DS7505(2015) 데이터 시트보기 (PDF) - Maxim Integrated
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DS7505 Datasheet PDF : 14 Pages
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DS7505
Digital Thermometer and Thermostat
Shutdown Mode
For power-sensitive applications, the DS7505 offers a
low-power shutdown mode. The SD bit in the configura-
tion register controls shutdown mode. When SD is pro-
grammed to 1, the conversion in progress is completed
and the result stored in the temperature register, after
which the DS7505 goes into a low-power standby state.
The O.S. output is cleared if the thermostat is operating
in interrupt mode and O.S remains unchanged in com-
parator mode. The 2-wire interface remains operational in
shutdown mode, and writing a 0 to the SD bit returns the
DS7505 to normal operation. Upon power-up in shutdown
mode, the DS7505 executes one temperature measure-
ment. The result is stored in the temperature register,
after which the DS7505 enters the shutdown state.
Operation—Thermostat
The DS7505 thermostat can be programmed to power
up in either comparator mode or interrupt mode, which
activate and deactivate the open-drain thermostat output
(O.S.) based on user-programmable trip points (TOS and
THYST). The THYST and TOS registers contain Celsius
temperature values in two’s complement format and
consist of EEPROM that is shadowed by SRAM. Once
written to the shadow SRAM, values can be stored in
EEPROM by issuance of a Copy Data command from the
master (see the Command Set section for more details).
The device can operate using the shadow SRAM only or
using the EEPROM. If the EEPROM is used, the values
are NV and can be programmed prior to installation of the
DS7505 for standalone operation. The factory power-up
settings for the DS7505 are with the thermostat in com-
parator mode, active-low O.S. polarity, overtemperature
trip-point (TOS) register set to 80°C, the hysteresis trip-
point (THYST) register set to +75°C, and the number of
consecutive conversion to trigger O.S. set to 1. If these
power-up settings are compatible with the application, the
DS7505 can be used as a stand-alone thermostat (i.e.,
no 2-wire communication required) with no programming
required prior to installation. If interrupt mode operation,
active-high O.S. polarity, different TOS and THYST values,
or a different number of conversions to trigger O.S. are
desired, they must be programmed into the EEPROM
either after initial power-up or prior to IC installation. The
programmed values then become the new power-up
defaults.
In both operating modes, the user can program the ther-
mostat-fault tolerance, which sets how many consecutive
temperature readings (1, 2, 4, or 6) must fall outside the
thermostat limits before the thermostat output is triggered.
The fault tolerance is set by the F1 and F0 bits in the con-
figuration register. The default factory power-up setting for
fault tolerance is 1 (F1 = 0, F0 = 0).
The data format of the TOS and THYST registers is identi-
cal to that of the temperature register (see Figure 3), i.e.,
a 2-byte two’s complement representation of the trip-point
temperature in degrees Celsius with bits 3 through 0
hardwired to 0. After every temperature conversion, the
measurement is compared to the values stored in the TOS
and THYST registers. The O.S. output is updated based
on the result of the comparison and the operating mode
of the IC. The number of TOS and THYST bits used dur-
ing the thermostat comparison is equal to the conversion
resolution set by the R1 and R0 bits in the configuration
register. For example, if the resolution is 9 bits, only the
9 MSBs of TOS and THYST are used by the thermostat
comparator.
The active state of the O.S. output can be programmed
by the POL bit in the configuration register. The powerup
factory default is active low (POL = 0).
If the user does not wish to use the thermostat capabili-
ties of the DS7505, the O.S. output should be left uncon-
nected. Note that if the thermostat is not used, the TOS
and THYST registers can be used for general storage of
system data.
Comparator Mode
When the thermostat is in comparator mode, O.S. can be
programmed to operate with any amount of hysteresis.
The O.S. output becomes active when the measured tem-
perature exceeds the TOS value a consecutive number of
times as defined by the F1 and F0 fault tolerance (FT) bits
in the configuration register. O.S. then stays active until
the first time the temperature falls below the value stored
in THYST. Putting the device into shutdown mode does
not clear O.S. in comparator mode. Thermostat compara-
tor mode operation with FT = 2 is illustrated in Figure 4.
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