typ Max Units TPROP(3VFAULT) Delay from 3V[A/B] overcurrent-limit to FAULT Output MIC2590A-2, VSENSE - VTHLIMIT = 200mV, CFILTER = open 1 s TPROP(5VFAULT) Delay from 5V[A/B] overcurrent-limit to FAULT Output MIC2590A-2, VSENSE - VTHLIMIT = 200mV, CFILTER = open 1 s tW ON[A/B], AUXEN[A/B] Pulse Width Note 5 100 ns tPOR MIC2590A Power-On Reset Time after VSTBY becomes valid Note 5 500 s Max Units +3 +3 % % 8-Bit Analog to Digital Converter Symbol Parameter Total Unadjusted Error Voltage, All Outputs Current, 3VOUT[A/B]/5VOUT[A/B] Current, VAUX[A/B], 12VOUT[A/B], 12MVOUT[A/B] tCONV Condition Min Measured as voltage across corresponding external RSENSE Typ -3 -3 3 Conversion Time 60 % 100 ms Resolution Specifications: VAUXA VAUXB Full Scale Voltage LSB of Voltage Full Scale Current LSB of Current 3.85 15.1 375 1.47 V mV mA mA 3VOUTA 3VOUTB Full Scale Voltage LSB of Voltage Full Scale Current LSB of Current 3.85 15.1 11.6 45.5 V mV A mA 5.89 23.1 6.96 27.3 V mV A mA Full Scale Voltage LSB of Voltage Full Scale Current LSB of Current 5VOUTA 5VOUTB External RSENSE = 6.00m External RSENSE = 10.0m 12VOUTA 12VOUTB Full Scale Voltage LSB of Voltage Full Scale Current LSB of Current 13.8 54.1 500 1.96 V mV mA mA 12MVOUTA 12MVOUTB Full Scale Voltage LSB of Voltage Full Scale Current LSB of Current -13.6 53.5 100 0.392 V mV mA mA SMBus Timing, Note 5 Symbol Parameter Condition Min t1 SCL (Clock) Period Figure 1 2.5 s t2 Data In Set-Up Time to SCL HIGH Figure 1 100 ns t3 Data Out Stable after SCL LOW Figure 1 300 ns t4 Data LOW Set-Up Time to SCL LOW Start Condition, Figure 1 100 ns t5 Data HIGH Hold Time after SCL HIGH Stop Condition, Figure 1 100 ns Note 1. Note 2. Note 3. Note 4. Note 5. Typ Max Units Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating ratings. Devices are ESD sensitive. Employ proper handling precautions. Human body model, 1.5k in series with 100pF. See the Applications Section. Parameters guaranteed by design. Not 100% production tested. March 2002 9 MIC2590A MIC2590A Micrel Timing Diagrams t1 SCL t4 t5 t2 SDA Data In t3 SDA Data Out Figure 1. SMBus Timing VTHFAST VTHFAST 1V 3VGATE/5VGATE tOFF35 Figure 2. 3V/5V Current Limit Response Timing ITHFAST ILIM12[M] IAUX(THRESH) Must Trip May Not Trip ILIM(AUX) IOUT IOUT(AUX) tOFF12[M] IOUT(AUX) Figure 4. VAUX Current Limit Threshold Figure 3. +12V/-12V Current Limit Response Timing ISC(TRAN) ILIMAUX IOUT(AUX) tSC(TRAN) Figure 5. VAUX Current Limit Response Timing MIC2590A 10 March 2002 MIC2590A Micrel outputs are enabled, and all input voltages are above their respective undervoltage lockout thresholds, all four main supplies execute a controlled turn on. At this time, the GATE voltages of the 5V and 3.3V MOSFETs are ramped at a controlled rate from 0V to approximately 11.5V. This is sufficient to fully enhance the external MOSFETs for lowest possible DC losses. The ramp rate is controlled by 25A(typ) current sources from the GATE pins charging each CGATE. The magnitude and slew rate of the output current is proportional to the value of CGATE and the load capacitance. The minimum value of CGATE is selected to ensure that during start-up the load current does not exceed the current-limit threshold. The following equation is used to determine the value of CGATE(min): Functional Description Hot Swap Insertion When circuit boards are inserted into systems carrying live supply voltages ("hot-plugged"), high inrush currents often result due to the charging of bulk capacitance that resides across the circuit board's supply pins. This transient inrush current can cause the system's supply voltages to temporarily go out of regulation, causing data loss or system lockup. In more extreme cases, the transients occurring during a hot-plug event may cause permanent damage to connectors or on-board components. The MIC2590A addresses these issues by limiting the inrush currents to the load (PCI Board), and thereby controlling the rate at which the load's circuits turn on. In addition, the MIC2590A offers input and output voltage supervisory functions and current-limiting to provide robust protection for both the host system and the PCI board. System Interfaces The MIC2590A employs two system interfaces. One is the Hot-Plug Interface (HPI) which includes ON[A/B], AUXEN[A/ B], and /FAULT[A/B]. The other is the System Management Interface (SMI) consisting of SDA, SCL and /INT, (whose signals conform to the specifications and format of Intel's SMBus standard). The MIC2590A can be operated exclusively from the SMI, or can employ the HPI for power control while continuing to use the SMI for access to all but the power control registers. In addition to the basic power control features of the MIC2590A accessible by the HPI, the SMI also gives the host access to the following information from the part: 1. Output voltage from each supply. 2. Output current from each supply. 3. Fault conditions occurring on each supply. When using the System Management Interface for power control, do not use the Hot-Plug Interface. Conversely, when using the HPI for power control, do not execute power control commands over the SMI bus (all other register accesses via the SMI bus remain permissible while in the HPI control mode). Power-On Reset and Power Cycling The MIC2590A utilizes VSTBY as the main supply input source. It is required for proper operation of the MIC2590A SMBus, registers and ADC and must be applied at all times. A Power-On Reset (POR) cycle is initiated after VSTBY rises above its UVLO threshold and remains valid at that voltage for 500s. All internal registers except RESULT are cleared after POR. If VSTBY is recycled the MIC2590A enters a new power-on reset cycle. VSTBY must be the first supply input applied. Following the POR interval, the MAIN supply inputs of 12VIN, 12MVIN, 5VIN and 3VIN may be applied in any order. The SMBus is ready for access at the end of the POR interval. During tPOR all outputs are off. Power-Up Cycle (See Typical Application Circuit) When a slot is off the 5VGATE and 3VGATE pins are held low with an internal pull-down current source. When a slot's main March 2002 I CGATE (min) = GATE x CLOAD ILIM Where CLOAD is the load capacitance connected to the 3.3V and 5V outputs and ILIM and IGATE are respectively the current-limit and gate charge current specifications as given in the Electrical Characteristics table. The output slew rate dv/dt is computed by: dv / dt (load) = IGATE CGATE x 106 ISLEW = 25A CGATE dv/dt (load) 0.001F 25000V/s 0.01F 2500V/s 0.1F 250V/s 1F 25V/s Table 1. 