provides temperature readings that indicate the device’s
temperature. Thermostat settings and temperature
readings are all communicated to/from the DS1775 over
a simple 2-wire serial interface. No additional components
are required; the device is truly a “temperature-to-digital”
converter.
For applications that require greater temperature resolution,
the user can adjust the readout resolution from 9 to 12
bits. This is particularly useful in applications where
thermal runaway conditions must be detected quickly.
The open-drain thermal alarm output, O.S., becomes
active when the temperature of the device exceeds a
user-defined temperature T
OS
. The number of consecutive
faults required to set O.S. active is configurable by the
user. The device can also be configured in the interrupt or
comparator mode, to customize the method which clears
the fault condition.
As a digital thermometer, the DS1775 is software compatible
with the DS75 2-wire thermal watchdog. The DS1775 is
assembled in a compact 5-pin SOT23 package, allowing
for low-cost thermal monitoring/control in space-
constrained applications. The low thermal mass allows for
time constants previously only possible with thermistors.
● Temperature Measurements Require No External
Components
●
Measures Temperatures from -55°C to +125°C
(-67°F to +257°F)
●
±2.0°C Thermometer Accuracy
●
Thermometer Resolution is Configurable from 9 Bits
to 12 Bits (0.5°C to 0.0625°C Resolution)
●
User-Definable Thermostat Settings
●
Data is Read From/Written to Through a
●
2-Wire Serial Interface
●
2.7V to 5.5V Wide Power-Supply Range
●
Software Compatible with DS75 2-Wire Thermal
Watchdog in Thermometer Mode
●
Space-Conscious 5-Pin SOT23 Package with Low
Thermal Time Constant
Ordering Information
appears at end of data sheet.
Benefits and Features
Applications
●
●
●
●
Personal Computers/Servers/Workstations
Cell Phones
Office Equipment
Any Thermally-Sensitive System
19-6687; Rev 1; 11/16
DS1775
Digital Thermometer and Thermostat in SOT23
Absolute Maximum Ratings
(Voltages relative to ground.)
Voltage Range on V
DD
.........................................-0.3V to +7.0V
Voltage Range on Any Other Pin .........................-0.3V to +7.0V
Operating Temperature Range ......................... -55°C to +125°C
Storage Temperature Range ............................ -55°C to +125°C
Lead Temperature (soldering, 10s) ................................. +300°C
Soldering Temperature (reflow) ....................................... +260°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these
or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
DC Electrical Characteristics
(2.7V ≤ V
DD
≤ 5.5V, T
A
= -55°C to +125°C, unless otherwise noted.)
PARAMETER
Supply Voltage
Input Logic-High
Input Logic-Low
SDA Output Logic-Low Voltage
O.S. Saturation Voltage
Input Current Each I/O Pin
I/O Capacitance
Standby Current
Active Current
DIGITAL THERMOMETER
Thermometer Error
Resolution
9-bit conversion
Conversion Time
t
CONVT
10-bit conversion
11-bit conversion
12-bit conversion
T
ERR
-10°C to +85°C (Notes 9, 10)
-55°C to +125°C (Notes 9, 10)
9
125
250
500
1000
±0.5
±1.0
±2.0
±3.0
12
187.5
375
750
1500
ms
°C
Bits
C
I/O
I
DD1
I
DD
(Notes 3, 4)
Active temp conversions (Notes 3, 4)
Communication only (Notes 3, 4)
SYMBOL
V
DD
V
IH
V
IL
V
OL1
V
OL2
V
OL
(Note 1)
(Note 1)
(Note 1)
3mA sink current (Note 1)
6mA sink current (Note 1)
4mA sink current (Notes 1, 9)
0.4 < V
I/O
< 0.9 x V
DD
(Note 2)
-10
CONDITION
MIN
2.7
0.7 x
V
DD
-0.5
0
0
TYP
MAX
5.5
V
DD
+
0.5
0.3 x
V
DD
0.4
0.6
0.8
+10
10
1
1000
100
UNITS
V
V
V
V
V
µA
pF
µA
µA
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2
DS1775
Digital Thermometer and Thermostat in SOT23
AC Electrical Characteristics-2 Wire Interface
(V
DD
= 2.7V to 5.5V, T
A
= -55°C to +125°C, unless otherwise noted.) (Figure 5)
PARAMETER
SCL Clock Frequency
Bus Free Time Between a
STOP and START Condition
Hold Time (Repeated) START
Condition
Low Period of SCL
High Period of SCL
Setup Time for a
Repeated START
Data Hold Time
Data Setup Time
Rise Time of Both SDA and
SCL Signals
Fall Time of Both SDA and SCL
Signals
Setup Time for STOP
Capacitive Load for Each Bus
Line
Input Capacitance
Note
Note
Note
Note
Note
Note
Note
1:
2:
3:
4:
5:
6:
7:
SYMBOL
f
SCL
t
BUF
t
HD:STA
t
LOW
t
HIGH
t
SU:STA
t
HD:DAT
t
SU:DAT
t
R
t
F
t
SU:STO
C
B
C
I
Fast mode
Standard mode
Fast mode
Standard mode
Fast mode (Note 5)
Standard mode (Note 5)
Fast mode
Standard mode
Fast mode
Standard mode
Fast mode
Standard mode
Fast mode (Note 6)
Standard mode (Note 6)
Fast mode (Note 7)
Standard mode (Note 7)
Fast mode (Note 8)
Standard mode (Note 8)
Fast mode (Note 8)
Standard mode (Note 8)
Fast mode
Standard mode
(Note 8)
5
1.3
4.7
0.6
4.0
1.3
4.7
0.6
4.0
0.6
4.7
0
0
100
250
20 + 0.1C
B
20 + 0.1C
B
20 + 0.1C
B
20 + 0.1C
B
0.6
4.0
400
300
1000
300
300
0.9
0.9
CONDITIONS
MIN
TYP
MAX
400
100
UNITS
kHz
µs
µs
µs
µs
µs
µs
ns
ns
ns
µs
pF
pF
All voltages are referenced to ground.
