Maxim DS7505 Digital thermometer and thermostat Datasheet

Rev 1; 3/08
Digital Thermometer and Thermostat
Applications
Networking Equipment
Features
♦ Operating Range from 1.7V to 3.7V
♦ Temperature Measurements Require No External
Components
♦ Measures Temperatures from -55°C to +125°C
(-67°F to +257°F)
♦ ±0.5°C Accuracy Over a 0°C to +70°C Range
♦ Thermometer Resolution is User-Configurable
from 9 (Default) to 12 Bits (0.5°C to 0.0625°C
Resolution)
♦ 9-Bit Conversion Time is 25ms (max)
♦ Thermostatic Settings are User-Definable and
Nonvolatile (NV)
♦ Stand-Alone Thermostat Capability
♦ Data Read/Write Occurs Through a 2-Wire Serial
Interface (SDA and SCL Pins)
♦ Data Lines Filtered Internally for Noise Immunity
(50ns Deglitch)
Cellular Base Stations
Office Equipment
♦ Optional Bus Timeout Feature Prevents Lockup
Problems on 2-Wire Interface
Medical Equipment
♦ Multidrop Capability Simplifies Distributed
Temperature-Sensing Applications
Any Thermally Sensitive System
Pin Configurations
♦ Pin/Software Compatible with the LM75
♦ Available in 8-Pin SO and µMAX® Packages
TOP VIEW
Ordering Information
SDA
1
8
VDD
SCL
2
7
A0
O.S.
3
6
A1
GND
4
5
A2
PART
DS7505
SO
SDA
1
SCL
2
O.S.
3
GND
4
8
DS7505
VDD
7
A0
6
A1
5
A2
TEMP RANGE
PIN-PACKAGE
DS7505S+
-55°C to +125°C
8 SO (150 mils)
DS7505S+T&R
-55°C to +125°C
8 SO (150 mils),
2500-Piece T&R
DS7505U+
-55°C to +125°C
8 µMAX
DS7505U+T&R
-55°C to +125°C
8 µMAX,
3000-Piece T&R
+Denotes a lead-free package.
T&R = Tape and reel.
Commands are capitalized for clarity.
µMAX
µMAX is a registered trademark of Maxim Integrated Products, Inc.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1
DS7505
General Description
The DS7505 low-voltage (1.7V to 3.7V) digital thermometer and thermostat provides 9-, 10-, 11-, or 12-bit
digital temperature readings over a -55°C to +125°C
range with ±0.5°C accuracy over a -0°C to +70°C range.
A 9-bit resolution mode is software compatible with the
LM75. Communication with the DS7505 is achieved
through a simple 2-wire serial interface. Three address
pins allow up to eight DS7505 devices to operate on the
same 2-wire bus, which greatly simplifies distributed
temperature-sensing applications.
The DS7505 thermostat has a dedicated open-drain output (O.S.) and programmable fault tolerance, which
allows the user to define the number of consecutive
error conditions that must occur before O.S. is activated.
There are two thermostatic operating modes that control
thermostat operation based on user-defined trip points
(TOS and THYST) that are stored in EEPROM registers.
DS7505
Digital Thermometer and Thermostat
ABSOLUTE MAXIMUM RATINGS
Voltage Range on VDD Relative to Ground ..........-0.3V to +4.0V
Voltage Range on Any Other Pin
Relative to Ground.............................................-0.3V to +6.0V
Operating Temperature Range .........................-55°C to +125°C
Storage Temperature Range .............................-55°C to +125°C
Soldering Temperature...........................Refer to the IPC/JEDEC
J-STD-020 Specification.
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
(1.7V ≤ VDD ≤ 3.7V, TA = -55°C to +125°C, unless otherwise noted.)
