LMP91000SDE National Semiconductor, LMP91000SDE Datasheet - Page 21

• Manufacturer Part Number: LMP91000SDE
• Description: AFE, SENSOR, 14LLP
• Manufacturer: National Semiconductor

Specifications of LMP91000SDE

• Brief Features: Programmable Cell Bias Voltage, Low Bias Voltage Drift, I2C Compatible Digital Interface
• Supply Voltage Range: 2.7V To 5.25V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: LLP
• Ic Function: Programmable Analogue Front End (AFE)
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

-Power On only happens a few times over life, so its power
consumption can be ignored
-Deep Sleep mode is not used
-The system is used about 8 hours a day, and 16 hours a day
it is in Standby mode.
-Temperature Measurement is done about once per minute
SENSOR TEST PROCEDURE
The LMP91000 has all the hardware and programmability
features to implement some test procedures. The purpose of
the test procedure is to:
a) test proper function of the sensor (status of health)
b) test proper connection of the sensor to the LMP91000
The test procedure is very easy. The variable bias block is
user programmable through the digital interface. A step volt-
age can be applied by the end user to the positive input of A1.
As a consequence a transient current will start flowing into the
sensor (to charge its internal capacitance) and it will be de-
tected by the TIA. If the current transient is not detected, either
a sensor fault or a connection problem is present. The slope
and the aspect of the transient response can also be used to
detect sensor aging (for example, a cell that is drying and no
longer efficiently conducts the current). After it is verified that
the sensor is working properly, the LMP91000 needs to be
reset to its original configuration. It is not required to observe
the full transient in order to contain the testing time. All the
needed information are included in the transient slopes (both
edges).
Carbon Monoxide sensor is connected to the LMP91000, two
pulses are then sequentially applied to the bias voltage:
first step: from 0mV to 40mV
second step : from 40mV to -40mV
Current consumption
(µA)
typical value
Time ON
(%)
Average
(µA)
Notes
A1
TIA
TEMP SENSOR
I
2
C interface
Figure 10
shows an example of the test procedure, a
Deep Sleep
0.6
0
0
OFF
OFF
OFF
ON
StandBy
6.5
60
3.9
ON
OFF
OFF
ON
Power Consumption Scenario
21
3-Lead
Amperometric
Cell
10
39
3.9
ON
ON
OFF
ON
This results in an average power consumption of approxi-
mately 7.95 µA. This can potentially be further reduced, by
using the Standby mode between gas measurements. It may
even be possible, depending on the sensor used, to go into
deep sleep for some time between measurements, further
reducing the average power consumption.
and finally the bias is set again at 0mV since this is the normal
operation condition for this sensor.
FIGURE 10. TEST PROCEDURE EXAMPLE
Temperature
Measurement
TIA OFF
11.4
0
0
ON
OFF
ON
ON
LMP91000 OUTPUT
TEST PULSE
TIME (25ms/DIV)
Temperature
Measurement
TIA ON
14.9
1
0.15
ON
ON
ON
ON
Total
7.95
www.national.com
30132561