NCT75
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6
Figure 4. One-shot OS
/ALERT
Pin Operation
OS
/ALERT
PIN
(COMPARATOR MODE)
POLARITY = 0
OS
/ALERT
PIN
(INTERRUPT MODE)
POLARITY = 0
OS
/ALERT
PIN
(COMPARATOR MODE)
POLARITY = 1
OS
/ALERT
PIN
(INTERRUPT MODE)
POLARITY = 1
T
HYST
T
OS
82癈
81癈
80癈
79癈
78癈
77癈
76癈
75癈
74癈
73癈
72癈
Fault Queue
A fault is defined as when the temperature exceeds
a pre-defined   temperature   limit.   This   limit   can   be
programmed in the T
HYST
and the T
OS
setpoint registers.
Bits 3 and 4 of the configuration register determine the
number of faults necessary to trigger the OS
/ALERT
pin. Up
to six faults can be programmed to prevent false tripping
when the NCT75 is used in a noisy temperature
environment. In order for the OS
/ALERT
output to be set
these faults must occur consecutively.
Registers
The NCT75 contains six registers for configuring and
reading the teperature: the address pointer register, 4 data
registers and a one-shot register. The configuration register,
the address pointer register and the one-shot register are all
8 bits wide while the temperature register, T
HYST
and T
OS
registers are all 16 bits wide. All registers, except for the
temperature register, can be be read from and written to (the
temperature register is read only). The power on state and
address of each register are listed in Table 9.
Address Pointer Register
The address pointer register is used to select which
register is to respond to a read or write operation. The three
LSBs (P2, P1 & P0) of this write only register are used to
select the appropriate register. On power up this register is
loaded with a value of 0x00 and so points to the temperature
register. Table 7 shows the bits of the address pointer register
and Table 8 shows the pointer address selecting each of the
registers available.
Table 7. ADDRESS POINTER REGISTER
P7
P6
P5
P4
P3
P2
P1
P0
Default
0
0
0
0
0
0
0
0
Table 8. REGISTER ADDRESSES SELECTION
P2
P1
P0
Register Selected
0
0
0
Stored Temperature
0
0
1
Configuration
0
1
0
T
HYST
Setpoint
0
1
1
T
OS
Setpoint
1
0
0
One-shot
Table 9. NCT75 REGISTER SET
Register
Address
Register Name
Power-on
Default Value
Hex
5C
0x00 (R)
Stored Temperature Value
0x0000
0
0x01 (R/W)
Configuration
0x00
0x02 (R/W)
T
HYST
0x4B00
75
0x03 (R/W)
T
OS
0x5000
80
0x04 (R/W)
One-shot
0xXX