LTC1422 Hot Swap Controller U DESCRIPTIO FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ 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. 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 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. U APPLICATIO S ■ ■ The LTC1422 is available in 8-pin PDIP and SO packages. Hot Board Insertion Electronic Circuit Breaker , LTC and LT are registered trademarks of Linear Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation. U TYPICAL APPLICATIO 5V Hot Swap Q1 R1 0.005Ω MTB50N06V VCC CONNECTOR 1 CONNECTOR 2 R2 10Ω 5% ON/RESET VOUT 5V + 8 2 7 VCC ON FB 5 LTC1422 RESET TIMER 3 GND C2 0.33µF 4 R3 6.81k 1% C1 0.1µF 6 SENSE GATE CLOAD 1 R4 2.43k 1% µP RESET GND 1422 TA01 BACKPLANE PLUG-IN CARD 1 LTC1422 U U W W W 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 W (Note 1) U ABSOLUTE MAXIMUM RATINGS PACKAGE/ORDER I FOR ATIO ORDER PART NUMBER TOP VIEW RESET 1 8 VCC ON 2 6 GATE GND 4 N8 PACKAGE 8-LEAD PDIP LTC1422CN8 LTC1422CS8 LTC1422IN8 LTC1422IS8 7 SENSE TIMER 3 5 FB S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 150°C, θJA = 130°C/W (N) TJMAX = 150°C, θJA = 150°C/W (S) S8 PART MARKING 1422 1422I Consult factory for Military grade parts. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VCC = 5V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 0.65 1.00 mA 2.47 2.55 DC Characteristics ICC VCC Supply Current ON = VCC VLKO VCC Undervoltage Lockout VLKH VCC Undervoltage Lockout Hysteresis VFB FB Pin Voltage Threshold ∆VFB FB Pin Threshold Line Regulation VFBHST FB Pin Voltage Threshold Hysteresis VTM TIMER Pin Voltage Threshold ∆VTM TIMER Pin Threshold Line Regulation VTMHST TIMER Pin Voltage Threshold Hystersis ITM TIMER Pin Current Timer On, GND ≤ VTIMER ≤ 1.5V Timer Off, VTIMER = 1.5V ● – 2.5 – 2.0 10 – 1.5 µA mA VCB Circuit Breaker Trip Voltage VCB = (VCC – VSENSE) ● 44 50 64 mV ICP GATE Pin Output Current Charge Pump On, VGATE = GND Charge Pump Off, VGATE = VCC ● – 12 – 10 10 –8 µA mA ∆VGATE External N-Channel Gate Drive VGATE – VCC ● 10 12 14 V VONHI ON Pin Threshold High ● 1.25 1.30 1.35 V VONLO ON Pin Threshold Low ● 1.20 1.23 1.26 V VONHYST ON Pin Hysteresis VOL Output Low Voltage RESET, IO = 3mA IPU Logic Output Pull-Up Current RESET = GND tRST Soft Reset Time ● 2.40 120 ● 3V ≤ VCC ≤ 12V 1.220 ● ● 3V ≤ VCC ≤ 12V 1.208 ● 1.232 1.244 0.5 2.5 1.232 1.256 2 15 22 30 V mV mV 0.4 V µA – 12 ● mV mV 80 0.14 V mV 45 ● V mV 2.0 Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. 2 ● 38 µs LTC1422 U W TYPICAL PERFORMANCE CHARACTERISTICS Supply Current vs Supply Voltage Supply Current vs Temperature 1200 VCC = 5V TA = 25°C 750 800 600 400 TA = 25°C IG = 0A 25 725 GATE VOLTAGE (V) SUPPLY CURRENT (µA) 1000 SUPPLY CURRENT (µA) Gate Voltage vs Supply Voltage 30 775 700 675 650 625 20 15 10 600 200 5 575 0 2 4 6 8 10 SUPPLY VOLTAGE (V) 12 550 – 55 – 35 –15 14 0 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G01 Gate Voltage vs Temperature 12 14 1422 G03 Gate Current vs Supply