PARAMETER
Supply Voltage
SYMBOL
Input Voltage Range (SDA, SCL,
O.S., A0, A1, A2)
Thermometer Error
(Note 2, 3)
CONDITIONS
MIN
MAX
UNITS
1.7
3.7
V
-0.3
+5.5
V
VDD
(Note 1)
T ERR
0°C to +70°C
± 0.5
-55°C to +125°C
± 2.0
Input Logic-High
VIH
(Note 1)
Input Logic-Low
VIL
(Note 1)
0.7 × VDD
SDA Output Logic-Low Voltage
VOL1
6mA sink current (Note 1)
O.S. Saturation Voltage
VOL2
4mA sink current (Notes 1, 2)
Input Current Each I/O pin
0.4V < VI/O < 0.9 x VDD
I/O Capacitance
CI/O
Standby Current
IDD1
Active Current
(Notes 4, 5, 6)
IDD
°C
V
0.3 × VDD
V
0
0.6
V
0.8
V
-10
+10
µA
(Notes 4, 5, 6)
10
pF
2
µA
Active temp conversions
750
Communication only
100
E2 Copy only
500
µA
AC ELECTRICAL CHARACTERISTICS
(1.7V ≤ VDD ≤ 3.7V, TA = -55°C to +125°C, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
Resolution
MIN
TYP
9
9-bit conversions
Temperature Conversion Time
tCONVT
SCL Frequency
f SCL
EEPROM Copy Time
tWR
EEPROM Copy Endurance
2
NEEWR
MAX
UNITS
12
Bits
25
10-bit conversions
50
11-bit conversions
100
12-bit conversions
200
ms
-40°C to +85°C
-40°C TA +85°C (Note 7)
10k
20k
TA = +25°C (Note 7)
40k
80k
400
kHz
10
ms
Cycles
_______________________________________________________________________________________
Digital Thermometer and Thermostat
DS7505
AC ELECTRICAL CHARACTERISTICS (continued)
(1.7V ≤ VDD ≤ 3.7V, TA = -55°C to +125°C, unless otherwise noted.)
PARAMETER
EEPROM Data Retention
Bus Free Time Between a STOP
and START Condition
START and Repeated START
Hold Time from Falling SCL
SYMBOL
t EEDR
tBUF
tHD:STA
CONDITIONS
MIN
TYP
MAX
UNITS
-40°C to +125°C (Note 8)
10
Years
(Note 9)
1.3
µs
(Notes 9, 10)
600
ns
Low Period of SCL
tLOW
(Note 9)
1.3
µs
High Period of SCL
tHIGH
(Note 9)
0.6
µs
Repeated START Condition
Setup Time to Rising SCL
t SU:STA
(Note 9)
600
ns
Data-Out Hold Time from Falling
SCL
tHD:DAT
(Notes 9, 11)
Data-In Setup Time to Rising
t SU:DAT
(Note 9)
0
0.9
100
µs
ns
Rise Time of SDA and SCL
(Receive)
tR
(Notes 9, 12)
20 +
0.1CB
Fall Time of SDA and SCL
(Receive)
tF
(Notes 9, 12)
20 +
0.1CB
300
ns
0
50
ns
Spike Suppression Filter Time
(Deglitch Filter)
STOP Setup Time to Rising SCL
Capacitive Load for Each Bus
Line
Input Capacitance
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
Note 10:
Note 11:
Note 12:
Note 13:
t SU:STO
(Note 9)
600
tTIMEOUT
400
pF
325
ms
5
SDA time low (Note 13)
75
ns
ns
CB
CI
Serial Interface Reset Time
Note 1:
Note 2:
t SS
300
pF
All voltages are referenced to ground.
Internal heating caused by O.S. loading causes the DS7505 to read approximately 0.5°C higher if O.S. is sinking the
max-rated current.
Specified in 12-bit conversion mode. Quantization error must be considered when converting in lower resolutions.
IDD specified with O.S. pin open.
IDD specified with VDD at 3.0V and SDA, SCL = 3.0V, TA = -55°C to +85°C.
IDD specified with A0, A1, A2 = 0V or VDD.
VDD must be > 2.0V.
E2 Copy occurs at +25°C.
