LMC7101 datasheet(14/18 Pages) NSC

14 / 18 page

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 k

Ω 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.

Applications that exceed this rating must externally limit the

maximum input current to ±5 mA with an input resistor as

shown in

Figure 3.

3.0 Rail-To-Rail Output

The approximate output resistance of the LMC7101 is 180

Ω

sourcing and 130

Ω sinking at V

S = 3V and 110Ω sourcing

and 80

Ω 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

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-

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

DS011991-10

FIGURE 3. R

I Input Current Protection for

Voltages Exceeding the Supply Voltage

LMC7101 Datasheet(PDF) 14 Page - National Semiconductor (TI)

LMC7101 Datasheet(HTML) 14 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Datasheet Download

Link URL