LTC1421

FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ LTC4223-1/LTC4223-2 Dual Supply Hot Swap Controller for Advanced Mezzanine Card DESCRIPTION The LTC®4223 positive voltage Hot SwapTM controller allows a board to be safely inserted and removed from a live AMC or MicroTCA backplane. It controls the main 12V supply with an external N-channel MOSFET and the 3.3V auxiliary supply with an integrated switch. The 12V output ramp rate is adjustable and includes inrush current limiting. The 12V output is also protected against short circuit faults with a fast acting current limit and a 5% accurate timed circuit breaker. The 3.3V output includes both soft start and overcurrent protection. The LTC4223 features a current monitor output for the 12V supply, and reports fault and power-good status for both supplies. It also detects card presence and allows independent control of the 12V and auxiliary 3.3V supply outputs. The LTC4223-1 features a latch-off circuit breaker, while the LTC4223-2 provides automatic retry after a fault. , LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Allows Safe Insertion into Live AMC or MicroTCA Backplane Controls 12V Main and 3.3V Auxiliary Supplies Limits Peak Fault Current in ≤1μs Adjustable Current Limit with Circuit Breaker Integrated 0.3Ω AUX Switch High Side Current Sense Gate Drive for External N-Channel MOSFET Adjustable Response Time for Overcurrent Protection Adjustable Supply Voltage Power-Up Rate Thermal Shutdown Protection LTC4223-1: Latch Off After Fault LTC4223-2: Automatic Retry After Fault 16-Lead SSOP and 5mm × 4mm DFN Packages APPLICATIONS ■ ■ ■ Advanced Mezzanine Card, MicroTCA Systems Workstations and Server I/O Telecom Networks TYPICAL APPLICATION Advanced Mezzanine Card Application 6mΩ 12V Si7336ADP 12V 7.4A 15nF Normal Power-Up Waveform EN 5V/DIV AUXOUT 5V/DIV 10Ω 47Ω 12VIN 12VSENSE 12VGATE 12VOUT 3.3V 150mA 12VOUT 5V/DIV AUXPGOOD 5V/DIV 12PGOOD 5V/DIV 3.3V 51Ω AUXIN AUXOUT VCC 330nF AUXON 12ON AUXPGOOD 12PGOOD FAULT IPMC ADC 12IMON GND TIMER 0.1μF 422312 TA01a LTC4223-1/LTC4223-2 20ms/DIV 422312 TA01b EN CARRIER MODULE CONNECTOR CONNECTOR 422312f 1 LTC4223-1/LTC4223-2 ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltages 12VIN ..................................................... –0.3V to 20V AUXIN .................................................... –0.3V to 10V VCC........................................................... –0.3V to 7V Input Voltages 12ON, AUXON, ⎯E⎯N ................................... –0.3V to 7V TIMER..........................................–0.3V to VCC + 0.3V 12VSENSE ............................................... –0.3V to 20V Output Voltages ⎯F⎯A⎯U⎯L⎯T, ⎯1⎯2⎯P⎯G⎯O⎯O⎯D, ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D, 12IMON ................................................... –0.3V to 7V 12VGATE ................................................. –0.3V to 25V 12VOUT - 12VGATE (Note 3) ................... –4.5V to 0.3V AUXOUT................................................. –0.3V to 10V Operating Temperature Range LTC4223-1C/ LTC4223-2C ....................... 0°C to 70°C LTC4223-1I/ LTC4223-2I ..................... –40°C to 85°C Storage Temperature Range GN Package ....................................... –65°C to 150°C DHD Package ..................................... –65°C to 125°C Lead Temperature (Soldering, 10sec) GN Package ...................................................... 300°C PIN CONFIGURATION TOP VIEW TOP VIEW 12VSENSE 12VIN 12IMON 12ON AUXIN VCC AUXON GND 1 2 3 4 5 6 7 8 16 12VGATE 15 12VOUT 14 12PGOOD 13 FAULT 12 AUXOUT 11 AUXPGOOD 10 EN 9 TIMER DHD PACKAGE 16-LEAD (5mm × 4mm) PLASTIC DFN 12VSENSE 12VIN 12IMON 12ON AUXIN VCC AUXON GND 1 2 3 4 5 6 7 8 17 16 12VGATE 15 12VOUT 14 12PGOOD 13 FAULT 12 AUXOUT 11 AUXPGOOD 10 EN 9 TIMER GN PACKAGE 16-LEAD PLASTIC SSOP TJMAX = 125°C, θJA = 110°C/W EXPOSED PAD (PIN 17) PCB GND CONNECTION OPTIONAL MUST BE SOLDERED TO PCB TO OBTAIN θJA = 43°C/W, OTHERWISE θJA = 140°C/W, TJMAX = 125°C ORDER INFORMATION LEAD FREE FINISH LTC4223CDHD-1#PBF LTC4223CDHD-2#PBF LTC4223IDHD-1#PBF LTC4223IDHD-2#PBF LTC4223CGN-1#PBF LTC4223CGN-2#PBF LTC4223IGN-1#PBF LTC4223IGN-2#PBF TAPE AND REEL LTC4223CDHD-1#TRPBF LTC4223CDHD-2#TRPBF LTC4223IDHD-1#TRPBF LTC4223IDHD-2#TRPBF LTC4223CGN-1#TRPBF LTC4223CGN-2#TRPBF LTC4223IGN-1#TRPBF LTC4223IGN-2#TRPBF PART MARKING* 42231 42232 42231 42232 42231 42232 4223I1 4223I2 PACKAGE DESCRIPTION 16-Lead (5mm × 4mm) Plastic DFN 16-Lead (5mm × 4mm) Plastic DFN 16-Lead (5mm × 4mm) Plastic DFN 16-Lead (5mm × 4mm) Plastic DFN 16-Lead Plastic SSOP 16-Lead Plastic SSOP 16-Lead Plastic SSOP 16-Lead Plastic SSOP TEMPERATURE RANGE 0°C to 70°C 0°C to 70°C –40°C to 85°C –40°C to 85°C 0°C to 70°C 0°C to 70°C –40°C to 85°C –40°C to 85°C Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ 422312f 2 LTC4223-1/LTC4223-2 ELECTRICAL CHARACTERISTICS SYMBOL Supplies VDD Input Supply Range VCC AUXIN 12VIN VCC AUXIN 12VIN VCC Rising VAUXIN Rising V12VIN Rising VCC AUXIN 12VIN ● ● ● ● ● ● ● ● ● ● ● ● The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C, VCC = 3.3V, VAUXIN = 3.3V, V12VIN =12V, unless otherwise specified. (Note 2) PARAMETER CONDITIONS MIN 2.7 2.7 10 0.8 0.4 0.6 2.3 2.4 9.4 40 70 70 2.45 2.5 9.7 110 110 110 TYP MAX 6 6 14 2 1 1 2.6 2.6 10 180 150 150 UNITS V V V mA mA mA V V V mV mV mV IDD Input Supply Current VDD(UVLO) Input Supply Undervoltage Lockout ΔVDD(UVLO, HYST) Current Limit ΔVSENSE(CB) ΔVSENSE(ACL) IAUX(ACL) RDS(ON) Gate Drive ΔVGATE IGATE(UP) IGATE(DN) IGATE(FPD) Current Sense G12IMON V12IMON ΔVSENSE(MAX) V12IMON(CLP) R12IMON V12IMON(MIN) VPG(TH) VPG(HYST) VTMR(TH) Input Supply Undervoltage Lockout Hysteresis Circuit Breaker Trip Sense Voltage, (V12VIN – V12VSENSE) Active Current Limit Sense Voltage, (V12VIN – V12VSENSE) AUXOUT Active Current Limit Switch Resistance (VAUXIN – VAUXOUT)/IAUXOUT External N-Channel Gate Drive (V12VGATE – V12VOUT) External N-Channel Gate Pull-Up Current External N-Channel Gate Pull-Down Current External N-Channel Gate Fast Pull-Down Current 12IMON Pin Gain Ratio ΔV12IMON/Δ(V12VIN – V12VSENSE) 12IMON Pin Output Voltage 12IMON Pin Maximum Input Sense Voltage 12IMON Pin Clamp Voltage 12IMON Pin Output Resistance 12IMON Pin Minimum Output Voltage Power Good Threshold Voltage Power Good Hysteresis TIMER Pin Threshold Voltage (V12VIN – V12VSENSE) = 150mV, VCC = 2.7V (V12VIN – V12VSENSE) = 0V (V12VIN – V12VSENSE) = 0V V12VOUT Falling VAUXOUT Falling V12VOUT