Rainbow Electronics MAX7502 - Manual (Page 8)

MAX7500/MAX7501/MAX7502
Register Descriptions
The MAX7500/MAX7501/MAX7502 have an internal pn-
junction-based temperature sensor whose analog out-
put is converted to digital form using a 9-bit
sigma-delta ADC. The measured temperature and tem-
perature configurations are controlled by the tempera-
ture, configuration, T
HYST
, and T
OS
registers. See
Table 2.
Temperature Register
Read the measured temperature through the tempera-
ture register. The temperature data format is 9 bits,
two’s complement, and the register is read out in 2
bytes: an upper byte and a lower byte. Bit D15 is the
sign bit. When bit D15 is 1, the temperature reading is
negative. When bit D15 is zero, the temperature read-
ing is positive. Bits D14–D7 contain the temperature
data, with the LSB representing 0.5
°C and the MSB
representing 64
°C (see
Table 3). The MSB is transmit-
ted first. The last 7 bits of the lower byte, bits D6–D0,
are don’t cares. When reading the temperature register,
bits D6–D0 must be ignored. When the measured tem-
perature is greater than +127.5
°C, the value stored in
the temperature register is clipped to 7F8h. When the
measured temperature is below -64
°C, the value in the
temperature register is clipped to BF8h.
During the time of reading the temperature register, any
changes in temperature are ignored until the read is
completed. The temperature register is updated upon
completion of the next conversion.
Table 3 lists the temperature register definition.
Configuration Register
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 to trip the OS output. The fault queue pre-
vents OS false tripping in noisy environments.
Set bit D2, the OS polarity bit, to zero to force the OS
output 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 resistor to
output a high voltage. See
Figure 4.
Set bit D1, the comparator/interrupt bit to zero to run
the over-temperature shutdown block in comparator
mode. In comparator mode, OS is asserted when the
Digital Temperature Sensors and Thermal
Watchdog with Bus Lockup Protection
8 _______________________________________________________________________________________
REGISTER NAME ADDRESS (hex) POR STATE (hex)
POR STATE
(BINARY)
POR STATE ( °C)
READ/
WRITE
Temperature 00 — — — Read only
Configuration 01 00 0000 0000 — R/W
T HYST 02 4B0 0100 1011 0 75 R/W
T OS 03 500 0101 0000 0 80 R/W
Table 2. Register Functions
UPPER BYTE LOWER BYTE
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0
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
DIGITAL OUTPUT
TEMPERATURE ( °C)
BINARY hex
+125 0111 1101 0xxx xxxx 7D0x
+25 0001 1001 0xxx xxxx 190x
+0.5 0000 0000 1xxx xxxx 008x
0 0000 0000 0xxx xxxx 000x
-0.5 1111 1111 1xxx xxxx FF8x
-25 1110 0110 0xxx xxxx E70x
-55 1100 1000 0xxx xxxx C90x
Table 3. Temperature Register Definition
Table 4. Temperature Data Output
X = Don’t care.