GENERAL DESCRIPTION

The ADM1281 is a hot-swap controller that allows a circuit board

to be removed from or inserted into a live backplane. It also

features current, voltage, power, and temperature readback through

an integrated 12-bit analog-to-digital converter (ADC), accessed

using a PMBus™ interface. The load current is measured using an

internal current sense amplifier that measures the voltage across a

sense resistor in the power path through the HS+ and HS− pins. A

default current limit of 20 mV is set, but this limit can be adjusted, if

required.

The ADM1281 limits the current through the sense resistor by controlling

the gate voltage of an external N-channel FET in the power

path, through the GATE pin. The sense voltage, and therefore

the load current, is maintained below the preset maximum. The

ADM1281 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 constant power foldback scheme is used

to control the power dissipation in the MOSFET during power-up

and fault conditions. The level of this power, along with the TIMER

regulation time, can be set to ensure that the MOSFET remains

within safe operating area (SOA) limits.

In case of a short-circuit event, a fast internal overcurrent detector

responds within 290 ns and signals the gate to shut down. A 2400

mA pull-down device ensures a fast FET response.

The ADM1281 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 PWGIN pin to accurately monitor

the output.

The ADM1281 is available in a 32-lead LFCSP with a RETRY pin

that can be configured for automatic retry or latch-off when an

overcurrent fault occurs.

FEATURES

► Drop-in replacement to ADM1278

► ±0.3% accurate, 12-bit ADC for IOUT, VIN, VOUT, and temperature

► 290 ns response time to short-circuit

► Shutdown on detection of FET health fault

► Constant power foldback for tighter FET SOA protection

► Remote temperature sensing with programmable warning and

shutdown thresholds

► Resistor-programmable 5 mV to 25 mV VSENSE current limit

► Programmable start-up current limit

► 1% accurate UV, OV, and PWRGD thresholds

► Split hot-swap and power monitor inputs to allow additional

external ADC filtering

► Reports power and energy consumption over time

► Peak detect registers for current, voltage, and power

► PROCHOT power throttling capability

► PMBus fast mode compliant interface

► Available in 5 mm × 5 mm, 32-lead LFCSP package

APPLICATIONS

► Servers

► Power monitoring and control/power budgeting

► Telecommunication and data communication equipment