LTC1422C

LTC1422 Hot Swap Controller FEATURES s s s s s s s s s DESCRIPTIO Allows Safe Board Insertion and Removal from a Live Backplane System Reset Output with Programmable Delay Programmable Electronic Circuit Breaker User-Programmable Supply Voltage Power-Up Rate High Side Driver for an External N-Channel FET Controls Supply Voltages from 2.7V to 12V Undervoltage Lockout Soft Reset Input Glitch Filter on RESET The LTC®1422 is an 8-pin Hot SwapTM controller that allows a board to be safely inserted and removed from a live backplane. Using an external N-channel pass transistor, the board supply voltage can be ramped up at a programmable rate. A high side switch driver controls the N-channel gate for supply voltages ranging from 2.7V to 12V. A programmable electronic circuit breaker protects against shorts. The RESET output can be used to generate a system reset when the supply voltage falls below a programmable voltage. The ON pin can be used to cycle the board power or to generate a soft reset. The LTC1422 is available in 8-pin PDIP and SO packages. , LTC and LT are registered trademarks of Linear Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation. APPLICATIO S s s Hot Board Insertion Electronic Circuit Breaker TYPICAL APPLICATIO 5V Hot Swap Q1 R1 0.005Ω MTB50N06V VCC R2 10Ω 5% R3 6.81k 1% C1 0.1µF 5 R4 2.43k 1% VOUT 5V CLOAD + CONNECTOR 2 CONNECTOR 1 8 2 VCC ON 7 6 FB SENSE GATE ON/RESET LTC1422 RESET TIMER 3 GND C2 0.33µF 4 1 µP RESET GND BACKPLANE PLUG-IN CARD 1422 TA01 U U U 1 LTC1422 ABSOLUTE MAXIMUM RATINGS (Note 1) PACKAGE/ORDER I FOR ATIO TOP VIEW RESET 1 ON 2 TIMER 3 GND 4 N8 PACKAGE 8-LEAD PDIP 8 VCC 7 SENSE 6 GATE 5 FB S8 PACKAGE 8-LEAD PLASTIC SO Supply Voltage (VCC) ........................................... 13.2V Input Voltage (TIMER, SENSE) ... – 0.3V to (VCC + 0.3V) Input Voltage (FB, ON) ........................... – 0.3V to 13.2V Output Voltage (RESET) ........................ – 0.3V to 13.2V Output Voltage (GATE) ............................. – 0.3V to 20V Operating Temperature Range LTC1422C ............................................... 0°C to 70°C LTC1422I ........................................... – 40°C to 85°C Storage Temperature Range ................ – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................. 300°C ORDER PART NUMBER LTC1422CN8 LTC1422CS8 LTC1422IN8 LTC1422IS8 S8 PART MARKING 1422 1422I TJMAX = 150°C, θJA = 130°C/W (N) TJMAX = 150°C, θJA = 150°C/W (S) Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS SYMBOL ICC VLKO VLKH VFB ∆VFB VFBHST VTM ∆VTM VTMHST ITM VCB ICP ∆VGATE VONHI VONLO VONHYST VOL IPU tRST PARAMETER VCC Supply Current VCC Undervoltage Lockout VCC Undervoltage Lockout Hysteresis FB Pin Voltage Threshold FB Pin Threshold Line Regulation FB Pin Voltage Threshold Hysteresis TIMER Pin Voltage Threshold TIMER Pin Threshold Line Regulation TIMER Pin Voltage Threshold Hystersis TIMER Pin Current Circuit Breaker Trip Voltage GATE Pin Output Current External N-Channel Gate Drive ON Pin Threshold High ON Pin Threshold Low ON Pin Hysteresis Output Low Voltage Logic Output Pull-Up Current Soft Reset Time DC Characteristics The q denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V unless otherwise noted. CONDITIONS ON = VCC q q MIN TYP 0.65 MAX 1.00 2.55 1.244 2.5 1.256 15 – 1.5 64 –8 14 1.35 1.26 0.4 38 UNITS mA V mV V mV mV V mV mV µA mA mV µA mA V V V mV V µA µs 2.40 1.220 2.47 120 1.232 0.5 2.0 q 3V ≤ VCC ≤ 12V q q 1.208 1.232 2 45 3V ≤ VCC ≤ 12V Timer On, GND ≤ VTIMER ≤ 1.5V Timer Off, VTIMER = 1.5V VCB = (VCC – VSENSE) Charge Pump On, VGATE = GND Charge Pump Off, VGATE = VCC VGATE – VCC q q q q q q q – 2.5 44 – 12 10 1.25 1.20 – 2.0 10 50 – 10 10 12 1.30 1.23 80 0.14 – 12 RESET, IO = 3mA RESET = GND q q 22 30 Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. 