LM96080
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SNAS465D –SEPTEMBER 2009–REVISED MARCH 2013
FUNCTIONAL DESCRIPTION
GENERAL DESCRIPTION
The LM96080 provides 7 analog inputs, a temperature sensor, a delta-sigma ADC (Analog-to-Digital Converter),
2 fan speed counters, WATCHDOG registers, and a variety of inputs and outputs on a single chip. A two wire
Serial Bus interface is also provided. The LM96080 can perform power supply, temperature and fan monitoring
for a variety of computer systems. The LM96080 is pin and software backwards compatible with the LM80.
The LM96080 continuously converts analog inputs to 10-bit resolution with a 2.5 mV LSb (Least Significant bit)
weighting, yielding input ranges of 0 to 2.56V. The Analog Inputs, IN0 - IN6, are intended to be connected to the
several power supplies present in a typical communications infrastructure system. Temperature can be converted
to a 9-bit or 12-bit two's complement word with resolutions of 0.5°C LSb or 0.0625°C LSb, respectively.
Fan inputs can be programmed to accept either fan failure indicator or tachometer signals. Fan failure signals
can be programmed to be either active high or active low. Fan inputs measure the period of tachometer pulses
from the the fans, providing a higher count for lower fan speeds. The fan inputs are digital inputs with transition
levels according to the Fan Tach Pulse Inputs in the Electrical Characteristics table. Full scale fan counts are 255
(8-bit counter), which represent a stopped or very slow fan. Nominal speeds, based on a count of 153, are
programmable from 1100 to 8800 RPM. Signal conditioning circuitry is included to accommodate slow rise and
fall times.
The LM96080 provides a number of internal registers. These include:
•Configuration Register: Provides control and configuration.
•Interrupt Status Registers: Two registers to provide status of each WATCHDOG limit or Interrupt event.
•Interrupt Mask Registers: Allows masking of individual Interrupt sources, as well as separate masking for
each of both hardware Interrupt outputs.
•Fan Divisor/RST_OUT/OS Registers: Bits 0-5 of this register contain the divisor bits for FAN1 and FAN2
inputs. Bits 6-7 control the function of the RST_OUT/OS output.
•OS Configuration/Temperature Resolution Register: The configuration of the OS (Overtemperature
Shutdown) is controlled by the lower 3 bits of this register. Bit 3 enables 12-bit temperature conversions. Bits
4-7 reflect the lower four bits of the temperature reading for a 12-bit resolution.
•Conversion Rate Register: Controls the conversion rate of the round robin cycle to either continuous or 728
ms.
•Voltage/Temperature Channel Disable Register: Allows voltage inputs and the local temperature
conversion to be disabled.
•Value RAM: The monitoring results: temperature, voltages, fan counts, and Fan Divisor/RST_OUT/OS
Register limits are all contained in the Value RAM. The Value RAM consists of a total of 32 bytes. The first 10
bytes are all of the results, the next 20 bytes are the Watchdog Register limits, and the last two bytes are at
the upper locations for Manufacturers ID and Device Stepping/Die Revision ID.
The LM96080 is compatible with Standard Mode (Sm, 100 kbits/s) and Fast Mode (Fm, 400 kbits/s) I2C interface
modes of operation. LM96080 includes an analog filter on the I2C digital control lines that allows improved noise
immunity and supports TIMEOUT reset function on SDA and SCL that prevents I2C bus lockup. Three address
pins, A0 - A2, allow up to 8 parts on a single bus.
When enabled, the LM96080 starts by cycling through each measurement in sequence, and it continuously loops
through the sequence based on the Conversion Rate Register (address 07h) setting. Each measured value is
compared to values stored in WATCHDOG, or Limit Registers (addresses 2Ah - 2Dh). When the measured value
violates the programmed limit, the LM96080 will set a corresponding Interrupt in the Interrupt Status Registers
(addresses 01h - 02h).
Two output Interrupt lines, INT and RST_OUT/OS, are available. INT is fully programmable with masking of each
Interrupt source, and masking of each output. RST_OUT/OS is dedicated to the temperature reading
WATCHDOG registers. In addition, the Fan Divisor register has control bits to enable or disable the hardware
Interrupts.
Additional digital inputs are provided for daisy chaining the Interrupt output pin, INT. This is done by connecting
multiple external temperature sensors (i.e. LM75 or LM73) to the BTI (Board Temperature Interrupt) input and/or
the GPI (Chassis Intrusion) input. The Chassis Intrusion input is designed to accept an active high signal from an
external circuit that latches, such as when the cover is removed from the computer.
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