3.3V/5V Output Slew-Rate Selection For the +12V and -12V supplies the output slew rate is controlled by capacitors connected to the 12VSLEWA and 12VSLEWB pins. To determine the minimum value of the slew rate capacitor, (CSLEW), connected to 12VSLEW[A/B], the following equation is used: I CSLEW (min) = SLEW x CLOAD ILIM where CLOAD is the load capacitance connected to the +12V and -12V outputs, and ILIM and ISLEW are respectively the current-limit and slew rate charge current values found in the Electrical Characteristics table. The equation above computes the minimum value to guarantee the device does not enter into current-limit. The slew rate dv/dt is computed by: dv / dt at load = ISLEW CSLEW x 106 By appropriate selection of the value of CSLEW, it can be ensured that the magnitude of the inrush current never exceeds the current-limit for a given load capacitance. Since one capacitor fixes the slew rate for both +12V and -12V, the capacitor value should be chosen to provide the slower slew rate of the two. Table 2 depicts the output slew rate for various values of CSLEW. 11 MIC2590A MIC2590A Micrel ISLEW = 22A CGATE dv/dt (load) 0.001F 22000V/s 0.01F 2200V/s 0.1F 220V/s 1F 22V/s Following a fault condition, the outputs can be turned on again via the ON inputs (if the fault occurred on one of the MAIN outputs), via the AUXEN inputs (if the fault occurred on the AUX outputs), or by cycling both ON and AUXEN (if faults occurred on both the MAIN and AUX outputs). A fault condition can alternatively be cleared under SMI control of the ENABLE bits in the CNTRL[A/B] registers. When the circuit breaker trips, /FAULT[A/B] will be asserted if the outputs were enabled through the Hot-Plug Interface (non-SMI mode) inputs. At the same time, /INT will be asserted (unless interrupts are masked). Note that /INT is de-asserted by writing a logic 1 back into the respective fault bit position(s) in the STAT[A/B] register or the Common Status Register. tFLT is set by external capacitors, CFIL[A/B], connected to the CFILTER[A/B] pins. The equation below can be used to determine the capacitor value for a given duration of tFLT: Table 2. 12V Output Slew-Rate Selection Power-Down Cycle When a slot is turned off, internal switches are connected to each of the outputs to discharge the PCI board's bypass capacitors to ground. Standby Mode Standby mode is entered when any one (or more) enabled MAIN supply input(s) (12VIN, 12MVIN, 5VIN and 3VIN) drops below its respective UVLO threshold. The MIC2590A supplies two 3.3V auxiliary outputs, VAUX[A/B], satisfying PCI 2.2 specifications. These outputs are fed via the VSTBY input, and controlled by the AUXEN[A/B] inputs or via their SMI bus Control Registers. These outputs are independent of the MAIN outputs: should one or more of the MAIN supply inputs move below its UVLO thresholds, VAUX[A/B] still function as long as VSTBY is present. Prior to entering standby mode, ONA and ONB (or the MAINA and MAINB bits in the Control Registers) inputs should be de-asserted. If this is not done, the MIC2590A will assert /FAULT, and also /INT if interrupts are enabled, when the MIC2590A detects an undervoltage condition on a supply input. Circuit Breaker Functions The MIC2590A provides an electronic circuit breaker function that protects against excessive loads such as short circuits at each supply. When the current from one or more of a slot's MAIN outputs exceeds the current-limit threshold (50mV/RSENSE for 3.3V and 5V, 1.0A for +12V, and/or 0.2A for -12V) for a duration greater than tFLT, the circuit breaker is tripped and all MAIN supplies (all outputs except VAUX[A/B]) are shut off. Should the load current exceed ITHFAST (+12V and -12V), or cause a MAIN output's VSENSE to exceed VTHFAST (+3.3V and +5V), the outputs are shut off with no delay. Undervoltage conditions on the MAIN supply inputs also trip the circuit breaker, but only when the MAIN outputs are enabled (to signal a supply input brown-out condition). The VAUX[A/B] outputs have their own separate circuit breaker functions. VAUX[A/B] do not incorporate a fast-trip threshold, but instead regulate the output current into a fault to avoid exceeding their operating current-limit. The circuit breaker will trip due to overcurrents on VAUX[A/B] when the fault timer expires. This use of the tFLT timer prevents the circuit breaker from tripping prematurely due to brief current transients. MIC2590A t CFIL 2.0F x FLT 1second Thermal Shutdown The internal +12V, -12V and VAUX MOSFETs are protected against damage not only by current-limiting, but by dualmode over-temperature protection as well. Each slot controller on the MIC2590A is thermally isolated from the other. Should an overcurrent condition raise the junction temperature of one slot's controller and internal pass elements to 140C, all of the outputs for that slot (including VAUX) will be shut off, and the slot's /FAULT output will be asserted. The other slot's operation will remain unaffected. However, should the MIC2590A's overall die temperature exceed 160C, both slots (all outputs, including VAUXA and VAUXB) will be shut off, whether or not a current-limit condition exists. A 160C overtemperature condition additionally sets the overtemperature bit (OT_INT) in the Common Status Register. A/D Converter The MIC2590A has a 20-channel, 8-bit A/D converter capable of monitoring the output voltage and current of each supply. This information is available via the System Management Interface. The information is particularly intended for use by systems that support the IPMI standard, but may be used for any desired purpose. 