ds7505 Maxim Integrated Products, Inc., ds7505 Datasheet - Page 6

• Manufacturer Part Number: ds7505
• Description: High-precision Digital Thermometer And Thermostat
• Manufacturer: Maxim Integrated Products, Inc.

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 tempera-
ture measurement. The result is stored in the tempera-
ture register, after which the DS7505 enters the
shutdown state.
The DS7505 thermostat can be programmed to power
up in either comparator mode or interrupt mode, which
activate and deactivate the open-drain thermostat out-
put (O.S.) based on user-programmable trip points
(T
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 com-
mand 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 pro-
grammed prior to installation of the DS7505 for stand-
alone operation. The factory power-up settings for the
DS7505 are with the thermostat in comparator mode,
active-low O.S. polarity, overtemperature trip-point
(T
(T
secutive 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 pro-
gramming required prior to installation. If interrupt
mode operation, active-high O.S. polarity, different T
and T
to trigger O.S. are desired, they must be programmed
Digital Thermometer and Thermostat
6
OS
HYST
OS
_______________________________________________________________________________________
) register set to 80°C, the hysteresis trip-point
and T
HYST
) register set to +75°C, and the number of con-
HYST
values, or a different number of conversions
). The T
OperationThermostat
HYST
Shutdown Mode
and T
OS
registers contain
OS
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
thermostat-fault tolerance, which sets how many con-
secutive temperature readings (1, 2, 4, or 6) must fall
outside the thermostat limits before the thermostat out-
put is triggered. The fault tolerance is set by the F1 and
F0 bits in the configuration register. The default factory
power-up setting for fault tolerance is 1 (F1 = 0, F0 = 0).
The data format of the T
tical 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 con-
version, the measurement is compared to the values
stored in the T
is updated based on the result of the comparison and
the operating mode of the IC. The number of T
T
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 T
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 power-
up 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
unconnected. Note that if the thermostat is not used,
the T
storage of system data.
When the thermostat is in comparator mode, O.S. can
be programmed to operate with any amount of hystere-
sis. The O.S. output becomes active when the mea-
sured temperature exceeds the T
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 tempera-
ture falls below the value stored in T
device into shutdown mode does not clear O.S. in com-
parator mode. Thermostat comparator mode operation
with FT = 2 is illustrated in Figure 4.
HYST
OS
bits used during the thermostat comparison is
and T
OS
HYST
and T
registers can be used for general
HYST
OS
and T
registers. The O.S. output
Comparator Mode
HYST
HYST
registers is iden-
OS
OS
. Putting the
and T
value a
OS
HYST
and