2 U W U U WW W LTC1422 TYPICAL PERFORMANCE CHARACTERISTICS Supply Current vs Supply Voltage 1200 1000 SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) 800 600 400 200 TA = 25°C GATE VOLTAGE (V) 0 2 4 6 8 10 SUPPLY VOLTAGE (V) Gate Voltage vs Temperature 18.2 18.0 17.8 GATE CURRENT (µA) GATE VOLTAGE (V) 16 VCC = 5V IG = 0A GATE CURRENT (µA) 17.6 17.4 17.2 17.0 16.8 16.6 16.4 – 55 – 35 –15 4 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G04 Feedback Threshold Voltage vs Supply Voltage 1.2350 FEEDBACK THRESHOLD VOLTAGE (V) TA = 25°C FEEDBACK THRESHOLD VOLTAGE (V) 1.2345 1.2340 1.2335 1.2330 1.2325 1.2320 2 4 HIGH THRESHOLD GLITCH FILTER TIME (µs) LOW THRESHOLD 6 8 10 SUPPLY VOLTAGE (V) UW 12 12 Supply Current vs Temperature 775 VCC = 5V 750 725 700 675 650 625 600 5 20 15 10 25 30 Gate Voltage vs Supply Voltage TA = 25°C IG = 0A 575 14 1422 G01 550 – 55 – 35 –15 0 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G02 2 4 6 8 10 SUPPLY VOLTAGE (V) 12 14 1422 G03 Gate Current vs Supply Voltage TA = 25°C VG = 0V 10.4 10.2 10.0 Gate Current vs Temperature VCC = 5V VG = 0V 14 12 10 8 6 9.8 9.6 9.4 9.2 9.0 8.8 2 4 6 8 10 SUPPLY VOLTAGE (V) 12 14 1422 G05 8.6 – 55 – 35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G06 Feedback Threshold Voltage vs Temperature 1.237 1.236 HIGH THRESHOLD 1.235 1.234 1.233 LOW THRESHOLD 1.232 1.231 1.230 1.229 1.228 – 55 – 35 –15 Glitch Filter Time vs Feedback Transient 70 60 50 40 30 20 10 TA = 25°C 14 1422 G07 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G08 0 40 200 80 120 160 FEEDBACK TRANSIENT (mV) 240 1422 G09 3 LTC1422 TYPICAL PERFORMANCE CHARACTERISTICS TIMER Threshold Voltage vs Supply Voltage 1.244 TIMER THRESHOLD VOLTAGE (V) TA = 25°C TIMER THRESHOLD VOLTAGE (V) 1.242 1.240 1.238 1.236 1.234 1.232 2 4 6 8 10 SUPPLY VOLTAGE (V) 12 14 1422 G10 1.239 1.238 1.237 1.236 1.235 VCC = 5V TIMER CURRENT (µA) TIMER Current vs Temperature 2.45 ON PIN THRESHOLD VOLTAGE (V) 1.32 2.40 2.35 TIMER CURRENT (µA) VCC = 5V 1.30 HIGH THRESHOLD 1.28 1.26 1.24 ON PIN THRESHOLD VOLTAGE (V) 2.30 2.25 2.20 2.15 2.10 2.05 2.00 – 55 – 35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G13 Current Limit Threshold vs Temperature 85 VCC = 5V CURRENT LIMIT THRESHOLD (mV) 80 RESET PULL-UP CURRENT (µA) 75 70 65 60 55 50 45 40 – 55 – 35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G17 4 UW TIMER Threshold Voltage vs Temperature 1.242 1.241 1.240 VCC = 12V TIMER Current vs Supply Voltage 2.6 2.5 2.4 2.3 2.2 2.1 TA = 25°C VCC = 3V 1.234 1.233 – 55 – 35 –15 2.0 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G11 2 4 6 8 10 SUPPLY VOLTAGE (V) 12 14 1422 G12 ON Pin Threshold Voltage vs Supply Voltage TA = 25°C 1.38 1.36 1.34 1.32 1.30 1.28 1.26 1.24 1.22 ON Pin Threshold Voltage vs Temperature VCC = 5V INPUT HIGH LOW THRESHOLD 1.22 1.20 2 4 6 8 10 SUPPLY VOLTAGE (V) 12 14 1422 G14 INPUT LOW 1.20 – 55 – 35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G15 RESET Pull-Up Current vs Temperature 22 VCC = 5V 20 18 16 14 12 10 8 6 4 – 55 – 35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G18 LTC1422 TYPICAL PERFORMANCE CHARACTERISTICS RESET Voltage vs Temperature 0.24 0.22 0.20 VCC = 5V 3mA PULL-UP 55 50 0.18 0.16 0.14 0.12 0.10 0.08 0.06 – 55 – 35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G19 ON PIN PULSE TIME (µs) RESET VOLTAGE (V) PIN FUNCTIONS RESET (Pin 1) : Open drain output to GND with a 12µA pull-up to VCC. This pin is pulled low when the voltage at the FB (Pin 5) goes below the FB pin threshold. The RESET pin will go high one timing cycle after the voltage at the FB pin goes above the FB pin threshold. An external pull-up resistor can be used to speed up the rising edge on the RESET pin or pull the pin to a voltage higher or lower than VCC. ON (Pin 2): Analog Input Pin. The threshold is set at 1.30V with 80mV hysteresis. When the ON pin is pulled high, the timer turns on for one cycle, then the charge pump turns on. When the ON pin is pulled low longer than 40µs, the GATE pin will be pulled low