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 tempera-

ture measurement. The result is stored in the tempera-

ture 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 out-

put (O.S.) based on user-programmable trip points

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

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

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

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).

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

is updated based on the result of the comparison and

equal to the conversion resolution set by the R1 and R0

bits in the configuration register. For example, if the

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,

storage of system data.

Comparator Mode

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

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-

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.

Digital Thermometer and Thermostat

6

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