PDF LTC1642CGN Data sheet ( Hoja de datos )

Número de pieza	LTC1642CGN
Descripción	Hot Swap Controller
Fabricantes	Linear Technology
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No Preview Available ! Final Electrical Specifications LTC1642 Hot Swap Controller May 1999 FEATURES s Single Channel Positive NFET Driver s Programmable Undervoltage and Overvoltage Protection s Foldback Current Limit s Adjustable Current Limit Time-Out s Latch Off or Automatic Retry on Current Fault s Driver for SCR Crowbar on Overvoltage s Programmable Reset Timer s Reference Output with Uncommitted Comparator s VCC: 2.97V to 16.5V Normal Operation, Protected Against Surges to 33V. s 16-Pin SSOP Package U APPLICATIO S s Hot Board Insertion s Electronic Circuit Breaker DESCRIPTIO The LTC®1642 is a 16-pin Hot SwapTM 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 2.97V to 16.5V. The SENSE pin allows foldback limiting of the load current, with circuit breaker action after a programmable delay time. The delay allows the part to power-up in current limit. The CRWBR output can be used to trigger an SCR for crowbar load protection after a programmable delay if the input supply exceeds a programmable voltage. The RESET output can be used to generate a system reset with programmable delay when the supply voltage falls below a programmable voltage. The ON pin can be used to cycle the board power. The LTC1642 is available in the 16-pin SSOP package. , LTC and LT are registered trademarks of Linear Technology Corporation. Hot Swap is a trademark of Linear Technology Corporation. TYPICAL APPLICATIO 12V R1 0.010Ω 5% Q1 FDR9410A C7 R5 0.1µF 110k 1% R2 100Ω 5% R8 330Ω 5% LATCH OFF: FLOAT FAULT AUTOMATIC RETRY: TIE FAULT TO ON 16 VCC 15 SENSE 14 GATE 5 RESET 10 COMPOUT 7 FB UNDERVOLTAGE = 10.8V R6 2.87k 1% OVERVOLTAGE = 13.2V RESET TIME = 200ms CURRENT LIMIT TIME = 20ms CROWBAR TIME = 90µs R7 11.3k 1% D1 1N4148 4 ON LTC1642 6 FAULT 9 OV GND BRK TMR 8 C3 0.33µF 2 1 CRWBR COMP– 12 COMP+ 11 13 REF RST TMR 3 C5 C2 0.1µF 0.33µF C1 0.047µF Q2 2N2222 C6 0.01µF R9 220Ω 5% 12V + AT 2.5A CLOAD R3 107k 1% POWER-GOOD = 11.4V Q3 MCR 12DC R4 13k 1% 1642 TA01 R9 REQUIRED ONLY WITH SENSITIVE GATE SCRs, NOT NEEDED WITH MCR12 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 represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 1 1 page LTC1642 APPLICATIO S I FOR ATIO Hot Circuit Insertion When a circuit board is inserted into a live backplane its supply bypass capacitors can draw large currents from the backplane power bus as they charge. These currents can permanently damage connector pins and can glitch the backplane supply, resetting other boards in the system. The LTC1642 limits the charging currents drawn by a board’s capacitors, allowing safe insertion in a live backplane. Power Supply Ramping In the circuit shown in Figure 1 the LTC1642 and the external N-channel pass transistor Q1 work together to limit charging currents. When power is first applied to VCC the chip holds Q1’s gate at ground. After a programmable delay a 25µA current source begins to charge the external capacitor C2, generating a voltage ramp of 25µA/C2 V/s at the GATE pin. Because Q1 acts as a source follower while its gate ramps, the current charging the board’s bypass capacitance CLOAD is limited to 25µA•CLOAD/C2. An internal charge pump supplies the 25µA gate current, ensuring sufficient gate drive to Q1. At 3V VCC the mini- mum gate drive is 4.5V; at 5V VCC the minimum is 10V; at 15V VCC the minimum is again 4.5V, due to a Zener clamp from the GATE pin to ground. Resistor R3 limits this Zener’s transient current during board insertion and re- moval and protects against high frequency FET oscilla- tions. VIN 12V 2.5A C7 0.1µF R2 0.010Ω Q1 FDR9410A 16 R1 10k VCC 4 ON 15 SENSE 14 GATE LTC1642 + R3 100Ω R4 330Ω C2 0.047µF VOUT CLOAD 25 BRK TMR RESET C4 0.33µF RST TMR C1 0.33µF 3 GND 8 1642 F01 ALL RESISTORS ±5% UNLESS NOTED RESET DELAY = 200ms SHORT-CIRCUIT DURATION = 20ms Figure 1. Supply Control Circuitry The delay before the GATE pin voltage begins ramping is determined by the system timer. It comprises an external capacitor C1 from the RST TMR pin to ground; an internal 2µA current source feeding RST TMR from VCC; an internal comparator, with the positive input tied to RST TMR and the negative input tied to the 1.23V reference; and an NMOS pull-down. In standby, the NMOS holds RST TMR at ground; when the timer starts the NMOS turns off and the RST TMR voltage ramps up as the current source charges the capacitor. When RST TMR reaches 1.23V the timer comparator trips; the GATE voltage begins ramping and RST TMR returns to ground. The ramp time ∆t needed to trip the comparator is : ∆t(ms) = 615•C1(µF). VIN RST TMR GATE SLOPE = 25µA/C(V/s) VOUT TIME 1642 F02 Figure 2. Supply Control Timing Powering-Up In Current Limit Ramping the GATE pin voltage indirectly limits the charg- ing current to I = 25µA•CLOAD/C2, where C2 is the external capacitor connected to the GATE and CLOAD is the load capacitance. If the value of CLOAD is uncertain, then a worst-case design can often result in needlessly long ramp times, and it may be better to limit the charging current directly. Current Limiting and Solid-State Circuit Breaker The board current can be limited by connecting a sense resistor between the LTC1642’s VCC and SENSE pins. An internal servo loop adjusts the GATE pin voltage such that Q1 acts as a constant current source if the voltage drop across the sense resistor reaches a limit. The voltage limit across the sense resistor increases as the output charges 5 5 Page PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted. LTC1642 GN Package 16-Lead Plastic SSOP (Narrow 0.150) (LTC DWG # 05-08-1641) 0.189 – 0.196* (4.801 – 4.978) 16 15 14 13 12 11 10 9 0.009 (0.229) REF 0.229 – 0.244 (5.817 – 6.198) 0.150 – 0.157** (3.810 – 3.988) 0.007 – 0.0098 (0.178 – 0.249) 0.015 (0.38 ± ± 0.004 0.10) × 45° 0° – 8° TYP 0.016 – 0.050 (0.406 – 1.270) * 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 1 234 5678 0.053 – 0.068 (1.351 – 1.727) 0.004 – 0.0098 (0.102 – 0.249) 0.008 – 0.012 (0.203 – 0.305) 0.025 (0.635) BSC GN16 (SSOP) 0398 11 11 Page

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