12 March 2002 MIC2590A Micrel Interrupt Generation In the MIC2590A the /INT pin can be asserted (driven low) whenever a fault condition trips the circuit breaker. The MIC2590A can thus operate in either polled mode or interrupt mode. In the polled mode the Interrupt Mask bit in the Common Status Register should be set, to prevent the /INT pin from being asserted. Upon a circuit breaker fault event the appropriate status bit is also set in the corresponding status registers. In order to clear the status bit the system must write a logic 1 back to same bit in the status register. Upon occurrence of the write the /INT pin will be de-asserted (if interrupts were enabled), if no other interrupts are pending. This method of "echo reset" allows data to be retained in the status registers until such time as the system software is ready to deal with that data, and then to control the earliest time at which the next interrupt might occur. AUXEN[x] ON[x] AUX OUT[x] MAIN OUT[x] FAULT DETECTED ON AUX OUT[x] FAULT DETECTED ON MAIN OUT[x] /FAULT OUTPUT[x] /INT OUTPUT (CLEARED BY SOFTWARE) Figure 6. Hot-Plug Interface Mode Operation System Management Interface (SMI) The MIC2590A's System Management Interface uses the Read_Byte and Write_Byte subset of the SMBus protocols to communicate with its host via the System Management Interface bus. Additionally, the /INT output signals the controlling processor that one or more events need attention, if an interrupt-driven architecture is used. Note that the MIC2590A does not participate in the SMBus Alert Response Address (ARA) portion of the SMBus protocol. The SMBus Read_Byte operation consists of sending the device's slave address, followed by the target register's internal address, and then clocking out the byte to be read from the target register. Similarly, the Write_Byte operation consists of sending the device's slave address, followed by the target register's internal address, and then clocking in the byte to be written to the target register. The target register addresses for the MIC2590A are given in Table 4. MIC2590A SMBus Address Configuration The MIC2590A responds to its own unique address which is assigned using A2, A1 and A0. These represent the 3 LSBs of its 7-bit address, as shown in Table 3. These address bits are assigned only during power up of the VSTBY supply input. These three bits allow up to eight MIC2590A devices in a single system. These pins are either grounded or left unconnected to specify a logical 0 or 1 respectively. A pin designated as a logical 1 may also be pulled up to VSTBY. Inputs MIC2590A Slave Address A2 A1 A0 Binary Hex 0 0 0 1000 000b 80h 0 0 1 1000 001b 82h 0 1 0 1000 010b 84h 0 1 1 1000 011b 86h 1 0 0 1000 100b 88h 1 0 1 1000 101b 8Ah 1 1 0 1000 100b 8Ch 1 1 1 1000 111b 8Eh Table 3. MIC2590A SMBus Addressing March 2002 13 MIC2590A MIC2590A Micrel MIC2590A Slave Address Target Register Value read from MIC2590A DATA S 1 0 0 0 A2 A1 A0 1 A 0 0 0 0 0 X X X A x START R/W = READ x ACKNOWLEDGE x x x x x x /A P NOT ACKNOWLEDGE STOP CLK x Master to slave transfer, i.e., DATA driven by master. x Slave to master transfer, i.e., DATA driven by slave. Figure 7. READ_BYTE Protocol MIC2590A Slave Address Target Register Value to be written to MIC2590A DATA S 1 0 0 0 A2 A1 A0 0 A 0 0 0 0 0 X X X A X X X X X X X X /A P START R/W = WRITE ACKNOWLEDGE NOT ACKNOWLEDGE STOP CLK x Master to slave transfer, i.e., DATA driven by master. x Slave to master transfer, i.e., DATA driven by slave. Figure 8. WRITE_BYTE Protocol Register Set and Programmer's Model Label Target Register Description RESULT ADC Conversion Result Register Command Power-On Byte Value Default Read Write 00h n/a n/a ADCNTRL ADC Control Regster 01h 01h 00h CNTRLA Control Register Slot A 02h 02h 00h CNTRLB Control Register Slot B 03h 03h 00h STATA Slot A Status 04h 04h 00h STATB Slot B Status 05h 05h 00h STAT Common Status Register 06h 06h 00h Table 4. MIC2590A Register Addresses MIC2590A 14 March 2002 MIC2590A Micrel Detailed Register Descriptions below: Control Register, Slot A (CNTRLA), 8-Bits Read/Write Conversion Result Register (RESULT), 8-Bits Read Only D[7] D[6] D[5] D[4] D[3] D[2] D[1] D[7] D[6] D[5] D[4] D[3] D[2] D[1] D[0] read-only read-only read-only read-only read-only read-only read-write read-write D[0] AUXAPG MAINAPG Reserved Reserved Reserved Reserved read-only read-only read-only read-only read-only read-only read-only read-only MAINA VAUXA Voltage or Current Data from ADC Bit(s) Bit Function Operation D[7:0] Measured data from ADC Read Only (ADC Control Register (ADCNTRL), 8-Bits Read/Write D[6] D[5] D[4] D[3] D[2] D[1] Bit(s) BUSY SEL Function PAR Supply Select SUP[2:0] 0 = ADC Quiescent, 1 = ADC Busy D[6] Reserved Always Read As Zero D[5] Reserved Always Read As Zero SEL A/D Slot Select Specifies Channel for A/D Conversion 0 = Slot A, 1 = Slot B PAR SUP[2:0] Always Read As Zero D[4] Reserved Always Read As Zero D[3] Reserved Always Read As Zero D[2] Reserved Always Read As Zero MAINA MAIN Enable Control, Slot A 0 = OFF, 1 = ON VAUXA VAUX Enable Control, Slot A 0 = OFF, 1 = ON Control Register, Slot B (CNTRLB), 8-Bits Read/Write D[7] D[6] D[5] D[4] D[3] D[2] D[1] D[0] read-only read-only read-only read-only read-only read-only read-write read-write AUXBPG MAINBPG Reserved Reserved Reserved Reserved Parameter Control Bit for 1 = Voltage, ADC Conversion 0 = Current Supply Select for ADC Conversion Reserved Power-Up Default Value: 0000 0000b = 00h Command Byte (R/W): 0000 0010b = 02h The power-up default value is 00h. Slot A is disabled upon power-up, i.e., all supply outputs are off. Operation ADC Status 1 = Power-Good (VAUXA output is above its VUVTH threshold) D[5] D[0] read-only read-only read-only read-write read-write read-write read-write read-write BUSY Reserved Reserved Operation AUX Output Power-Good Status, Slot A MAINAPG MAIN Output Power-Good 1 = Power-Good Status, Slot A (MAINA outputs are above their VUVTH thresholds) Power-Up Default Value: Undefined following POR Read Command Byte: 0000 0000b = 00h D[7] Function AUXAPG Bit(s) 000 = No Conversion 001 = 3.3V Suppy 010 = 5.0V Supply 011 = +12V Supply 100 = -12V Supply 101 = VAUX Supply AUXBPG Function AUX Output Power-Good Status, Slot B MAINB VAUXB Operation 1 = Power-Good (VAUXB output is above its VUVTH threshold) MAINBPG MAIN Output Power-Good 1 = Power-Good Status, Slot B (MAINB outputs are above their VUVTH thresholds) Power-Up Default Value: 0000 0000b = 00h Command Byte (R/W): 0000 0001b = 01h To operate the ADC the ADCNTRL register must first be initialized by selecting a slot, specifying whether voltage or current is to be measured and then specifying the specific supply that is to be monitored. The software must then wait 100ms, or poll the BUSY bit until it is zero. The RESULT register will then contain the valid result of the conversion. D[5] Reserved Always Read As Zero D[4] Reserved Always Read As Zero D[3] Reserved Always Read As Zero D[2] Reserved Always Read As Zero MAINB MAIN Enable Control, Slot B 0 = OFF, 1 = ON VAUXB VAUX Enable Control, Slot B 0 = OFF, 1 = ON Power-Up Default Value: 0000 0000b = 00h Command Byte (R/W): 0000 0011b = 03h The power-up default value is 00h. Slot B is disabled upon power-up, i.e., all supply outputs are off. March 2002 15 MIC2590A MIC2590A Micrel Status Register, Slot A (STATA), 8-Bits Read Only D[7] D[6] D[5] D[4] D[3] D[2] D[1] Status Register, Slot B (STATB), 8-Bits Read Only D[0] D[7] D[6] D[5] D[4] D[3] D[2] D[1] D[0] read-only read-only read-only read-write read-write read-write read-write read-write read-only read-only read-only read-write read-write read-write read-write read-write FAULTA MAINA VAUXA VAUXAF 12MVAF 12VAF FAULTA MAINA VAUXA VAUXAF 12MVAF 12VAF Bit(s) Function 5VAF 3VAF Operation Bit(s) Function 5VAF 3VAF Operation FAULTA FAULT Pin Status, Slot A Notes 1 & 2 FAULTB FAULT Pin Status, Slot B Notes 1 & 2 MAINA MAIN Enable Status, Slot A Represents actual state (on/off) of the four main power outputs for Slot A (+12V, +5V, +3.3V and -12V) 1 = MAIN Power On 0 = MAIN Power Off MAINB MAIN Enable Status, Slot B Represents actual state (on/off) of the four main power outputs for Slot B (+12V, +5V, +3.3V and -12V) 1 = MAIN Power On 0 = MAIN Power Off VAUXA VAUX Enable Status Slot A Represents actual state (on/off) of the auxiliary power outputs for Slot A 1 = AUX Power On 0 = AUX Power Off VAUXB VAUX Enable Status Slot B Represents actual state (on/off) of the auxiliary power outputs for Slot B 1 = AUX Power On 0 = AUX Power Off VAUXFA Overcurrent Fault VAUX Supply 1 = Fault; 0 = No Fault VAUXFB Overcurrent Fault VAUX Supply 1 = Fault; 0 = No Fault 12MVFA Overcurrent Fault -12V Supply 1 = Fault; 0 = No Fault 12MVFB Overcurrent Fault -12V Supply 1 = Fault; 0 = No Fault 12VFA Overcurrent Fault +12V Supply 1 = Fault; 0 = No Fault 12VFB Overcurrent Fault +12V Supply 1 = Fault; 0 = No Fault 5VFA Overcurrent Fault 5V Supply 1 = Fault; 0 = No Fault 5VFB Overcurrent Fault 5V Supply 1 = Fault; 0 = No Fault 3VFA Overcurrent Fault 3.3V Supply 1 = Fault; 0 = No Fault 3VFB Overcurrent Fault 3.3V Supply 1 = Fault; 0 = No Fault Power-Up Default Value: 0000 0000b = 00h Read Command Byte (R/W): 0000 0100b = 04h The power-up default value is 00h. The slot is disabled upon power-up, i.e., all supply outputs are off. In response to an overcurrent fault condition, writing a logical 1 back into the active (or set) bit position will clear the bit and deassert /INT. The status of the /FAULTA pin is not affected by reading the Status Register. Note 1. Power-Up Default Value: 0000 0000b = 00h Read Command Byte (R/W): 0000 0101b = 05h The power-up default value is 00h. The slot is disabled upon power-up, i.e., all supply outputs are off. In response to an overcurrent fault condition, writing a logical 1 back into the active (or set) bit position will clear the bit and deassert /INT. The status of the /FAULTB pin is not affected by reading the Status Register. 1 = /FAULT[A/B] pin asserted, indicating a fault condition (/FAULT is LOW). 