AD8290
Rev. B | Page 18 of 20
PRESSURE SENSOR BRIDGE APPLICATION
Given its excitation current range, the AD8290 provides a good
match with pressure sensor circuits. Two such sensors are the
Fujikura FGN-615PGSR and the Honeywell HPX050AS.
Figure 47
shows the AD8290 paired with the Honeywell bridge and the
appropriate connections. In this example, a resistor, R
P
, is added
to the circuit to ensure that the maximum output voltage of the
AD8290 is not exceeded. Depending on the sensors specifications,
R
P
may not be necessary.
The specifications for the bridge are show in
Table 5 and the
chosen conditions for the AD8290 are listed in
Table 6.
Given these specifications, calculations should be made to ensure
that the AD8290 is operating within its required ranges. The
combination of the excitation current and R
P
must be chosen
to ensure that the conditions stay within the minimum and
maximum specifications of the AD8290. For this example,
because the specifications of the HPX050AS are for a bridge
excitation voltage of 3.0 V, care must be taken to scale the
resulting voltage calculations to the actual bridge voltage. The
required calculations are shown in
Table 7.
06745-030
ENBL
VOUT
VCC
NC NC
VINP
VINN
IOUT
RSET
GND
NC
AD8290
NC NC NC
161
4
3
2
129
10
11
15
14
13
C
FILTER
6.8nF
C1
0.1µF
CF2CF1
5
6
7
8
C2
68nF
C
BRIDGE
0.1µF
R
SET
2.7kΩ
R
P
2kΩ
3.3V
4
5
6
8
HPX050AS
2
NC = NO CONNECT
Figure 47. HPX050AS Pressure Sensor Application
Table 5. HPX050AS Specifications
Bridge Impedance (Ω) Rated Offset (mV) Rated Output Span (mV)
Minimum Maximum Minimum Maximum Minimum Maximum Bridge Excite Voltage (V)
4000 6000 −30 +30 0 80 3.0
Table 6. Typical AD8290 Conditions for Pressure Sensor Circuit
AD8290 V
CC
(V) Excitation Current (μA) Parallel Resistor R
P
(Ω)
3.3 (2.6 to 5.5) 333.3 (300 to 1300) 2000
Table 7. Pressure Sensor Circuit Calculations Compared to AD8290 Minimum/Maximum Specifications
Specification Calculation Unit Allowable Range of AD8290
Supply Current 1.867 mA
Current Setting Resistor (R
SET
) 2700 Ω 692 Ω to 3000 Ω
Minimum Equivalent Resistance to IOUT Pin 1333 Ω
Maximum Equivalent Resistance to IOUT Pin 1500 Ω
Minimum Current into Bridge 83.333 μA
Maximum Current into Bridge 111.111 μA
Minimum Bridge Midpoint Voltage (Excluding Offset/Span) 0.222 V
Maximum Bridge Midpoint Voltage (Excluding Offset/Span) 0.250 V
Minimum Voltage at Current Output Pin (IOUT) 0.444 V >0.0 V
Maximum Voltage at Current Output Pin (IOUT) 0.500 V <2.3 V
Input Voltage Minimum 0.218 V >0.2 V
Input Voltage Maximum 0.266 V <1.6 V
Output Voltage Minimum 0.643 V >0.075 V
Output Voltage Maximum 1.852 V <3.225 V
