LM96080CIMTX/NOPB National Semiconductor, LM96080CIMTX/NOPB Datasheet - Page 15

• Manufacturer Part Number: LM96080CIMTX/NOPB
• Description: IC HARDWARE MONITOR 24-TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM96080CIMTX/NOPB

• Function: Hardware Monitor
• Topology: ADC (Sigma Delta), Comparator, Fan Speed Counter, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: -40°C ~ 125°C, External Sensor
• Output Type: I²C™
• Output Alarm: No
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 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: LM96080CIMTX

6.0 LAYOUT AND GROUNDING
Analog inputs will provide best accuracy when referred to the
AGND pin or a supply with low noise. A separate, low-
impedance ground plane for analog ground, which provides
a ground point for the voltage dividers and analog compo-
nents, will provide best performance but is not mandatory.
Analog components such as voltage dividers should be lo-
cated physically as close as possible to the LM96080.
The power supply bypass, a parallel combination of 10 μF
(electrolytic or tantalum) and 0.1 μF (ceramic) bypass capac-
itors connected between V
be located as close as possible to the LM96080.
7.0 FAN INPUTS
Inputs are provided for signals from fans equipped with
tachometer outputs. These are logic-level inputs set accord-
ing to the Fan Tach Pulse Inputs in the Electrical Character-
istic table. Signal conditioning in the LM96080 accommo-
dates the slow rise and fall times typical of fan tachometer
outputs. The maximum input signal range is 0 to +5.5V. In the
event these inputs are supplied from fan outputs which ex-
ceed 0 to +5.5V, either resistive division or diode clamping
must be included to keep inputs within an acceptable range.
R2 is selected so that it does not develop excessive error
voltage due to input leakage. R1 is selected based on R2 to
provide a minimum input of 2V and a maximum of 5.5V. R1
should be as low as possible to provide the maximum possible
input up to 5.5V for best noise immunity. Alternatively, use a
shunt reference or zener diode to clamp the input level.
If fans can be powered while the power to the LM96080 is off,
the LM96080 inputs must be protected to meet the ABSO-
(b) Fan with Tach Pull-Up to +12V, or Totem-Pole Output and Resistor Attenuator
+
, pin 9, and ground, should also
(a) Fan with Tach Pull-Up to +5V
15
LUTE MAXIMUM RATINGS section. In most cases, open
collector outputs with pull-up resistors inherently limit this cur-
rent. If this maximum current could be exceeded, either a
larger pull up resistor should be used or resistors connected
in series with the fan inputs.
The Fan Inputs gate an internal 22.5 kHz oscillator for one
period of the Fan signal into an 8-bit counter (maximum count
= 255). The default divisor is set to 2 (choices are 1, 2, 4, and
8) providing a nominal count of 153 for a 4400 RPM fan with
two pulses per revolution. Typical practice is to consider 70%
of normal RPM a fan failure, at which point the count will be
219.
Determine the fan count according to:
For example, if the frequency of the tachometer were 150 Hz,
the RPM would be 4,500 [RPM = (freq) × (60 seconds/min) /
(2 pulses/revolution) ]. Since the default divisor is 2, the count
would be 150 according to the equation above.
Note that Fan 1 and Fan 2 Divisors are programmable via the
Fan Divisor/RST_OUT/OS Register (address 05h).
FAN1 and FAN2 inputs can also be programmed to be level
sensitive interrupt inputs.
Fans that provide only one pulse per revolution would require
a divisor set twice as high as fans that provide two pulses,
thus maintaining a nominal fan count of 153. Therefore, the
divisor should be set to 4 for a fan that provides 1 pulse per
revolution with a nominal RPM of 4400.
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