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DS1775 Schematic ( PDF Datasheet ) - Maxim Integrated

Teilenummer DS1775
Beschreibung Digital Thermometer and Thermostat
Hersteller Maxim Integrated
Logo Maxim Integrated Logo 




Gesamt 14 Seiten
DS1775 Datasheet, Funktion
GENERAL DESCRIPTION
The DS1775 digital thermometer and thermostat
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 TOS.
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.
APPLICATIONS
Personal Computers/Servers/Workstations
Cell Phones
Office Equipment
Any Thermally-Sensitive System
DS1775
Digital Thermometer
and Thermostat in SOT23
FEATURES
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
PIN CONFIGURATION
SCL 1 5 SDA
GND 2
O.S. 3 4
SOT23
VDD
PIN DESCRIPTION
GND
Ground
SCL 2-Wire Serial Clock
SDA
2-Wire Serial Data Input/Output
VDD Power-Supply Voltage
O.S. Thermostat Output Signal
Ordering Information appears at end of data sheet.
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19-6687; Rev 5/13






DS1775 Datasheet, Funktion
DS1775
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 4. 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 configuration
register. The entire register is volatile, and thus it powers up in the default state.
Table 4. Configuration/Status Register
0 R1 R0 F1
MSb
F0 POL TM SD
LSb
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 and stored; then the device reverts to a low-power standby mode. The O.S. output is cleared if
the device is in the interrupt mode and remains unchanged in the comparator 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 description 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 5 defines the four settings. The DS1775 powers up
with F0 = F1 = 0, such that a single occurrence triggers a fault.
Table 5. Fault Tolerance Configuration
F1
F0
CONSECUTIVE CONVERSIONS BEYOND LIMITS
TO GENERATE FAULT
00
1
01
2
10
4
11
6
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DS1775 pdf, datenblatt
DS1775
AC ELECTRICAL CHARACTERISTICS: 2-WIRE INTERFACE
(VDD = 2.7V to 5.5V, TA = -55°C to +125°C, unless otherwise noted.) (Figure 5)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SCL Clock Frequency
fSCL
Fast mode
Standard mode
400
100
kHz
Bus Free Time
Between a STOP and
START Condition
Fast mode
tBUF
Standard mode
1.3
4.7
µs
Hold Time (Repeated)
START Condition
tHD:STA
Fast mode
Standard mode
0.6
4.0
µs
Low Period of SCL
tLOW
Fast mode
Standard mode
1.3
4.7
µs
High Period of SCL
tHIGH
Fast mode
Standard mode
0.6
4.0
µs
Setup Time for a
Repeated START
tSU:STA
Fast mode
Standard mode
0.6
4.7
µs
Data Hold Time
tHD:DAT
Fast mode
Standard mode
0
0
0.9
0.9
µs
Data Setup Time
tSU:DAT
Fast mode
Standard mode
100
250
ns
Rise Time of Both SDA
and SCL Signals
tR
Fast mode
Standard mode
20 + 0.1CB
20 + 0.1CB
300
1000
ns
Fall Time of Both SDA
and SCL Signals
tF
Fast mode
Standard mode
20 + 0.1CB
20 + 0.1CB
300
300
ns
Setup Time for STOP
tSU:STO
Fast mode
Standard mode
0.6
4.0
µs
Capacitive Load for
Each Bus Line
CB
400 pF
Input Capacitance
CI
5 pF
NOTES
5
6
7
8
8
8
NOTES:
1. All voltages are referenced to ground.
2. I/O pins of fast mode devices must not obstruct the SDA and SCL lines if VDD is switched off.
3. IDD specified with O.S. pin open.
4. IDD specified with VDD at 5.0V and VSDA, VSCL = 5.0V, 0°C to +70°C.
5. After this period, the first clock pulse is generated.
6. The maximum tHD:DAT has only to be met if the device does not stretch the low period (tLOW ) of the
SCL signal.
7. A fast mode device can be used in a standard mode system, but the requirement tSU: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 tR MAX +tSU:DAT = 1000 + 250 = 1250ns before the SCL line is released.
8. CB = Total capacitance of one bus line in pF.
9. Internal heating caused by O.S. loading causes the DS1775 to read approximately 0.5ºC higher if O.S.
is sinking the max rated current.
10. Contact the factory for operation requiring temperature readings greater than +120°C.
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