Rainbow Electronics MAX7502 - Manual (Page 9)

temperature rises above the T OS value. OS is deassert-
ed when the temperature drops below the T
HYST
value.
See Figure 4. Set bit D1 to 1 to run the over-tempera-
ture shutdown block in interrupt mode. OS is asserted
in interrupt mode when the temperature rises above the
T
OS value or falls below the T HYST value. OS is
deasserted only after performing a read operation.
Set bit D0, the shutdown bit, to zero for normal opera-
tion. Set bit D0 to 1 to shut down the MAX7500/
MAX7501/MAX7502 internal blocks, dropping the sup-
ply current to 3µA. The I
2 C interface remains active as
long as the shutdown bit is set. The T
OS
, T
HYST
, and
configuration registers can still be written to and read
from while in shutdown.
T OS and T HYST Registers
In comparator mode, the OS output behaves like a ther-
mostat. The output asserts when the temperature rises
above the limit set in the T
OS
register. The output
deasserts when the temperature falls below the limit set
in the T
HYST register. In comparator mode, the OS output
can be used to turn on a cooling fan, initiate an emer-
gency shutdown signal, or reduce system clock speed.
In interrupt mode, exceeding T
OS
also asserts OS. OS
remains asserted until a read operation is performed on
any of the registers. Once OS has asserted due to
crossing above T
OS and is then reset, it is asserted
again only when the temperature drops below T HYST .
The output remains asserted until it is reset by a read.
Putting the MAX7500/MAX7501/MAX7502 into shut-
down mode also resets OS.
The T OS and T HYST registers are accessed with 2
bytes, with bits D15–D7 containing the data. Bits
D6–D0 are don’t cares when writing to these two regis-
ters and read-back zeros when reading from these reg-
isters. The LSB represents 0.5
°C while the MSB
represents 64
°C. See
Table 7.
MAX7500/MAX7501/MAX7502
Digital Temperature Sensors and Thermal
Watchdog with Bus Lockup Protection
_______________________________________________________________________________________ 9
D7 D6 D5 D4 D3 D2 D1 D0
0 0 0 Fault queue Fault queue OS polarity
Comparator/
interrupt
Shutdown
Table 5. Configuration Register Definition
D4 D3 NO. OF FAULTS
0 0 1 (POR state)
0 1 2
1 0 4
1 1 6
Table 6. Configuration Register Fault
Queue Bits
T OS
T
HYST
OS OUTPUT
(COMPARATOR MODE)
OS SET ACTIVE LOW
OS OUTPUT
(INTERRUPT MODE)
OS SET ACTIVE LOW
READ
OPERATION
READ
OPERATION
READ
OPERATION
TEMPERATURE
Figure 4. OS Timing Diagram
UPPER BYTE LOWER BYTE
COMMAND
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
Write
Sign bit
1 = negative
0 = positive
MSB
64 °C
32 °C 16 °C 8 °C 4 °C 2 °C 1 °C
LSB
0.5 °C
x x x x x x x
Read
Sign bit
1 = negative
0 = positive
MSB
64 °C
32 °C 16 °C 8 °C 4 °C 2 °C 1 °C
LSB
0.5 °C
0 0 0 0 0 0 0
Table 7. T
OS
and T
HYST
Register Definitions
X = Don’t care.