Voltage Gate Current vs Temperature 16 VCC = 5V IG = 0A 10.4 TA = 25°C VG = 0V 14 VCC = 5V VG = 0V 10.2 10.0 17.6 17.4 17.2 17.0 GATE CURRENT (µA) GATE CURRENT (µA) 17.8 GATE VOLTAGE (V) 6 8 10 SUPPLY VOLTAGE (V) 4 1422 G02 18.2 18.0 2 12 10 8 9.8 9.6 9.4 9.2 9.0 16.8 6 8.8 16.6 16.4 – 55 – 35 –15 4 5 25 45 65 85 105 125 TEMPERATURE (°C) 2 4 6 8 10 SUPPLY VOLTAGE (V) 12 Feedback Threshold Voltage vs Supply Voltage 1422 G06 Feedback Threshold Voltage vs Temperature 1.2350 Glitch Filter Time vs Feedback Transient 70 1.237 HIGH THRESHOLD 1.2340 1.2335 LOW THRESHOLD 1.2330 1.2325 1.2320 2 4 6 8 10 SUPPLY VOLTAGE (V) 12 14 1422 G07 TA = 25°C 1.236 60 HIGH THRESHOLD 1.235 1.234 1.233 LOW THRESHOLD 1.232 1.231 1.230 GLITCH FILTER TIME (µs) FEEDBACK THRESHOLD VOLTAGE (V) TA = 25°C 1.2345 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G05 1422 G04 FEEDBACK THRESHOLD VOLTAGE (V) 8.6 – 55 – 35 –15 14 50 40 30 20 1.229 1.228 – 55 – 35 –15 10 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 U W TYPICAL PERFORMANCE CHARACTERISTICS TIMER Threshold Voltage vs Supply Voltage TIMER Threshold Voltage vs Temperature 1.244 TA = 25°C TA = 25°C 1.241 1.240 1.238 1.236 1.234 VCC = 12V 1.240 2.5 TIMER CURRENT (µA) 1.242 TIMER THRESHOLD VOLTAGE (V) TIMER THRESHOLD VOLTAGE (V) TIMER Current vs Supply Voltage 2.6 1.242 1.239 VCC = 5V 1.238 1.237 VCC = 3V 1.236 2.4 2.3 2.2 1.235 2.1 1.234 1.232 4 6 8 10 SUPPLY VOLTAGE (V) 12 14 1.233 – 55 – 35 –15 2.0 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G10 ON PIN THRESHOLD VOLTAGE (V) TA = 25°C TIMER CURRENT (µA) 2.25 2.20 2.15 2.10 1.36 1.30 HIGH THRESHOLD 1.28 1.26 1.24 LOW THRESHOLD 1.22 2.05 2.00 – 55 – 35 –15 1.20 5 25 45 65 85 105 125 TEMPERATURE (°C) 2 4 6 8 10 SUPPLY VOLTAGE (V) 14 1.32 INPUT HIGH 1.30 1.28 1.26 1.24 INPUT LOW 1.22 1.20 – 55 – 35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G15 22 85 VCC = 5V VCC = 5V 20 80 RESET PULL-UP CURRENT (µA) CURRENT LIMIT THRESHOLD (mV) 12 1.34 RESET Pull-Up Current vs Temperature Current Limit Threshold vs Temperature 75 70 65 60 55 50 18 16 14 12 10 8 6 45 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G17 4 14 VCC = 5V 1422 G14 1422 G13 40 – 55 – 35 –15 12 1.38 VCC = 5V 2.30 6 8 10 SUPPLY VOLTAGE (V) ON Pin Threshold Voltage vs Temperature 1.32 2.45 2.35 4 1422 G12 ON Pin Threshold Voltage vs Supply Voltage TIMER Current vs Temperature 2.40 2 1422 G11 ON PIN THRESHOLD VOLTAGE (V) 2 4 – 55 – 35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G18 LTC1422 U W TYPICAL PERFORMANCE CHARACTERISTICS ON Pin Pulse (Soft Reset) Time vs Temperature RESET Voltage vs Temperature 0.24 0.22 55 VCC = 5V 3mA PULL-UP 50 ON PIN PULSE TIME (µs) RESET VOLTAGE (V) 0.20 0.18 0.16 0.14 0.12 0.10 0.08 45 40 35 VCC = 3V 30 25 20 VCC = 5V VCC = 12V 15 0.06 – 55 – 35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 10 – 55 – 35 –15 5 25 45 65 85 105 125 TEMPERATURE (°C) 1422 G19 1422 G20 U U U 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. 