LM87CIMT/NOPB National Semiconductor, LM87CIMT/NOPB Datasheet - Page 8

• Manufacturer Part Number: LM87CIMT/NOPB
• Description: IC INTERFACE SER MONITOR 24TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM87CIMT/NOPB

• Function: Hardware Monitor
• Topology: ADC (Sigma Delta), Comparator, Fan Speed Control, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: I²C™/SMBus™
• Output Alarm: No
• Output Fan: Yes
• Voltage - Supply: 2.8 V ~ 3.8 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 24-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM87CIMT; *LM87CIMT/NOPB; LM87CIMT

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Test Circuit
Typical Performance Characteristics
Functional Description
1.0 GENERAL DESCRIPTION
The LM87 provides 7 analog inputs, an internal junction type
temperature sensor, two remote junction temperature sens-
ing channels, a Delta-Sigma ADC (Analog-to-Digital Convert-
er), a DAC output, 2 fan speed counters, WATCHDOG
registers, and a variety of inputs and outputs on a single chip.
A two wire SMBus Serial Bus interface is included. The LM87
performs power supply, temperature, fan control and fan
monitoring for personal computers.
The analog inputs are useful for monitoring several power
supplies present in a typical computer. The LM87 includes
internal resistor dividers that scale external Vccp1, Vccp2,
+2.5V, +5.0 V, +12 V and internal +3.3V power supply volt-
ages to a 3/4 scale nominal ADC output. Two additional
FIGURE 3. Digital Output Load Test Circuitry
DAC Power Supply Sensitivity
8
inputs, +AIN1 and +AIN2 (2.5V full scale) are input directly
with no resistive dividers. The LM87 ADC continuously con-
verts the scaled inputs to 8-bit digital words. Measurement of
negative voltages (such as -5 V and -12 V power supplies)
can be accommodated with an external resistor divider ap-
plied to the +AIN1 or +AIN2 inputs. Internal and external
temperature is converted to 8-bit two's-complement digital
words with a 1 °C LSB.
Fan inputs measure the period of tachometer pulses from the
fans, providing a higher count for lower fan speeds. The fan
inputs are Schmitt-Trigger digital inputs with an acceptable
range of 0 V to V
2. Full scale fan counts are 255 (8-bit counter) and this rep-
resents a stopped or very slow fan. Nominal speeds, based
on a count of 153, are programmable from 1100 to 8800 RPM
on FAN1 and FAN2. Schmitt-Trigger input circuitry is included
+
10099536
and a transition level of approximately V
10099506
+
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