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SPECIAL FEATURES

 Digital Thermometer Measures Temperatures

from -55°C to +100°C in Typically 0.2s

 Zero Standby Power

 0.5°C Resolution, Digital Temperature

Reading is Two’s Complement of °C Value

 Access to Internal Counters Allows

Increased Resolution Through Interpolation

 Reduces control, Address, Data, and Power

to a Single Data Contact

 8-Bit Device-Generated CRC for Data

Integrity

 8-Bit Family Code Specifies DS1920

Communications Requirements to Reader

 Special Command Set Allows User to Skip

ROM Section and Perform Temperature

Measurements Simultaneously for All

Devices on the Bus

 2 Bytes of EEPROM to Be Used Either as

Alarm Triggers or User Memory

 Alarm Search Directly Indicates Which

Device Senses Alarming Temperatures

ORDERING INFORMATION

PART

PIN-PACKAGE

DS1920-F5+

F5 MicroCAN

+Denotes a lead(Pb)-free/RoHS-compliant package.

F5 MicroCAN

DATA

GROUND

0.51

5.89

16.25

17.35

A0 10

000000FBC52B

1-Wire



COMMON iButton FEATURES

 Unique, Factory-Lasered and Tested 64-Bit

Registration Number (8-Bit Family Code +

48-Bit Serial Number + 8-Bit CRC Tester)

Assures Absolute Traceability Because No

Two Parts Are Alike

 Multidrop Controller for MicroLAN

 Digital Identification and Information by

Momentary Contact

 Chip-Based Data Carrier Compactly Stores

Information

 Data Can Be Accessed While Affixed To

Object

 Economically Communicates to Bus Master

with a Single Digital Signal at 16.3kbps

 Standard 16mm Diameter and 1-Wire



Protocol Ensure Compatibility with iButton



Family

 Button Shape is Self-Aligning with Cup-

Shaped Probes

 Durable Stainless Steel Case Engraved with

Registration Number Withstands Harsh

Environments

 Easily Affixed with Self-Stick Adhesive

Backing, Latched by Its Flange, or Locked

with a Ring Pressed Onto Its Rim

 Presence Detector Acknowledges When

Reader First Applies Voltage

EXAMPLES OF ACCESSORIES

DS9096P Self-Stick Adhesive Pad

DS9101 Multipurpose Clip

DS9093RA Mounting Lock Ring

DS9093F Snap-In Fob

DS9092 iButton Probe

ALL DIMENSIONS ARE SHOWN IN MILLIMETERS.

iButton and 1-Wire are registered trademarks of Maxim Integrated

Products, Inc.

19-4886; Rev 8/09

DS1920

Temperature iButton

Summary of content (22 pages)

