ADM1026JST ON Semiconductor, ADM1026JST Datasheet - Page 23

• Manufacturer Part Number: ADM1026JST
• Description: IC CNTRL SYS REF/EEPROM 48LQFP
• Manufacturer: ON Semiconductor

Specifications of ADM1026JST

• Rohs Status: RoHS non-compliant
• Function: Hardware Monitor
• Topology: ADC, Comparator, Multiplexer, Register Bank
• Sensor Type: External & Internal
• Sensing Temperature: 0°C ~ 100°C, External Sensor
• Output Type: SMBus™
• Output Alarm: No
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: 0°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 48-LFQFP

exceeds the corresponding T
2 seconds with the fan drive set to maximum (full scale from
the DAC or 100% PWM duty cycle). The fan speed is then
set to the minimum as previously defined. As the
temperature increases, the fan drive increases until the
temperature reaches T
is given by:
DAC code increases linearly up to 240, not its full scale of
255. However, when the temperature exceeds T
the DAC output jumps to full scale. To ensure that the
maximum cooling capacity is always available, the fan drive
is always set by the sensor channel demanding the highest
fan speed.
temperature measured by all three temperature sensors has
fallen to their corresponding T
fan from cycling on and off continuously when the
temperature is close to T
control, a one−off interrupt is generated at the INT output.
This is described in more detail in the section on the
ADM1026 Interrupt Structure.
PWM + PWM
OUTPUT
DAC + DAC
PWM
When the temperature measured by any of the sensors
The fan drive at any temperature up to 20°C above T
For simplicity of the automatic fan speed algorithm, the
If the temperature falls, the fan does not turn off until the
Whenever a fan starts or stops during automatic fan speed
100%
Figure 41. Automatic PWM Fan Control Transfer
MIN
or
MIN
MIN
T
) 240 * DAC
) 100 * PWM
MIN
SPIN UP FOR 2 SECONDS
ć 45C
MIN
Function
MIN
+ 20°C.
TEMPERATURE
T
.
MIN
MIN
MIN
MIN
, the fan is spun up for
MIN
− 4°C. This prevents the
T
T
ACTUAL
ACTUAL
T
MIN
+ 205C
MIN
20
20
* T
* T
(eq. 13)
(eq. 14)
+20°C,
http://onsemi.com
MIN
MIN
MIN
23
Fan Inputs
measuring inputs by clearing the corresponding bit(s) of
Configuration
general−purpose logic inputs/outputs by setting bits in this
register. The power−on default value for this register is 00h,
which means all the inputs are set for fan speed
measurement.
slow rise and fall times typical of fan tachometer outputs.
The fan tach inputs have internal 10 kW pullup resistors to
3.3 V STBY. In the event that these inputs are supplied from
fan outputs that exceed the supply, either resistive
attenuation of the fan signal or diode clamping must be
included to keep inputs within an acceptable range.
Figure 44 through Figure 47 show circuits for common fan
tach outputs.
pullup to V
input, as shown in Figure 44.
voltage greater than 3.3 V STBY), the fan output can be
clamped with a Zener diode, as shown in Figure 46. The
Zener voltage should be chosen so that it is greater than V
but less than 3.3 V STBY, allowing for the voltage tolerance
of the Zener.
OUTPUT
DAC
Pins 3 to 6 and 9 to 12 may be configured as fan speed
Signal conditioning in the ADM1026 accommodates the
If the fan tach output is open−drain or has a resistive
If the fan output has a resistive pullup to +12 V (or other
Figure 42. Automatic DAC Fan Control Transfer
MIN
255
Figure 43. Fan with Tach Pullup to +V
CC
12 V
, then it can be connected directly to the fan
PULLUP
4.7kΩ
TYP
Register
T
MIN
SPIN UP FOR 2 SECONDS
- 45C
Function
TEMPERATURE
T
2
MIN
(Address
FAN(0–7)
FAN SPEED
T
COUNTER
01h),
MIN
V
CC
+ 205C
CC
240
or
as
IH