DS7505 Datasheet, PDF (5/14 Pages) Maxim Integrated Products – Digital Thermometer and Thermostat

Digital Thermometer and Thermostat
OperationMeasuring
Temperature
The DS7505 measures temperature using a bandgap
temperature-sensing architecture. An on-board delta-
sigma analog-to-digital converter (ADC) converts the
measured temperature to a digital value that is calibrat-
ed in degrees Celsius; for Fahrenheit applications a
lookup table or conversion routine must be used. The
DS7505 is factory-calibrated and requires no external
components to measure temperature.
The DS7505 can be configured to power up either
automatically converting temperature or in a low-power
standby state. The preferred power-up mode can be
set using the SD bit in the configuration register as
explained in the Configuration Register section. The
resolution of the digital output data is user-configurable
to 9, 10, 11, or 12 bits, corresponding to temperature
increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C,
respectively. The factory default resolution at power-up
is 9 bits (R1 = 0, R0 = 0), however this can be pro-
grammed to 10, 11, or 12 bits using the R0 and R1 bits
in the configuration register as explained in the
Configuration Register section. Note that the conver-
sion time doubles for each additional bit of resolution.
After each temperature measurement and analog-to-
digital (A/D) conversion, the DS7505 stores the temper-
ature as a 16-bit two’s complement number in the
2-byte temperature register (see Figure 3). The sign bit
(S) indicates if the temperature is positive or negative:
for positive numbers S = 0 and for negative numbers S
= 1. The most recently converted digital measurement
can be read from the temperature register at any time.
Since temperature conversions are performed in the
background, reading the temperature register does not
affect the operation in progress.
Bits 3 through 0 of the temperature register are hard-
wired to 0. When the DS7505 is configured for 12-bit
resolution, the 12 MSBs (bits 15 through 4) of the tem-
perature register contain temperature data. For 11-bit
resolution, the 11 MSBs (bits 15 through 5) of the tem-
perature register contain data, and bit 4 reads out as 0.
Likewise, for 10-bit resolution, the 10 MSBs (bits 15
through 6) contain data, and for 9-bit the 9 MSBs (bits
15 through 7) contain data and all unused LSBs con-
tains 0s. Table 1 gives examples of 12-bit resolution dig-
ital output data and the corresponding temperatures.
MS Byte
LS Byte
Bit 15
S
Bit 7
2^-1
Bit 14
2⁶
Bit 6
2^-2
Bit 13
2⁵
Bit 5
2^-3
Figure 3. Temperature, T_OS, and T_HYST Register Format
Bit 12
2⁴
Bit 4
2^-4
Bit 11
2³
Bit 3
0
Bit 10
2²
Bit 2
0
Table 1. 12-Bit Resolution Temperature/Data Relationship
TEMPERATURE (°C)
+125
+25.0625
+10.125
+0.5
0
-0.5
-10.125
-25.0625
-55
DIGITAL OUTPUT
(BINARY)
0111 1101 0000 0000
0001 1001 0001 0000
0000 1010 0010 0000
0000 0000 1000 0000
0000 0000 0000 0000
1111 1111 1000 0000
1111 0101 1110 0000
1110 0110 1111 0000
1100 1001 0000 0000
Bit 9
2¹
Bit 1
0
Bit 8
2⁰
Bit 0
0
DIGITAL OUTPUT
(HEX)
7D00
1910
0A20
0080
0000
FF80
F5E0
E6F0
C900
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