VAUXOUT VTIMER Rising VTIMER Falling VAUXOUT = 0V IAUXOUT = 150mA (Note 4) ● ● ● 47.5 54 165 50 60 240 0.3 52.5 66 330 0.5 mV mV mA Ω Integrated Switch ● (Note 3) Gate Drive On, V12VGATE = 0V Gate Drive Off V12VGATE = 17V, V12VOUT = 12V Fast Turn Off V12VGATE = 17V, V12VOUT = 12V (V12VIN – V12VSENSE) = (75mV, 25mV) (V12VIN – V12VSENSE) = 75mV, VCC = 2.7V ● ● ● ● 4.5 –7 0.5 90 6.2 –10 1 160 7.9 –14 2 250 V μA mA mA ● ● ● ● ● ● 30 2.25 82.5 2.9 115 33 2.475 3.2 165 0 36 2.7 3.5 215 130 10.6 2.97 110 30 1.272 0.25 V/V V mV V kΩ mV V V mV mV V V Comparator Inputs ● ● ● ● ● ● 10 2.8 20 5 1.198 0.15 10.3 2.885 60 16 1.235 0.2 422312f 3 LTC4223-1/LTC4223-2 ELECTRICAL CHARACTERISTICS SYMBOL ITMR(UP) PARAMETER TIMER Pull-Up Current The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C, VCC = 3.3V, VAUXIN = 3.3V, V12VIN =12V, unless otherwise specified. (Note 2) CONDITIONS VTIMER = 1V, Initial Timing Cycle VTIMER = 0V, In AUX Fault Mode VTIMER = 0V, In 12V Fault Mode VTIMER = 2V, No Faults VTIMER = 2V, In Reset Mode IOL = 3mA (Note 5) VPU = 1.5V ● ● ● ● ● MIN –7 –7 –140 1.3 2 TYP –10 –10 –200 2 8 0.15 MAX –13 –13 –260 2.6 16 0.4 UNITS μA μA μA μA mA V V ITMR(DN) TIMER Pull-Down Current Open Drain Outputs VOL VOH IPU Logic Inputs VIN(TH) IIN(LEAK) RPU I12VSENSE I12VOUT ROUT(DIS) Logic Input Threshold (12ON, AUXON, ⎯E⎯N) Input Leakage Current (12ON, AUXON) ⎯E⎯N Pin Pull-Up Resistance 12VSENSE Pin Input Current 12VOUT Pin Input Current OUT Pin Discharge Resistance 12VOUT AUXOUT AUX Circuit Breaker Trip Delay Sense Voltage, (12VIN – 12VSENSE) High to 12VGATE Low AUXON High to AUXOUT High 12ON High to 12VGATE High Input Low (12ON, AUXON) to ⎯F⎯A⎯U⎯L⎯T High VCC Low to ⎯F⎯A⎯U⎯L⎯T High 12VIN Low to 12VGATE Low AUXIN Low to ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D High tPHL(GATE) tPLH(PG) tP(12IMON) ⎯EN High to 12VGATE Low ⎯ 12VOUT Low to ⎯1⎯2⎯P⎯G⎯O⎯O⎯D High AUXOUT Low to ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D High Input Sense Voltage Step to 12IMON Propagation Delay ΔVSENSE = 100mV V12VSENSE = 12V Gate Drive On, V12VOUT = 12V Gate Drive Off V12VOUT = 6V VAUXVOUT = 2V After Power Up ΔVSENSE = 300mV, C12VGATE = 10nF ΔVSENSE = 100mV, C12VGATE = 10nF VIN = VCC ● ● ● Output Low Voltage (⎯F⎯A⎯U⎯L⎯T, ⎯1⎯2⎯P⎯G⎯O⎯O⎯D, ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D) ⎯⎯⎯ ⎯⎯ ⎯⎯⎯⎯ ⎯ ⎯ ⎯ Output High Voltage (FAULT, 12PGOOD, ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D) ⎯⎯⎯ ⎯⎯ Output Pin Pull-Up Current (FAULT, ⎯1⎯2⎯P⎯G⎯O⎯O⎯D, ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D) ● ● ● VCC – 1 –6 –10 –14 μA 0.8 60 10 20 400 375 12 100 50 50 800 750 25 0.5 5 15 30 20 80 6 6 12 12 20 20 20 2 2 ±1 140 100 100 1600 1500 50 1 12 30 60 40 150 18 18 40 40 40 6 V μA kΩ μA μA Ω Ω μs μs μs μs μs μs μs μs μs μs μs μs μs Other Pin Functions ● ● ● ● Propagation Delays tCB tPHL(SENSE) tPHH(AUXON) tPHH(12ON) tRST(ON) tRST(VCC) tPLL(UVLO) ● ● ● ● ● ● ● ● ● ● ● ● ● Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All currents into device pins are positive; all currents out of the device pins are negative. All voltages are referenced to GND unless otherwise specified. Note 3: An internal clamp limits the 12VGATE pin to a minimum of 4.5V above 12VOUT. Driving this pin to voltages beyond the clamp may damage the device. Note 4: For the DFN package, the AUX switch on resistance, RDS(ON) limit is guaranteed by correlation to wafer test measurements. ⎯⎯⎯ ⎯⎯ ⎯⎯⎯⎯ ⎯ ⎯ ⎯ ⎯⎯⎯⎯⎯⎯⎯⎯ Note 5: The output pins FAULT, 12PGOOD and AUXPGOOD have an internal pull-up to VCC of 10μA. However, an external pull-up resistor may be used when faster rise time is required or for VOH voltages greater than VCC. 422312f 4 LTC4223-1/LTC4223-2 TYPICAL PERFORMANCE CHARACTERISTICS 3.3V, V12VIN =12V, unless otherwise specified. ICC vs VCC 1.6 1.0 Specifications are TA = 25°C, VCC = 3.3V, VAUXIN = 12IMON Gain Ratio vs Temperature 35 Supply Current vs Temperature SUPPLY CURRENT (mA) 1.2 ICC (mA) 12IMON GAIN RATIO (V/V) 75 100 0.8 VCC 12VIN AUXIN 34 0.6 0.8 33 0.4 0.4 32 0.2 0 2.5 3.0 3.5 4.0 4.5 VCC (V) 5.0 5.5 6.0 0 – 50 – 25 0 25 50 TEMPERATURE (°C) 31 –50 –25 0 25 50 TEMPERATURE (°C) 70 100 422312 G01 422312 G02 422312 G03 12IMON Output Voltage vs Sense Voltage 4 10.4 12VOUT POWER-GOOD THRESHOLD (V) 12VOUT Power-Good Threshold vs Temperature 2.92 AUXOUT POWER-GOOD THRESHOLD (V) AUXOUT Power-Good Threshold vs Temperature 12IMON OUTPUT VOLTAGE (V) 3 10.3 RISING FALLING 2.90 RISING FALLING 2.88 2 10.2 1 10.1 2.86 0 0 20 40 60 80 100 SENSE VOLTAGE (mV) 120 140 10.0 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 2.84 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 422312 G04 422312 G05 422312 G06 Circuit Breaker Trip Voltage vs Temperature ACTIVE CURRENT LIMIT SENSE VOLTAGE (mV) 52 CIRCUIT BREAKER TRIP VOLTAGE (mV) 62 Active Current Limit Sense Voltage vs Temperature 250 AUX ACTIVE CURRENT LIMIT (mA) –25 0 25 50 TEMPERATURE (°C) 75 100 AUX Active Current Limit vs Temperature 51 61 240 230 50 60 220 49 59 210 48 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 58 –50 200 – 50 – 25 0 25 50 TEMPERATURE (°C) 75 100 422312 G07 422312 G08 422312 G09 422312f 5 LTC4223-1/LTC4223-2 TYPICAL PERFORMANCE CHARACTERISTICS 3.3V, V12VIN =12V, unless otherwise specified. AUX Switch On Resistance vs Temperature 0.5 AUX SWITCH-ON RESISTANCE (Ω) 6.3 Specifications are TA = 25°C, VCC = 3.3V, VAUXIN = Gate Drive vs Temperature 7 6 Gate Drive vs IGATE 0.4 GATE DRIVE (ΔVGATE) (V) 6.2 GATE DRIVE (ΔVGATE) (V) 5 4 3 2 1 0.3 6.1 0.2 6.0 0.1 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 5.9 –50 0 –25 0 25 50 TEMPERATURE (°C) 75 100 0 –2 –4 –8 –6 IGATE (μA) –10 –12 422312 G10 422312 G11 422312 G12 Gate Pull-Up Current vs Temperature –11.0 AUX CIRCUIT BREAKER TRIP DELAY (µs) 30 AUX Circuit Breaker Trip Delay vs Temperature 100 ACTIVE CURRENT LIMIT DELAY (µs) – 25 0 25 50 TEMPERATURE (°C) 75 100 Active Current Limit Delay vs Sense Voltage GATE PULL-UP CURRENT (µA) –10.5 10 25 –10.0 1 20 –9.5 0.1 –9.0 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 15 – 50 0.01 50 100 150 200 250 SENSE VOLTAGE (mV) 300 422312 G13 422312 G14 422312 G15 Gate Fast Pull-Down Current vs Temperature 250 GATE FAST PULL-DOWN CURRENT (mA) OUTPUT DISCHARGE RESISTANCE (Ω) 1200 Output Discharge Resistance vs Temperature 3.0 2.5 Logic Input Threshold vs VCC 200 1000 12VOUT 800 AUXOUT 600 LOGIC INPUT THRESHOLD (V) HIGH 2.0 LOW 1.5 1.0 0.5 0 2.5 150 100 400 50 –50 –25 0 25 50 TEMPERATURE (°C) 75 100 200 – 50 – 25 0 25 50 TEMPERATURE (°C) 75 100 3.0 3.5 4.0 4.5 VCC (V) 5.0 5.5 6.0 422312 G16 422312 G17 422312 G18 422312f 6 LTC4223-1/LTC4223-2 PIN FUNCTIONS 12VSENSE (Pin 1): 12V Current Sense Input. Connect this pin to the output of the current sense resistor. The electronic circuit breaker trips if the voltage across the sense resistor exceeds 50mV for more than a fault filter delay. 