Pressure sensors
C29 series Absolute pressure sensor die for wet media
AS SEN PD 2009-08-03
Please read Cautions and warnings and Page 5 of 8
Important notes at the end of this document.
Symbols and terms
1)
Maximum power supply V
DD
This is the maximal allowed voltage, which may be applied to the piezoresistive bridge circuit without damage.
2)
Operating temperature range T
a
This is the operating Temperature range T
a,min
to T
a,max
.
Because most of the sensor parameters depend on assembling
conditions like gluing, wire bonding etc, the die has to be tested over the operating temperature range by the customer
fully assembled. For design verification and process control samples, mounted in AK transducer package (AK2 series)
are tested over a reduced measuring temperature range of T
meas,min
to T
meas,max
.
3)
Storage temperature range T
st
If the pressure sensor dies are stored in the temperature range T
st,min
to T
st,max
without applied voltage power supply, this
will not affect the performance of the pressure sensor dies.
4)
Operating pressure range p
r
In the operating pressure range 0 to p
r,max
the pressure sensor die output characteristic is as defined in this specification.
5)
Over pressure p
OV
Pressure cycles in the pressure range 0 to p
ov
do not affect the performance of the pressure sensor dies.
6)
Burst pressure p
berst
Up to the burst pressure p
berst
the diaphragm of the sensor die will not be destroyed mechanically. This parameter is
tested at room temperature on samples mounted on an aluminium socket by applying the specified burst pressure for
10 minutes. The evaluation of this test is done by optical inspection of the diaphragm.
7)
Operating power supply V
DD
The pressure sensor parameters are defined for a power supply voltage of V
DD
= 5 V. In the operating power supply
voltage range V
DD,min
to V
DD,max
the ratiometric parameters r(V
DD
) like sensitivity, offset voltage and the temperature
coefficient of the offset voltage are defined by:
( )
]V[5
V
])V[5(rVr
DD
DD
=
8)
Total bridge resistance R
S
The total bridge resistance is defined between pad X5 and X2, (see the dimensional drawing in this data sheet) of the
closed piezoresistive bridge circuit. The total bridge resistance is in a good approximation the output impedance of the
piezoresistive bridge circuit. This parameter is tested completely on a wafer (wafer level test measurement).
9)
Temperature coefficients of resistance α
αα
α
Rs
and β
ββ
β
Rs
:
The temperature coefficients of resistance are tested for design verification on samples, mounted on AK transducer
package (AK2 series) over a reduced temperature range T
meas
,
min
= –20 °C to T
meas
,
max
= 80 °C with T
R
= 25 °C.
The temperature coefficients of first and second order are defined with the polynomial:
°−β+°−α+°==
2
RsRs
SS
C25TC25T1)C25T(R)T(R
The coefficients α
Rs
and β
Rs
are calculated using the three measurement points of R
s
(T) at T
meas,min
, T
R
and T
meas,max
.
10)
Offset voltage V
0
The offset voltage V
0
is the output voltage V
out
(p = 0 bar absolute) at zero absolute pressure and for a bridge voltage
power supply V
DD
= 5 V. The high range of the allowed offset voltage is due to the reference pressure in the glass cap
from 0 to 0.3 bar and to the tolerance of the sensitivity. The typical value of the reference pressure is 0.2 bar.
Before anodic glass bonding the offset voltage is tested completely on a wafer (wafer level test measurement)
with limits –25 mV < V
0
< 25 mV. For design verification V
0
is measured on samples, mounted in AK transducer package
(AK2 series) by extrapolating the output characteristic to zero bar.
It should be noted that this parameter may be influenced by assembly.
11)
Temperature coefficients of offset voltage TCV
0
+
and TCV
0
–
The temperature coefficients of offset voltage are defined for a bridge voltage power supply V
DD
= 5 V.
These parameters strongly depend on assembly conditions like gluing, wire bonding etc.
The temperature coefficients of offset voltage are tested for design verification on samples, mounted on AK transducer
package (AK2 series) over a reduced temperature range T
meas
,
min
= –20 °C to T
meas
,
max
= 80 °C with T
R
= 25 °C.
Assuming the offset voltage is mainly due to induce stress TCV
0
may be calculated by extrapolating using:
2
21o
2
ss0
)C25T(v)C25T(v)C25(V)C25T()C25T(1)T(V °−+°−+°°−β+°−α+=