0 = /FAULT[A/B] pin is de-asserted (/FAULT is HIGH). If FAULT[A/B] has been set by an overcurrent condition on one (or more) of the main outputs, the corresponding ON[A/B] must go LOW to reset FAULT. If FAULT[A/B] has been set by an overcurrent on a VAUX output, the corresponding AUXEN[A/B] must go LOW to reset FAULT. If an overcurrent has occurred on both a main output and VAUX output of a slot, both ON[A/B] and AUXEN[A/B] of the corresponding slot must go LOW to reset FAULT. Note 2. The FAULT bits, and the /FAULT pins, are not active when the MIC2590A power paths are controlled by the System Management Interface (SMBus). When using SMI power path control for a slot, the AUXEN and ON pins for that slot must be tied to ground. MIC2590A 16 March 2002 MIC2590A Micrel Common Status Register, (STAT), 8-Bits Read/Write D[7] D[6] D[5] D[4] D[3] D[2] D[1] D[0] read-only read-only read-only read-only read-write read-write read-write read-only Reserved Reserved Bit(s) GPIB GPIA Function INTMSK UV_INT OT_INT Reserved Operation D[7] Reserved Always read as zero Always read as zero D[6] Reserved GPIB General Purpose Input, State of GPIB pin Slot B GPIA General Purpose Input, State of GPIA pin Slot A INTMSK Interrupt Mask 0 = /INT generation is enabled; 1 = /INT generation is disabled. The MIC2590A does not participate in the SMBus Alert Response Address (ARA) Protocol. UV_INT Undervoltage Interrupt Set whenever a circuit breaker fault condition occurs as a result of an undervoltage lockout condition on one of the main supply inputs. This bit is only set if a UVLO condition occurs while one or both of the ON[A/B] pins are asserted or the MAIN[A/B] enable control bits are set. OT_INT Overtemperature Interrupt Set whenever a circuit breaker fault occurs as a result of an overtemperature condition exceeding 160C shutting both channels off. Reserved Read Undefined D[0] Power-Up Default Value: 0000 0000b = 00h Command Byte (R/W): 0000 0110b = 06h To reset the OT_INT and UV_INT fault bits a logical 1 must be written back to these bits. March 2002 17 MIC2590A MIC2590A Micrel Kelvin Sensing Because of the low values of the sense resistors, special care must be used to accurately measure the voltage drop across them. Specifically, the voltage across each RSENSE must employ Kelvin sensing. This is simply a means of making sure that any voltage drops in the power traces connecting to the resistors are not picked up in addition to the voltages across the sense resistors themselves. If accuracy must be paid for, it's worth keeping. Figure 9 illustrates how Kelvin sensing is performed. As can be seen, all the high current in the circuit (let us say, from +5VINA through RSENSE and then to the drain of the +5VA output MOSFET) flows directly through the power PCB traces and RSENSE. The voltage drop resulting across RSENSE is sampled in such a way that the high currents through the power traces will not introduce any extraneous IR drops. Application Information Current Sensing For the three power supplies switched with internal MOSFETs (+12V, -12V, and VAUX), the MIC2590A provides all necessary current sensing functions to protect the IC, the load, and the power supply. For the remaining four supplies which the part is designed to control, the high currents at which these supplies typically operate makes sensing the current inside the MIC2590A impractical. Therefore, each of these supplies (3VA, 5VA, 3VB, and 5VB) requires an external current sensing resistor. The VIN connection to the IC from each supply (e.g., 5VINA) is connected to the positive terminal of the slot's current sense amplifier, and the corresponding SENSE input (in this case, 5VSENSEA) is connected to the negative terminal of the current sense amplifier. Sense Resistor Selection The MIC2590A uses low-value sense resistors to measure the current flowing through the MOSFET switches to the loads. These sense resistors are nominally valued at 50m/ILOAD(CONT). To accommodate worst-case tolerances for both the sense resistor, (allow 3% over time and temperature for a resistor with 1% initial tolerance) and still supply the maximum required steady-state load current, a slightly more detailed calculation must be used. The current-limit threshold voltage (the "trip point") for the MIC2590A may be as low as 35mV, which would equate to a sense resistor value of 35m/ILOAD(CONT). Carrying the numbers through for the case where the value of the sense resistor is 3% high, this yields: RSENSE = 35 (1.03)(ILOAD(CONT) ) = Power Trace From VCC Signal Trace to MIC2590A VCC Signal Trace to MIC2590A VSENSE MOSFET Selection Selecting the proper MOSFET for use as current pass and switching element for each of the 3V and 5V slots of the MIC2590A involves four straightforward tasks: 1. Choice of a MOSFET which meets the minimum voltage requirements. 2. Determination of maximum permissible on-state resistance [RD-S(ON)]. 3. Selection of a device to handle the maximum continuous current (steady-state thermal issues). 4. Verification of the selected part's ability to withstand current peaks (transient thermal issues). MOSFET Voltage Requirements The first voltage requirement for each MOSFET is easily stated: the drain-source breakdown voltage of the MOSFET must be greater than VIN(MAX) for the slot in question. For instance, the 5V input may reasonably be expected to see high-frequency transients as high as 5.5V. Therefore, the drain-source breakdown voltage of the MOSFET must be at least 6V. The second breakdown voltage criteria which must be met is a bit subtler than simple drain-source breakdown voltage, but is not hard to meet. Low-voltage MOSFETs generally have low breakdown voltage ratings from gate to source as well. In MIC2590A applications, the gates of the external MOSFETs are driven from the +12V input to the IC. That supply may well be at 12V + (5% x 12V) = 12.6V. At the same time, if the output of the MOSFET (its source) is suddenly shorted to ground, the gate-source voltage will go to (12.6V - 0V) = 12.6V. This 34m ILOAD(CONT) 65mV 67mA = (0.97)(RSENSE(NOM) ) RSENSE(NOM) As an example, if an output must carry a continuous 4.4A without nuisance trips occurring, RSENSE for that output should be 34m/4.4A = 7.73m. The nearest standard value is 7.5m, so a 7.5m 1% resistor would be a good choice. At the other set of tolerance extremes, ILOAD(CONT, MAX) for the output in question is then simply 67mV/7.5m = 8.93A. Knowing this final datum, we