LMC7101_09 Datasheet, PDF (18/24 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 print-
ed circuit boards, and enable the design of smaller electronic
products. Because they are easier to carry, many customers
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 signal 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 device, long pc traces may be avoid-
ed.
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 allows 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 signal pro-
cessing.
Low Supply Current
The typical 0.5 mA supply current of the LMC7101 extends
battery life in portable applications, and may allow the reduc-
tion of the size of batteries in some applications.
Wide Voltage Range
The LMC7101 is characterized at 15V, 5V and 3V. Perfor-
mance 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 input
voltage exceeds the negative supply voltage. Figure 1 shows
an input voltage exceeding both supplies with no resulting
phase inversion of the output.
The absolute maximum input voltage is 300 mV beyond either
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.
1199108
FIGURE 1. An Input Voltage Signal Exceeds the
LMC7101 Power Supply Voltages with
No Output Phase Inversion
1199109
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.
1199110
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 resis-
tance, maximum output voltage swing can be estimated as a
function of load.
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