LMC6484AIMX Datasheet, PDF (12/24 Pages) Texas Instruments – LMC6484 CMOS Quad Rail-to-Rail Input and Output Operational Amplifier

Typical Performance Characteristics V_S = +15V, Single Supply, T_A = 25˚C unless otherwise
specified (Continued)
Stability vs
Capacitive Load
Stability vs
Capacitive Load
DS011714-89
Application Information
1.0 Amplifier Topology
The LMC6484 incorporates specially designed
wide-compliance range current mirrors and the body effect to
extend input common mode range to each supply rail.
Complementary paralleled differential input stages, like the
type used in other CMOS and bipolar rail-to-rail input ampli-
fiers, were not used because of their inherent accuracy
problems due to CMRR, cross-over distortion, and
open-loop gain variation.
The LMC6484’s input stage design is complemented by an
output stage capable of rail-to-rail output swing even when
driving a large load. Rail-to-rail output swing is obtained by
taking the output directly from the internal integrator instead
of an output buffer stage.
2.0 Input Common-Mode Voltage Range
Unlike Bi-FET amplifier designs, the LMC6484 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 on
the output.
DS011714-90
ceeding this absolute maximum rating, as in Figure 2, can
cause excessive current to flow in or out of the input pins
possibly affecting reliability.
DS011714-12
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.
DS011714-10
FIGURE 1. An Input Voltage Signal Exceeds the
LMC6484 Power Supply Voltages with
No Output Phase Inversion
The absolute maximum input voltage is 300 mV beyond
either supply rail at room temperature. Voltages greatly ex-
DS011714-11
FIGURE 3. R_I Input Current Protection for
Voltages Exceeding the Supply Voltage
3.0 Rail-To-Rail Output
The approximated output resistance of the LMC6484 is
180Ω sourcing and 130Ω sinking at V_S = 3V and 110Ω
sourcing and 83Ω sinking at V_S = 5V. Using the calculated
output resistance, maximum output voltage swing can be
estimated as a function of load.
4.0 Capacitive Load Tolerance
The LMC6484 can typically directly drive a 100 pF load with
V_S = 15V at unity gain without oscillating. The unity gain
follower is the most sensitive configuration. Direct capacitive
11
www.national.com