See the timing diagram (Figure 1). All timing is referenced to 0.9 x VDD and 0.1 x VDD.
After this period, the first clock pulse is generated.
The DS7505 provides an internal hold time of at least 75ns on the SDA signal to bridge the undefined region of SCL’s
falling edge.
For example, if CB = 300pF, then tR(MIN) = tF(MIN) = 50ns.
This timeout applies only when the DS7505 is holding SDA low. Other devices can hold SDA low indefinitely and the
DS7505 does not reset.
_______________________________________________________________________________________
3
Digital Thermometer and Thermostat
DS7505
Pin Description
PIN
NAME
1
SDA
Data Input/Output. For 2-wire serial communication port. Open drain.
FUNCTION
2
SCL
Clock Input. For 2-wire serial communication port.
3
O.S.
Thermostat Output. Open drain.
4
GND
Ground
5
A2
Address Input
6
A1
Address Input
7
A0
8
VDD
Address Input
Supply Voltage. +1.7V to +3.7V supply pin.
SDA
tF
tSU:DAT
tLOW
tF
tSP
tR
tBUF
tHD:STA
tR
SCL
tHD:STA
tSU:STA
tHD:DAT
tSU:STO
SR
P
S
Figure 1. Timing Diagram
PRECISION
REFERENCE
OVERSAMPLING
MODULATOR
DIGITAL
DECIMATOR
VDD
CONFIGURATION
REGISTER
SCL
SDA
A0
A1
A2
ADDRESS
AND
I/O CONTROL
RF
TEMPERATURE
REGISTER
TOS AND THYST
REGISTERS
O.S.
THERMOSTAT
COMPARATOR
GND
DS7505
Figure 2. Block Diagram
4
_______________________________________________________________________________________
Digital Thermometer and Thermostat
The DS7505 measures temperature using a bandgap
temperature-sensing architecture. An on-board deltasigma analog-to-digital converter (ADC) converts the
measured temperature to a digital value that is calibrated in degrees Celsius; for Fahrenheit applications a
lookup table or conversion routine must be used. The
DS7505 is factory-calibrated and requires no external
components to measure temperature.
The DS7505 can be configured to power up either
automatically converting temperature or in a low-power
standby state. The preferred power-up mode can be
set using the SD bit in the configuration register as
explained in the Configuration Register section. The
resolution of the digital output data is user-configurable
to 9, 10, 11, or 12 bits, corresponding to temperature
increments of 0.5°C, 0.25°C, 0.125°C, and 0.0625°C,
respectively. The factory default resolution at power-up
is 9 bits (R1 = 0, R0 = 0), however this can be programmed to 10, 11, or 12 bits using the R0 and R1 bits
in the configuration register as explained in the
Configuration Register section. Note that the conversion time doubles for each additional bit of resolution.
MS Byte
LS Byte
After each temperature measurement and analog-todigital (A/D) conversion, the DS7505 stores the temperature as a 16-bit two’s complement number in the
2-byte temperature register (see Figure 3). The sign bit
(S) indicates if the temperature is positive or negative:
for positive numbers S = 0 and for negative numbers S
= 1. The most recently converted digital measurement
can be read from the temperature register at any time.
Since temperature conversions are performed in the
background, reading the temperature register does not
affect the operation in progress.
Bits 3 through 0 of the temperature register are hardwired to 0. When the DS7505 is configured for 12-bit
resolution, the 12 MSBs (bits 15 through 4) of the temperature register contain temperature data. For 11-bit
resolution, the 11 MSBs (bits 15 through 5) of the temperature register contain data, and bit 4 reads out as 0.
Likewise, for 10-bit resolution, the 10 MSBs (bits 15
through 6) contain data, and for 9-bit the 9 MSBs (bits
15 through 7) contain data and all unused LSBs contains 0s. Table 1 gives examples of 12-bit resolution digital output data and the corresponding temperatures.
