LM87CIMT/NOPB National Semiconductor, LM87CIMT/NOPB Datasheet - Page 14

• 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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Bit 4 of the Channel Mode Register, when set to 1, enables
pin 24 as an active low (IRQ0) interrupt input. When set to 0,
this input is disabled as an IRQ interrupt.
Bit 5 of the Channel Mode Register, when set to 1, enables
pin 23 as an active low (IRQ1) interrupt input. When set to 0,
this input is disabled as an IRQ interrupt.
Bit 6 of the Channel Mode Register, when set to 1, enables
pin 22 as an active low (IRQ2) interrupt input. When set to 0,
this input is disabled as an IRQ interrupt.
Bit 7 of the Channel Mode Register, when set to 1, configures
pins 20 to 24 as interrupt inputs. When set to 0, pins 20 to 24
are configured as processor voltage ID pins.
3.4 Starting Conversions
The monitoring function (Analog inputs, temperature, and fan
speeds) in the LM87 is started by writing to Configuration
Register 1 and setting INT_Clear (Bit 3) low, and Start (bit 0)
high. The LM87 then performs a “round-robin” monitoring of
all analog inputs, temperature, and fan speed inputs approx-
imately once every 0.3 s. The sequence of items being mon-
itored is:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10. +5Vin
11. +12Vin
12. +Vccp2
13. AIN1
14. AIN2
15. Fan 1
16. Fan 2
DACOut immediately changes after the DAC Data Register
in the Value RAM has been updated. For a zero to full scale
transition DACOut will typically settle within 100 μsec of the
stop by master in the write to the DAC Data Register Serial
Bus transaction. The DAC Data Register is not reset by the
INITIALIZATION bit found in the Configuration Register.
3.5 Reading Conversion Results
The conversion results are available in the Value RAM. Con-
versions can be read at any time and will provide the result of
the last conversion. Because the ADC stops, and starts a new
conversion whenever it is read, reads of any single value
should not be done more often than once every 56 ms. When
reading all values, allow at least 0.6 seconds between reading
groups of values. Reading more frequently than once every
0.6 seconds can also prevent complete updates of Interrupt
Status Registers and Interrupt Output's.
A typical sequence of events upon power on of the LM87
would consist of:
1.
2.
3.
4.0 ANALOG INPUTS
All analog input voltages are digitized to 8-bits of resolution.
For safety purposes, and to provide maximum accuracy, a
Check D1 connections
Check D2 connections
Internal Temperature
External D1 Temperature
External D2 Temperature
+2.5V
+Vccp1
Vcc 3.3V
Vcc 5.0V
Set WATCHDOG Limits
Set Interrupt Masks
Start the LM87 monitoring process
14
510 Ω resistor should be placed in series with all analog volt-
age inputs. The resistors will limit the possible current drawn
from the power supplies in the event that circuit board traces
are bridged, or accidentally shorted during test. All analog in-
puts, except for AIN1 and AIN2, include internal resistor at-
tenuators. The theoretical LSB size, theoretical voltage input
required for an ADC reading of 192 (3/4 scale) and 255 (full
scale) for each analog input is detailed in the table below:
Thus monitoring power supplies within a system can be easily
accomplished by tying the Vccp, +2.5Vin, +5Vin and +12Vin
analog inputs to the corresponding system supply. Vcc of the
LM87 will also be monitored. A digital reading can be con-
verted to a voltage by simply multiplying the decimal value of
the reading by the LSB size.
For inputs with attenuators the input impedance is greater
than 90 kΩ. AIN inputs do not have resistor attenuators and
are directly tied to the ADC, therefore having a much larger
input impedance.
A negative power supply voltage can be applied to a AIN input
through a resistor divider referenced to a known positive DC
voltage as shown in
the table below for the circuit of
imately 1.25 V at the AIN analog inputs of the LM87 for a
nominal reading of 128.
Measurement
Input
2.5Vin
3.3Vcc
5Vin/Vcc
12Vin
Vccp1, Vccp2
AIN1/AIN2
table provide approximately 1.25V at the Vccp inputs.
FIGURE 6. Input Examples. Resistor values shown in
Voltage
−12V
(V
−5V
s
S
)
20 kΩ
20 kΩ
R2
Figure
LSB size
13 mV
17.2 mV
26 mV
62.5 mV
14.1 mV
9.8 mV
61.0 kΩ
130 kΩ
6. The resistor values shown in
R1
Figure 6
Vin for 192 Vin for 255
2.5 V
3.3 V
5 V
12 V
2.7 V
1.875 V
+3.3 V
+3.3 V
V
will provide approx-
+
( ADC code
3.320 V
4.383 V
6.641 V
15.93 V
3.586 V
2.49 V
Voltage
Analog
+1.25 V
+1.25 V
Inputs
128)
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