12VIN (Pin 2): 12V Supply Input. Undervoltage lockout disables the 12V supply until the input at 12VIN exceeds 9.7V. 12IMON (Pin 3): 12V Current Sense Monitoring Output. This pin monitors the sense voltage between 12VIN and 12VSENSE. The gain ratio between this pin’s voltage and the sense voltage is 33. 12ON (Pin 4): 12V Supply On Control Digital Input. A rising edge turns on the external N-channel MOSFET if ⎯E⎯N is pulled low and a falling edge turns it off. A high-to-low transition on this pin will clear the 12V supply faults. AUXIN (Pin 5): Auxiliary Supply Input. An internal 0.3Ω switch is connected between AUXIN and AUXOUT pins. Undervoltage lockout holds the switch off until the input at AUXIN exceeds 2.5V. VCC (Pin 6): Bias Supply Input. This pin provides power to the device’s internal circuitry and operates from 2.7V to 6V. Undervoltage lockout circuit disables the device until the input at VCC exceeds 2.45V. Bypass with 330nF. AUXON (Pin 7): Auxiliary Supply On Control Digital Input. A rising edge turns on the internal switch if ⎯E⎯N is pulled low and a falling edge turns it off. A high-to-low transition on both this pin and 12ON pin will clear the auxiliary supply faults. GND (Pin 8): Device Ground. TIMER (Pin 9): Timer Capacitor Terminal. Connect a capacitor between this pin and ground to set a 741ms/μF duration for initial timing cycle, 123ms/μF for AUX current limit during power-up and 6ms/μF duration for 12V current limit before the external MOSFET is turned off. ⎯E⎯N (Pin 10): Enable Input Intended for Card Presence Detect. Ground this pin to enable the external N-channel MOSFET and internal switch to turn on. If this pin is pulled high, the switches are not allowed to turn on. An internal 100k resistor pulls up this pin. A high-to-low transition will clear faults. ⎯AU⎯X⎯P⎯G⎯O⎯O⎯D (Pin 11): Auxiliary Supply Power Status ⎯ Output. Open drain output that is normally pulled high by an internal 10μA current source or an external pull-up resistor to VCC. It pulls low when the AUXOUT pin voltage exceeds the power-good threshold of 2.901V. AUXOUT (Pin 12): Auxiliary Supply Output. This pin is the output from the internal switch connected between AUXIN and AUXOUT pins. It signals ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D low when it exceeds 2.901V. A 750Ω active pull-down discharges AUXOUT to ground when the internal switch is turned off. ⎯F⎯A⎯U⎯L⎯T (Pin 13): Auxiliary and 12V Supply Fault Status Output. Open drain output that is normally pulled high by an internal 10μA current source or an external pull-up resistor to VCC. It pulls low when the circuit breaker is tripped due to an overcurrent fault on auxiliary or 12V supply. ⎯1⎯2⎯P⎯G⎯O⎯O⎯D (Pin 14): 12V Supply Power Status Output. Open drain output that is normally pulled high by an internal 10μA current source or an external pull-up resistor to VCC. It pulls low when the 12VOUT pin voltage exceeds the power-good threshold of 10.36V. 12VOUT (Pin 15): 12V Gate Drive Return and Power-Good Input. Connect this pin to the source of the external Nchannel MOSFET for gate drive return. This pin signals ⎯1⎯2⎯P⎯G⎯O⎯O⎯D low when it exceeds 10.36V. When the external MOSFET is turned off, 12VOUT is discharged to ground through a 800Ω active pull-down. 12VGATE (Pin 16): Gate Drive for 12V Supply External NChannel MOSFET. An internal 10μA current source charges the gate of the external N-channel MOSFET. An internal clamp limits the gate voltage to 6.2V above 12VOUT. A resistor and capacitor network from this pin to ground sets the turn-on rate and compensates the active current limit. During turn-off, a 1mA pull-down current discharges 12VGATE to ground. During short circuit or undervoltage lockout, a 160mA pull-down current between 12VGATE and 12VOUT is activated. Exposed Pad (Pin 17, DHD Package): Exposed pad may be left open or connected to device ground. 422312f 7 LTC4223-1/LTC4223-2 FUNCTIONAL DIAGRAM RIN 5k + – A1 10μA CHARGE PUMP 60mV ROUT 165k 12IMON 12VGATE 6.2V 1mA GATE DRIVER 12VOUT 12VIN 12VSENSE +– 50mV + – + – ACL +– ECB 12V PWRGD PG2 12V SUPPLY CONTROL 12ON 12V FET ON VCC 10μA + – 10.3V 12PGOOD VCC R2 EN CARD PRESENCE VCC 12VIN 9.7V VCC 2.45V VCC 200μA VCC 10μA AUXIN 2.5V 0.2V + – + – + – + – + – UVLO3 10μA FAULT UVLO2 12V FAULT SYSTEM CONTROL UVLO1 CP2 AUX FAULT TIMER CP1 VCC 10μA AUXPGOOD 1.235V 2μA AUXON AUX FET ON GND AUX SUPPLY CONTROL AUX PWRGD THERMAL SHUTDOWN PG1 + – 2.885V CHARGE PUMP AUXIN RSNS MFET 422312 FD 10μA AUXOUT 422312f 8 LTC4223-1/LTC4223-2 OPERATION The LTC4223 is designed to control the power on an Advanced Mezzanine Card (AMC) or MicroTCA backplane, allowing boards to be safely inserted and removed. It controls the 12V main and 3.3V auxiliary power through an external N-channel MOSFET and integrated pass transistor. These two supplies can be turned on and off independently by their respective ON control pins. If either AUXON or 12ON is pulled high, an initial timing cycle set by the TIMER capacitor value is initiated once all these conditions are met: input supplies out of undervoltage lockout; TIMER < 0.2V and ⎯E⎯N low. At the end of the initial timing cycle, if the AUXON pin is high, the internal pass transistor turns on. It enters into an active current limit loop if the inrush current charging the load capacitor exceeds 240mA. When the load is in current limit, a 10μA pull-up charges the TIMER pin capacitor. If the load capacitor is fully charged and the switch is no longer in current limit before the TIMER reaches 1.235V, ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D pulls low indicating that power is good. Otherwise the internal switch turns off and ⎯F⎯A⎯U⎯L⎯T pulls low when TIMER reaches 1.235V. If 12ON pin is high at the end of the initial timing cycle, an internal charge pump charges the gate of the external MOSFET with 10μA pull-up. Connecting an external gate capacitor limits the inrush current charging the load capacitor. If the inrush current exceeds its limited current value, an internal analog current limit (ACL) amplifier servos the gate to force 60mV