can determine the necessary wattage of the sense resistor, using P = I2R. Here I will be ILOAD(CONT, MAX), and R will be (0.97)(RSENSE(NOM)). These numbers yield the following: PMAX = (8.93A)2(7.28m) = 0.581W A 1.0W sense resistor would work well in this application. MIC2590A Power Trace To MOSFET Drain Figure 9. Kelvin Sensing Connections for RSENSE Once the value of RSENSE has been chosen in this manner, it is good practice to check the maximum ILOAD(CONT) which the circuit may let through in the case of tolerance build-up in the opposite direction. Here, the worst-case maximum is found using a 65mV trip voltage and a sense resistor which is 3% low in value. The resulting current is: ILOAD(CONT.MAX) = RSENSE 18 March 2002 MIC2590A Micrel means that the external MOSFETs must be chosen to have a gate-source breakdown voltage in excess of 13V; after 12V absolute maximum the next commonly available voltage class has a permissible gate-source voltage of 20V maximum. This is a very suitable class of device. 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, look to surface-mount devices with a drainsource rating of 30V as a starting point. MOSFET Maximum On-State Resistance The MOSFETs in the +3.3V and +5V MAIN power paths will have a finite voltage drop, which must be taken into account during component selection. A suitable MOSFET's data sheet will almost always give a value of on resistance for the MOSFET at a gate-source voltage of 4.5V, and another value at a gate-source voltage of 10V. As a first approximation, add the two values together and divide by two to get the on resistance of the device with 7 Volts of enhancement (keep this in mind; we'll use it in the following Thermal Issues sections). The resulting value is conservative, but close enough. Call this value RON. Since a heavily enhanced MOSFET acts as an ohmic (resistive) device, almost all that is required to calculate the voltage drop across the MOSFET is to multiply the maximum current times the MOSFET's RON. The one addendum to this is that MOSFETs have a slight increase in RON with increasing die temperature. A good approximation for this value is 0.5% increase in RON per C rise in junction temperature above the point at which RON was initially specified by the manufacturer. For instance, the Vishay (Siliconix) Si4430DY, which is a commonly used part in this type of application, has a specified RDS(ON) of 8.0m max. at VG-S = 4.5V, and RDS(ON) of 4.7m max. at VG-S = 10V. Then RON is calculated as: RON * The value of ILOAD(CONT, MAX) for the output in question (see Sense Resistor Selection). * The manufacturer's data sheet for the candidate MOSFET. * The maximum ambient temperature in which the device will be required to operate. * 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?). Now it gets easy: steady-state power dissipation is found by calculating I2R. As noted in "MOSFET Maximum On-State Resistance," above, the one further concern is the MOSFET's increase in RON with increasing die temperature. Again, use the Si4430DY MOSFET as an example, and assume that the actual junction temperature ends up at 110C. Then RON at temperature is again approximately 9.05m. Again allow a maximum IDRAIN of 7.6A: Power dissipation IDRAIN2 x RON = (7.6A) x 9.05m 0.523W 2 The next 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. Formally put, the steady-state electrical model of power dissipated at the MOSFET junction is analogous to a current source, and anything in the path of that power being dissipated as heat into the environment is analogous to a resistor. It's therefore necessary to verify that the thermal resistance from the junction to the ambient is equal to or lower than that value of thermal resistance (often referred to as R(JA)) for which the operation of the part is guaranteed. As an applications issue, surface-mount MOSFETs are often less than ideally specified in this regard--it's become common practice simply to state that the thermal data for the part is specified under the conditions "Surface mounted on FR-4 board, t 10seconds," or something equally mystifying. So 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 soldered down to one square inch or more of copper the copper will act as the heat sink for the part. This copper must be on the same layer of the board as the MOSFET drain. 2. Since the rating for the part is given as "for 10 seconds," derate the maximum junction temperature by 35C. This is the standard good practice derating of 25C, plus another 10C to allow for the time element of the specification. 3. Airflow, if available, works wonders. This is not the place for a dissertation on how to perform airflow calculations, but even a few LFM (linear feet per minute) of air will cool a MOSFET down (4.7m + 8.0m) = 6.35m 2 at 25C TJ. If the actual junction temperature is estimated to be 110C, a reasonable approximation of RON for the Si4430DY at temperature is: 0.5% 0.5% 6.35m 1+ (110 - 25) = 6.35m 1+ (85) 9.05m C C Note that this is not a closed-form equation; if more precision were required, several iterations of the calculation might be necessary. This is demonstrated in the section "MOSFET Transient Thermal Issues." For the given case, if Si4430DY is operated at an IDRAIN of 7.6A, the voltage drop across the part will be approximately (7.6A)(9.05m) = 69mV. MOSFET Steady-State Thermal Issues The selection of a MOSFET to meet the maximum continuous current is a fairly straightforward exercise. First, arm yourself with the following data: March 2002 19 MIC2590A MIC2590A Micrel In terms related directly to the specification and use of power MOSFETs, this is known as "transient thermal impedance." Almost all power MOSFET data sheets give a Transient