LM75ADP View Datasheet(PDF) - Philips Electronics
Part Name
Description
Manufacturer
LM75ADP Datasheet PDF : 18 Pages
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Philips Semiconductors
Digital temperature sensor and thermal Watchdog™
Product data sheet
LM75A
OS output and polarity
The OS output is an open-drain output and its state represents
results of the device Watchdog operation as described in the
“General operation” section. In order to observe this output state, an
external pull-up resistor is needed. The resistor should be as large
as possible, up 200 kΩ, to minimize the temp reading error due to
internal heating by the high OS sinking current.
The OS output active state can be selected as HIGH or LOW by
programming bit B2 of the Configuration register: setting B2 to 1
selects OS active HIGH and setting B2 to 0 sets OS active LOW.
At power-up, this bit is equal to 0 and the OS active state is LOW.
OS comparator and interrupt modes
As described in the “General operation” section, the device OS
output responds to the result of the comparison between the Temp
data and the programmed limits, Tos and Thyst, in different ways
depending on the selected OS mode: OS comparator or OS
interrupt. The OS mode is selected by programming bit B1 of the
configuration register: setting B1 to 1 selects the OS interrupt mode,
and setting B1 to 0 selects the OS comparator mode. At power up,
this bit is equal to 0 and the OS comparator is selected.
The main difference between the two modes is that in OS
comparator mode, the OS output becomes active when the Temp
has exceeded the Tos and reset when the Temp has dropped below
the Thyst, reading a register or putting the device into shut-down
does not change the state of the OS output; while in OS interrupt
mode, once it has been activated either by exceeding the Tos or
dropping below the Thyst, the OS output will remain active
indefinitely until reading a register or putting the device into
shut-down occurs, then the OS output is reset.
The Tos & Thyst limits must be selected so that Tos temp value >
Thyst temp value. Otherwise, the OS output state will be undefined.
OS fault queue
Fault queue is defined as the number of faults that must occur
consecutively to activate the OS output. It is provided to avoid false
tripping due to noise. Because faults are determined at the end of
data conversions, fault queue is also defined as the number of
consecutive conversions returning a temperature trip. The value of
fault queue is selectable by programming the two bits B4 and B3 of
the configuration register. Notice that the programmed data and the
fault queue value are not the same. The Fault queue table (Table 11)
shows the one-to-one relationship between them. At power-up, fault
queue data = 0 and fault queue value = 1.
Table 11. Fault queue table
Fault queue data
B4
B3
0
0
0
1
1
0
1
1
Fault queue value
Decimal
1
2
4
6
Shutdown mode
The device operation mode is selected by programming bit B0 of the
Configuration register: Setting B0 to 1 will put the device into
shut-down mode. Resetting B0 to 0 for the device normal mode.
In shut-down mode, the device draws a small current of about
3.5 µA and the power dissipation is minimized; the temperature
conversion stops, but the I2C interface remains active and register
write/read operation can be performed. If the OS output is in
comparator mode, then it remains unchanged. Otherwise, the OS
output is reset in interrupt mode.
Power-up default and Power-on Reset
The LM75A always powers-up in its default state with:
– Normal operation mode
– OS comparator mode
– Tos = 80 °C
– Thyst = 75 °C
– OS output active state = LOW
– Pointer value = 0.
When the power supply voltage is dropped below the device
power-on reset level of about 1.9 V (POR) and then rises up again,
the device will be reset to its default condition as listed above.
2004 Oct 05
11
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