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
S
26
25
24
23
22
21
20
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
2-1
2-2
2-3
2-4
0
0
0
0
Figure 3. Temperature, TOS, and THYST Register Format
Table 1. 12-Bit Resolution Temperature/Data Relationship
TEMPERATURE (°C)
DIGITAL OUTPUT
(BINARY)
DIGITAL OUTPUT
(HEX)
7D00
+125
0111 1101 0000 0000
+25.0625
0001 1001 0001 0000
1910
+10.125
0000 1010 0010 0000
0A20
+0.5
0000 0000 1000 0000
0080
0
0000 0000 0000 0000
0000
-0.5
1111 1111 1000 0000
FF80
-10.125
1111 0101 1110 0000
F5E0
-25.0625
1110 0110 1111 0000
E6F0
-55
1100 1001 0000 0000
C900
_______________________________________________________________________________________
5
DS7505
OperationMeasuring
Temperature
DS7505
Digital Thermometer and Thermostat
Shutdown Mode
For power-sensitive applications, the DS7505 offers a
low-power shutdown mode. The SD bit in the configuration register controls shutdown mode. When SD is programmed 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 comparator 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 temperature measurement. The result is stored in the temperature 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 output (O.S.) based on user-programmable trip points
(TOS and THYST). The THYST and TOS registers contain
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 command 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 programmed prior to installation of the DS7505 for standalone 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 OS ) register set to 80°C, the hysteresis trip-point
(THYST) register set to +75°C, and the number of consecutive 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 programming required prior to installation. If interrupt
mode operation, active-high O.S. polarity, different TOS
and THYST values, or a different number of conversions
to trigger O.S. are desired, they must be programmed
6
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 consecutive temperature readings (1, 2, 4, or 6) must fall
outside the thermostat limits before the thermostat output 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 TOS and THYST registers is identical 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 conversion, the measurement is compared to the values
stored in the TOS and THYST registers. The O.S. output
is updated based on the result of the comparison and
the operating mode of the IC. The number of TOS and
THYST bits used during the thermostat comparison is
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 TOS and THYST
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 powerup factory default is active low (POL = 0).
If the user does not wish to use the thermostat capabilities of the DS7505, the O.S. output should be left
unconnected. Note that if the thermostat is not used,
the TOS and THYST registers can be used for general
storage of system data.
Comparator Mode
When the thermostat is in comparator mode, O.S. can
be programmed to operate with any amount of hysteresis. The O.S. output becomes active when the measured temperature exceeds the T OS value a
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 temperature falls below the value stored in THYST. Putting the
device into shutdown mode does not clear O.S. in comparator mode. Thermostat comparator mode operation
with FT = 2 is illustrated in Figure 4.
_______________________________________________________________________________________
Digital Thermometer and Thermostat
DS7505
IN THIS EXAMPLE, THE DS7505 IS CONFIGURED
TO HAVE A FAULT TOLERANCE OF 2.
TOS
TEMPERATURE
THYST
INACTIVE
O.S. OUTPUT—COMPARATOR MODE
ACTIVE
INACTIVE
O.S. OUTPUT—INTERRUPT MODE
ACTIVE
ASSUMES A READ
HAS OCCURED
CONVERSIONS
Figure 4. O.S. Output Operation Example
Interrupt Mode
In interrupt mode, the O.S. output first becomes active
when the measured temperature exceeds the T OS
value a consecutive number of times equal to the FT
value in the configuration register. Once activated, O.S.
can only be cleared by either putting the DS7505 into
shutdown mode or by reading from any register (temperature, configuration, TOS, or THYST) on the device.
Once O.S. has been deactivated, it is only reactivated
when the measured temperature falls below the THYST
value a consecutive number of times equal to the FT
value. Again, O.S can only be cleared by putting the
device into shutdown mode or reading any register.
Thus, this interrupt/clear process is cyclical between
TOS and THYST events (i.e, TOS, clear, THYST, clear,
T OS, clear, T HYST, clear, etc.). Thermostat interrupt
mode operation with FT = 2 is illustrated in Figure 4.
