SHT71 SENSIRION, SHT71 Datasheet - Page 5

• Manufacturer Part Number: SHT71
• Description: Humidity Sensor
• Manufacturer: SENSIRION

Specifications of SHT71

• Sensing Accuracy: 3%
• Sensor Output: Digital
• Sensor Terminals: Through Hole
• Peak Reflow Compatible (260 C): Yes
• Terminal Type: PCB Surface Mount
• Humidity Range: 0 To 100% RH
• Response Time: 8s
• Humidity Accuracy ±: 3%
• Rohs Compliant: Yes
• Leaded Process Compatible: Yes
• Package / Case: 4-SIP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Datasheet SHT7x
microcontrollers. See Table 2 for detailed I/O characteristic
of the sensor.
2.4
The electrical characteristics such as power consumption,
low and high level, input and output voltages depend on
the supply voltage. Table 2 gives electrical characteristics
of SHT7x with the assumption of 5V supply voltage if not
stated otherwise. For proper communication with the
sensor it is essential to make sure that signal design is
strictly within the limits given in Table 3 and Figure 6.
Absolute maximum ratings for VDD versus GND are +7V
and -0.3V. Exposure to absolute maximum rating
conditions for extended periods may affect the sensor
reliability (e.g. hot carrier degradation, oxide breakdown).
Parameter
Power supply DC
Supply current
Low level output
voltage
High level output
voltage
Low level input
voltage
High level input
voltage
Input current on
pads
Output current
Table 2: SHT7x DC characteristics. R
resistor, while I
Figure 6: Timing Diagram, abbreviations are explained in
Table 3. Bold DATA line is controlled by the sensor, plain DATA
line is controlled by the micro-controller. Note that DATA valid
read time is triggered by falling edge of anterior toggle.
10
11
www.sensirion.com
SCK
DATA
Recommended voltage supply for highest accuracy is 3.3V, due to sensor
calibration.
Minimum value with one measurement of 8 bit resolution without OTP reload
per second, typical value with one measurement of 12bit resolution per
second.
T
SU
Electrical Characteristics
DATA valid write
OL
10
is low level output current.
T
SCKH
Conditions
measuring
average
sleep
I
R
Negative going
Positive going
on
Tri-stated (off)
OL
P
< 4 mA
< 25 kΩ
T
SCK
11
T
SCKL
T
HO
DATA valid read
T
V
T
90%
80%
min
R
2.4
0%
2
0
P
stands for pull up
0.55
typ
3.3
0.3
28
10
T
F
100% VDD
100% VDD
20% VDD
max Units
250
5.5
1.5
20
1
1
4
Version 4.3 – May 2010
T
mA
mV
mA
µA
µA
µA
µA
V
RO
20%
80%
20%
T
80%
FO
Table 3: SHT7x I/O signal characteristics, OL stands for Output
Load, entities are displayed in Figure 6.
3 Communication with Sensor
3.1
As a first step the sensor is powered up to chosen supply
voltage VDD. The slew rate during power up shall not fall
below 1V/ms. After power-up the sensor needs 11ms to
get to Sleep State. No commands must be sent before
that time.
3.2
To initiate a transmission, a Transmission Start sequence
has to be issued. It consists of a lowering of the DATA line
while SCK is high, followed by a low pulse on SCK and
raising DATA again while SCK is still high – see Figure 7.
Figure 7: "Transmission Start" sequence
The subsequent command consists of three address bits
(only ‘000’ is supported) and five command bits. The
SHT7x indicates the proper reception of a command by
pulling the DATA pin low (ACK bit) after the falling edge of
the 8th SCK clock. The DATA line is released (and goes
high) after the falling edge of the 9th SCK clock.
F
T
T
T
T
T
T
T
*
**
***
****
SCK
SCKx
R
FO
RO
V
SU
HO
SCK
DATA
/T
F
Parameter
SCK Frequency
SCK hi/low time
SCK rise/fall time
DATA fall time
DATA rise time
DATA valid time
DATA setup time
DATA hold time
T
T
T
line capacitance (Cbus) at DATA line
T
Start up Sensor
Sending a Command
R_max
R0
V_max
H0_max
is determined by the R
and T
+ T
< T
F_max
V
SU_max
– max (T
= (F
depend on external pull-up resistor (R
SCK
R0
)
-1
, T
Conditions
VDD > 4.5V
VDD < 4.5V
OL = 5pF
OL = 100pF 30
– T
F0
P
SCKH
)
*C
bus
– T
time-constant at DATA line
SCKL
min typ max Units
100
200 250
100 150
3.5
10
**
0
0
1
200
0.1
0.1
10
40
15
**
P
) and total bus
200
****
20
***
***
**
5
1
*
MHz
MHz
ns
ns
ns
ns
ns
ns
ns
ns
5/11
20%
80%
20%
80%