Thermal Impedance Curve, which is a handy tool for making sure that you can safely get by with a less expensive MOSFET than you thought you might need. For example, take the case where tFLT for the 5V supply has been set to 50msec, ILOAD(CONT, MAX) is 5.0A, the slow-trip threshold is 50mV nominal, and the fast-trip threshold is 100mV. If the output is connected to a 0.60 load, the output current from the MOSFET for the slot in question will be regulated to 5.0A for 50ms before the part's circuit breaker trips. During that time, the dissipation in the MOSFET is given by: P = E x I EMOSFET = [5V-5A(0.6)] = 2V dramatically. If you can position the MOSFET(s) in question near the inlet of a power supply's fan, or the outlet of a processor's cooling fan, that's always a good free ride. 4. Although it seems a rather unsatisfactory statement, 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. The ideal evaluation is in the actual layout of the expected final circuit, at full operating current. The use of a thermocouple on the drain leads, or in infrared pyrometer on the package, will then give a reasonable idea of the device's junction temperature. MOSFET Transient Thermal Issues Having chosen a MOSFET that will withstand the imposed voltage stresses, and be able to handle the worst-case continuous I2R power dissipation which it will see, it remains only to verify the MOSFET's ability to handle short-term overload power dissipation without overheating. Here, nature and physics work in our favor: a MOSFET can handle a much higher pulsed power without damage than its continuous dissipation ratings would imply. The reason for this is that, like everything else, semiconductor devices (silicon die, lead frames, etc.) have thermal inertia. This is easily understood by all of us who have stood waiting for a pot of water to boil. PMOSFET = (2V x 5A) = 10W for 50msec. Wow! Looks like we need a really hefty MOSFET to withstand just this unlikely--but plausible enough to protect against-- fault condition. Or do we? This is where the transient thermal impedance curves become very useful. Figure 10 shows those curves for the Vishay (Siliconix) Si4430DY, a commonly used SO-8 power MOSFET: Normalized Thermal Transient Impedance, Junction-to-Ambient Normalized Effective Transient Thermal Impedance 2 1 Duty Cycle = 0.5 0.2 Notes: 0.1 PDM 0.1 0.05 t1 t2 1. Duty Cycle, D = t1 t2 2. Per Unit Base = RthJA = 67C/W 0.02 3. TJM - TA = PDMZthJA(t) Single Pulse 4. Surface Mounted 0.01 10-4 10-3 10-2 10-1 1 Square Wave Pulse Duration (sec) 10 100 600 Figure 10. Si4430DY MOSFET Transient Thermal Impedance Curve Using this graph is not nearly as daunting as it may at first appear. 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 slot is reset. In such a case, we can approximate this as a "single pulse" event, that is to say, there's no significant duty cycle. Then, reading up from the X-axis at the point where "Square Wave Pulse Duration" is equal to 0.1sec (=100msec), we see that the effective thermal impedance of this MOSFET MIC2590A to a single pulse event of this duration is only 6% of its continuous R(JA). This particular part is specified as having an R(JA) of 50C/W for intervals of 10 seconds or less. So, some further math, just to get things ready for the finale: Assume TA = 55C maximum, 1 square inch of copper at the drain leads, no airflow. 20 March 2002 MIC2590A Micrel the MOSFET be able to handle the increased dissipation? We get the following: The same part is operating into a persistent fault, so it is cycling in a square-wave fashion (no steady-state load) with a duty cycle of (50msec/second = 0.05). On the Transient Thermal Impedance Curves, read up from the X-axis to the line showing Duty Cycle equaling 0.05. The effective R(JA) = (0.7 x 67C/W) = 4.7C/W. Calculating the peak junction temperature: TJ(PEAK MAX) = [(10W)(4.7C/W) + 55C] = 102C. And finally, checking the RMS power dissipation just to be complete: Assume the MOSFET has been carrying just about 5A for some time. Then the starting (steady-state)TJ is: TJ 55C + (7.3m)(5A)2(30C/W) TJ 60.5C Iterate the calculation once to see if this value is within a few percent of the expected final value. For this iteration we will start with TJ equal to the already calculated value of 67C: RON at TJ = 60.5C = [1+(60.5C-25)(0.5%/C)]x6.35m RON at TJ = 60.5C 7.48m TJ 55C + (7.3m)(5A)2(30C/W) TJ 60.6C At this point, the simplest thing to do is to approximate TJ as 61C, which will be close enough for all practical purposes. Finally, add (10W)(67C/W)(0.03) = 21C to the steady-state TJ to get TJ(TRANSIENT MAX) = 82C. The Si4430DY can easily handle this value of TJ(MAX). A second illustration of the use of the transient thermal impedance curves: assume that the system will attempt multiple retries on a slot showing a fault, with a one second interval between retry attempts. This frequency of restarts will significantly increase the dissipation in the Si4430DY MOSFET. Will PRMS = (5A ) (7.47m) 0.05 = 0.042W which will result in a negligible temperature rise. The Si4430DY is electrically and thermally suitable for this application. MOSFET and Sense Resistor Selection Guide Listed below, by Manufacturer and Type Number, are some of the more popular MOSFET and resistor types used in PCI hot-plug applications. Although far from comprehensive, this information will constitute a good starting point for most designs. 