_______________________________________________________________________________________
7
DS7505
Digital Thermometer and Thermostat
Configuration Register
The configuration register allows the user to program
various DS7505 options such as conversion resolution,
thermostat fault tolerance, thermostat polarity, thermostat operating mode, and shutdown mode. The configuration register is arranged as shown in Figure 5 and
detailed descriptions of each bit are provided in Table
2. The user has read/write access to all bits in the configuration register except the MSB (NVB bit), which is a
read-only bit. All bits in the register but the NVB bit are
NV EEPROM backed by shadow SRAM, and thus
power-up in their programmed state. Once written to
the shadow SRAM, values can be stored in EEPROM
by issuance of a Copy Data command from the master
(see the Command Set section for more details). If the
values are not copied to the EEPROM, the device powers up with the factory default settings or the last values
that were copied to the EEPROM. The NVB bit is SRAM
and powers up in the state shown in Table 2.
MSB
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
LSB
NVB
R1
R0
F1
F0
POL
TM
SD
Figure 5. Configuration Register
Table 2. Configuration Register Bit Descriptions
BIT NAME
FUNCTIONAL DESCRIPTION
NVB
NV Memory Status
Power-up state = 0, read only
NVB = 1—Write to an NV memory cell is in progress.
NVB = 0—NV memory is not busy.
R1
Conversion Resolution Bit 1
Factory power-up state = 0
Sets conversion resolution (see Table 3).
R0
Conversion Resolution Bit 0
Factory power-up state = 0
Sets conversion resolution (see Table 3).
F1
Thermostat Fault Tolerance Bit 1
Factory power-up state = 0
Sets the thermostat fault tolerance (see Table 4).
F0
Thermostat Fault Tolerance Bit 0
Factory power-up state = 0
Sets the thermostat fault tolerance (see Table 4).
POL
Thermostat Output (O.S.) Polarity
Factory power-up state = 0
POL = 0—O.S. is active low.
POL = 1—O.S. is active high.
TM
Thermostat Operating Mode
Factory power-up state = 0
TM = 0—Comparator mode.
TM = 1—Interrupt mode.
See the Operation—Thermostat section for a detailed description of these modes.
SD
Shutdown
Factory power-up state = 0
SD = 0—Active conversion and thermostat operation.
SD = 1—Shutdown mode.
See the Shutdown Mode section for a detailed description of this mode.
8
_______________________________________________________________________________________
Digital Thermometer and Thermostat
THERMOMETER
RESOLUTION (BITS)
MAX CONVERSION
TIME (ms)
R1
R0
0
0
9
25
0
1
10
50
1
0
11
100
1
1
12
200
Table 4. Fault Tolerance Configuration
F1
F0
CONSECUTIVE OUT-OF-LIMITS
CONVERSIONS TO TRIGGER O.S.
0
0
1
0
1
2
1
0
4
1
1
6
Register Pointer
The four DS7505 registers each have a unique 2-bit
pointer designation, which is defined in Table 5. When
reading from or writing to the DS7505, the user must
“point” the DS7505 to the register that is to be
accessed. When reading from the DS7505, once the
pointer is set, it remains pointed at the same register
until it is changed. For example, if the user desires to
perform consecutive reads from the temperature register, then the pointer only has to be set to the temperature register one time, after which all reads are
automatically from the temperature register until the
pointer value is changed. When writing to the DS7505,
the pointer value must be refreshed each time a write is
performed, even if the same register is being written to
twice in a row.
At power-up, the pointer defaults to the temperature
register location. The temperature register can be read
immediately without resetting the pointer.
Changes to the pointer setting are accomplished as
described in the 2-Wire Serial Data Bus section.
Table 5. Pointer Definition
P1
P0
Temperature
REGISTER
0
0
Configuration
0
1
THYST
1
0
T OS
1
1
The DS7505 communicates over a standard bidirectional 2-wire serial data bus that consists of a serial clock
(SCL) signal and serial data (SDA) signal. The DS7505
interfaces to the bus through the SCL input pin and
open-drain SDA I/O pin. All communication is MSB first.
