1FEATURES

234• Remote diode temperature sensing (2

channels)

• 8 positive voltage inputs with scaling resistors

for monitoring +5 V, +12 V, +3.3 V, +2.5 V,

Vccp power supplies directly

• 2 inputs selectable for fan speed or voltage

monitoring

• 8-bit DAC output for controlling fan speed

• Chassis Intrusion Detector input

• WATCHDOG comparison of all monitored

values

• SMBus™ or I2C Serial Bus interface

compatibility

• VID0-VID4 or IRQ0-IRQ4 monitoring inputs

• On chip temperature sensor

APPLICATIONS

• System Thermal and Hardware Monitoring for

Servers, Workstations and PCs

• Networking and Telecom Equipment

• Office Electronics

• Electronic Test Equipment and

Instrumentation

KEY SPECIFICATIONS

• Voltage Monitoring Error ±2 % (max)

• External Temperature Error ±4 °C (max)

• Internal Temperature Error

– −40 °C to +125 °C ± 3 °C (typ)

• Supply Voltage Range 2.8 to 3.8 V

• Supply Current 0.7 mA (typ)

• ADC and DAC Resolution 8 Bits

• Temperature Resolution 1.0 °C

DESCRIPTION

The LM87 is a highly integrated data acquisition

system for hardware monitoring of servers, Personal

Computers, or virtually any microprocessor-based

system. In a PC, the LM87 can be used to monitor

power supply voltages, motherboard and processor

temperatures, and fan speeds. Actual values for

these inputs can be read at any time. Programmable

WATCHDOG limits in the LM87 activate a fully

programmable and maskable interrupt system with

two outputs (INT# and THERM#).

The LM87 has an on-chip digital output temperature

sensor with 8-bit resolution as well as the capability of

monitoring 2 external diode temperatures to 8-bit

resolution, an 8 channel analog input ADC with 8-bit

resolution and an 8-bit DAC. A channel on the ADC

measures the supply voltage applied to the LM87,

nominally 3.3 V. Two of the ADC inputs can be

redirected to a counter that can measure the speed of

up to 2 fans. A slow speed ΣΔ ADC architecture

allows stable measurement of signals in an extremely

noisy environment. The DAC, with a 0 to 2.5 V output

voltage range, can be used for fan speed control. Additional inputs are provided for Chassis Intrusion

detection circuits, and VID monitor inputs. The VID

monitor inputs can also be used as IRQ inputs if VID

monitoring is not required. The LM87 has a Serial

Bus interface that is compatible with SMBus™ and I2C™.