ADM1276:  Hot Swap Controller and Digital Power and Energy Monitoringwith PMBus Interface

The ADM1276 is a hot swap controller that allows a circuit board to be removed from or inserted into a live backplane. It also features current and voltage readback via an integrated 12-bit analog-to-digital converter (ADC), accessed using a PMBus&tm; interface.

The load current is measured using an internal current sense amplifier that measures the voltage across a sense resistor in the power path via the SENSE+ and SENSE− pins. A default limit of 20 mV is set, but this limit can be adjusted, if required, using a resistor divider network from the internal reference voltage to the ISET pin.

The ADM1276 limits the current through the sense resistor by controlling the gate voltage of an external N-channel FET in the power path, via the GATE pin. The sense voltage--and, therefore, the load current--is maintained below the preset maximum. The ADM1276 protects the external FET by limiting the time that the FET remains on while the current is at its maximum value. This current-limit time is set by the choice of capacitor connected to the TIMER pin. In addition, a foldback resistor network can be used to actively lower the current limit as the voltage across the FET is increased. This helps to maintain constant power in the FET and allows the safe operating area (SOA) to be adhered to in an effective manner.

In case of a short-circuit event, a fast internal overcurrent detector responds within 370 ns and signals the gate to shut down. A 1500 mA pull-down device ensures a fast FET response. The ADM1276 features overvoltage (OV) and undervoltage (UV) protection, programmed using external resistor dividers on the UV and OV pins. A PWRGD signal can be used to detect when the output supply is valid, using the FLB pin to monitor the output. GPO pins can be configured as various output signals that can be asserted when a programmed current or voltage level is reached.

The 12-bit ADC can measure the current in the sense resistor, as well as the supply voltage on the SENSE+ pin or the output voltage. A PMBus interface allows a controller to read current and voltage data from the ADC. Measurements can be initiated by a PMBus command. Alternatively, the ADC can run conti¬nuously, and the user can read the latest conversion data whenever required. As many as four unique PMBus addresses can be selected, depending on the way that the ADR pin is connected.

The ADM1276 is available in a 20-lead LFCSP and has a LATCH pin that can be configured for automatic retry or latch-off when an overcurrent fault occurs.

APPLICATIONS

• Power monitoring and control/power budgeting
• Central office equipment
• Telecommunication and data communication equipment
• PCs/servers