The following terminology is used to describe 2-wire
communication:
Master Device: Microprocessor/microcontroller that
controls the slave devices on the bus. The master
device generates the SCL signal and START and STOP
conditions.
Slave: All devices on the bus other than the master.
The DS7505 always functions as a slave.
Bus Idle or Not Busy: Both SDA and SCL remain high.
SDA is held high by a pullup resistor when the bus is
idle, and SCL must either be forced high by the master
(if the SCL output is push-pull) or pulled high by a
pullup resistor (if the SCL output is open drain).
Transmitter: A device (master or slave) that is sending
data on the bus.
Receiver: A device (master or slave) that is receiving
data from the bus.
START Condition: Signal generated by the master to
indicate the beginning of a data transfer on the bus.
The master generates a START condition by pulling
SDA from high to low while SCL is high (see Figure 6).
A “repeated” START is sometimes used at the end of a
data transfer (instead of a STOP) to indicate that the
master performs another operation.
STOP Condition: Signal generated by the master to
indicate the end of a data transfer on the bus. The master generates a STOP condition by transitioning SDA
from low to high while SCL is high (see Figure 6). After
the STOP is issued, the master releases the bus to its
idle state.
Acknowledge (ACK): When a device (either master or
slave) is acting as a receiver, it must generate an
acknowledge (ACK) on the SDA line after receiving
every byte of data. The receiving device performs an
ACK by pulling the SDA line low for an entire SCL period (see Figure 6). During the ACK clock cycle, the
transmitting device must release SDA. A variation on
the ACK signal is the “not acknowledge” (NACK). When
the master device is acting as a receiver, it uses a
NACK instead of an ACK after the last data byte to indicate that it is finished receiving data. The master indicates a NACK by leaving the SDA line high during the
ACK clock cycle.
_______________________________________________________________________________________
9
DS7505
2-Wire Serial Data Bus
Table 3. Resolution Configuration
DS7505
Digital Thermometer and Thermostat
Slave Address: Every slave device on the bus has a
unique 7-bit address that allows the master to access
that device. The DS7505’s 7-bit bus address is 1 0 0 1
A2 A1 A0, where A2, A1, and A0 are user-selectable
through the corresponding input pins. The three
address pins allow up to eight DS7505s to be multidropped on the same bus.
Address Byte: The control byte is transmitted by the
master and consists of the 7-bit slave address plus a
read/write (R/W) bit (see Figure 7). If the master is
going to read data from the slave device then R/W = 1,
and if the master is going to write data to the slave
device then R/W = 0.
Pointer Byte: The pointer byte is used by the master to
tell the DS7505 which register is going to be accessed
during communication. The six MSBs of the pointer
byte (see Figure 8) are always 0 and the two LSBs correspond to the desired register as shown in Figure 8.
SDA
SCL
START
CONDITION
ACK (OR NACK)
STOP
FROM RECEIVER CONDITION
Figure 6. Start, Stop, and ACK Signals
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
1
0
0
1
A2
A1
A0
R/W
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
0
0
0
0
0
P1
P0
Figure 7. Address Byte
Figure 8. Pointer Byte
10
______________________________________________________________________________________
Digital Thermometer and Thermostat
Writing to the DS7505: To write to the DS7505, the
master must generate a START followed by an address
byte containing the DS7505 bus address. The value of
the R/W bit must be a 0, which indicates that a write is
about to take place. The DS7505 responds with an
ACK after receiving the address byte. The master then
sends a pointer byte which tells the DS7505 which register is being written to. The DS7505 again responds
with an ACK after receiving the pointer byte. Following
this ACK the master device must immediately begin
transmitting data to the DS7505. When writing to the
configuration register, the master must send one byte
of data (see Figure 9B), and when writing to the TOS or
THYST registers the master must send two bytes of data
(see Figure 9C). After receiving each data byte, the
DS7505 responds with an ACK, and the transaction is
finished with a STOP from the master. All writes to the
DS7505 are made to shadow SRAM. Once data is written to the shadow SRAM, it is only stored to EEPROM
by issuance of a Copy Data command from the master.