and remain off until the ON pin is pulled high. If the ON pin is pulled low for less than 15µs a soft reset will occur. The charge pump remains on, and the RESET pin is pulled low for one timing cycle starting 30µs from the falling edge of the ON pin. The ON pin is also used to reset the electronic circuit breaker. If the ON pin is cycled low and high following the trip of the circuit breaker, the circuit breaker is reset and a normal power-up sequence will occur. TIMER (Pin 3): Analog system timing generator pin. This pin is used to set the delay before the charge pump turns on after the ON pin goes high. It also sets the delay before the RESET pin goes high, after the output supply voltage is good, as sensed by the FB pin. When the timer is off, an internal N-channel shorts the TIMER pin to ground. When the timer is turned on, a 2µA current from VCC is connected to the TIMER pin and the voltage starts to ramp up with a slope given by: dV/dt = 2µA/CTIMER. When the voltage reaches the trip point (1.232V), the timer will be reset by pulling the TIMER pin back to ground. The timer period is given by: (1.232V • CTIMER )/2µA. GND (Pin 4): Chip Ground. FB (Pin 5): Analog comparator input used to monitor the output supply voltage with an external resistive divider. When the voltage on the FB pin is lower than the 1.232V, the RESET pin will be pulled low. An internal filter helps prevent negative voltage glitches from triggering a reset. When the voltage on the FB pin rises above the trip point, the RESET pin will go high after one timing cycle. UW ON Pin Pulse (Soft Reset) Time vs Temperature 45 40 35 30 25 20 15 10 – 55 – 35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G20 VCC = 3V VCC = 5V VCC = 12V U U U 5 LTC1422 PIN FUNCTIONS GATE (Pin 6): The high side gate drive for the external N-Channel. An internal charge pump guarantees at least 10V of gate drive. The slope of the voltage rise or fall at the GATE is set by an external capacitor connected between GATE and GND, and the 10µA charge pump output current. When the circuit breaker trips, the undervoltage lockout circuit monitoring VCC trips, or the ON pin is pulled low for more than 40µs, the GATE pin is immediately pulled to GND. SENSE (Pin 7) : Circuit Breaker Set Pin. With a sense resistor placed in the supply path between VCC and SENSE, the circuit breaker will trip when the voltage across the resistor exceeds 50mV for more than 10µs. If the circuit breaker trip current is set to twice the normal operating current, only 25mV is dropped across the sense resistor during normal operation. To disable the circuit breaker, VCC and SENSE can be shorted together. VCC (Pin 8): The positive supply input, ranging from 2.7V to 13.2V for normal operation. ICC is typically 0.6mA. An undervoltage lockout circuit disables the chip until the voltage at VCC is greater than 2.47V. BLOCK DIAGRA COMP 3 ON 2 + COMP 1 REF 2.47V UVL 10µs FILTER – 1.232V REFERENCE LOGIC GLITCH FILTER COMP 2 5 REF 2µA TIMER 3 + COMP 4 REF 12µA 1 RESET – Q2 Q1 6 – + + – – + W U U U VCC 8 SENSE 7 GATE 6 50mV Q3 CHARGE PUMP FB 4 GND 1422 BD LTC1422 APPLICATIONS INFORMATION Hot Circuit Insertion When circuit boards are inserted into a live backplane, the supply bypass capacitors on the board can draw huge transient currents from the backplane power bus as they charge up. The transient currents can cause permanent damage to the connector pins and cause glitches on the system supply, causing other boards in the system to reset. The LTC1422 is designed to turn a board’s supply voltage on and off in a controlled manner, allowing the board to be safely inserted or removed from a live backplane. The chip also provides a system reset signal to indicate when board supply voltage drops below a programmable voltage. Power Supply Ramping The onboard power supply is controlled by placing an external N-channel pass transistor in the power path (Figure 