PAGE 1
9-4886; Rev 8/09 DS1920 Temperature iButton SPECIAL FEATURES COMMON iButton FEATURES            Digital Thermometer Measures Temperatures from -55°C to +100°C in Typically 0.2s Zero Standby Power 0.
PAGE 2
DS1920 iButton DESCRIPTION The DS1920 Temperature iButton provides 9-bit temperature readings, which indicate the temperature of the device. Information is sent to/from the DS1920 over a 1-Wire interface. Power for reading, writing, and performing temperature conversions is derived from the data line itself. Because each DS1920 contains a unique silicon serial number, multiple DS1920s can exist on the same 1-Wire bus. This allows for placing temperature sensors in many different places.
PAGE 3
DS1920 DS1920 BLOCK DIAGRAM Figure 1 PARASITE POWER The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power whenever the data contact is high. Data will provide sufficient power as long as the specified timing and voltage requirements are met (see the 1-Wire Bus System section). The advantage of parasite power is that no local power source is needed for remote sensing of temperature.
PAGE 4
DS1920 STRONG PULLUP FOR SUPPLYING DS1920 DURING TEMPERATURE CONVERSION Figure 2 OPERATION—MEASURING TEMPERATURE The DS1920 measures temperatures through the use of an on-board proprietary temperature measurement technique. A block diagram of the temperature measurement circuitry is shown in Figure 3.
PAGE 5
DS1920 The most significant (sign) bit is duplicated into all of the bits in the upper MSB of the 2-byte temperature register in memory. This “sign-extension” yields the 16-bit temperature readings as shown in Table 1. Higher resolutions may be obtained by the following procedure. First, read the temperature, and truncate the 0.5°C bit (the LSB) from the read value. This value is TEMP_READ. The value left in the counter may then be read.
PAGE 6
DS1920 OPERATION—ALARM SIGNALING After the DS1920 has performed a temperature conversion, the temperature value is compared to the trigger values stored in TH and TL. Since these registers are 8 bits only, the 0.5°C bit is ignored for comparison. The most significant bit of TH or TL directly corresponds to the sign bit of the 16-bit temperature register. If the result of a temperature measurement is higher than TH or lower than TL, an alarm flag inside the device is set.
PAGE 7
DS1920 64-BIT LASERED ROM Figure 4 8-BIT CRC CODE MSB 48-BIT SERIAL NUMBER 8-BIT FAMILY CODE (10H) LSB MSB LSB MSB LSB ROM FUNCTIONS FLOWCHART Figure 5 7 of 22
PAGE 8
DS1920 1-Wire CRC CODE Figure 6 MEMORY The DS1920’s memory is organized as shown in Figure 7. The memory consists of a scratchpad and 2 bytes of EEPROM that store the high and low temperature triggers TH and TL. The scratchpad helps insure data integrity when communicating over the 1-Wire bus. Data is first written to the scratchpad where it can be read back. After the data has been verified, a copy scratchpad command will transfer the data to the EEPROM.
PAGE 9
DS1920 1-Wire BUS SYSTEM The 1-Wire bus is a system that has a single bus master and one or more slaves. The DS1920 behaves as a slave. The discussion of this bus system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing). HARDWARE CONFIGURATION The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to drive it at the appropriate time.
PAGE 10
DS1920 ROM FUNCTION COMMANDS Once the bus master has detected a presence pulse, it can issue one of the five ROM function commands. All ROM function commands are eight bits long. A list of these commands follows (see the flowchart in Figure 5). Read ROM [33h] This command allows the bus master to read the DS1920’s 8-bit family code, unique 48-bit serial number, and 8-bit CRC. This command can only be used if there is a single DS1920 on the bus.
PAGE 11
DS1920 MEMORY AND CONTROL FUNCTION COMMANDS The following command protocols are summarized in Table 2, and by the flowchart of Figure 9. Write Scratchpad [4Eh] This command writes to the scratchpad of the DS1920, starting at address 2. The next 2 bytes written will be saved in scratchpad memory, at address locations 2 and 3. Writing may be terminated at any point by issuing a reset. However, if a reset occurs before both bytes have been completely sent, the contents of these bytes will be indeterminate.