At that time, all registers are copied to EEPROM except
the Temperature register which is SRAM only.
Reading from the DS7505: When reading from the
DS7505, if the pointer was already pointed to the
desired register during a previous transaction, the read
can be performed immediately without changing the
pointer setting. In this case the master sends a START
followed by an address byte containing the DS7505
bus address. The R/W bit must be a 1, which tells the
DS7505 that a read is being performed. After the
DS7505 sends an ACK in response to the address
byte, the DS7505 begins transmitting the requested
data on the next clock cycle. When reading from the
configuration register, the DS7505 transmits one byte of
data, after which the master must respond with a NACK
followed by a STOP (see Figure 9E). For two-byte reads
(i.e., from the temperature, TOS or THYST register), the
DS7505 transmits two bytes of data, and the master
must respond to the first data byte with an ACK and to
the second byte with a NACK followed by a STOP (see
Figure 9A). If only the most significant byte of data is
needed, the master can issue a NACK followed by a
STOP after reading the first data byte in which case the
transaction is the same as for a read from the configuration register.
If the pointer is not already pointing to the desired register, the pointer must first be updated as shown in
Figure 9D, which shows a pointer update followed by a
single-byte read. The value of the R/W bit in the initial
address byte is a 0 (“write”) since the master is going
to write a pointer byte to the DS7505. After the DS7505
responds to the address byte with an ACK, the master
sends a pointer byte that corresponds to the desired
register. The master must then perform a repeated start
followed by a standard one or two byte read sequence
(with R/W =1) as described in the previous paragraph.
The Recall Data command should be issued before a
read if assurance is needed that the contents of the
EEPROM in the Shadow SRAM when read.
Bus Timeout: The DS7505 has a bus timeout feature
that prevents communication errors from leaving the IC
in a state where SDA is held low disrupting other
devices on the bus. If the DS7505 holds the SDA line
low for a period of tTIMEOUT, its bus interface automatically resets and release the SDA line. Bus communication frequency must be fast enough to prevent a reset
during normal operation. The bus timeout feature only
applies to when the DS7505 is holding SDA low. Other
devices can hold SDA low for an undefined period without causing the interface to reset.
Command Set
Recall Data [B8h]
1011 1000
Refreshes SRAM shadow register with EEPROM data. It
is recommended that a Recall command be performed
before reading EEPROM-backed memory locations.
The master sends a START followed by an address
byte containing the DS7505 bus address. The R/W bit
must be a 0. The DS7505 responds with an ACK. If the
next byte is a 0xB8, the DS7505 recalls all EEPROM
data into shadow RAM locations.
______________________________________________________________________________________
11
DS7505
General 2-Wire Information
• All data is transmitted MSB first over the 2-wire bus.
• One bit of data is transmitted on the 2-wire bus each
SCL period.
• A pullup resistor is required on the SDA line, and,
when the bus is idle, both SDA and SCL must remain
in a logic-high state.
• All bus communication must be initiated with a
START condition and terminated with a STOP condition. During a START or STOP is the only time SDA is
allowed to change states while SCL is high. At all
other times, changes on the SDA line can only occur
when SCL is low; SDA must remain stable when SCL
is high.
• After every 8-bit (1-byte) transfer, the receiving
device must answer with an ACK (or NACK), which
takes one SCL period. Therefore, nine clocks are
required for every 1-byte data transfer.
DS7505
Digital Thermometer and Thermostat
Copy Data [48h]
0100 1000
Copies data from all SRAM shadow registers to
EEPROM. It is recommended that a Copy Data command be performed after writing EEPROM-backed
memory locations to guarantee data integrity in the
event of a power loss. The master sends a START followed by an address byte containing the DS7505 bus
address. The R/W bit must be a 0. The DS7505
responds with an ACK. If the next byte is a 0x48, the
DS7505 copies all Shadow RAM locations in EEPROM
memory.
