ADI ADM1073ARUZ-REEL7

The ADM1073 is a full-feature, negative voltage, hot swap controller that allows boards to be safely inserted and removed from a live -48 V backplane. The part provides precise and robust current limiting, and protection against both transient and nontransient short circuits in overvoltage and undervoltage conditions. The ADM1073 can operate from a negative voltage of -18 V to -80 V and can tolerate transient voltages of up to -200 V.

Inrush current is limited to a programmable value by controlling the gate drive of an external N-channel FET. The maximum current limit is set by the choice of the sense resistor, RSENSE.

A built-in soft start function allows control of the inrush current profile by an external capacitor on the soft start (SS) pin.

An external capacitor on the TIMER pin determines the time for which the FET gate is controlled to be high when maximum inrush current flows. The ADM1073 employs a limited consecutive retry scheme, whereby, if the load capacitance is not fully charged within one attempt, the FET gate is pulled low and retries after a cooling period.

Further control of the inrush current is provided by modulating the width of the pulses, depending on the drain-source voltage across the FET. This allows maximum charge transfer to the load capacitance while maintaining the FET in its safe operating area (SOA).

The default duty cycle of the pulse train is 6%, decreasing to 2.5% with maximum FET drain-source voltage, with a maximum of seven successive autorestarts. After seven successive autorestarts, the fault is latched and the part goes into shutdown, with the result that the external FET is disabled until the power is reset. The LATCHED output signal indicates when the seven retries are complete.

Further programmability is offered by allowing alteration of the default 6% ratio. An extra resistor between the TIMER pin and VEE allows the ratio of on-time to off-time to be decreased, while a resistor between TIMER and VIN allows the ratio to be increased.

The ADM1073 has separate UV and OV pins for undervoltage and overvoltage detection. The FET is turned off, if a nontransient voltage less than the undervoltage threshold (typically -36 V) is detected on the UV pin, or if greater than the overvoltage threshold (typically -80 V) is detected on the OV pin. The operating voltage window of the ADM1073 is programmable via resistor networks on the UV and OV pins. The hysteresis levels on the undervoltage and overvoltage detectors can also be altered (see the Undervoltage/Overvoltage Detection section). The SPLYGD output signal indicates when the backplane supply is within the externally programmable operating voltage range.

Other functions include PWRGD output, which can be used to enable a power module (the DRAIN pin is monitored to determine when the load capacitance is fully charged) SHDN input to manually disable the GATE drive RESTART input to remotely initiate a 5 second shutdown

The ADM1073 is fabricated using BiCMOS technology for minimal power consumption and is available in a 14-lead TSSOP package.

• Precision inrush linear current limit
• Soft start inrush current limit profiling
• Precision maximum on-time in current limit
• Maximum on-time modulated by FET drain voltage for additional SOA protection
• Adjustable PWM retry scheme and multiple device cascading capability for charging large capacitive loads
• Limited number of PWM cycles for FET SOA protection under short circuit condition
• Ability to configure device as continuous autoretry with a 5-second cooling period
• Shunt regulator topology to allow very large transient input supplies
• Separate UV and OV pins for programming allowable input supply window
• Programmable OV hysteresis using current source into pin when supply is high
• Programmable UV hysteresis using current sink from pin when supply is low
• PWRGD output indicates when capacitor charging complete
• SPLYGD output indicates when supply is within valid window
• LATCHED output indicates the end of the retry cycle before load capacitance is charged
• SHDN input for user-commanded shutdown
• RESTART input for user-triggered 5-second shutdown and autorestart— virtual card reseat

• Central office switching
• Telecommunication and data communication equipment
• -48 V distributed power systems
• Negative power supply control
• High availability servers
• -48 V power supply modules
• Disk arrays