MCP18480-ISS Microchip

MCP18480 MCP18480 M -48V Hot Swap Controller Features Description Allows safe board removal and insertion from a The MCP18480 is a Hot Swap controller that allows live backplane boards to be safely removed or inserted from an active backplane using -48V. Accurate (<1.5%) internal voltage reference for fault detection and precision timing When PCBs are inserted into a live backplane, high- Programmable foldback current limiting peak or transient currents from the source are gener- ated due to the charging of the bypass capacitors on Programmable circuit breaker current limiting the supply. The high transient currents can destroy Auto restart option for all faults connectors and capacitors. The high inrush current can Adjustable Undervoltage lockout thresholds pull the input voltage BUS down and reset the system. Adjustable Overvoltage protection threshold The MCP18480 solves this problem by controlling the Adjustable Power Good delay slew rate of the backplane voltage to the board so that Configurable Power Good output polarity these transients are eliminated. This allows boards to Low-side drive of an external N-channel FET be removed and inserted without causing damage to connector pins and input bulk capacitors, in addition to CMOS Technology preventing false resets to the other boards on the backplane. High-Voltage Operation The MCP18480 can be used in applications in several Temperature range: Industrial (I): -40C to +85C areas including: Packaging Telecom Line Cards Network Switches 20-lead SSOP Network Routers and Servers Package Type Base Station Line Cards Power-Over-LAN SSOP Power-Over-MDI V POS 1 20 RESTART IP Phone Switches/Routers OV 2 19 ENABLE TH Mid-Span, Power-Over-MDI UV PWRGOOD 3 18 TH Two forms of current limit are provided in the UV 4 17 OVO MCP18480. These are: HYS UV 5 16 DRAIN D TH Foldback V 6 15 V REFOUT FB Circuit breaker 14 GATE V 7 REFIN The foldback current-limiting circuit uses an external CL 8 13 SENSE sense resistor and a voltage that is proportional to the external MOSFETs drain voltage. These are used to I 12 R 9 DISCH SET keep the MOSFET in its Safe Operating Area (SOA). TIMER 10 11 V NEG If the device remains in current limit for a programmed time period, the external N-channel FET is turned off. The option exists to configure the device to automati- cally restart after a programmed time delay. A program- mable catastrophic current limit threshold shuts down the switch (circuit breaker) if excessive current is sensed due to a short-circuit condition. 2003 Microchip Technology Inc. DS20091B-page 1MCP18480 Internal comparators are incorporated to add hystere- The PWRGOOD pin indicates the status of the sis for adjusting the Undervoltage Lockout (UVLO) MCP18480 and is active when the device has com- threshold. The external N-channel MOSFET is turned pleted power-up and the system is not in an Undervolt- on when the input is below the user-programmable, age, Overvoltage or current-limit condition. Overvoltage threshold and above the user- PWRGOOD can be externally configured to either programmable, Undervoltage threshold. active-high or active-low to accommodate external cir- cuitry (power supplies) that have either enabling logic. A block diagram of the MCP18480 is shown below. MCP18480 Block Diagram V DRAIN POS TH V POS FET Good (1) (Section 6.8.3) PWRGOOD PWRGOOD Output Block (Section 6.8.8) BIAS (Section 6.8.9) V NEG 12V Regulator GATE 12V OUT Drive 5V GATE Reg. (Section 6.8.7) 5V OUT V REFOUT SENSE V Internal REFIN Bias I SET Generation 5V OV OUT TH OVO Overvoltage (Section 6.8.2) ENABLE UV TH RESTART UV HYS Undervoltage UV Latch D (Section 6.8.1) (Section V 6.8.6) NEG V FB TIMER SENSE Current Limit Current Limit Timer CL Timer R (Section 6.8.4) DISCH Circuit Breaker (Section 6.8.5) MCP18480 Note 1: The PWRGOOD output pin can be either active-high or active-low. This polarity is determined by the voltage (either the level on the V pin or level on the V pin) on the I pin: REFIN NEG SET - Connecting the external R resistor to V configures the PWRGOOD pin as active-low ISET REFIN - Connecting the external R resistor to V configures the PWRGOOD pin as active-high ISET NEG DS20091B-page 2 2003 Microchip Technology Inc. Overvoltage Active Undervoltage Active Current Limit Feedback LATCHOFF TIMEOUT