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DS1775R4U

Digital Thermometer and Thermostat in SOT23

Maxim Integrated 

DS1775

Digital Thermometer and Thermostat in SOT23

The DS1775 powers up with the temperature register

selected. If the host wishes to change the data pointer, it

simply addresses the DS1775 in the write mode (R/W=

0), receives an acknowledge, and writes the 8 bits that

correspond to the new desired location. The last pointer

location is always maintained so that consecutive reads

from the same register do not require the host to always

provide a pointer address. The only exception is at power-

up, in which case the pointer is always set to 00h, the

temperature register. The pointer address must always

precede data in writing to a register, regardless of which

address is currently selected. See the 2-Wire Serial Data

Bus section for details of the 2-wire bus protocol.

Configuration Register Programming

The configuration register is accessed if the DS1775

pointer is currently set to the 01h location. Writing to or

reading from the register is determined by the R/W bit of

the 2-wire control byte (see the 2-Wire Serial Data Bus

section). Data is read from or written to the configuration

register MSb first. The format of the register is illustrated

in Table 3. The effect each bit has on DS1775 functionality

is described below along with the power-up state of the

bit. The user has read/write access to all bits in the con-

figuration register. The entire register is volatile, and thus

it powers up in the default state.

SD = Shutdown bit. If SD is 0, the DS1775 continuously

performs temperature conversions and stores the last

completed result in the thermometer register. If SD is

changed to 1, the conversion in progress is completed

Table 3. Configuration/Status Register

and stored; then the device reverts to a low-power stand-

by mode. The O.S. output is cleared if the device is in the

interrupt mode and remains unchanged in the compara-

tor mode. The 2-wire port remains active. The power-up

default state is 0 (continuous conversion mode).

TM = Thermostat mode. If TM = 0, the DS1775 is in the

comparator mode. TM = 1 sets the device to the interrupt

mode. See the Thermostat Control section for a descrip-

tion of the difference between the two modes. The power-

up default state of the TM bit is 0 (comparator mode).

POL = O.S. Polarity Bit. If POL = 1, the active state of

the O.S. output is high. A 0 stored in this location sets the

thermostat output to an active-low state. The user has

read/write access to the POL bit, and the power-up default

state is 0 (active low).

F0, F1 = O.S. Fault Tolerance bits. The fault tolerance

defines the number of consecutive conversions returning

a temperature beyond limits is required to set the O.S.

output in an active state. This may be necessary to add

margin in noisy environments. Table 4 defines the four

settings. The DS1775 powers up with F0 = F1 = 0, such

that a single occurrence triggers a fault.

R0, R1 = Thermometer resolution bits. Table 5 defines

the resolution of the digital thermometer, based on the

settings of these two bits. There is a direct trade-off

between resolution and conversion time, as shown in the

AC Electrical Characteristics. The default state is R0 = 0

and R1 = 0 (9-bit conversions).

0

R1

R0

F1

F0

POL

TM

SD

MSb

LSb

Table 4. Fault Tolerance Configuration

F1

F0

0

0

0

1

1

0

1

1

CONSECUTIVE CONVERSIONS BEYOND LIMITS TO GENERATE FAULT

1

2

4

6

Table 5. Thermometer Resolution Configuration

R1

R0

THERMOMETER RESOLUTION (BITS)

MAX CONVERSION TIME (SECONDS)

0

0

9

0.1875

0

1

10

0.375

1

0

11

0.75

1

1

12

1.5

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