5 LTC1422 U U U 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. 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. SENSE (Pin 7) : Circuit Breaker Set Pin. With a sense resistor placed in the supply path between VCC and SENSE, W BLOCK DIAGRA VCC SENSE GATE 7 8 6 50mV + – Q3 CHARGE PUMP – + COMP 3 ON 2 + COMP 1 REF 2.47V UVL 10µs FILTER – 1.232V REFERENCE REF – LOGIC GLITCH FILTER COMP 2 5 FB + 2µA TIMER 3 + COMP 4 REF Q1 12µA – 1 Q2 4 1422 BD 6 RESET GND LTC1422 U U W U APPLICATIONS INFORMATION Hot Circuit Insertion VCC + 10V 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 GATE SLOPE = 10µA/C1 VOUT VCC t1 t2 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 Q1 Q1 VCC VOUT VCC 1422 F02 + + 8 2 7 SENSE GATE ON FB R3 C1 8 5 LTC1422 RESET 1 SENSE R4 GATE FB 5 + ON GND 3 VCC 6 7 R3 LTC1422 TIMER R2 C1 6 VCC CLOAD CLOAD R2 10Ω VOUT 2 R4 COMP 2 LOGIC – 4 C2 12µA 1422F01 1.232V REFERENCE TIMER 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 µP 1 RESET Q2 3 4 C2 1422 F03 Figure 3. Supply Monitor Block Diagram 7 LTC1422 U U W U APPLICATIONS INFORMATION 1 2 V2 3 V1 V2 4 V1 1 2 30µs 3 30µs 4 5 6 V2 VOUT ON 1.232V 15µs 1.232V TIMER TIMER RESET GATE 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). VOUT RESET 20µs 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. 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. R1 Q2 VCC + CLOAD C1 8 LTC1422 ON VCC 6 7 SENSE GATE R3 2 5 LOGIC Soft Reset R4 + COMP 4 1.232V SUPPLY MONITOR – 1 RESET Q1 TIMER 3 1422 F06 4 C2 Figure 6. System Timing Block Diagram 8 VOUT R2 2µA 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. 1422 F05 LTC1422 U W U U 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. 1 2 3 4 5 6 7 8 9 10 VCC ON VCC – VSENSE TIMER GATE 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 Figure 7. Current Fault Timing R1 CF Q1 RF R2 8 VCC 7 SENSE 6 C1 GATE LTC1422 1422 F08 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 U U W U APPLICATIONS INFORMATION R1 Q1 VCC VOUT + CLOAD R2 10k CONNECTOR 1 CONNECTOR 2 8 10k 10k 7 C1 6 R3 GATE SENSE VCC FB 5 LOGIC 2 ON R4 + COMP 5 Q4 REF Q3 1 RESET LTC1422 TIMER 3 Q2 ON/RESET – 4 C2 1422 F09 Q2: 2N7002LT1 Q3, Q4: MMBT3904LT1 Figure 9. ON Pin Circuitry 5V OUT 3.3V OUT Q2 1/2 Si99436 VIN 3.3V VOUT 3.3V + R2 0.01Ω 5% CURRENT LIMIT: 5A VIN 5V CLOAD R7 10Ω 5% Q1 1/2 Si9436 VOUT 5V + LTC1422 RESET ON 1 2 3 C1 0.33µF 16V 4 VCC RESET ON SENSE TIMER GND GATE FB 8 7 6 R3 10Ω 5% R1 10k 5% D1 1N4148 CLOAD R6 1M 5% R4 2.74k 1% TRIP POINT: 4.6V 5 C3 0.047µF 25V C2 0.022µF 25V R5 1k 1% 1422 F10 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 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 U U W U 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. 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. 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. 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. 