DS1821S+ Maxim Integrated Products, DS1821S+ Datasheet - Page 5
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DS1821S+
Manufacturer Part Number
DS1821S+
Description
IC THERMOMETER/STAT PROG 8-SOIC
Manufacturer
Maxim Integrated Products
Datasheet
1.DS1821.pdf
(18 pages)
Specifications of DS1821S+
Function
Thermometer, Thermostat
Topology
Comparator, Register Bank
Sensor Type
Internal
Sensing Temperature
-55°C ~ 125°C
Output Type
Digital
Output Alarm
No
Output Fan
No
Voltage - Supply
2.7 V ~ 5.5 V
Operating Temperature
-55°C ~ 125°C
Mounting Type
Surface Mount
Package / Case
8-SOIC (5.3mm Width), 8-SOP, 8-SOEIAJ
Temperature Threshold
Programmable
Full Temp Accuracy
+/- 1 C
Digital Output - Bus Interface
1-Wire
Digital Output - Number Of Bits
8 bit
Supply Voltage (max)
5.5 V
Supply Voltage (min)
2.7 V
Maximum Operating Temperature
+ 125 C
Minimum Operating Temperature
- 55 C
Supply Current
1000 uA
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Nonvolatile write status can be monitored by reading the NVB bit in the status/configuration register:
NVB = 1 – a write to EEPROM memory is in progress, NVB = 0 – nonvolatile memory is idle.
THERMOSTAT MODE
In thermostat mode (T/R ¯ = 1), the DS1821 can operate as a standalone thermostat that triggers according
to the T
DS1821 powers-up performing continuous temperature conversions, and the DQ pin acts as the
thermostat output.
STANDALONE THERMOSTAT section of this datasheet.
Communications can be re-established with the DS1821 while it is in thermostat mode by pulling V
0V while the DQ line is held high, and then toggling the DQ line low 16 times as shown in Figure 12.
This temporarily places the DS1821 in 1-Wire mode, allowing microprocessor communication with the
DS1821 via the DQ pin. At this time any I/O function can be performed, such as reading/writing the T
T
procedure can be performed (pulling V
line 16 times) or the power can be cycled. Note that temporarily putting the DS1821 into 1-Wire mode
does not change the power-up mode of the device; this can only be changed by rewriting the T/R ¯ bit in
the status/configuration register.
approximately 10 seconds will cause the DS1821 to be powered down.
OPERATION – MEASURING TEMPERATURE
DS1821 output temperature data is calibrated in degrees centigrade and is stored in two’s complement
format in the 1-byte (8-bit) temperature register (see Figure 3), which the user can access when the
DS1821 is in 1-Wire mode (T/R ¯ = 0 in the status/configuration register). The sign bit (S) indicates if the
temperature is positive or negative; for positive numbers S = 0 and for negative numbers S = 1. Table 2
gives examples of digital output data and the corresponding temperature reading. For Fahrenheit
measurements, a lookup table or conversion routine must be used.
The DS1821 can be configured by the user to take continuous temperature measurements (continuous
conversion mode) or single measurements (one-shot mode). The desired configuration can be achieved
by setting the nonvolatile1SHOT bit in the status/configuration register: 1SHOT = 0 – continuous
conversion mode, 1SHOT = 1 – one-shot mode. Note that the 1SHOT setting only controls the operation
of the device in 1-Wire mode; in thermostat mode, continuous temperature conversions are started
automatically at power-up.
In continuous conversion mode, the Start Convert T [EEh] command initiates continuous temperature
conversions, which can be stopped using the Stop Convert T [22h] command. In one-shot mode the Start
Convert T [EEh] command initiates a single temperature conversion after which the DS1821 returns to a
low-power standby state.
configuration register to determine when the conversion is complete: DONE = 0 ― conversion in
progress, DONE = 1 ― conversion complete. The DONE bit does not provide conversion status in
continuous conversion mode since measurements are constantly in progress (i.e., DONE will always be
0).
TEMPERATURE, T
L
or configuration registers or reading the temperature register. To return to thermostat mode, the same
H
and T
bit 7
S
L
trip-points programmed while the device was in 1-Wire mode. In thermostat mode the
bit 6
Detailed operation of the thermostat output is provided in the OPERATION –
2
6
H
and T
In this mode, the microprocessor can monitor the DONE bit in the
bit 5
2
L
5
Also note that holding both V
REGISTER FORMAT Figure 3
DD
to 0V while the DQ line is held high, and then clocking the DQ
bit 4
2
4
5 of 18
bit 3
2
3
bit 2
2
2
DD
and DQ low for more than
bit 1
2
1
bit 0
2
0
DD
to
H
,