across the external sense resistor connected between 12VIN and 12VSENSE pins. During this period, TIMER pin capacitor is charged by a 200μA pull-up. If the load is fully charged and no longer in current limit before the TIMER reaches 1.235V, ⎯1⎯2⎯P⎯G⎯O⎯O⎯D pulls low. Otherwise 12V shuts off and ⎯F⎯A⎯U⎯L⎯T pulls low when TIMER reaches 1.235V. If an overcurrent fault occurs on the auxiliary supply after power-up, the current is limited to 240mA and after a 25μs delay, the circuit breaker trips and ⎯F⎯A⎯U⎯L⎯T pulls low. Thermal shutdown protects the internal pass transistor from overheating by shutting it off at 150°C. If an overcurrent fault occurs on the 12V supply, the current is limited to 60mV/RSENSE. After a timing cycle delay set by 200μA charging the TIMER capacitor, the circuit breaker trips and ⎯F⎯A⎯U⎯L⎯T pulls low. An overcurrent fault on the auxiliary supply shuts off 12V; a fault on the 12V supply does not affect the auxiliary supply. The LTC4223 provides high side current sensing information for the 12V supply at the 12IMON pin. The 12IMON output voltage is 33 times the sense voltage, allowing it to be used with an external ADC. In the off condition, 12VOUT and AUXOUT are discharged to ground by internal N-channel pull downs. 422312f 9 LTC4223-1/LTC4223-2 APPLICATIONS INFORMATION RS 6mΩ 12V BULK SUPPLY BYPASS CAPACITOR 2 5 R2 51Ω 12VIN AUXIN 1 R3 10Ω 16 15 12 MP 3.3V 150mA CG RG 15nF 47Ω Q1 Si7336ADP CARRIER AMC MODULE AMC CONNECTOR CONNECTOR PWR 12V 7.4A 12VSENSE 12VGATE 12VOUT AUXOUT 3.3V BULK SUPPLY BYPASS CAPACITOR MP ENABLE PWR ENABLE 3.3V 3.3V 3.3V R4* 10k 6 C2 330nF 7 4 VCC AUXON 12ON LTC4223-1 MP GOOD PWR GOOD FAULT R6* 10k R5* 10k 11 14 13 AUXPGOOD 12PGOOD FAULT 3.3V INTELLIGENT PLATFORM MANAGEMENT CONTROLLER 3 7 6 1 3.3V 2.2k PRESENCE CLK 1μF 5 VREF 8 VCC +IN 2 3 12IMON EN 10 PS1 PS0 DOUT LTC1197L CS GND 4 –IN 3 GND 8 9 TIMER CT 0.1μF 422312 F01 3.3V 10k RESET *OPTIONAL ENABLE Figure 1. Advanced Mezzanine Card/MicroTCA Application The typical LTC4223 application is in a Carrier board for Advanced Mezzanine Cards (AMC), delivering 3.3V auxiliary and 12V power to the AMC module. A controller on the Carrier board sequences the turn-on of power supplies and manages the fault and power-good reports from the LTC4223. The LTC4223 detects board presence during insertion and extraction, allowing power to be delivered in a controlled manner without damaging the connector. The typical LTC4223 application circuit is shown in Figure 1. External component selection is discussed in detail in the Design Example section. Turn-On Sequence The power supplies delivered to an AMC module are controlled by the external N-channel pass transistor, Q1 in the 12V power path and an internal pass transistor in the 3.3V auxiliary power path. Sense resistor RS monitors the 12V load current for fault detection and current sensing information. GATE capacitor CG provides gate slew rate control to limit the inrush current. Resistor RG with CG compensates the current control loop while R3 prevents parasitic oscillations in Q1. 422312f 10 LTC4223-1/LTC4223-2 APPLICATIONS INFORMATION Several conditions must be met before the external and internal switches are allowed to turn on. First VCC and the input supplies (12VIN, AUXIN) must exceed their undervoltage lockout thresholds. Next TIMER must be UVLO AUXON and 12ON Low, ⎯E⎯N High-to-Low, UVLO on VCC ⎯⎯ 12ON Low, EN High-toLow, UVLO on VCC AUXON and 12ON Low, ⎯E⎯N High-to-Low, UVLO on VCC, Temperature < 120°C CLEARED BY No Effect Turns Off Turns Off Turns Off 20ms/DIV 422312 F02 Figure 2. Normal Power-Up Sequence 422312f 11 LTC4223-1/LTC4223-2 APPLICATIONS INFORMATION Turn-Off Sequence The switches can be turned off by various conditions and this is summarized in Table 1. When the 12ON pin goes low, the external switch is turned off with the GATE pin pulled to ground by 1mA current sink. The ⎯1⎯2⎯P⎯G⎯O⎯O⎯D pin pulls high indicating that power is no longer good, while an internal N-channel transistor discharges the output to ground. Similarly, when the AUXON pin goes low, the internal switch is turned off, ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D pulls high while its output is discharged to ground through an internal N-channel transistor. Figure 3 shows the two supplies being turned off by ⎯E⎯N going high. Card Presence Detect In an AMC system, ⎯P⎯S⎯1 and ⎯P⎯S⎯0 signals are used to detect the presence of a card upon insertion or removal. Normally ⎯P⎯S⎯1 is connected to the ⎯E⎯N pin with a pull-up resistor. If AUXON or 12ON is high when the ⎯E⎯N pin goes low, indicating a board insertion, a timing cycle for contact debouncing is initiated. Upon insertion, any bounces on the ⎯E⎯N pin will re-start the timing cycle. When TIMER finally reaches its threshold during ramp up, the fault latches will be cleared. If the ⎯E⎯N pin remains low at the end of the timing cycle, the switches are allowed to turn on. If the ⎯E⎯N pin is toggled from low to high, indicating board removal, all the switches will be turned off after a 20μs delay. Any latched faults will not be cleared. However, removing the card could cause the ⎯E⎯N pin voltage to bounce, clearing the fault latches undesirably. This is prevented by blanking EN 5V/DIV AUXOUT 5V/DIV the bounces internally with a TIMER ramp up period given by CT • 123[ms/μF] as shown in Figure 4. Timer Functions An external capacitor CT connected from the TIMER pin to ground is used to perform several functions. 1. Ignore contact debouncing during card insertion when the device is enabled. The debounce cycle is given by ramping up CT with 10μA current to TIMER high threshold (1.235V) and then ramping down with 2μA current to below TIMER low threshold (0.2V). This gives an average debounce cycle time of CT • 741[ms/μF]. After that, if any ON pin is pulled high and ⎯E⎯N pin is low, the switches can be turned on. 2. Blanking contact bounce on the ⎯E⎯N pin that might trigger unwanted fault clearing during card removal. The blanking time is given by CT • 123[ms/μF]. 3. Fault filtering during auxiliary supply power-up in analog current limit. TIMER pulls up with 10μA and pulls down with 2μA. The filter time is given by CT • 123[ms/μF]. 4. 12V supply fault filtering during and after power-up in analog current limit. TIMER pulls up with 200μA and pulls down with 2μA. The filter time is given by CT • 6[ms/μF]. 