lm9040 National Semiconductor Corporation, lm9040 Datasheet - Page 8

• Manufacturer Part Number: lm9040
• Description: Dual Lambda Sensor Interface Amplifier
• Manufacturer: National Semiconductor Corporation

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Open Input Pins Defaults
connected to the Lambda sensor ground, so any common
mode signals would still need to be allowed for in this con-
dition. See Figure 9 .
For the case of an open connection of the inverting input, the
device output stage switches from the amplifier output to a
resistive voltage divider. In this case, the default V
dependent on the gain stage, and any signal on the
non-inverting input will have no effect on the output. Each
amplifier has a comparator to monitor the voltage on the
inverting input pin. When the voltage on an inverting pin
In the cases where both the inverting and non-inverting pins
are open, the non-inverting condition (i.e.: voltage divider
across the output) will be the dominant condition.
Any common mode signal seen by inverting input pin should
not be allowed to exceed the Common Mode voltage range.
Exceeding the positive Common Mode voltage limit could
cause the inverting input pin voltage comparator to act as if
the inverting input pin is open. Since the comparator circuit is
not part of the switched capacitor network there is no fre-
quency limitation on the signal to the comparator. Any tran-
sient on the inverting input pin which goes above the com-
parator threshold will immediately cause the output to switch
to the open sensor mode. The output will return to normal
operation when the voltage on the inverting input falls below
the comparator threshold.
FIGURE 10. V
(Continued)
OUT
is not
OUT
with Open Inverting Input
8
goes above typically 2.5V, the comparator will switch the
output from the amplifier output to the voltage divider stage.
To fully implement this function requires external pull-up
resistors for each of the inverting inputs. To minimize signal
errors due to DC currents through the 4 k
pull-up resistors need to be added in the application circuit
between the 4 k
Lambda sensor ground point. A typical pull-up value of 51 k
to V
resistance of the output stage will be 3.5 k
Figure 10 .
Supply Bypassing
For best performance the LM9040 requires a V
which is stable and noise free. The same 5V V
used for the A/D converter is the recommended V
During operation the device will generate current spikes
coincident with the clock edges. Inadequate bypassing will
cause excessive clock noise on the outputs, as well as noise
on the V
with a minimum 0.1 µF capacitor to the Signal Ground pin,
and should be located as close to the device as possible.
Some applications may require an additional 4.7 µF tantalum
capacitor, especially if there are several other switched ca-
pacitor devices running off the same 5V supply line. The
Signal and Digital Ground pins should be tied together as
close to the device as possible.
CC
is recommended. During this condition, the effective
CC
line. The LM9030 V
input resistor and the connection to the
01237220
CC
pin should be bypassed
resistors, the
typically. See
REF
CC
CC
supply.
supply
supply