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™.