DS18S20 Maxim Integrated Products, DS18S20 Datasheet - Page 3

• Manufacturer Part Number: DS18S20
• Description: Board Mount Temperature Sensors
• Manufacturer: Maxim Integrated Products

Specifications of DS18S20

• Full Temp Accuracy: +/- 2 C
• Package / Case: TO-92
• Digital Output - Bus Interface: Serial (1-Wire)
• Digital Output - Number Of Bits: 9 bit
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 55 C
• Output Type: Digital
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

bus is virtually unlimited. The 1-Wire bus protocol, including detailed explanations of the commands and
“time slots,” is covered in the 1-Wire Bus System section.
Another feature of the DS18B20 is the ability to operate without an external power supply. Power is
instead supplied through the 1-Wire pullup resistor via the DQ pin when the bus is high. The high bus
signal also charges an internal capacitor (C
low. This method of deriving power from the 1-Wire bus is referred to as “parasite power.” As an
alternative, the DS18B20 may also be powered by an external supply on V
Figure 1. DS18B20 Block Diagram
OPERATION—MEASURING TEMPERATURE
The core functionality of the DS18B20 is its direct-to-digital temperature sensor. The resolution of the
temperature sensor is user-configurable to 9, 10, 11, or 12 bits, corresponding to increments of 0.5°C,
0.25°C, 0.125°C, and 0.0625°C, respectively. The default resolution at power-up is 12-bit. The DS18B20
powers up in a low-power idle state. To initiate a temperature measurement and A-to-D conversion, the
master must issue a Convert T [44h] command. Following the conversion, the resulting thermal data is
stored in the 2-byte temperature register in the scratchpad memory and the DS18B20 returns to its idle
state. If the DS18B20 is powered by an external supply, the master can issue “read time slots” (see the
1-Wire Bus System section) after the Convert T command and the DS18B20 will respond by transmitting
0 while the temperature conversion is in progress and 1 when the conversion is done. If the DS18B20 is
powered with parasite power, this notification technique cannot be used since the bus must be pulled high
by a strong pullup during the entire temperature conversion. The bus requirements for parasite power are
explained in detail in the Powering the DS18B20 section.
The DS18B20 output temperature data is calibrated in degrees Celsius; for Fahrenheit applications, a
lookup table or conversion routine must be used. The temperature data is stored as a 16-bit sign-extended
two’s complement number in the temperature register (see Figure 2). The sign bits (S) indicate if the
temperature is positive or negative: for positive numbers S = 0 and for negative numbers S = 1. If the
DS18B20 is configured for 12-bit resolution, all bits in the temperature register will contain valid data.
For 11-bit resolution, bit 0 is undefined. For 10-bit resolution, bits 1 and 0 are undefined, and for 9-bit
resolution bits 2, 1, and 0 are undefined. Table 1 gives examples of digital output data and the
corresponding temperature reading for 12-bit resolution conversions.
4.7k
V
GND
PU
V
DQ
DD
PARASITE POWER
C
PP
CIRCUIT
INTERNAL V
POWER-
SUPPLY
SENSE
DD
PP
), which then supplies power to the device when the bus is
1-Wire PORT
64-BIT ROM
AND
3 of 22
SCRATCHPAD
MEMORY CONTROL
LOGIC
DD
.
CONFIGURATION REGISTER
ALARM HIGH TRIGGER (T
ALARM LOW TRIGGER (T
TEMPERATURE SENSOR
REGISTER (EEPROM)
REGISTER (EEPROM)
8-BIT CRC GENERATOR
DS18B20
(EEPROM)
DS18B20
L
H
)
)