Datasheet

OUTPUT VOLTTAGE (500mV/DIV)
TIME (25ms/DIV)
INPUT PULSE (50mV/DIV)
LMP91000 OUTPUT
TEST PULSE
LMP91002
www.ti.com SNIS163A –APRIL 2012–REVISED MARCH 2013
This results in an average power consumption of approximately 7.8 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.
Table 2. Power Consumption Scenario
Deep Sleep StandBy 3-Lead Amperometric Cell Total
Current consumption (µA) typical value 0.6 6.5 10
Time ON (%) 0 60 39
Average (µA) 0 3.9 3.9 7.8
Notes
A1 OFF ON ON
TIA OFF OFF ON
I
2
C interface ON ON ON
SENSOR TEST PROCEDURE
The LMP91002 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 LMP91002
The test procedure is very easy. The diagnostic block is user programmable through the digital interface. A step
voltage 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 detected 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 LMP91002 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). Figure 26 shows an example test
procedure, a Carbon Monoxide sensor is connected to the LMP91002, a 25mVpp pulse is applied between
Reference and Working pin.
The following procedure shows how to implement the sensor test. Preliminary conditions:
The LMP91002 is unlocked and it is in 3-Lead Amperometric Cell Mode
1. Put in the [3:0] bit of the register REFCN (0x11) the 0001b value, leaving the other bit unchanged.
This operation will apply a potential (V
RW
) between RE and WE pin (V
RE
> V
WE
), V
RW
= 1% Source reference
2. Put in the [3:0] bit of the register REFCN (0x11) the 0000b value, leaving the other bit unchanged.
This operation will remove the potential (V
RW
) between RE and WE pin (V
RE
> V
WE
), V
RW
= 0V.
The width of the pulse is simply the time between the two writing operation.
Figure 26. TEST PROCEDURE EXAMPLE
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