5. For cooling off during an auto-retry cycle after an overcurrent fault on auxiliary or 12V supply (LTC4223-2). The cool-off time is given by CT • 1482 [ms/μF] after an auxiliary supply fault and CT • 1358[ms/ μF] after a 12V supply fault. EN 2V/DIV 12VOUT 5V/DIV AUXPGOOD 5V/DIV 12PGOOD 5V/DIV TIMER 1V/DIV FAULT 2V/DIV 100ms/DIV 422312 F03 5ms/DIV 422312 F04 Figure 3. Normal Power-Down Sequence Figure 4. Debouncing by TIMER during Card Removal 422312f 12 LTC4223-1/LTC4223-2 APPLICATIONS INFORMATION As the TIMER capacitor is used for fault filtering during power-up for both the auxiliary and 12V supplies, only one supply can be started up at any one time. The other supply waits until the power-good signal is generated by the powering-up supply and the TIMER pin voltage falls below 0.2V. By default, the 3.3V auxiliary supply starts up first if both AUXON and 12ON are high at the end of the debounce cycle. Whenever both AUXON and 12ON are pulled low, the device is in reset mode and TIMER capacitor is discharged to ground by an 8mA current sink. Thermal Shutdown The internal 3.3V auxiliary supply switch is protected by thermal shutdown. If the switch’s temperature reaches 150°C, the aux switch will shut off immediately and ⎯F⎯A⎯U⎯L⎯T will pull low. The external 12V supply switch also turns off. The switches are allowed to turn on again by cycling both the AUXON and 12ON pins low then high after the internal switch’s temperature falls below 120°C. Overcurrent Fault The LTC4223 features an adjustable current limit with circuit breaker function that protects the external MOSFET against FAULT 5V/DIV ILOAD 5A/DIV 12VOUT 5V/DIV short circuits or excessive load current on 12V supply. The voltage across the external sense resistor is monitored by the analog current limit (ACL) amplifier and the electronic circuit breaker (ECB) comparator. If an overcurrent fault occurs that causes the sense voltage to reach the ACL threshold (60mV), the ACL amplifier regulates the MOSFET to prevent any further increase in current. This overcurrent condition results in a sense voltage that exceeds the ECB threshold. As a result, the TIMER capacitor is charged by a 200μA current. If the condition persists, the TIMER pin voltage will reach its threshold (1.235V). When this occurs, the ⎯F⎯A⎯U⎯L⎯T pin pulls low and a 1mA current pulls the GATE pin to ground causing the MOSFET to turn off. The circuit breaker time delay, the time required for the TIMER pin capacitor to charge from ground to the TIMER pin threshold, is given by CT • 6[ms/μF]. After the MOSFET turns off, the TIMER pin capacitor discharges with a 2μA pull-down current. For the auto-retry version (LTC4223-2), if the TIMER discharges to below 0.2V, a new start-up cycle will begin. The TIMER starts ramping up and clears faults when it exceeds 1.235V; thereafter it ramps down (see the section on Auto-Retry for details). Figure 5 shows an overcurrent fault on the 12V output. In the event of a severe short-circuit fault on 12V output as shown in Figure 6, the output current can surge to tens of amperes. The LTC4223 responds within a very short time to bring the current under control by pulling the MOSFET’s GATE-to-SOURCE pin voltage down to zero volts. Thereafter, the GATE of the MOSFET recovers rapidly due to the RG/CG compensation network and enters into active current limiting until the TIMER times out. Due to parasitic supply lead inductance, an input supply without any bypass capacitor will collapse during the high current surge and then spike upwards when the current is interrupted. An input supply transient protection network comprising of Z1, R1 and C1 shown in Figure 13 is recommended if there is no input capacitance. 12VGATE 5V/DIV 0.1ms/DIV 422312 F05 Figure 5. Overcurrent Fault on 12V Output 422312f 13 LTC4223-1/LTC4223-2 APPLICATIONS INFORMATION There are two different modes of fault time-out for the 3.3V auxiliary supply: adjustable delay through TIMER capacitor during power-up when ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D not asserted; fixed 25μs delay after power-up when ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D asserted low. Under the situation whereby AUXON toggles low then high for short duration after power-up while ⎯A⎯U⎯X⎯P⎯G⎯O⎯O⎯D still pulling low due to output load capacitor, 25μs fault time-out applies. When the auxiliary supply is powered up into an output short, the ACL amplifier will regulate the gate of the internal pass transistor to produce 240mA output current. At this time a 10μA pull-up current starts charging up the TIMER pin capacitor until it exceeds its threshold (1.235V). The internal pass transistor then turns off and ⎯F⎯A⎯U⎯L⎯T pulls low. Thereafter, the TIMER is discharged by a 2μA pull-down current. The fault filter delay is given by CT • 123[ms/μF]. After a successful power-up cycle, the ACL amplifier protects the auxiliary supply from overcurrent by pulling down the gate of the internal pass transistor rapidly as shown in Figure 7. Thereafter, the gate recovers and servos the output current to about 240mA for 25μs before pulling down to ground gently, turning the transistor off. At this time, ⎯F⎯A⎯U⎯L⎯T pulls low and the 12V external MOSFET is also turned off by the 1mA GATE pull-down current. Whenever the 3.3V auxiliary supply trips off due to an overcurrent fault, the 12V supply also shuts off. The auxiliary supply is, however, unaffected by faults on the 12V supply. In either case ⎯F⎯A⎯U⎯L⎯T latches low when the affected channels turn off, and ⎯F⎯A⎯U⎯L⎯T is cleared by toggling the ON pins. Faults are cleared automatically in the LTC4223-2 auto-retry version. If there is significant supply lead inductance, a severe output short may collapse the input to ground before the LTC4223 can bring the current under control. In this case the undervoltage lockout will activate after a 12μs filter delay, and pull the gate down. Then the ACL amplifier will take control and regulate the output in active current limit. Under this situation, the fault time-out is set by TIMER delay instead of 25μs filter delay. Undervoltage Fault An undervoltage fault occurs if either AUXIN or 12VIN falls below its undervoltage threshold for longer than 12μs. This turns off the affected supply’s switch instantly, but does not clear the fault latches. Further, an undervoltage fault on one supply does not affect the operation of the other supply. If the bias supply input, VCC falls below its UVLO threshold for more than 80μs, all supply switches are turned off and the fault latches are cleared. Operation resumes from a fresh start-up cycle when VCC is restored. FAULT 5V/DIV ΔVSENSE 200mV/DIV 12VOUT 5V/DIV ILOAD 1A/DIV 12VGATE 5V/DIV AUXOUT 5V/DIV 5μs/DIV 422312 F06 5μs/DIV 422312 F07 Figure 6. Short-Circuit Fault on 12V Output Figure 7. Short-Circuit Fault on 3.3VAUX Output 422312f 14 LTC4223-1/LTC4223-2 APPLICATIONS INFORMATION Power-Good Monitor Internal circuitry monitors the output voltages, AUXOUT and 12VOUT. The power-good status is reported via their ⎯⎯⎯⎯⎯⎯⎯⎯ ⎯⎯⎯⎯⎯⎯⎯ respective open drain outputs, AUXPGOOD and 12PGOOD. Several conditions must be met before the power-good outputs assert low. 1. The monitored output should be above its powergood threshold and hysteresis. 