Datasheet

Preliminary Data Sheet SHT3x-ARP
www.sensirion.com November 2014 - 0.9 5/11
3 Pin Assignment
The SHT3x-ARP comes in a tiny 8-pin DFN package –
see Table 6.
Pin
Name
Comments
1
RH
Analog voltage out; output
2
R
No electrical function; recommended to
connected to VSS
3
R
No electrical function; recommended to
connected to VSS
4
T
Analog voltage out; output
5
VDD
Supply voltage; input
6
nRESET
Reset pin active low; Input; if not used it
is recommended to connect to VDD
7
R
No electrical function; recommended to
connected to VSS
8
VSS
Ground
Table 6 SHT3x-ARP pin assignment (Transparent top view).
Dashed lines are only visible from the bottom. The die pad is
internally connected to VSS.
3.1 Power Pins (VDD, VSS)
The electrical specifications of the SHT3x-ARP are
shown in Table 3. The power supply pins must be
decoupled with a 100 nF capacitor that shall be placed
as close to the sensor as possible – see Figure 7 for a
typical application circuit.
3.2 Temperature and Humidity Pin
The physical output of temperature and humidity can be
read out at separated pins, as shown in Table 6. Data is
supplied as ratiometric voltage output, ranging from 10
to 90% of VDD. The specification of the Analog voltage
signal and its conversion to physical values is explained
in Section 4.
3.3 nRESET Pin
The nReset pin may be used to generate a reset of the
sensor. A minimum pulse duration of 350 ns is required
to reliably trigger a reset of the sensor. If not used it is
recommended to connect to VDD.
Figure 7 Typical application circuit. Please note that the
positioning of the pins does not reflect the position on the real
sensor. This is shown in Table 6.
3.4 Die Pad (center pad)
The die pad or center pad is visible from below and
located in the center of the package. It is electrically
connected to VSS. Hence electrical considerations do
not impose constraints on the wiring of the die pad.
However, due to mechanical reasons it is
recommended to solder the center pad to the PCB. For
more information on design-in, please refer to the
document “SHTxx Design Guide”.
4 Operation and Communication
4.1 Start-up of the sensor
As a first step, the sensor needs to be powered up to
VDD (between 2.4 and 5.5 V). After power-up, the
sensor needs at most 15 ms for providing data as
voltage output on the respective output pins. During
that time the temperature and humidity pins have an
undefined state.
4.2 Conversion of the Signal Output
The physical values as measured by the sensor are
mapped to a ratiometric voltage output (V
X
, x=T, RH as
10 to 90% of V
DD
). Prior to conversion into a voltage
signal, the physical values are linearized and
compensated for temperature and supply voltage
effects by the sensor. Additionally, the voltage output is
calibrated for each sensor. Hence the relationship
between temperature and humidity and the voltage
output is the same for each sensor, within the limits
given by the accuracy.
This allows to describe the relationship between
physical values (RH and T) and the voltage output for
temperature and humidity (V
X
, x=T, RH) through a
generic linear formula shown in Equation 1 (for RH) and
Equation 2 (for T), its graphical representation can be
found in Figure 8 & Figure 9.
1
2
3
4
5
8
7
6
V
DD
R(2,3,7)
RH(1)
T(4)
VDD(5)
VSS(8)
die
pad
100nF
nRESET(6)
0.1nF
0.1nF