1). R1 provides current fault detection and R2 prevents high frequency oscillation. By ramping up the gate of the pass transistor at a controlled rate, the transient surge current (I = C • dV/dt) drawn from the main backplane supply can be limited to a safe value when the board makes connection. R1 VCC R2 10Ω 8 2 VCC ON LTC1422 RESET TIMER 3 C2 1422F01 Q1 VOUT + CLOAD R3 C1 8 7 SENSE 6 GATE R3 R2 C1 7 6 FB 5 SENSE GATE 1 R4 ON 2 LOGIC COMP 2 GND 4 Figure 1. Supply Control Circuitry When power is first applied to the chip, the gate of the N-channel (Pin 6) is pulled low. After the ON pin is held high for at least one timing cycle, the charge pump is turned on. The voltage at GATE begins to rise with a slope U W U U VCC + 10V GATE SLOPE = 10µA/C1 VCC VOUT t1 t2 1422 F02 Figure 2. Supply Turn-On equal to 10µA/C1 (Figure 2), where C1 is the external capacitor connected between the GATE pin and GND. The ramp time for the supply is equal to: t = (VCC • C1)/ 10µA. After the ON pin has been pulled low for more than 40µs, the GATE is immediately pulled to GND. Voltage Monitor The LTC1422 uses a 1.232V bandgap reference, precision voltage comparator and a resistive divider to monitor the output supply voltage (Figure 3). R1 VCC Q1 VOUT CLOAD + LTC1422 VCC + – FB 5 R4 12µA TIMER 1.232V REFERENCE Q2 3 C2 4 1 µP RESET 1422 F03 Figure 3. Supply Monitor Block Diagram 7 LTC1422 APPLICATIONS INFORMATION 1 V2 VOUT 1.232V TIMER 1.232V TIMER 2 V1 V2 3 V1 V2 4 ON RESET 1422 F04 Figure 4. Supply Monitor Waveforms When the voltage at the FB pin rises above its reset threshold (1.232V), the comparator COMP 2 output goes high, and a timing cycle starts (Figure 4, time points 1 and 4). After a complete timing cycle, RESET is pulled high. The 12µA pull-up current source to VCC on RESET has a series diode so the pin can be pulled above VCC by an external pull-up resistor without forcing current back into supply. When the supply voltage at the FB pin drops below its reset threshold, the comparator Comp 2 output goes low. After passing through a glitch filter, RESET is pulled low (time point 2). If the FB pin rises above the reset threshold for less than a timing cycle, the RESET output will remain low (time point 3). Glitch Filter The LTC1422 has a glitch filter to prevent RESET from generating a system reset when there are transients on the FB pin. The filter is 20µs for large transients (greater than 150mV) and up to 80µs for small transients. The relationship between glitch filter time and the transient voltage is shown in Typical Performance curve: Glitch Filter Time vs Feedback Transient. Soft Reset In some cases a system reset is desired without a power down. The ON pin can signal the RESET pin to go low without turning off the external N-channel (a soft reset). This is accomplished by holding the ON pin low for only 15µs or less (Figure 5, time point 1). At about 30µs from the falling edge of the ON pin (time point 2) the RESET pin goes low and stays low for one timing cycle. 8 U W U U 1 30µs 2 3 30µs 4 5 6 15µs GATE VOUT RESET 20µs 1422 F05 Figure 5. Soft Reset Waveforms If the ON pin is held low for longer than 40µs, the gate will turn off and the RESET pin will eventually go low (time points 4, 5 and 6). Timer The system timing for the LTC1422 is generated by the circuitry shown in Figure 6. The timer is used to set the turn-on delay after the ON pin goes high and the delay before the RESET pin goes high after the output supply voltage is good as sensed by the FB pin. R1 VCC Q2 + R2 C1 8 7 SENSE 6 GATE 5 R4 COMP 4 SUPPLY MONITOR 1 R3 VOUT CLOAD LTC1422 ON 2 VCC LOGIC 2µA + 1.232V – Q1 RESET TIMER 3 C2 4 1422 F06 Figure 6. System Timing Block Diagram LTC1422 APPLICATIONS INFORMATION When the timer is off, the internal N-channel Q1 shorts the TIMER pin to ground. When the timer is turned on, a 2µA current from VCC is connected to the TIMER pin and the voltage on the