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LMC6482IMM

Part # LMC6482IMM
Description CMOS DUAL RAIL-TO-RAIL INPUTAND OUTPUT - Tape and Reel
Category IC
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Technical Document


DISCLAIMER: The information provided herein is solely for informational purposes. Customers must be aware of the suitability of this product for their application, and consider that variable factors such as Manufacturer, Product Category, Date Codes, Pictures and Descriptions may differ from available inventory.

LMC6482
SNOS674D NOVEMBER 1997REVISED MARCH 2013
www.ti.com
APPLICATION INFORMATION
AMPLIFIER TOPOLOGY
The LMC6482 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 amplifiers, were not used because of their inherent
accuracy problems due to CMRR, cross-over distortion, and open-loop gain variation.
The LMC6482'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.
INPUT COMMON-MODE VOLTAGE RANGE
Unlike Bi-FET amplifier designs, the LMC6482 does not exhibit phase inversion when an input voltage exceeds
the negative supply voltage. Figure 56 shows an input voltage exceeding both supplies with no resulting phase
inversion on the output.
An input voltage signal exceeds the lmc6482 power supply voltages with no output phase inversion.
Figure 56. Input Voltage
The absolute maximum input voltage is 300mV beyond either supply rail at room temperature. Voltages greatly
exceeding this absolute maximum rating, as in Figure 57, can cause excessive current to flow in or out of the
input pins possibly affecting reliability.
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Product Folder Links: LMC6482
LMC6482
www.ti.com
SNOS674D NOVEMBER 1997REVISED MARCH 2013
A ±7.5V input signal greatly exceeds the 3V supply in Figure 58 causing no phase inversion due to R
I
.
Figure 57. Input Signal
Applications that exceed this rating must externally limit the maximum input current to ±5mA with an input
resistor (R
I
) as shown in Figure 58.
R
I
input current protection for voltages exceeding the supply voltages.
Figure 58. R
I
Input Current Protection for
Voltages Exceeding the Supply Voltages
RAIL-TO-RAIL OUTPUT
The approximated output resistance of the LMC6482 is 180Ω sourcing and 130Ω sinking at V
S
= 3V and 110Ω
sourcing and 80Ω sinking at Vs = 5V. Using the calculated output resistance, maximum output voltage swing can
be estimated as a function of load.
CAPACITIVE LOAD TOLERANCE
The LMC6482 can typically directly drive a 100pF load with V
S
= 15V at unity gain without oscillating. The unity
gain follower is the most sensitive configuration. Direct capacitive loading reduces the phase margin of op-amps.
The combination of the op-amp's output impedance and the capacitive load induces phase lag. This results in
either an under damped pulse response or oscillation.
Capacitive load compensation can be accomplished using resistive isolation as shown in Figure 59. This simple
technique is useful for isolating the capacitive inputs of multiplexers and A/D converters.
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Product Folder Links: LMC6482
LMC6482
SNOS674D NOVEMBER 1997REVISED MARCH 2013
www.ti.com
Figure 59. Resistive Isolation of a 330pF Capacitive Load
Figure 60. Pulse Response of the LMC6482 Circuit in Figure 59
Improved frequency response is achieved by indirectly driving capacitive loads, as shown in Figure 61.
Compensated to handle a 330pF capacitive load.
Figure 61. LMC6482 Noninverting Amplifier
R1 and C1 serve to counteract the loss of phase margin by feeding forward the high frequency component of the
output signal back to the amplifiers inverting input, thereby preserving phase margin in the overall feedback loop.
The values of R1 and C1 are experimentally determined for the desired pulse response. The resulting pulse
response can be seen in Figure 62.
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