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 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 VOUT 3.3V + R1 0.02Ω 5% VIN CURRENT LIMIT: 2.5A 5V 2 3 4 RESET ON TIMER GND VCC SENSE GATE FB CLOAD R2 10Ω 5% VOUT 5V + LTC1422 1 Q1 MMFT2N02ELT1 8 7 6 CLOAD R3 10Ω 5% R6 1.6M 5% R7 360k 5% Q3 PN2222 5 C2 0.1µF 16V C1 0.0033µF 16V R4 2.74k 1% C3 0.1µF 16V R5 1.62k 1% 1422 F11 Figure 11. Switching 5V and Generating 3.3V 11 LTC1422 U W U U 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 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. Table 1. N-Channel Selection Guide CURRENT LEVEL (A) PART NUMBER DESCRIPTION MANUFACTURER 0 to 2 MMDF3N02HD Dual N-Channel SO-8 RDS(ON) = 0.1Ω ON Semiconductor 2 to 5 MMSF5N02HD Single N-Channel SO-8 RDS(ON) = 0.025Ω ON Semiconductor 5 to 10 MTB50N06V Single N-Channel DD Pak RDS(ON) = 0.028Ω ON Semiconductor 10 to 20 MTB75N05HD Single N-Channel DD Pak RDS(ON) = 0.0095Ω ON Semiconductor Table 2. Sense Resistor Selection Guide CURRENT LIMIT VALUE PART NUMBER DESCRIPTION MANUFACTURER 1A LR120601R050 0.05Ω 0.25W 1% Resistor IRC-TT 2A LR120601R025 0.025Ω 0.25W 1% Resistor IRC-TT 2.5A LR120601R020 0.02Ω 0.25W 1% Resistor IRC-TT 3.3A WSL2512R015F 0.015Ω 1W 1% Resistor Vishay-Dale 5A LR120601R010 0.01Ω 0.25W 1% Resistor IRC-TT 10A WSR2R005F 0.005Ω 2W 1% Resistor Vishay-Dale Table 3. Manufacturers’ Web Sites MANUFACTURER WEB SITE TEMIC Semiconductor www.temic.com International Rectifier www.irf.com ON Semiconductor www.onsemiconductor.com Harris Semiconductor www.semi.harris.com IRC-TT www.irctt.com Vishay-Dale www.vishay.com 12 LTC1422 U W U U APPLICATIONS INFORMATION AT&T JW050A1-E 50W R1 36k 5% C3 100µF 100V R5 10k 5% + VIN+ VOUT+ 5V SENSE + SENSE – VIN– VOUT– ON/OFF + LTC1422 48V – 1 Q2 MMBT5551LT1 RESET 2 FUSE SENSE ON 3 R2 1.2k 5% TIMER 4 VCC GND GATE FB 8 7 6 5 C1 0.47µF 25V D1 7.5V 1N755A C4 1µF 25V R6 1M 5% R7 270k 5% R3 10Ω 5% C2 0.1µF 25V Q1 IRF530 CIRCUIT TURNS ON WHEN VIN > 38V CIRCUIT FOR ACTIVE LOW TURN-ON MODULES R4 510Ω 5% OPTIONAL PRECHARGE RESISTOR 1422 F12 Figure 12. Switching 48V to an AT&T Module R1 36k 5% C3 100µF 100V R5 10k 5% + + – 1 Q2 MMBT5551LT1 2 3 R2 1.2k 5% FUSE 4 C1 0.1µF 25V RESET ON TIMER GND VCC SENSE GATE FB _ R4 5.1k 5% LTC1422 48V + VICOR VI-J30-CY GATE IN + 5V _ Q3 MMBT5551LT1 8 7 6 5 D1 7.5V 1N755A C4 1µF 25V R6 1M 5% R7 270k 5% C2 0.1µF 25V R3 10Ω 5% Q1 IRF530 CIRCUIT TURNS ON WHEN VIN > 38V CIRCUIT FOR ACTIVE HIGH TURN-ON MODULES R8 510Ω 5% OPTIONAL PRECHARGE RESISTOR 1422 F13 Figure 13. Switching 48V to a Vicor Module 13 LTC1422 U U W U APPLICATIONS INFORMATION COMMON RETURN R6 10k 5% R7 10k 5% D4 1N4148 R1 36k 5% R5 10k 5% R10 5.1k 5% D5 1N4148 FAULT FUSE 1 D2 MUR415 FUSE 2 D3 MUR415 3 4 4N25 8 VCC RESET TIMER 5 FB R9 1k 5% C1 0.33µF 16V D1 7.5V 1N755A 5V _ Q2 MPSA56 C2 0.1µF 25V C4 1µF 25V – 48V R3 10Ω 5% Q1 IRF530 Q1 TURNS ON WHEN VIN > 38V FAULT GOES LOW WHEN EITHER SUPPLY FAILS – 48V GATE IN + 6 GATE GND _ VICOR VI-J30-CY 7 SENSE ON + + R4 10k 5% LTC1422 1 2 R2 1.2k 5% C3 100µF 100V R8 510Ω 5% OPTIONAL PRECHARGE RESISTOR 1422 F14 Figure 14. Hop Swapping Redundant 48V Supplies Q4 5V R9 0.5Ω 5% LTC1422 1 