LM75BIMM-3+ Maxim Integrated Products, LM75BIMM-3+ Datasheet - Page 10

• Manufacturer Part Number: LM75BIMM-3+
• Description: IC TEMP SENSOR WATCHDOG 8MSOP
• Manufacturer: Maxim Integrated Products

Specifications of LM75BIMM-3+

• Function: Temp Sensor, Watchdog
• Topology: ADC (Sigma Delta), Comparator, Register Bank
• Sensor Type: Internal
• Sensing Temperature: -55°C ~ 125°C
• Output Type: I²C™
• Output Alarm: Yes
• Output Fan: Yes
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -55°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Digital Temperature Sensor and Thermal
Watchdog with 2-Wire Interface
The 8-bit Configuration register sets the fault queue, OS
polarity, shutdown control, and whether the OS output
functions in comparator or interrupt mode. When writing
to the Configuration register, set bits D7, D6, and D5 to
zero (see Table 5).
Bits D4 and D3, the fault queue bits, determine the
number of faults necessary to trigger an OS condition
(see Table 6). The number of faults set in the queue
must occur consecutively to trip the OS output. The
fault queue prevents OS false tripping in noisy environ-
ments.
Set bit D2, the OS polarity bit, to zero to force the OS
output polarity to active low. Set bit D2 to 1 to set the
OS output polarity to active high. OS is an open-drain
output under all conditions and requires a pullup resis-
tor to output a high voltage (see Figure 1).
Set bit D1, the comparator/interrupt bit to zero to oper-
ate OS in comparator mode. In comparator mode, OS
is asserted when the temperature rises above the T
value. OS is deasserted when the temperature drops
below the T
operate OS in interrupt mode. OS is asserted in inter-
rupt mode when the temperature rises above the T
value or falls below the T
only after performing a read operation.
Set bit D0, the shutdown bit, to zero for normal opera-
tion. Set bit D0 to 1 to shutdown the LM75’s internal
blocks. The I
shutdown bit is set. The T
registers can still be written to and read from while in
shutdown.
LM75 measures the temperature of its own die. The
thermal path between the die and the outside world
determines the accuracy of temperature measure-
ments. Most of the heat flows in to or out of the die
Table 5. Configuration Register Definition
10
______________________________________________________________________________________
D7
0
HYST
2
C interface remains active as long as the
Applications Information
value (see Figure 1). Set bit D1 to 1 to
D6
0
HYST
OS
Configuration Register
, T
value. OS is deasserted
HYST
D5
0
, and Configuration
Fault Queue
D4
OS
OS
Fault Queue
Table 6. Configuration Register Fault
Queue Bits
through the leads. Because of this, the LM75 most easi-
ly measures the PCB temperature. For ambient temper-
ature measurements, mount the LM75 on a separate
PCB away from high power sources. Temperature
errors due to self heating of the LM75 die is minimal
due to the low supply current.
The lowpass filters in the SCL and SDA digital lines miti-
gate the effects of bus noise, and make communica-
tions in noisy environments more robust. Good layout
practices also help. Keep switching power supplies
away from digital lines, and arrange for high-speed dig-
ital traces to cross SCL and SDA at right angles.
Properly terminate long PCB traces and bus traces
connected to multiple slaves.
Serial bus no-acknowledge (which causes unnecessary
bus traffic) is the most common symptom of excessive
noise coupling into the SDA and SCL lines. Noise with
amplitude greater than the LM75’s hysteresis (400mV
typ), overshoot greater than 300mV above +V
undershoot more than 300mV below GND may prevent
successful serial communication.
Resistance can be added in series with the SDA and
SCL lines to help filter noise and ringing. A 5kΩ resistor
placed in series with the SCL line and as close as pos-
sible to the SCL pin, with the 5pF to 10pF stray capaci-
tance of the device, provides a 6MHz to 12MHz
lowpass filter, which is sufficient filtering in many cases.
D3
D4
0
0
1
1
OS Polarity
D3
0
1
0
1
D2
Comparator/
NUMBER OF FAULTS
Digital Noise Issues
Interrupt
D1
1 (POR state)
2
4
6
Shutdown
D0
S
, and
P-P
,