external capacitor C2 starts to ramp up with a slope given by: dV/dt = 2µA/C2. When the voltage reaches the trip point (1.232V), the timer will be reset by pulling the TIMER pin back to ground. The timer period is given by: (1.232V • C2)/2µA. For a 200ms delay, use a 0.33µF capacitor. Electronic Circuit Breaker The LTC1422 features an electronic circuit breaker function that protects against short circuits or excessive currents on the supply. By placing a sense resistor between the supply input and SENSE pin, the circuit breaker will be tripped whenever the voltage across the sense resistor is greater than 50mV for more than 10µs. When the circuit breaker trips, the GATE pin is immediately pulled to ground and the external N-channel is quickly turned off. When the ON pin is cycled off for greater than 40µs and then on as shown in Figure 7, time point 7, the circuit breaker is reset and another timing cycle is started. At the end of the timer cycle (time point 8), the charge pump will turn on again. If the circuit breaker feature is not required, the SENSE pin should be shorted to VCC. If more than 10µs of response time is needed to reject supply noise, an external resistor and capacitor can be added to the sense circuit as shown in Figure 8. Connection Sense with ON Pin The ON pin can be used to sense board connection to the backplane as shown in Figure 9. Using staggered connection pins, ground mates first to discharge any static build up on the board, followed by the VCC connection and all other pins. When VCC makes connection, the bases of transistors Q3 and Q4 are pulled high turning them on and pulling the ON pin to ground. When the base connector pins of Q3 and Q4 finally mate to the backplane, the bases are shorted to ground. This turns off Q3 and Q4 and allows the ON pin to pull high and start a power-up cycle. The base connection pins of Q3 and Q4 should be located at opposite ends of the connector VOUT RESET 1422 F07 U W U U 12 VCC ON VCC – VSENSE TIMER 3 4 5 6 7 8 9 10 GATE Figure 7. Current Fault Timing R1 RF R2 8 VCC 7 SENSE LTC1422 1422 F08 Q1 CF 6 GATE C1 Figure 8. Extending the Short-Circuit Protection Delay because most people will rock the board back and forth to get it seated properly. A software-initiated power-down cycle can be started by momentarily turning on transistor Q2, which will pull the ON pin to ground. If the ON pin is held low for greater than 40µs, the GATE pin is pulled to ground. If the low pulse on the ON pin is less than 15µs, a soft reset is generated. Hot Swapping Two Supplies With two external pass transistors, the LTC1422 can switch two supplies. In some cases, it is necessary to bring up the dominant supply first during power-up and ramp it down last during the power-down phase. The circuit in Figure 10 shows how to program two different delays for the pass transistors. The 5V supply is powered up first. R1 9 LTC1422 APPLICATIONS INFORMATION R1 VCC Q1 CONNECTOR 2 CONNECTOR 1 10k 10k ON/RESET 5V OUT 3.3V OUT VIN 3.3V CURRENT LIMIT: 5A VIN 5V LTC1422 RESET ON 1 2 3 C1 0.33µF 16V 4 RESET ON TIMER GND VCC SENSE GATE FB 8 7 6 5 C3 0.047µF 25V R2 0.01Ω 5% Q1 1/2 Si9436 Figure 10. Switching 5V and 3.3V and C3 are used to set the rise and fall delays on the 5V supply. Next, the 3.3V supply ramps up with a 20ms delay set by R6 and C2. On the falling edge, the 3.3V supply ramps down first because R6 is bypassed by the diode D1. Using the LTC1422 as a Linear Regulator The LTC1422 can be used to Hot Swap the primary supply and generate a secondary low dropout regulated supply. Figure 11 shows how to switch a 5V supply and create a 3.3V supply using the reset comparator and one additional transistor. The FB pin is used to monitor the 3.3V output. When the voltage on the gate of Q2 increases, the 3.3V increases. At the 3.3V threshold, the reset comparator will trip. The RESET pin goes high which turns on Q3. This lowers the voltage on the gate of Q2. This feedback loop is compensated by the capacitor C1 and the resistors R6 and R7. 