2 3 4 VCC RESET SENSE ON GATE TIMER FB GND 8 R10 10Ω 5% 7 6 C6 0.022µF 16V R1 36k 5% R4 5.1k 5% 48V – 2 3 4 4N25 C1 0.1µF 25V RESET ON TIMER GND VCC SENSE GATE FB C3 100µF 100V + + _ VICOR VI-J30-CY GATE IN 4N25 7 6 5 D1 7.5V 1N755A C4 1µF 25V R6 1M 5% R7 270k 5% ON GND 8 CIRCUIT TURNS ON WHEN VIN > 38V CIRCUIT FOR ACTIVE HIGH TURN-ON MODULES C2 0.1µF 25V R3 10Ω 5% Q1 IRF530 R8 510Ω 5% OPTIONAL PRECHARGE RESISTOR Figure 15. Switching 48V to a Vicor Module with Isolated Controller 14 µP RESET PWRGD LTC1422 1 R11 5.1k 5% VCC C7 47µF 16V R14 10k 1% R5 6.2k 5% + FUSE + 5 C5 0.33µF 16V R2 1.2k 5% R13 28k 1% 1422 F15 + _ 5V R12 5.1k 5% LTC1422 U U W U APPLICATIONS INFORMATION VIN 3.3V Q1 1/2 MMDF 2N02E VIN 5V R1 1.3k 1% R2 1k 1% 1 RESET VCC Q1 1/2 MMDF 2N02E 8 7 SENSE LTC1422 6 3 TIMER GATE 5 4 GND FB 2 VOUT 3.3V D1 MBRS120T3 VOUT 5V ON R4 2.74k 1% R3 10Ω 5% C1 0.047µF 25V R5 1k 1% 1422 F16 Figure 16. Power Supply Sequencer U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) 0.300 – 0.325 (7.620 – 8.255) 0.009 – 0.015 (0.229 – 0.381) ( 0.045 – 0.065 (1.143 – 1.651) +0.889 –0.381 0.130 ± 0.005 (3.302 ± 0.127) 0.065 (1.651) TYP +0.035 0.325 –0.015 8.255 0.400* (10.160) MAX ) 8 7 6 5 1 2 3 4 0.255 ± 0.015* (6.477 ± 0.381) 0.125 (3.175) 0.020 MIN (0.508) MIN 0.018 ± 0.003 0.100 (2.54) BSC (0.457 ± 0.076) N8 1098 *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) 0.053 – 0.069 (1.346 – 1.752) 0°– 8° TYP 0.016 – 0.050 (0.406 – 1.270) 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 8 7 6 5 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) BSC 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 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. 2 3 4 SO8 1298 15 LTC1422 U 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 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. 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. LTC1422 1 2 3 4 R2 1.2k 5% + RESET ON TIMER GND – VCC SENSE GATE FB C5 0.22µF 100V RTRIP 10Ω 5% 8 7 R4 10k 5% 6 R6 1M 5% 5 IMIRROR C1 0.47µF 25V 48V + R5 15k 5% + R1 36k 5% C4 1µF 25V D1 7.5V 1N755A 7 + Q2 VN2222L 3 C3 100µF 100V + LOAD – R3 10Ω 5% Q1 IRF530 C2 0.1µF 25V R7 270k 5% LT1006 – 2 RSENSE 0.02Ω 5% 4 OPAMP IMIRROR FUSE ILOAD RMIRROR 39Ω 5% 1422 F17 Figure 17. Switching 48V with Current Sensing RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC1421 Hot Swap Controller 24-Pin Multiple Supplies LT1640L/LT1640H Negative Voltage Hot Swap Controller in SO-8 Operates from –10V to – 80V LT1641 High Voltage Hot Swap Controller in SO-8 Operates from 9V to 80V LT1642 Fault Protected Hot Swap Controller Operates Up to 16.5V, Protected to 33V LTC1643L/LTC1643H PCI-Bus Hot Swap Controller 3.3V, 5V and ±12V in Narrow 16-Pin SSOP LT1645 2-Channel Hot Swap Controller Operates from 1.2V to 12V, Power Sequencing LTC1647 Dual Hot Swap Controller in SO-8 or SSOP-16 Two ON Pins, Operates from 2.7V to 16.5V 16 Linear Technology Corporation 1422fa LT/TP 0300 2K REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1997