DS18S20-PAR/T&R Maxim Integrated Products, DS18S20-PAR/T&R Datasheet - Page 3

• Manufacturer Part Number: DS18S20-PAR/T&R
• Description: Board Mount Temperature Sensors
• Manufacturer: Maxim Integrated Products

Specifications of DS18S20-PAR/T&R

• Full Temp Accuracy: +/- 0.5 C
• Package / Case: TO-92
• Digital Output - Bus Interface: Serial (1-Wire)
• Digital Output - Number Of Bits: 9 bit
• Maximum Operating Temperature: + 100 C
• Minimum Operating Temperature: - 55 C
• Output Type: Digital
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

PARASITE POWER
The DS18S20-PAR’s parasite power circuit allows the DS18S20-PAR to operate without a local external
power supply. This ability is especially useful for applications that require remote temperature sensing or
that are very space constrained. Figure 1 shows the DS18S20-PAR’s parasite-power control circuitry,
which “steals” power from the 1-Wire bus via the DQ pin when the bus is high. The stolen charge
powers the DS18S20-PAR while the bus is high, and some of the charge is stored on the parasite power
capacitor (C
The 1-Wire bus and C
as long as the specified timing and voltage requirements are met (refer to the DC ELECTRICAL
CHARACTERISTICS and the AC ELECTRICAL CHARACTERISTICS sections of this data sheet).
However, when the DS18S20-PAR is performing temperature conversions or copying data from the
scratchpad memory to EEPROM, the operating current can be as high as 1.5 mA. This current can cause
an unacceptable voltage drop across the weak 1-Wire pullup resistor and is more current than can be
supplied by C
provide a strong pullup on the 1-Wire bus whenever temperature conversions are taking place or data is
being copied from the scratchpad to EEPROM. This can be accomplished by using a MOSFET to pull
the bus directly to the rail as shown in Figure 2. The 1-Wire bus must be switched to the strong pullup
within 10 ms (max) after a Convert T [44h] or Copy Scratchpad [48h] command is issued, and the bus
must be held high by the pullup for the duration of the conversion (t
No other activity can take place on the 1-Wire bus while the pullup is enabled.
SUPPLYING THE DS18S20-PAR DURING TEMPERATURE CONVERSIONS
Figure 2
OPERATION – MEASURING TEMPERATURE
The core functionality of the DS18S20-PAR is its direct-to-digital temperature sensor. The temperature
sensor output has 9-bit resolution, which corresponds to 0.5°C steps. The DS18S20-PAR 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 DS18S20-PAR returns to its idle state. The
DS18S20-PAR output data is calibrated in degrees centigrade; 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 3).
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.
Resolutions greater than 9 bits can be calculated using the data from the temperature, COUNT REMAIN
and COUNT PER °C registers in the scratchpad. Note that the COUNT PER °C register is hard-wired to
processor
Micro-
PP
) to provide power when the bus is low.
PP
. To assure that the DS18S20-PAR has sufficient supply current, it is necessary to
PP
can provide sufficient parasite power to the DS18S20-PAR for most operations
V
PU
4.7K
V
PU
3 of 20
1-Wire Bus
DS18S20-PAR
GND
conv
The sign bits (S) indicate if the
DQ
) or data transfer (t
To Other
1-Wire Devices
wr
= 10 ms).