10 U Q4 W U U + R2 C1 R3 FB LOGIC 2 ON 5 R4 VOUT CLOAD 8 10k VCC 7 SENSE 6 GATE + COMP 5 REF – LTC1422 4 1 Q3 Q2 RESET TIMER 3 C2 1422 F09 Q2: 2N7002LT1 Q3, Q4: MMBT3904LT1 Figure 9. ON Pin Circuitry Q2 1/2 Si99436 + R7 10Ω 5% CLOAD VOUT 3.3V + R3 10Ω 5% R1 10k 5% D1 1N4148 R6 1M 5% CLOAD VOUT 5V R4 2.74k 1% TRIP POINT: 4.6V C2 0.022µF 25V R5 1k 1% 1422 F10 Hot Swapping 48V DC/DC Module with Active Low On/Off Control Signal Using a 7.5V Zener and a resistor, the LTC1422 can switch supplies much greater than the 12V VCC pin rating. As shown in Figure 12, the switching FET Q1 is connected as a common source driver rather than the usual source follower used in previous applications. This allows the ground of the LTC1422 to sit at the negative terminal of the 48V input. The clamp circuit of R5 and D1 provides power to the LTC1422. The resistive divider R1 and R2 at the ON pin monitors the input supply. The switching FET Q1 is prevented from turning on until the input supply is at least 38V. Using the reset comparator to monitor the gate voltage allows the module to be turned on after the gate has reached a minimum level plus one timing cycle. A high voltage transistor Q2 is used to translate the RESET signal to the module On/Off input. LTC1422 APPLICATIONS INFORMATION Since the pass transistor is in a common source configuration, care must be taken to limit the inrush current into capacitor C3. One way is to precharge C3 using resistor R4. As the input supply is ramping up, current is flowing through R4 and charging the capacitor C3. Once the input supply crosses 38V, there is a timing cycle followed by the ramp-up of the GATE pin. By this time the capacitor C3 is sufficiently charged, thereby limiting the inrush current. Another method to limit the inrush current is to slow down the ramp-up rate of the GATE pin. Hot Swapping 48V DC/DC Module with Active High On/Off Control Signal This application is identical to the previous except for the polarity of the module’s on/off signal. The polarity reversal is accomplished by transistor Q3 in Figure 13. Hot Swapping Redundant 48V In critical situations, redundant input supplies are necessary. In Figure 14 a redundant 48V input is switched to a power module. Supplies 1 and 2 are wire OR’ed using two diodes D2 and D3. This results in the most negative of these two supplies being used to drive the power module. If one of the supplies is disconnected or a fuse opens, the fault signal will be activated via diodes D4 and D5 and the reset comparator at the FB pin. The GATE IN signal on the Vicor module is controlled using the high voltage PNP Q2. Once the module’s minus input pin is more negative than the base of Q2 plus a diode drop, Q2 will turn off and the module will turn on. This occurs when the source of Q1 plus a Zener voltage (D1) is more positive than the drain of Q1 (in other words, when the switching FET Q1 has only 7.5V across its drain source). Hot Swapping 48V Module with Isolated Controller A power supervisory controller will sometimes reside on an isolated supply with responsibility for other supplies. Figure 15 shows how to Hot Swap a controller’s 5V supply and a 48V module using two LTC1422s. Assuming the 5V supply comes up first, the controller waits for a power good signal from the 48V circuit. Once it receives the right signals the controller activates the GATE IN pin of the Vicor power module. Power Supply Sequencer A circuit that forces two supply voltages to power up together is shown in Figure 16. The input supply voltages may power up in any sequence, but both input voltages must be within tolerance before Q1 and Q2 turn on. Backto-back transistors Q1 and Q2 ensure isolation between the two supplies. When the 5V input powers up before 3.3V, Q1 and Q2 remain off and the 5V output remains