Texas Instruments LM96080 Evaluation Board LM96080EB/NOPB LM96080EB/NOPB 데이터 시트
제품 코드
LM96080EB/NOPB
I+ = (1293 x I
+
TEMP
) + (1116 x 7 x I
+
VOLTAGE
) + (253037 x I
+
SHUTDOWN
)
262,142
SNAS465D – SEPTEMBER 2009 – REVISED MARCH 2013
SUPPLY CURRENT (I
+
)
The measured supply current (I
+
) in the Electrical Characteristics are only for the round robin conversion and the
shutdown mode at a certain supply voltage. To calculate the supply current I
+
in the round robin mode at different
supply voltages, use the equation below.
(3)
The I
+
TEMP
, I
+
VOLTAGE
, and I
+
SHUTDOWN
values can be obtained from the plots shown in
.
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 components, will provide best performance but is not mandatory. Analog components such as voltage
dividers should be located physically as close as possible to the LM96080.
low-impedance ground plane for analog ground, which provides a ground point for the voltage dividers and
analog components, will provide best performance but is not mandatory. Analog components such as voltage
dividers should be located physically as close as possible to the LM96080.
The power supply bypass, a parallel combination of 10
μ
F (electrolytic or tantalum) and 0.1
μ
F (ceramic) bypass
capacitors connected between V
+
, pin 9, and ground, should also be located as close as possible to the
LM96080.
FAN INPUTS
Inputs are provided for signals from fans equipped with tachometer outputs. These are logic-level inputs set
according to the Fan Tach Pulse Inputs in the
according to the Fan Tach Pulse Inputs in the
table. Signal conditioning in the LM96080
accommodates 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 exceed 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.
0 to +5.5V. In the event these inputs are supplied from fan outputs which exceed 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
section. In most cases, open collector outputs with pull-up resistors inherently limit
this current. 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.
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.
(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:
(4)
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.
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.
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.
Copyright © 2009–2013, Texas Instruments Incorporated
17
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