LMC7101 Datasheet, PDF (14/18 Pages) National Semiconductor (TI) – Tiny Low Power Operational Amplifier with Rail-To-Rail Input and Output

Application Information
1.0 Benefits of the LMC7101
Tiny Amp
Size. The small footprint of the SOT 23-5 packaged Tiny
amp, (0.120 x 0.118 inches, 3.05 x 3.00 mm) saves space on
printed circuit boards, and enable the design of smaller elec-
tronic products. Because they are easier to carry, many cus-
tomers prefer smaller and lighter products.
Height. The height (0.056 inches, 1.43 mm) of the Tiny amp
makes it possible to use it in PCMCIA type III cards.
Signal Integrity. Signals can pick up noise between the sig-
nal source and the amplifier. By using a physically smaller
amplifier package, the Tiny amp can be placed closer to the
signal source, reducing noise pickup and increasing signal
integrity. The Tiny amp can also be placed next to the signal
destination, such as a buffer for the reference of an analog to
digital converter.
Simplified Board Layout. The Tiny amp can simplify board
layout in several ways. First, by placing an amp where amps
are needed, instead of routing signals to a dual or quad de-
vice, long pc traces may be avoided.
By using multiple Tiny amps instead of duals or quads, com-
plex signal routing and possibly crosstalk can be reduced.
Low THD. The high open loop gain of the LMC7101 amp al-
lows it to achieve very low audio distortion — typically 0.01%
at 10 kHz with a 10 kΩ load at 5V supplies. This makes the
Tiny an excellent for audio, modems, and low frequency sig-
nal processing.
Low Supply Current. The typical 0.5 mA supply current of
the LMC7101 extends battery life in portable applications,
and may allow the reduction of the size of batteries in some
applications.
Wide Voltage Range. The LMC7101 is characterized at
15V, 5V and 3V. Performance data is provided at these
popular voltages. This wide voltage range makes the
LMC7101 a good choice for devices where the voltage may
vary over the life of the batteries.
2.0 Input Common Mode
Voltage Range
The LMC7101 does not exhibit phase inversion when an in-
put voltage exceeds the negative supply voltage. Figure 1
shows an input voltage exceeding both supplies with no re-
sulting phase inversion of the output.
The absolute maximum input voltage is 300 mV beyond ei-
ther rail at room temperature. Voltages greatly exceeding
this maximum rating, as in Figure 2, can cause excessive
current to flow in or out of the input pins, adversely affecting
reliability.
DS011991-8
FIGURE 1. An Input Voltage Signal Exceeds the
LMC7101 Power Supply Voltages with
No Output Phase Inversion
DS011991-9
FIGURE 2. A ±7.5V Input Signal Greatly
Exceeds the 3V Supply in Figure 3 Causing
No Phase Inversion Due to R_I
Applications that exceed this rating must externally limit the
maximum input current to ±5 mA with an input resistor as
shown in Figure 3.
DS011991-10
FIGURE 3. R_I Input Current Protection for
Voltages Exceeding the Supply Voltage
3.0 Rail-To-Rail Output
The approximate output resistance of the LMC7101 is 180Ω
sourcing and 130Ω sinking at V_S = 3V and 110Ω sourcing
and 80Ω sinking at V_S = 5V. Using the calculated output re-
sistance, maximum output voltage swing can be estimated
as a function of load.
4.0 Capacitive Load Tolerance
The LMC7101 can typically directly drive a 100 pF load with
V_S = 15V at unity gain without oscillating. The unity gain fol-
lower is the most sensitive configuration. Direct capacitive
loading reduces the phase margin of op-amps. The combi-
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