off until the 3.3V input is within tolerance as sensed by resistors R1 and R2. When the 3.3V input powers up before 5V, the diode D1 will pull up the 5V supply output with it. Once the 5V input powers up and is within tolerance as sensed by R4 and R5, Q1 and Q2 will turn on in about 1ms and pull the 5V output up to its final voltage. Q2 MMFT2N02ELT1 VIN CURRENT LIMIT: 2.5A 5V LTC1422 1 2 3 4 RESET ON TIMER GND VCC SENSE GATE FB 8 7 6 5 R1 0.02Ω 5% Figure 11. Switching 5V and Generating 3.3V U W U U + Q1 MMFT2N02ELT1 R2 10Ω 5% CLOAD VOUT 3.3V + R3 10Ω 5% R6 1.6M 5% CLOAD R7 360k 5% Q3 PN2222 C1 0.0033µF 16V VOUT 5V R4 2.74k 1% R5 1.62k 1% C3 0.1µF 16V C2 0.1µF 16V 1422 F11 11 LTC1422 APPLICATIONS INFORMATION Power N-Channel and Sense Resistor Selection The decision of which external power N-Channel to use is dependent on its maximum current rating and the maximum allowed current times RDS(ON) drop across the transistor. Table 1 lists some transistors that are available. Table 1. N-Channel Selection Guide CURRENT LEVEL (A) 0 to 2 2 to 5 5 to 10 10 to 20 PART NUMBER MMDF3N02HD MMSF5N02HD MTB50N06V MTB75N05HD DESCRIPTION Dual N-Channel SO-8 RDS(ON) = 0.1Ω Single N-Channel SO-8 RDS(ON) = 0.025Ω Single N-Channel DD Pak RDS(ON) = 0.028Ω Single N-Channel DD Pak RDS(ON) = 0.0095Ω MANUFACTURER ON Semiconductor ON Semiconductor ON Semiconductor ON Semiconductor Table 2. Sense Resistor Selection Guide CURRENT LIMIT VALUE 1A 2A 2.5A 3.3A 5A 10A PART NUMBER LR120601R050 LR120601R025 LR120601R020 WSL2512R015F LR120601R010 WSR2R005F DESCRIPTION 0.05Ω 0.25W 1% Resistor 0.025Ω 0.25W 1% Resistor 0.02Ω 0.25W 1% Resistor 0.015Ω 1W 1% Resistor 0.01Ω 0.25W 1% Resistor 0.005Ω 2W 1% Resistor MANUFACTURER IRC-TT IRC-TT IRC-TT Vishay-Dale IRC-TT Vishay-Dale Table 3. Manufacturers’ Web Sites MANUFACTURER TEMIC Semiconductor International Rectifier ON Semiconductor Harris Semiconductor IRC-TT Vishay-Dale WEB SITE www.temic.com www.irf.com www.onsemiconductor.com www.semi.harris.com www.irctt.com www.vishay.com 12 U W U U Table 2 lists some current sense resistors that can be used with the circuit breaker. Since this information is subject to change, please verify the part numbers with the manufacturer. Table 3 lists the web sites of several manufacturers. LTC1422 APPLICATIONS INFORMATION AT&T JW050A1-E 50W C3 100µF 100V VIN+ VOUT+ SENSE + SENSE – VIN– VOUT– 5V R1 36k 5% + 48V LTC1422 Q2 MMBT5551LT1 1 2 3 R2 1.2k 5% FUSE 4 C1 0.47µF 25V RESET ON TIMER GND VCC SENSE GATE FB 8 7 6 5 D1 7.5V 1N755A C4 1µF 25V R6 1M 5% R7 270k 5% C2 0.1µF 25V R3 10Ω 5% – CIRCUIT TURNS ON WHEN VIN > 38V CIRCUIT FOR ACTIVE LOW TURN-ON MODULES Figure 12. Switching 48V to an AT&T Module R1 36k 5% + 48V LTC1422 Q2 MMBT5551LT1 1 2 3 R2 1.2k 5% FUSE 4 C1 0.1µF 25V RESET ON TIMER GND VCC SENSE GATE FB 8 7 6 5 D1 7.5V 1N755A C4 1µF 25V R6 1M 5% R7 270k 5% C2 0.1µF 25V R3 10Ω 5% – CIRCUIT TURNS ON WHEN VIN > 38V CIRCUIT FOR ACTIVE HIGH TURN-ON MODULES Figure 13. Switching 48V to a Vicor Module U W U U + R5 10k 5% ON/OFF Q1 IRF530 R4 510Ω 5% OPTIONAL PRECHARGE RESISTOR 1422 F12 R5 10k 5% C3 100µF 100V + + _ R4 5.1k 5% VICOR VI-J30-CY GATE IN + _ 5V Q3 MMBT5551LT1 Q1 IRF530 R8 510Ω 5% OPTIONAL PRECHARGE RESISTOR 1422 F13 13 LTC1422 APPLICATIONS INFORMATION COMMON RETURN R7 10k 5% D4 1N4148 R1 36k 5% R5 10k 5% C3 100µF 100V R6 10k 5% D5 1N4148 R10 5.1k 5% FAULT R2 1.2k 5% 4N25 C1 0.33µF 16V FUSE 1 – 48V D2 MUR415 FUSE 2 – 48V D3 MUR415 Figure 14. Hop Swapping Redundant 48V Supplies Q4 5V LTC1422 1 2 3 4 C5 0.33µF 16V RESET ON TIMER GND VCC SENSE GATE FB 8 7 6 5 C6 0.022µF 16V R14 10k 1% R9 0.5Ω 5% R11 5.1k 5% R12 5.1k 5% R1 36k 5% + 48V – R4 5.1k 5% LTC1422 1 2 3 RESET ON TIMER GND VCC SENSE GATE FB 8 7 6 5 D1 7.5V 1N755A C4 1µF 25V R6 1M 5% R7 270k 5% C2 0.1µF 25V R3 10Ω 5% R2 1.2k 5% FUSE 4 4N25 C1 0.1µF 25V CIRCUIT TURNS ON WHEN VIN > 38V CIRCUIT FOR ACTIVE HIGH TURN-ON MODULES Figure 15. Switching 48V to a