Software POR [54h]
0101 0100
The master sends a START followed by an address
byte containing the DS7505 bus address. The R/W bit
must be a 0. The DS7505 responds with an ACK. If the
next byte is a 0x54, the DS7505 resets as if power had
been cycled, which stops temperature conversions and
resets all registers to their power-up states. No ACK is
sent by the IC after the POR command is received.
Afterwards, the DS7505 makes a single temperature
conversion or continuous temperature conversions,
depending on the state of the SD bit.
A) READ 2 BYTES FROM THE TEMPERATURE, TOS, OR THYST REGISTER (CURRENT POINTER LOCATION)
SCL
SDA
S 1
0
START
0
1
A2 A1 A0 R
ADDRESS BYTE
A D7 D6 D5 D4 D3 D2 D1 D0 A D7 D6 D5 D4 D3 D2 D1 D0 N
ACK
(SLAVE)
MS DATA BYTE
(FROM SLAVE)
ACK
(MASTER)
LS DATA BYTE
(FROM SLAVE)
P
NACK STOP
(MASTER)
B) WRITE TO THE CONFIGURATION REGISTER
SCL
SDA
S 1
0
START
0
1
A2 A1 A0 W
ADDRESS BYTE
A
0
0
0
ACK
(SLAVE)
0
0
0
POINTER BYTE
0
1
A D7 D6 D5 D4 D3 D2 D1 D0 A
ACK
(SLAVE)
DATA BYTE
(FROM MASTER)
P
ACK STOP
(SLAVE)
C) WRITE TO THE TOS OR THYST REGISTER
SCL
SDA
S 1
0
START
0
1
A2 A1 A0 W
ADDRESS BYTE
A
0
0
0
ACK
(SLAVE)
0
0
0
POINTER BYTE
P1 P0
A D7 D6 D5 D4 D3 D2 D1
A D7 D6 D5 D4 D3 D2 D1 D0
ACK
(SLAVE)
MS DATA BYTE
(FROM MASTER)
ACK
(SLAVE)
LS DATA BYTE
(FROM MASTER)
A
P
ACK STOP
(SLAVE)
D) READ SINGLE BYTE (NEW POINTER LOCATION)
SCL
SDA
S 1
0
START
0
1
A2 A1 A0 W
ADDRESS BYTE
A
0
ACK
(SLAVE)
0
0
0
0
0
P1 P0 A
POINTER BYTE
ACK
(SLAVE)
S 1
REPEAT
START
0
0
1
A2 A1 A0 R
ADDRESS BYTE
A D7 D6 D5 D4 D3 D2 D1 D0 N
ACK
(SLAVE)
DATA BYTE
(FROM SLAVE)
E) READ FROM THE CONFIGURATION REGISTER (CURRENT POINTER LOCATION)
SCL
SDA
S 1
START
0
0
1
A2 A1 A0 R
ADDRESS BYTE
A D7 D6 D5 D4 D3 D2 D1 D0 N
ACK
(SLAVE)
MS DATA BYTE
(FROM SLAVE)
P
NACK STOP
(MASTER)
Figure 9. 2-Wire Interface Timing
12
______________________________________________________________________________________
P
NACK STOP
(MASTER)
Digital Thermometer and Thermostat
DS7505
Package Information
(For the latest package outline information, go to
www.maxim-ic.com/DallasPackInfo.)
PACKAGE TYPE
DOCUMENT NO.
8 SO (150 mils)
56-G2008-001
8 µMAX
21-0036
______________________________________________________________________________________
13
DS7505
Digital Thermometer and Thermostat
Revision History
REVISION
NUMBER
REVISION
DATE
0
2/08
Initial release.
1
3/08
Removed references to exposed pad (µMAX package does not have an EP);
corrected package information outline document number.
DESCRIPTION
PAGES
CHANGED
—
1, 4, 13
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implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
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