LMC8101TP Datasheet, PDF (15/19 Pages) National Semiconductor (TI) – Rail-to-Rail Input and Output, 2.7V Op Amp in micro SMD package with Shutdown

Application Notes
SHUTDOWN FEATURES
The LMC8101 is capable of being turned off in order to
conserve power. Once in shutdown, the device supply cur-
rent is drastically reduced (1µA maximum) and the output will
be "Tri-stated".
The shutdown feature of the LMC8101 is designed for flex-
ibility. The threshold level of the SD input can be referenced
to either V^- or V⁺ by setting the level on the SL input. When
the SL input is connected to V^-, the SD threshold level is
referenced to V^- and vice versa. This threshold will be about
1.5V from the supply tied to the SL pin. So, for this example,
the device will be in shutdown as long as the SD pin voltage
is within 1V of V^-. In order to ensure that the device would not
"chatter" between active and shutdown states, hysteresis is
built into the SD pin transition (see Figure 1 for an illustration
of this feature). The shutdown threshold and hysteresis level
are independent of the supply voltage. Figure 1 illustration
applies equally well to the case when SL is tied to V⁺ and the
horizontal axis is referenced to V⁺ instead. The SD pin
should not be set within the voltage range from 1.1V to 1.9V
of the selected supply voltage since this is a transition region
and the device status will be undetermined.
operational state. Some applications may be sensitive to this
output spike and proper precautions should be taken in order
to ensure proper operation at all times.
TINY PACKAGE
The LMC8101 is available in the micro SMD package as well
the 8 pin MSOP package. The micro SMD package requires
approximately 1/4 the board area of a SOT23. This package
is less than 1mm in height allowing it to be placed in absolute
minimum height clearance areas such as cellular handsets,
LCD panels, PCMCIA cards, etc. More information about the
micro SMD package can be found at: http://
www.national.com/appinfo/microsmd.
CONVERSION BOARDS
In order to ease the evaluation of tiny packages such as the
micro SMD, there is a conversion board (LMC8101CONV)
available to board designers. This board converts a micro
SMD device into an 8 pin DIP package (see Figure 2,
Conversion Board Pin out diagram) for easier handling and
evaluation. This board can be ordered from National Semi-
conductor by contacting http://www.national.com .
10124082
FIGURE 1. Supply Current vs. "SD" Voltage
Table 1, below, summarizes the status of the device when
the SL and SD pins are connected directly to V^- or V⁺:
TABLE 1. LMC8101 Status Summary
SL
SD
LMC8101 Status
V^−
V^−
Shutdown
V^−
V⁺
Active
V⁺
V⁺
Shutdown
V⁺
V^−
Active
In case shutdown operation is not needed, as can be seen in
Table 1, the two pins SL and SD can simply be connected to
opposite supply nodes to achieve "Active" operation. The SL
and SD should always be tied to a node; if left unconnected,
these high impedance inputs will float to an undetermined
state and the device status will be undetermined as well.
With the device in shutdown, once "Active" operation is
initiated, there will be a finite amount of time required before
the device output is settled to its final value. This time is less
than 15µs. In addition, there may be some output spike
during this time while the device is transitioning into a fully
10124089
FIGURE 2. micro SMD Conversion Board pin-out
INCREASED OUTPUT CURRENT
Compared to the LMC7101, the LMC8101 has an improved
output stage capable of up to three times larger output
sourcing and sinking current. This improvement would allow
a larger output voltage swing range compared to the
LMC7101 when connected to relatively heavy loads. For
lower supply voltages this is an added benefit since it in-
creases the output swing range. For example, the LMC8101
can typically swing 2.5Vpp with 2mA sourcing and sinking
output current (Vs = 2.7V) whereas the LMC7101 output
swing would be limited to 1.9Vpp under the same conditions.
Also, compared to the LMC7101 in the SOT23 package, the
LMC8101 can dissipate more power because both the
MSOP and the micro SMD packages have 40% better heat
dissipation capability.
LOWER 1/f NOISE
The dominant input referred noise term for the LMC8101 is
the input noise voltage. Input noise current for this device is
of no practical significance unless the equivalent resistance
it looks into is 5MΩ or higher.
The LMC8101’s low frequency noise is significantly lower
than that of the LMC7101. For example, at 10Hz, the input
referred spot noise voltage density is 85 nV as com-
pared to about 200nV for the LMC7101. Over a fre-
quency range of 0.1Hz to 100Hz, the total noise of the
LMC8101 will be approximately 60% less than that of the
LMC7101.
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