These are stress ratings 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 reliability.
DC Electrical Characteristics
(V
DD
= 3.0V to 5.5V, T
A
= -55°C to +125°C, unless otherwise noted.)
PARAMETER
Supply Voltage
Pullup Supply Voltage
Thermometer Error
Input Logic-Low
Input Logic-High
Sink Current
Standby Current
Active Current
DQ Input Current
Drift
SYMBOL
V
DD
V
PU
t
ERR
V
IL
V
IH
I
L
I
DDS
I
DD
I
DQ
CONDITIONS
Local Power (Note 1)
Parasite Power
Local Power
-10°C to +85°C
-55°C to +125°C
(Note 1, 4, 5)
Local Power
Parasite Power
V
I/O
= 0.4V (Note 1)
(Note 7, 8)
V
DD
= 5V (Note 9)
(Note 10)
(Note 11)
(Note 1, 6)
(Note 1, 2)
(Note 3)
-0.3
+2.2
+3.0
4.0
750
1
5
±0.2
1000
1.5
MIN
+3.0
+3.0
+3.0
TYP
MAX
+5.5
+5.5
V
DD
±0.5
±2
+0.8
The lower of
5.5 or V
DD
+ 0.3
UNITS
V
V
°C
V
V
mA
nA
mA
µA
°C
Note 1:
All voltages are referenced to ground.
Note 2:
The Pullup Supply Voltage specification assumes that the pullup device is ideal, and therefore the high level of the pul-
lup is equal to V
PU
. In order to meet the V
IH
spec of the DS18S20, the actual supply rail for the strong pullup transistor
must include margin for the voltage drop across the transistor when it is turned on; thus: V
PU_ACTUAL
= V
PU_IDEAL
+
V
TRANSISTOR
.
Note 3:
See typical performance curve in
Figure 1.
Note 4:
Logic-low voltages are specified at a sink current of 4mA.
Note 5:
To guarantee a presence pulse under low voltage parasite power conditions, VILMAX may have to be reduced to as
low as 0.5V.
Note 6:
Logic-high voltages are specified at a source current of 1mA.
Note 7:
Standby current specified up to +70°C. Standby current typically is 3µA at +125°C.
Note 8:
To minimize I
DDS
, DQ should be within the following ranges: GND ≤ DQ ≤ GND + 0.3V or V
DD
– 0.3V ≤ DQ ≤ V
DD
.
Note 9:
Active current refers to supply current during active temperature conversions or EEPROM writes.
Note 10:
DQ line is high (“high-Z” state).
Note 11:
Drift data is based on a 1000-hour stress test at +125°C with V
DD
= 5.5V.
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2
DS18S20
High-Precision 1-Wire Digital Thermometer
DS18S20 TYPICAL ERROR CURVE
0.5
0.4
THERMOMETER ERROR (°C)
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
-0.5
0
MEAN ERROR
+3s ERROR
-3s ERROR
10
20
30
40
50
60
70
TEMPERATURE (°C)
Figure 1. Typical Performance Curve
AC Electrical Characteristics—NV Memory
(V
DD
= 3.0V to 5.5V, T
A
= -55°C to +100°C, unless otherwise noted.)
PARAMETER
NV Write Cycle Time
EEPROM Writes
EEPROM Data Retention
SYMBOL
t
WR
N
EEWR
t
EEDR
-55°C to +55°C
-55°C to +55°C
50k
10
CONDITIONS
MIN
TYP
2
MAX
10
UNITS
ms
writes
years
AC Electrical Characteristics
(V
DD
= 3.0V to 5.5V; T
A
= -55°C to +125°C, unless otherwise noted.)
PARAMETER
Temperature Conversion Time
Time to Strong Pullup On
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
Capacitance
SYMBOL
t
CONV
t
SPON
t
SLOT
t
REC
t
LOW0
t
LOW1
t
RDV
t
RSTH
t
RSTL
t
PDHIGH
t
PDLOW
C
IN/OUT
(Note 12)
Start Convert T Command Issued
(Note 12)
(Note 12)
(Note 12)
(Note 12)
(Note 12)
(Note 12)
(Note 12, 13)
(Note 12)
(Note 12)
480
480
15
60
60
240
25
60
1
60
1
120
15
15
CONDITIONS
MIN
TYP
MAX
750
10
120
UNITS
ms
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
pF
Note 12:
See the timing diagrams in
Figure 2.
Note 13:
Under parasite power, if t
RSTL
> 960µs, a power-on reset may occur.
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DS18S20
High-Precision 1-Wire Digital Thermometer
1-Wire WRITE ZERO TIME SLOT
t
REC
t
SLOT
START OF NEXT CYCLE
t
LOW0
1-Wire READ ZERO TIME SLOT
t
SLOT
t
REC
START OF NEXT CYCLE
t
RDV
1-Wire RESET PULSE
RESET PULSE FROM HOST
t
RSTL
t
RSTH
1-Wire PRESENCE DETECT
PRESENCE DETECT
t
PDHIGH
t
PDLOW
Figure 2. Timing Diagrams
Pin Description
PIN
TO-92
1
2
3
—
SO
5
4
3
1, 2, 6, 7, 8
NAME
GND
DQ
V
DD
N.C.
Ground
Data Input/Output. Open-drain 1-Wire interface pin. Also provides power to the
device when used in parasite power mode (see the
Powering the DS18S20
section.)
Optional V
DD
. V
DD
must be grounded for operation in parasite power mode.
No Connection
FUNCTION
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DS18S20
High-Precision 1-Wire Digital Thermometer
Overview
Figure 3
shows a block diagram of the DS18S20, and
pin descriptions are given in the
Pin Description
table.
The 64-bit ROM stores the device’s unique serial code.
The scratchpad memory contains the 2-byte temperature
register that stores the digital output from the temperature
sensor. In addition, the scratchpad provides access to the
1-byte upper and lower alarm trigger registers (T
H
and
T
L
). The T
H
and T
L
registers are nonvolatile (EEPROM),
so they will retain data when the device is powered down.
The DS18S20 uses Maxim’s exclusive 1-Wire bus proto-
col that implements bus communication using one control
signal. The control line requires a weak pullup resistor
since all devices are linked to the bus via a 3-state or
open-drain port (the DQ pin in the case of the DS18S20).
In this bus system, the microprocessor (the master
device) identifies and addresses devices on the bus
using each device’s unique 64-bit code. Because each
device has a unique code, the number of devices that
can be addressed on one 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 DS18S20 is the ability to operate
without an external power supply. Power is instead sup-
plied 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
PP
), which then supplies power to the
device when the bus is low. This method of deriving power
from the 1-Wire bus is referred to as “parasite power.” As
an alternative, the DS18S20 may also be powered by an
external supply on V
DD
.
Operation—Measuring Temperature
The core functionality of the DS18S20 is its direct-to-dig-
ital temperature sensor. The temperature sensor output
has 9-bit resolution, which corresponds to 0.5°C steps.
The DS18S20 powers-up in a low-power idle state; to
initiate a temperature measurement and A-to-D conver-
sion, 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 scratch-
pad memory and the DS18S20 returns to its idle state.
If the DS18S20 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
DS18S20 will respond by transmitting 0 while the tem-
perature conversion is in progress and 1 when the con-
version is done. If the DS18S20 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
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