2. The input supply is above undervoltage lockout. 3. ⎯E⎯N is low. 4. The associated ON pin is high. 5. Thermal shutdown is not activated. If any of the supply outputs falls below its power-good threshold for more than 20μs, the respective power-good output will be pulled high by the external pull-up resistor or internal 10μA pull-up. Resetting Faults (LTC4223-1) Any supply faults tripping the circuit breaker are latched and ⎯F⎯A⎯U⎯L⎯T asserts low. For the latched-off version (LTC4223-1), to reset a fault latch due to overcurrent or thermal shutdown on auxiliary supply, pull both AUXON and 12ON pins low together for at least 100μs, after which the ⎯FAULT will go high. Toggling both the ON pins high together ⎯⎯⎯⎯ again initiates the debounce timing cycle, thereafter the auxiliary supply starts up first followed by 12V supply. To skip the debounce timing cycle, first pull only AUXON low then high for at least 50μs before toggling 12ON low then high. The fault latch clears on the falling edge of 12ON and the auxiliary supply powers up. Thereafter, the 12V supply powers up if 12ON pulls high. To reset a fault on the 12V supply and re-start the output, toggle only the 12ON pin low and then high again. Toggling the ⎯E⎯N pin high then low again or bringing the bias input, VCC below its UVLO threshold for more than 100μs will initiate the debounce timing cycle and reset all fault latches before power-up. Bringing AUXIN or 12VIN below its undervoltage threshold will not reset the fault latches. For the auto-retry version (LTC4223-2), the latched fault will be cleared automatically after a cool-off timing cycle. Auto-Retry after a Fault (LTC4223-2) At time point 1 in Figure 8, if a fault latched-off the 3.3V auxiliary supply after power-up, a cool-off cycle begins. The TIMER capacitor charges up to 1.235V with a 10μA current and then discharges with a 2μA current to 0.2V at time point 3. This is followed by a debounce timing cycle whereby the fault latch is cleared, and ⎯F⎯A⎯U⎯L⎯T pulls high when TIMER reaches its threshold at time point 4. At the end of debounce cycle, the internal switch is allowed to turn on. If the output short persists, the auxiliary supply powers up into a short with active current limiting. At time point 7, the fault filter delay begins with TIMER ramping up with a 10μA current. If the TIMER times out at time point 8, ⎯F⎯A⎯U⎯L⎯T will be pulled low and a new cool-off cycle begins with TIMER ramping down with a 2μA current. The whole process repeats itself until the output-short is removed. In Figure 9, a fault latches off the 12V supply at time point 1; a cool-off cycle begins by discharging the TIMER capacitor with 2μA current from 1.235V to 0.2V threshold. At time point 2 a new debounce timing cycle is initiated where the fault latch is cleared, and ⎯F⎯A⎯U⎯L⎯T pulls high when TIMER reaches its threshold at time point 3. At the end of the debounce cycle, the 12V GATE is allowed to start up. If the output short persists, the 12V supply powers up into a short with active current limiting. At time point 6, the fault filter delay begins with TIMER ramping up with a 200μA current. The TIMER times out at time point 7, ⎯F⎯A⎯U⎯L⎯T pulls low and a new cool-off cycle begins with TIMER ramping down with a 2μA current. The whole process repeats itself until the output-short is removed. The auto-retry duty cycle is given by: DutyCycle = tFILTER • 100% tCOOL + tDEBOUNCE + tFILTER For example, if TIMER capacitor, CT = 0.1μF, the auto-retry duty cycle for auxiliary and 12V supply is 6.5% and 0.5% respectively. 422312f 15 LTC4223-1/LTC4223-2 APPLICATIONS INFORMATION GATE Pin Voltage The gate drive at 12VGATE is compatible with any logic level MOSFET. The guaranteed range of gate drive is 4.5V to 7.9V, with a typical of 6.2V. Active Current Loop Compensation The compensation network consisting of resistor RG and gate slew rate control capacitor CG stabilizes the internal active current limit circuit. The value of CG is selected based on the inrush current allowed. The suggested value for RG is 47Ω. The value of CG should be ≤330nF and RG is between 10Ω and 100Ω for optimum performance. High Side Current Sense The 12V load current is monitored via the voltage across an external sense resistor. The LTC4223 features a high side current sense amplifier that translates the sense voltage from the positive rail to the negative rail using a resistor ratio of 33 times. The output voltage at 12IMON pin can FAULT PULLS LOW DUE TO AUX OVERCURRENT FAULT AFTER POWER UP START OF COOL-OFF CYCLE START OF DEBOUNCE CYCLE RESET FAULT HIGH then be fed into an LTC1197L ADC as shown in Figure 10 for data conversion. The current sense information can be used by the system controller to manage the power budget allocated to the modules on the card. Full scale input to the current sense amplifier is 82.5mV, corresponding to an output of about 2.7V. If the input exceeds 100mV, the output clamps at 3.2V. VCC Supply Filtering The internal circuitry of the LTC4223 is powered from the VCC pin. Bypass VCC with at least 330nF to ground. If VCC is derived from the same supply as is AUXIN, include a decoupling resistor as shown in Figure 11. This RC network allows the VCC pin to ride out supply glitches caused by short circuits on the auxiliary output or on adjacent boards, thus preventing an undervoltage lockout condition on VCC. Since the absolute maximum rating for VCC is 7V as compared to 10V for AUXIN, select R2 and C2 to keep the peak voltage seen by VCC below 7V during any voltage spikes. START AUX INTERNAL GATE RAMP WHEN STARTUP CONDITIONS ARE MET AUX OUTPUT IN CURRENT LIMIT FAULT PULLS LOW AND RESTART OF COOL-OFF CYCLE DURING POWER UP RESTART OF DEBOUNCE