PAGE 12
DS1920 MEMORY AND CONTROL FUNCTIONS FLOWCHART Figure 9 12 of 22
PAGE 13
DS1920 MEMORY AND CONTROL FUNCTIONS FLOWCHART (continued) Figure 9 FROM FIGURE 9 FIRST PART TO FIGURE 9 THIRD PART 13 of 22
PAGE 14
DS1920 MEMORY AND CONTROL FUNCTIONS FLOWCHART (continued) Figure 9 1-Wire SIGNALING The DS1920 requires strict protocols to ensure data integrity. The protocol consists of five types of signaling on one line: Reset Sequence with Reset Pulse and Presence Pulse, Write 0, Write 1, Read Data and Strong Pullup. All these signals except Presence Pulse are initiated by the bus master. The initialization sequence required to begin any communication with the DS1920 is shown in Figure 10.
PAGE 15
DS1920 READ/WRITE TIME SLOTS The definitions of write and read time slots are illustrated in Figure 11. All time slots are initiated by the master driving the data line low. The falling edge of the data line synchronizes the DS1920 to the master by triggering a delay circuit in the DS1920. During write time slots, the delay circuit determines when the DS1920 will sample the data line.
PAGE 16
DS1920 DS1920 MEMORY AND CONTROL FUNCTION COMMANDS Table 2 INSTRUCTION Convert Temperature Read Scratchpad Write Scratchpad Copy Scratchpad Recall 1-Wire BUS DESCRIPTION PROTOCOL AFTER ISSUING PROTOCOL TEMPERATURE CONVERSION COMMANDS Initiates temperature 44h strong pullup conversion MEMORY COMMANDS Reads bytes from scratchpad Writes bytes into scratchpad
PAGE 17
DS1920 READ/WRITE TIMING DIAGRAM (continued) Figure 11 Write-0 Time Slot 60µs ≤ tLOW0 < tSLOT < 120µs 1µs ≤ tREC < ∞ Read-Data Time Slot RESISTOR MASTER DS1920 60µs ≤ tSLOT < 120µs 1µs ≤ tLOWR < 15µs 0 ≤ tRELEASE < 45µs 1µs ≤ tREC < ∞ tRDV = 15µs tSU < 1µs 17 of 22
PAGE 18
DS1920 MEMORY FUNCTION EXAMPLE Table 3 Example: Bus Master initiates temperature conversion, then reads temperature. MASTER MODE Tx Rx Tx Tx Tx DATA (LSB FIRST) Reset Presence 55h <64-bit ROM code> 44h Tx Tx Rx Tx Tx Tx Reset Presence 55h <64-bit ROM code> BEh Rx <9 data bytes> Tx Rx Reset Presence COMMENTS Reset pulse(480–960µs) Presence pulse Issue “Match ROM” command Issue address for DS1920 Issue “Convert Temperature” command Data line is held high for at least 0.
PAGE 19
DS1920 ABSOLUTE MAXIMUM RATINGS Voltage on Any Pin Relative to Ground Operating Temperature Storage Temperature -0.5V to +7.0V -55°C to +100°C -55°C to +100°C This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect device reliability. DC ELECTRICAL CONDITIONS (TA = -55°C to +100°C.
PAGE 20
DS1920 AC ELECTRICAL CHARACTERISTICS: 1-Wire INTERFACE (VPUP = 2.8V to 6.0V, TA = -55°C to +100°C.) PARAMETER SYMBOL MIN Time Slot tSLOT 60 Write 1 Low Time tLOW1 1 Write 0 Low Time tLOW0 60 Read Data Valid tRDV Release Time tRELEASE 0 Read Data Setup tSU Recovery Time tREC 1 Reset Time High tRSTH 480 Reset Time Low tRSTL 480 Presence Detect High tPDHIGH 15 Presence Detect Low tPDLOW 60 TYP exactly 15 15 MAX 120 15 120 45 1 4800 60 240 UNITS µs µs µs µs µs µs µs µs µs µs µs NOTES 8 6, 7 NOTES: 1.
PAGE 21
DS1920 TYPICAL PERFORMANCE CURVE DS1920 TEMPERATURE iButton TRUE TEMPERATURE (°C) ERROR = READING - TRUE TEMPERATURE WHEN COLD, THE TRUE TEMPERATURE IS TYPICALLY COLDER THAN THE TEMPERATURE READING. PACKAGE INFORMATION For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE F5 MicroCAN PACKAGE CODE IB+5NS 21 of 22 DOCUMENT NO.
PAGE 22
DS1920 REVISION HISTORY REVISION DATE 082906 110806 040108 8/09 DESCRIPTION In the Common iButton Features, reworded the UL statement. Extended the temperature conversion time from 0.5s to 0.75s maximum. Removed F3 MicroCAN drawing and ordering information; added lead-free DS1920-F5+ and removed leaded package from the Ordering Information table. Corrected the Ordering Information PART information (added hyphen to the part number). Removed the UL#913 bullet from the Common iButton Features section.