ADM1026JST ON Semiconductor, ADM1026JST Datasheet - Page 25

• 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

per revolution at 60%, 70%, and 100% of nominal RPM for
fan speeds of 1100, 2200, 4400, and 8800 RPM, and the
divisor that would be used for each of these fans, based on
two tach pulses per revolution.
Limit Values
voltage, so the failure condition of interest is under speed
due to electrical or mechanical failure. For this reason, only
low speed limits are programmed into the limit registers for
the fans. It should be noted that because fan period rather
than speed is being measured, a fan failure interrupt occurs
when the measurement exceeds the limit value.
Fan Monitoring Cycle Time
monitoring cycle time depends on the fan speed, the number
of tach output pulses per revolution, and the number of fans
being monitored.
counter reaches 255 before the second tach pulse after
Chassis Intrusion Input
for detection and signaling of unauthorized tampering with
the system. When this input goes high, the event is latched
in Bit 6 of Status Register 4, and an interrupt is generated.
The bit remains set until cleared by writing a 1 to CI clear,
Bit 1 of Configuration Register 3 (05h), as long as battery
voltage is connected to the V
is cleared by writing a 0 to it.
the ADM1026 is powered off (provided battery voltage is
applied to V
interrupt. Once a chassis intrusion event is detected and
latched, an interrupt is generated when the system is
powered on.
an external circuit that detects, for example, when the cover
has been removed. A wide variety of techniques may be used
for the detection, for example:
•
•
•
Table 5. Fan Speeds and Divisors
Table 5 shows the relationship between fan speed and time
Fans generally do not over−speed if run from the correct
The fan speeds are measured in sequence from 0 to 7. The
If a fan is stopped or running so slowly that the fan speed
The chassis intrusion input is an active high input intended
The CI input detects chassis intrusion events even when
The actual detection of chassis intrusion is performed by
A microswitch that opens or closes when the cover is
removed.
A reed switch operated by magnet fixed to the cover.
A hall−effect switch operated by magnet fixed to the
cover.
Divisor RPM
÷ 1
÷ 2
÷ 4
÷ 8
BAT
) but does not immediately generate an
Nominal Rev
8800
4400
2200
1100
BAT
input. The CI clear bit itself
RPM (ms)
13.64
27.27
54.54
6.82
http://onsemi.com
70% RPM
25
6160
3080
1540
770
initialization or before the fourth tach pulse during
measurement, the measurement is terminated. This also
occurs if an input is configured as GPIO instead of fan. Any
channels connected in this manner time out after 255 clock
pulses.
channel occurs when the counter reaches 254 from start to
the second tach pulse and reaches 255 after the second tach
pulse. Taking into account the tolerance of the oscillator
frequency, the worst−case measurement time is:
509 is the total number of clock pulses.
D is the divisor: 1, 2, 4, or 8.
0.05 ms is the worst−case oscillator period in ms.
the worst−case measurement time for each fan.
monitoring cycle are started together, they are not
synchronized in any other way.
•
of alarm input. Figure 48 shows a temperature alarm circuit
using an AD22105 temperature switch sensor. This
produces a low−going output when the preset temperature is
exceeded, so the output is inverted by Q1 to make it
compatible with the CI input. Q1 can be almost any
small−signal NPN transistor, or a TTL or CMOS inverter
gate may be used if one is available.
General−Purpose I/O Pins (Open Drain)
general−purpose logic input/output (Pins 1, 2, and 43 to 48),
eight pins that can be configured as general−purpose logic
Figure 48. Using the CI Input with a Temperature Sensor
The worst−case measurement time for a fan−configured
The worst−case fan monitoring cycle time is the sum of
Although the fan monitoring cycle and the analog input
The chassis intrusion input can also be used for other types
The ADM1026 has eight pins that are dedicated to
A phototransistor that detects light when the cover is
removed.
where:
Rev 70% (ms)
R
SET
Time Per
19.48
38.96
77.92
9.74
TEMPERATURE
6
3
AD22105
SENSOR
509
7
1
2
D
60% RPM
5280
2640
1320
660
0.05 ms
10kΩ
R1
Q1
V
Rev 60% (ms)
CC
CI
11.36
22.73
45.45
18
90.9
(eq. 17)