DS1821S Maxim Integrated Products, DS1821S Datasheet
![IC THERMOMETER/STAT PROG 8-SOIC](/photos/6/58/65843/8-soic_21-0262_sml.jpg)
DS1821S
Specifications of DS1821S
Available stocks
Related parts for DS1821S
DS1821S Summary of contents
Page 1
... Dallas Semiconductor Corp., a wholly owned subsidiary of Maxim Integrated Products, Inc. Programmable Digital Thermostat and PIN ASSIGNMENT DALLAS DS1821 (BOTTOM VIEW) PR35 (DS1821) PIN DESCRIPTION GND - Ground DQ - Data In/Out and Thermostat Output V - Power Supply Voltage Connect DS1821 Thermometer GND 8-pin 208-mil SO (DS1821S) 071107 ...
Page 2
... PACKAGE NUMBER MARKING DS1821 DS1821 DS1821+ DS1821 (See Note) DS1821S DS1821S DS1821S/T&R DS1821S DS1821S+ DS1821S (See Note) DS1821S+T&R DS1821S (See Note) Note: A “+” symbol will also be marked on the package. + Denotes lead-free package. DETAILED PIN DESCRIPTIONS Table 1 PR35 8-PIN SYMBOL SO GND ...
Page 3
DS1821 BLOCK DIAGRAM Figure 1 DS1821 V DD 4.7K DQ POWER V SUPPLY DD SENSE GND TEMPERATURE SENSOR FUNCTIONALITY The core functionality of the DS1821 is its proprietary direct-to-digital temperature sensor, which provides 8-bit (1°C increment) centigrade temperature readings over ...
Page 4
TEMPERATURE MEASURING CIRCUITRY Figure 2 PRESET LOW TEMPERATURE COEFFICIENT OSCILLATOR HIGH TEMPERATURE COEFFICIENT OSCILLATOR OPERATING MODES The DS1821 has two operating modes: 1-Wire mode and thermostat mode. The power-up operating mode is determined by the user-programmable T/R ¯ bit in ...
Page 5
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 ...
Page 6
TEMPERATURE/DATA RELATIONSHIP Table 2 TEMPERATURE +125°C* +85°C +25°C 0°C -1°C -25°C -55°C HIGH-RESOLUTION TEMPERATURE READINGS The user can calculate temperature values with higher than 8-bit resolution using the data remaining in the counter and slope accumulator when the temperature conversion ...
Page 7
OPERATION – THERMOSTAT When the DS1821 is in thermostat mode (T/R ¯ the status/configuration register), temperature conversions are performed continuously beginning at power-up (regardless of the value of the 1SHOT bit), and the DQ pin serves as ...
Page 8
CONFIGURATION REGISTER BIT DESCRIPTIONS Table 3 Bit Name (User Access) DONE — Temperature Conversion Done (Read Only) NVB — Non-volatile Memory Busy (Read Only) THF* — Temperature High Flag (Read/Write) TLF* — Temperature Low Flag (Read/Write) T/R ¯ * — ...
Page 9
BUS SYSTEM The 1-Wire bus system uses a single bus master (i.e., a microprocessor) to control slave devices. The DS1821 functions as a slave device when it is used in 1-Wire mode; however, since the DS1821 is not addressable ...
Page 10
INITIALIZATION All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a reset pulse transmitted by the bus master followed by a presence pulse transmitted by the DS1821. The presence pulse lets the bus ...
Page 11
DS1821 FUNCTION COMMAND SET Table 4 Command TEMPERATURE CONVERSION COMMANDS Read Reads last converted temperature Temperature value from temperature register. Start Convert T Initiates temperature conversions. Stop Convert T Halts temperature conversions. THERMOSTAT and STATUS/CONFIGURATION COMMANDS Write TH Writes data ...
Page 12
INITIALIZATION TIMING Figure 7 MASTER T 480 μs minimum V DD 1-WIRE BUS GND READ/WRITE TIME SLOTS The bus master writes data to the DS1821 during write time slots and reads data from the DS1821 during read time slots. One ...
Page 13
Figure 9 illustrates that the sum of T Figure 10 shows that system timing margin is maximized by keeping T and by locating the master sample time during read time slots towards the end of the 15 μs period. READ/WRITE ...
Page 14
DS1821 OPERATION EXAMPLE In this example, the master device programs the DS1821 with T that the data has been saved correctly. The master then programs the status/configuration register so that the device will power-up in thermostat mode (T/R ¯ = ...
Page 15
ABSOLUTE MAXIMUM RATINGS* Voltage on any pin relative to ground Operating temperature Storage temperature Soldering temperature *These are stress ratings only and functional operation of the device at these or any other conditions above those indicated in the operation sections ...
Page 16
AC ELECTRICAL CHARACTERISTICS: PARAMETER Temperature Conversion Time EEPROM Write Time Time Slot Recovery Time Write 0 Low Time Write 1 Low Time Read Data Valid Reset Time High Reset Time Low Presence Detect High Presence Detect Low V Low to ...
Page 17
TYPICAL PERFORMANCE CURVE Figure 11 MODE TOGGLE TIMING WHEN T/R ¯ Figure ...
Page 18
TIMING DIAGRAMS Figure ...