CYCLE END OF DEBOUNCE CYCLE 1 2 3 4 567 8 9 10 FAULT 10μA TIMER VTMR 2μA 10μA VTMR 2μ A 10μA VTMR 2μA 10μA VTMR 2μA 10μA FILTER DELAY COOL-OFF CYCLE DEBOUNCE CYCLE COOL-OFF CYCLE AUX INTERNAL GATE REGULATES IAUXOUT 12VOUT 422312 F08 Figure 8. Auto-Retry after AUX Overcurrent Fault 422312f 16 LTC4223-1/LTC4223-2 APPLICATIONS INFORMATION FAULT PULLS LOW DUE TO 12V OVERCURRENT FAULT START OF COOL-OFF CYCLE START OF DEBOUNCE CYCLE RESET FAULT HIGH END OF DEBOUNCE CYCLE START 12V GATE RAMP WHEN STARTUP CONDITIONS ARE MET 12V OUTPUT IN CURRENT LIMIT FAULT PULLS LOW AND RESTART OF COOL-OFF CYCLE RESTART OF DEBOUNCE CYCLE 1 2 3 45 6 7 8 FAULT 200μA TIMER VTMR 2μA 10μA VTMR 2μA 200μA VTMR 2μA 10μA FILTER DELAY COOL-OFF CYCLE DEBOUNCE CYCLE COOL-OFF CYCLE 12VGATE REGULATES 12VGATE 60mV 60mV 12VIN - 12VSENSE 12VOUT 422312 F08 Figure 9. Auto-Retry after 12V Overcurrent Fault Supply Transient Protection The supply inputs, AUXIN and 12VIN are fed directly from the regulated output of the backplane supply, where bulk bypassing assures a spike-free operating environment. In other applications where the bulk bypassing is located far from the LTC4223, spikes generated during output short circuit events could exceed the absolute maximum ratings for AUXIN and 12VIN. To minimize such spikes, use wider traces or heavier trace plating to reduce the power trace inductance. Also, bypass locally with a 10μF electrolytic and 100nF ceramic, or alternatively clamp the input with a transient voltage suppressor (Z1, Z2) as shown in Figure 13. A 10Ω, 100nF snubber damps the response and eliminates ringing. A recommended layout of the 12V transient protection devices Z1, R1 and C1 around the LTC4223 is shown in Figure 12. ILOAD Q1 VSENSE –+ 12V 12VSENSE 12VIN RIN 5k 12VGATE LOAD + – 1μF 12IMON VOUT VREF LTC1197L –IN GND 422312 F10 3.3V +IN VCC CLK TO SYSTEM CONTROLLER ROUT 165k LTC4223 DOUT CS VOUT = ROUT RIN • VSENSE = 33 • VSENSE Figure 10. High Side Current Sense with LTC1197L ADC 422312f 17 LTC4223-1/LTC4223-2 APPLICATIONS INFORMATION R2 51Ω AUXIN C2 330nF VCC 12VIN W W 12VOUT CURRENT FLOW TO LOAD SENSE RESISTOR POWER PAK SO-8 CURRENT FLOW TO LOAD 422312 F11 Figure 11. RC Network for VCC Filtering TRACK WIDTH W: 0.03" PER AMPERE ON 1OZ Cu FOIL R3 12VGATE RG CG • VIA TO GND PLANE PCB Layout Considerations For proper operation of the LTC4223’s circuit breaker, Kelvin-connection to the sense resistor is strongly recommended. The PCB layout should be balanced and symmetrical to minimize wiring errors. In addition, the PCB layout for the sense resistor and the power MOSFET should include good thermal management techniques for optimal device power dissipation. A recommended PCB layout for the 12V sense resistor and the power MOSFET is illustrated in Figure 12. In applications where load current exceeds 10A, wide PCB traces are recommended to minimize resistance and temperature rise. The suggested trace width for 1 oz copper foil is 0.03” for each ampere of DC current to keep PCB trace resistance, voltage drop and temperature rise to a minimum. Note that the sheet resistance of 1 oz copper foil is approximately 0.5mΩ/square, and voltage drops due to trace resistance add up quickly in high current applications. In most applications, it will be necessary to use platedthrough via to make circuit connections from component layers to power and ground layers internal to the PCB. For 1 oz copper foil plating, a general rule is 1A of DC current per via. Consult your PCB fabrication facility for design rules pertaining to other plating thicknesses. It is important to place the VCC bypass capacitor C2 as close as possible between VCC and GND. The transient voltage suppressors Z1 and Z2 are also placed between the supply inputs and ground using short wide traces. Design Example As a design example, consider the AMC Hot Swap application shown earlier in Figure 1 with the power supply requirements given in Table 2. Z1 R1 C1 1 LTC4223CGN* 2 16 15 8 CURRENT FLOW TO SOURCE VIA TO GND PLANE • GND W GND 422312 F12 *ADDITIONAL DETAILS OMITTED FOR CLARITY, DRAWING NOT TO SCALE! Figure 12. Recommended Layout for Power MOSFET, Sense Resistor and GATE Components on 12V Rail The first step is to select the appropriate value of RSENSE for the 12V supply. Calculating RSENSE value is based on the maximum load current and the lower limit for the circuit breaker threshold, ΔVSENSE(CB)(MIN). RSENSE = ΔVSENSE(CB)(MIN) ILOAD(MAX ) = 47.5mV = 6mΩ 7.4A If a 1% tolerance is assumed for the 6mΩ sense resistor, the minimum and maximum circuit breaker trip current is calculated as follows: Table 2. AMC Power Supply Requirements SUPPLY VOLTAGE 12V 3.3VAUX MAXIMUM LOAD CURRENT 7.4A 150mA MAXIMUM LOAD CAPACITANCE 800μF 150μF Table 3. MicroTCA Power Supply Requirements SUPPLY VOLTAGE 12V 3.3VAUX MAXIMUM LOAD CURRENT 7.6A 150mA MAXIMUM LOAD CAPACITANCE 1600μF 150μF 422312f 18 LTC4223-1/LTC4223-2 APPLICATIONS INFORMATION ITRIP(MIN) = ITRIP(MAX ) = ΔVSENSE(CB)(MIN) RSENSE(MAX ) RSENSE(MIN) = 47.5mV = 7.8 A 6.06mΩ 52.5mV = 8.8 A 5.94mΩ CL1 • 12VOUT2 PAVG = 2 • tCHARGE The inrush current can be limited by using the GATE capacitance (CG) so that the power dissipated in the MOSFET is well within its safe operating area (SOA). For IGATE = 10μA and CL1 = 800μF, we choose CG = 15nF to set the inrush current to 0.5A. IINRUSH = CL1 • IGATE = 0.5A CG CL1 • 12VOUT = 19ms IINRUSH ΔVSENSE(CB)(MAX ) = For proper operation, ITRIP(MIN) must exceed the maximum load current with margin, so RSENSE = 6mΩ should suffice for the 12V supply. The second step is to determine the TIMER capacitance based on the time required to charge up completely the output load capacitor on auxiliary supply in active current limit without exceeding the fault filter delay. The worstcase start-up time is calculated using the minimum active current limit value for the auxiliary supply. tSTUP( AUX ) = CL2 • 3.3VAUX 150µF • 3.3V = 3ms = 165mA IAUX( ACL)(MIN) tCHARGE = For a start-up time of 3ms with a 2x safety margin, the TIMER capacitance is calculated as: CT = 2 • tSTUP( AUX ) 123[ms / µF ] = 6ms ≅ 0.05µF 123[ms / µF ] This results in PAVG = 3W and the MOSFET selected must be able to tolerate 3W for 19ms. The increase in steady state junction temperature due to power dissipated in the MOSFET is ΔT = PAVG • Zth where Zth is the thermal impedance. Under this condition, the Si7336ADP datasheet’s Transient Thermal Impedance plot indicates that the junction temperature