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LTC1422

1422fb

Hot Swap Controller

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Allows Safe Board Insertion and Removal

from a Live Backplane

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System Reset Output with Programmable Delay

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Programmable Electronic Circuit Breaker

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User-Programmable Supply Voltage Power-Up Rate

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High Side Driver for an External N-Channel FET

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Controls Supply Voltages from 2.7V to 12V

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Undervoltage Lockout

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Soft Reset Input

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Glitch Filter on RESET

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Available in 8-Pin Narrow PDIP and SO Packages

5V Hot Swap

The LTC

1422 is an 8-pin Hot Swap

controller that

allows a board to be safely inserted and removed from a

live backplane. Using an external N-channel pass transis-

tor, 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.

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Hot Board Insertion

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Electronic Circuit Breaker

SENSE GATE

LTC1422

GNDTIMER

10Ω

6.81k

2.43k

0.005Ω

MTB50N06V

0.1µF

LOAD

OUT

ON/RESET

GND

1422 TA01

PLUG-IN CARDBACKPLANE

0.33µF

RESET

µP

CONNECTOR 1

CONNECTOR 2

APPLICATIO S

FEATURES

TYPICAL APPLICATIO

DESCRIPTIO

Summary of content (16 pages)

PAGE 1
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.
PAGE 2
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 20V Output Voltage (GATE) ............................. – 0.3V to 20V Operating Temperature Range LTC1422C ............................................... 0°C to 70°C LTC1422I ...........................................
PAGE 3
LTC1422 U W TYPICAL PERFORMANCE CHARACTERISTICS Supply Current vs Supply Voltage 1200 30 775 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 (VGATE) vs Supply Voltage Supply Current vs Temperature 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 12 Gate Current vs Supply Voltage VCC = 5V IG = 0A
PAGE 4
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.
PAGE 5
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.
PAGE 6
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 when VCC is 5V. 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.
PAGE 7
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.
PAGE 8
LTC1422 U U W U APPLICATIONS INFORMATION 1 2 V2 3 V1 V2 4 V1 1 3 30µs (typ) 4 2 30µs 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.
PAGE 9
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.
PAGE 10
LTC1422 U U W U APPLICATIONS INFORMATION R1 Q1 VCC VOUT + CLOAD R2 10k CONNECTOR 1 CONNECTOR 2 8 10k 10k C1 6 7 SENSE VCC R3 GATE 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.
PAGE 11
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.
PAGE 12
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.
PAGE 13
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.
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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 1 FAULT FUSE 1 D2 MUR415 FUSE 2 D3 MUR415 VCC RESET SENSE ON 3 TIMER 4 GATE GND 4N25 FB 8 _ VICOR VI-J30-CY GATE IN + 5V _ Q2 MPSA56 7 6 5 R9 1k 5% C1 0.33µF 16V D1 7.5V 1N755A 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 + + R4 10k 5% LTC1422 2 R2 1.
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LTC1422 U U W U APPLICATIONS INFORMATION VIN 3.3V Q1 1/2 MMDF 2N02E VIN 5V VOUT 3.3V D1 MBRS120T3 VOUT 5V Q1 1/2 MMDF 2N02E R6 10k 5% R1 1.3k 1% 1 RESET VCC 8 7 SENSE LTC1422 6 3 TIMER GATE 5 4 GND FB 2 R2 1k 1% R4 2.74k 1% ON R3 10Ω 5% C1 0.047µF 25V R5 1k 1% 1422 F16 Figure 16. Power Supply Sequencer U PACKAGE DESCRIPTION N8 Package 8-Lead PDIP (Narrow .300 Inch) (Reference LTC DWG # 05-08-1510) .300 – .325 (7.620 – 8.255) .045 – .065 (1.143 – 1.651) .065 (1.651) TYP .008 – .
PAGE 16
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.