2 MOSFET Vendors Key MOSFET Type(s) Web Address Vishay (Siliconix) Si4430DY ("LittleFoot" Series) Si4420DY ("LittleFoot" Series) www.siliconix.com International Rectifier IRF7413A (SO-8 package part) Si4420DY (second source to Vishay) www.irf.com Fairchild Semiconductor FDS6644 (SO-8 package part) FDS6670A (SO-8 package part) FDS6688 (SO-8 package part) www.fairchildsemi.com Resistor Vendors Vishay (Dale) IRC Sense Resistors "WSL" Series "OARS" Series "LR" Series (second source to "WSL") Web Address Power Supply Decoupling In general, prudent system design requires that power supplies used for logic functions should have less than 100mV of noise at frequencies of 100kHz and above. This is especially true given the speeds of modern logic families, such as the 1.2 micron CMOS used in the MIC2590A. The internal logic of the MIC2590A is powered from the 3.3VAUX supply, and that supply should not carry HF noise in excess of 100mV peak-to-peak with respect to chip ground, especially at frequencies 1MHz. Less obviously but equally importantly, the -12V supply should have less than 100mV of peak-to-peak noise at frequencies of 1MHz or higher. This is because the -12V supply is the most negative potential applied to the IC, and is therefore connected to the device's substrate. All of the March 2002 www.vishay.com/docs/wsl_30100.pdf irctt.com/pdf_files/OARS.pdf irctt.com/pdf_files/LRC.pdf subcircuits integrated onto the silicon chip are hence subjected by capacitive coupling to any HF noise on the -12V supply. While the individual capacitances are quite low, the amount of injected energy required to cause a "glitch" can also be quite low at the internal nodes of high speed logic circuits. If either the 3.3VAUX source supply, the -12V source supply, or both supplies do carry significant HF noise (as can happen when they are locally derived by a switching converter), the solution is both small and inexpensive. A simple LC filter made of a ferrite bead between the noisy power supply input and the MIC2590A, followed by one 1F and one 10nF ceramic capacitor from the MIC2590A input pin to ground will suffice for almost any situation. A suggested ferrite bead for 21 MIC2590A MIC2590A Micrel with such a transient is to clamp it with a Schottky diode. The diode's anode should be physically placed directly at the -12V input to the MIC2590A, and its cathode should have as short a path as possible back to the part's ground. A good SMT part for this application is ON Semiconductor's type MBRS140T3 (1A, 40V). Although the 40V rating of this part is a bit gratuitous, it is an inexpensive industry-standard part with many second sources. Unless it is absolutely known in advance that the voltage on the "-12V" inputs will never exceed 0.0V at the IC's -12V input pins, it's wise to at least leave a position for this diode in the board layout and then remove it later. This final determination should be made by observations of the voltage at the -12V input with a fast storage oscilloscope, under turn-on and turn-off conditions. Gate Resistor Guidelines The MIC2590A controls four external power MOSFETs, which handle the high currents for each of the two 3.3V and 5V outputs. A capacitor (CGATE) is connected in the application circuit from each GATE pin of the MIC2590A to ground. Each CGATE controls the ramp-up rate of its respective power output (e.g., 5VOUTB). These capacitors, which are typically in the 10nF range, cause the GATE outputs of the MIC2590A to have very low AC impedances to ground at any significant frequency. It is therefore necessary to place a modest value of gate damping resistance (RGATE) between each CGATE and the gate of its associated MOSFET. These resistances prevent high-frequency MOSFET source-follower oscillations from occurring. The exact value of the resistors used is not critical; 47 is usually a good choice. Each RGATE should be physically located directly adjacent to the MOSFET gate lead to which it connects. such use is Fair-Rite Products Corporation part # 2743019447 (this is a surface-mountable part). Similar parts from other vendors will also work well, or a 0.27H, air-core coil can be used. Noisy VIN SMT Ferrite Bead Fair-Rite Products Type 2743019447 To MIC2590A 1F Ceramic 1F Ceramic Figure 11. Filter Circuit for Noisy Supplies (+3.3V and/or -12V) It is theoretically possible that high-amplitude, HF noise reflected back into one or both of the MIC2590A's -12V outputs could interfere with proper device operation, although such noisy loads are unlikely to occur in the real world. If this becomes an application-specific concern, a pair of filters similar to that in Figure 11 will provide the required HF bypassing. The capacitors would be connected to the MIC2590A's -12V output pins, and the ferrite beads would be placed between the -12V output pins and the loads. -12V Input Clamp Diode The -12V input to the MIC2590A is the most negative potential on the part, and is therefore connected to the chip's substrate (as described in "Power Supply Decoupling," above). Although no particular sequencing of the -12V supply relative to the other MIC2590A supplies is required for normal operation, this substrate connection does mean that the -12V input must never exceed the voltage on the GROUND pin of the IC by more than 0.3 volts. In some systems, even though the -12V supply will discharge towards ground potential when it is turned OFF, the possibility exists that power supply output ringing or L(di/dt) effects in the wiring and on the PCB itself will cause brief transient voltages in excess of +0.3V to appear at the -12V input. The simplest way to deal MIC2590A GATE RGATE 47 External MOSFET CGATE Figure 12. Proper Connection of CGATE and RGATE MIC2590A 22 March 2002 MIC2590A Micrel Package Information 48-Pin TQFP (BTQ) March 2002 23 MIC2590A MIC2590A Micrel MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB USA http://www.micrel.com This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc. (c) 2002 Micrel Incorporated MIC2590A 24 March 2002