will increase by 2.4°C using ZthJC = 0.8°C/W (single pulse). The duration and magnitude of the power pulse that results during a short-circuit condition on the 12V output are a function of the TIMER capacitance and LTC4223’s analog current limit. The short-circuit duration is given as 0.1μF • 6[ms/μF] = 600μs for CT = 0.1μF. The maximum shortcircuit current is calculated using the maximum analog current limit threshold, ΔVSENSE(ACL)(MAX) and minimum RSENSE value. ISHORT(MAX ) = ΔVSENSE( ACL)(MAX ) RSENSE(MIN) = 66mV = 11A 5.94mΩ Considering the tolerances for the TIMER charging rate and capacitance, a value of 0.1μF (±10%) for CT should suffice. Since the TIMER charging rate during fault time-out is 20 times faster for the 12V supply as compared to the auxiliary supply during start-up, this scheme ensures that the external MOSFET will not overheat under any outputshort condition. The fault filter delay for the 12V supply is given by 0.1μF • 6[ms/μF] = 600μs versus 12ms for the auxiliary supply. The next step is to verify that the thermal ratings of the selected external MOSFET for the 12V supply aren’t exceeded during power-up or an output-short. Assuming the MOSFET dissipates power only due to inrush current charging the load capacitor, the energy dissipated in the MOSFET during power-up is the same as that stored into the load capacitor. The average power dissipated in the MOSFET is given by: So the maximum power dissipated in the MOSFET is 11A • 12V or 132W for 600μs. The Si7336ADP datasheet’s Transient Thermal Impedance plot indicates that the worse-case increase in junction temperature during the short-circuit condition is 13.2°C using ZthJC = 0.1°C/W (single pulse). This will not cause the maximum junction temperature to be exceeded. The SOA curves of the Si7336ADP are also checked to be safe under this condition. 422312f 19 LTC4223-1/LTC4223-2 TYPICAL APPLICATION Card Resident Application with 5V Auxiliary Supply BACKPLANE CARD CONNECTOR CONNECTOR 12V Z1 SMAJ13A R1 10Ω C1 100nF 12VIN R3 10Ω CG RG 15nF 47Ω RS 4mΩ Q1 Si7336ADP 12V 10A + CL1 1000μF 12VSENSE 12VGATE 12VOUT 5V R6 Z2 10k SMAJ7.0A R7 2.7Ω C3 100nF R2 51Ω C2 330nF AUXIN AUXOUT 5VAUX 150mA + VCC CL2 150μF PWRFLT PWREN R8 10k BD_SEL FAULT 5V AUXON LTC4223-1 12ON EN AUXPGOOD 12PGOOD 5V R4 10k R5 10k 5V 1μF GND 12IMON +IN VCC LTC1197 TIMER CT 0.1μF GND –IN GND 422312 TA02 VREF CLK TO SYSTEM CONTROLLER DOUT CS 422312f 20 LTC4223-1/LTC4223-2 TYPICAL APPLICATION Card Resident Application with 12V Power Up First Followed by 3.3V Auxiliary BACKPLANE CARD CONNECTOR CONNECTOR 12V Z1 SMAJ13A R1 10Ω C1 100nF 12VIN R3 10Ω CG RG 15nF 47Ω RS 4mΩ Q1 Si7336ADP 12V 10A + CL1 1000μF 12VSENSE 12VGATE 12VOUT 3.3V Z2 SMAJ5.0A R7 2.7Ω C3 100nF R2 51Ω C2 330nF AUXIN AUXOUT 3.3VAUX 150mA + VCC CL2 150μF PWREN R8 10k 3.3V R9 10k 3.3V R5 10k 12ON 3.3V LTC4223-1 AUXON 3.3V R6 10k Q2 2N7002K 12PGOOD 3.3V FAULT EN 1μF VCC LTC1197L TIMER CT 0.1μF GND –IN GND 422312 TA03 R4 10k AUXPGOOD PWRFLT BD_SEL GND 12IMON +IN VREF CLK TO SYSTEM CONTROLLER DOUT CS 422312f 21 LTC4223-1/LTC4223-2 PACKAGE DESCRIPTION GN Package 16-Lead Plastic SSOP (Narrow .150 Inch) (Reference LTC DWG # 05-08-1641) .045 ± .005 .189 – .196* (4.801 – 4.978) 16 15 14 13 12 11 10 9 .009 (0.229) REF .254 MIN .150 – .165 .229 – .244 (5.817 – 6.198) .150 – .157** (3.810 – 3.988) .0165 ± .0015 .0250 BSC 1 .015 ± .004 × 45° (0.38 ± 0.10) .0532 – .0688 (1.35 – 1.75) 23 4 56 7 8 .004 – .0098 (0.102 – 0.249) RECOMMENDED SOLDER PAD LAYOUT .007 – .0098 (0.178 – 0.249) 0° – 8° TYP .016 – .050 (0.406 – 1.270) NOTE: 1. CONTROLLING DIMENSION: INCHES INCHES 2. DIMENSIONS ARE IN (MILLIMETERS) 3. DRAWING NOT TO SCALE *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE .008 – .012 (0.203 – 0.305) TYP .0250 (0.635) BSC GN16 (SSOP) 0204 422312f 22 LTC4223-1/LTC4223-2 PACKAGE DESCRIPTION DHD Package 16-Lead Plastic DFN (5mm × 4mm) (Reference LTC DWG # 05-08-1707) 0.70 ± 0.05 4.50 ± 0.05 3.10 ± 0.05 2.44 ± 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 4.34 ± 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 5.00 ± 0.10 (2 SIDES) R = 0.20 TYP R = 0.115 TYP 9 16 0.40 ± 0.10 4.00 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) 2.44 ± 0.10 (2 SIDES) PIN 1 NOTCH (DHD16) DFN 0504 8 0.200 REF 0.75 ± 0.05 4.34 ± 0.10 (2 SIDES) 1 0.25 ± 0.05 0.50 BSC 0.00 – 0.05 BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WJGD-2) IN JEDEC PACKAGE OUTLINE MO-229 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 422312f Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 23 LTC4223-1/LTC4223-2 TYPICAL APPLICATION 12V/18A Card Resident Application BACKPLANE CARD CONNECTOR CONNECTOR 12V Z1 SMAJ13A R1 10Ω C1 100nF 12VIN R3 10Ω CG RG 15nF 47Ω RS 2.5m Q1 HAT2160H 12V 18A + CL1 1000μF 12VSENSE 12VGATE 12VOUT 3.3V Z2 SMAJ5.0A R7 2.7Ω C3 100nF R2 51Ω C2 330nF R9 10k AUXIN AUXOUT 3.3VAUX 150mA + VCC CL2 150μF 3.3V AUXON R4 10k AUXPGOOD 12PGOOD FAULT 3..3V R5 10k R6 10k R8 10k BD_SEL LTC4223-1 12ON EN 1μF VCC LTC1197L TIMER CT 0.1μF GND –IN GND 422312 TA04 12IMON +IN VREF CLK TO CONTROLLER DOUT CS RELATED PARTS PART NUMBER LTC1421 LTC1645 DESCRIPTION Dual Channel, Hot Swap Controller Dual Channel, Hot Swap Controller COMMENTS Operates from 3V to 12V, Supports –12V, SSOP-24 Operates from 3V to 12V, Power Sequencing, SO-8 or SO14 Operates from 2.7V to 16.5V, SO-8 or SSOP-16 Operates from 2.7V to 16.5V, Active Current Limiting, SOT23-6 Operates from 2.7V to 16.5V, Multifunction Current Control, MSOP-8 or MSOP-10 Operates from 2.9V to 15V, I2C Compatible Monitoring, SSOP-16 or QFN-24 (4mm × 5mm) Operates from 0V to 6V, MSOP-10 or DFN-12 (4mm × 3mm) Operates from 1V to 13.5V, Multifunction Current Control, SSOP-16 3.3V, 5V, ±12V Supplies, I2C Compatible Monitoring, SSOP-36 or QFN-38 (5mm × 7mm) Fast Active Current Limiting with Drain Accelerated Response, Supplies from –15V, MSOP-8 or MSOP-10 LTC1647-1/LTC1647-2/ Dual Channel, Hot Swap Controller LTC1647-3 LTC4210 LTC4211 LTC4215 LTC4216 LTC4221 LTC4245 Single Channel, Hot Swap Controller Single Channel, Hot Swap Controller Single Channel, Hot Swap Controller Single Channel, Hot Swap Controller Dual Channel, Hot Swap Controller Multiple Channel, Hot Swap Controller LTC4252-1/LTC4252-2/ –48V Hot Swap Controller LTC4252A-1/ LTC4252A-2 422312f 24 Linear Technology Corporation (408) 432-1900 ● FAX: (408) 434-0507 ● LT 0807 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 www.linear.com © LINEAR TECHNOLOGY CORPORATION 2007