I/O pins of fast mode devices must not obstruct the SDA and SCL lines if V
DD
is switched off.
I
DD
specified with O.S. pin open.
I
DD
specified with V
DD
at 5.0V and V
SDA
, V
SCL
= 5.0V, 0°C to +70°C.
After this period, the first clock pulse is generated.
The maximum t
HD:DAT
has only to be met if the device does not stretch the low period (t
LOW
) of the SCL signal.
A fast mode device can be used in a standard mode system, but the requirement t
SU:DAT
≥
250ns must then be met. This is
automatically the case if the device does not stretch the low period of the SCL signal. If such a device does stretch the low
period of the SCL signal, it must output the next data bit to the SDA line t
R MAX
+ t
SU:DAT
= 1000 + 250 = 1250ns before the
SCL line is released.
Note 8:
C
B
= Total capacitance of one bus line in pF.
Note 9:
Internal heating caused by O.S. loading causes the DS1775 to read approximately 0.5°C higher if O.S. is sinking the max
rated current.
Note 10:
Contact the factory for operation requiring temperature readings greater than +120°C.
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DS1775
Digital Thermometer and Thermostat in SOT23
Pin Configuration
TOP VIEW
SCL 1
GND 2
O.S. 3
+
DS1775
5
SDA
4
V
DD
SOT-23
GND
SCL
SDA
V
DD
O.S.
GROUND
2-WIRE SERIAL CLOCK
2-WIRE SERIAL DATA INPUT/OUTPUT
POWER-SUPPLY VOLTAGE
THERMOSTAT OUTPUT SIGNAL
Pin Description
PIN
1
2
3
4
5
NAME
SCL
GND
O.S.
V
DD
SDA
FUNCTION
Clock Input/Output for 2-Wire Serial Communication Port. This input should be tied to GND for
stand-alone thermostat operation.
Ground
Thermostat Output. Open-drain output becomes active when temperature exceeds T
OS
.
Device configuration defines means to clear overtemperature state.
Supply Voltage 2.7V to 5.5V Input Power Pin
Data Input/Output for 2-Wire Serial Communication Port. In the stand-alone thermostat mode,
this input selects hysteresis.
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4
DS1775
Digital Thermometer and Thermostat in SOT23
Detailed Description
1)
2)
3)
4)
5)
Figure 1 shows a block diagram of the DS1775. The
DS1775 consists of five major components:
Precision temperature sensor
Analog-to-digital converter
2-wire interface electronics
Data registers
Thermostat comparator
doubles the conversion time. This is accomplished by
programming the configuration register. The configuration
register defines the conversion state, thermometer resolu-
tion/conversion time, active state of the thermostat output,
number of consecutive faults to trigger an alarm condition,
and the method to terminate an alarm condition.
The user can also program overtemperature (T
OS
) and
undertemperature (T
HYST
) setpoints for thermostatic
operation. The power-up state of T
OS
is +80°C and that
for T
HYST
is +75°C. The result of each temperature con-
version is compared with the T
OS
and T
HYST
setpoints.
The DS1775 offers two modes for temperature control,
the comparator mode and the interrupt mode. This allows
the user the flexibility to customize the condition that
would generate and clear a fault condition. Regardless of
the mode chosen, the O.S. output becomes active only
after the measured temperature exceeds the respective
trip-point a consecutive number of times; the number of
consecutive conversions beyond the limit to generate an
O.S. is programmable. The power-up state of the DS1775
is in the comparator mode with a single fault generating
an active O.S.
Digital data is written to/read from the DS1775 via a
2-wire interface, and all communication is MSb first.
The factory-calibrated temperature sensor requires no
external components. Upon power-up, the DS1775 begins
temperature conversions with the default resolution of 9
bits (0.5°C resolution). The host can periodically read the
value in the temperature register, which contains the last
completed conversion. As conversions are performed in
the background, reading the temperature register does
not affect the conversion in progress.
In power-sensitive applications, the user can put the
DS1775 into a shutdown mode, under which the sensor
complete and store the conversion in progress and revert
to a low-power standby state. In applications where small
incremental temperature changes are critical, the user
can change the conversion resolution from 9 bits to 10,
11, or 12. Each additional bit of resolution approximately
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