Vicor Module with Isolated Controller 14 U W U U + + _ VICOR VI-J30-CY GATE IN + _ 5V LTC1422 1 2 3 4 RESET ON TIMER GND VCC SENSE GATE FB 8 7 6 5 R9 1k 5% D1 7.5V 1N755A R4 10k 5% Q2 MPSA56 C4 1µF 25V C2 0.1µF 25V R3 10Ω 5% Q1 TURNS ON WHEN VIN > 38V FAULT GOES LOW WHEN EITHER SUPPLY FAILS Q1 IRF530 R8 510Ω 5% OPTIONAL PRECHARGE RESISTOR 1422 F14 R10 10Ω 5% R13 28k 1% + VCC C7 47µF 16V µP RESET GND ON PWRGD R5 6.2k 5% C3 100µF 100V + + _ VICOR VI-J30-CY GATE IN + _ 5V 4N25 Q1 IRF530 R8 510Ω 5% OPTIONAL PRECHARGE RESISTOR 1422 F15 LTC1422 APPLICATIONS INFORMATION VIN 3.3V Q1 1/2 MMDF 2N02E Q1 1/2 MMDF 2N02E VOUT 3.3V D1 MBRS120T3 VOUT 5V VIN 5V R1 1.3k 1% 1 2 8 RESET ON R2 1k 1% 7 SENSE LTC1422 6 3 TIMER GATE 5 4 GND FB Figure 16. Power Supply Sequencer PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 0.400* (10.160) MAX 8 7 6 5 0.300 – 0.325 (7.620 – 8.255) 0.045 – 0.065 (1.143 – 1.651) 0.009 – 0.015 (0.229 – 0.381) 0.065 (1.651) TYP 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 ± 0.003 (0.457 ± 0.076) ( +0.035 0.325 –0.015 8.255 +0.889 –0.381 ) 0.100 (2.54) BSC *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm) S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 0°– 8° TYP 0.053 – 0.069 (1.346 – 1.752) 8 0.004 – 0.010 (0.101 – 0.254) 0.228 – 0.244 (5.791 – 6.197) 0.150 – 0.157** (3.810 – 3.988) 7 6 5 0.014 – 0.019 (0.355 – 0.483) TYP *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 0.016 – 0.050 (0.406 – 1.270) 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. U U W U U VCC R4 2.74k 1% R3 10Ω 5% C1 0.047µF 25V 1422 F16 R5 1k 1% 0.130 ± 0.005 (3.302 ± 0.127) 0.255 ± 0.015* (6.477 ± 0.381) 1 2 3 4 N8 1098 0.050 (1.270) BSC 1 2 3 4 SO8 1298 15 LTC1422 TYPICAL APPLICATION Current Sensing with 48V Applications In the LTC1422, the SENSE pin threshold is 50mV below the VCC pin. Typically, the current sense resistor is connected to the VCC pin, but in 48V applications the sense resistor is connected to the negative terminal of the 48V supply. The circuit in Figure 17 translates the current in the sense resistor to a resistor connected to the LTC1422 SENSE pin. The voltage drop across the current sense resistor RSENSE is proportional to the load current ILOAD. The voltage drop across RSENSE is buffered by the op amp follower and is forced on RMIRROR. R1 36k 5% 1 2 3 R2 1.2k 5% C1 0.47µF 25V 4 R5 15k 5% 8 7 6 5 IMIRROR D1 7.5V 1N755A Q2 VN2222L C4 1µF 25V R6 1M 5% R7 270k 5% RTRIP 10Ω 5% R4 10k 5% LTC1422 RESET ON TIMER GND VCC SENSE GATE FB + 48V – FUSE RELATED PARTS PART NUMBER LTC1421 LT1640L/LT1640H LT1641 LT1642 LTC1643L/LTC1643H LT1645 LTC1647 DESCRIPTION Hot Swap Controller Negative Voltage Hot Swap Controller in SO-8 High Voltage Hot Swap Controller in SO-8 Fault Protected Hot Swap Controller PCI-Bus Hot Swap Controller 2-Channel Hot Swap Controller Dual Hot Swap Controller in SO-8 or SSOP-16 COMMENTS 24-Pin Multiple Supplies Operates from –10V to – 80V Operates from 9V to 80V Operates Up to 16.5V, Protected to 33V 3.3V, 5V and ± 12V in Narrow 16-Pin SSOP Operates from 1.2V to 12V, Power Sequencing Two ON Pins, Operates from 2.7V to 16.5V 1422fa LT/TP 0300 2K REV A • PRINTED IN USA 16 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 q FAX: (408) 434-0507 q www.linear-tech.com U The mirror current can be described as: IMIRROR = ILOAD • RSENSE/RMIRROR. The mirror current flows through the trip resistor RTRIP. When the mirror current generates 50mV across RTRIP, the LTC1422 will latch the GATE pin low (50mV = IMIRROR • RTRIP = ILOAD • RSENSE/RMIRROR • RTRIP). This example uses a 48V input but this translation circuit can be used anywhere the current sense resistor is not tied to VCC. + C5 0.22µF 100V C3 100µF 100V R3 10Ω 5% + LOAD + C2 0.1µF 25V – Q1 IRF530 7 + LT1006 3 – 4 2 RSENSE 0.02Ω 5% ILOAD OPAMP IMIRROR RMIRROR 39Ω 5% 1422 F17 Figure 17. Switching 48V with Current Sensing © LINEAR TECHNOLOGY CORPORATION 1997