LMC6681 National Semiconductor, LMC6681 Datasheet - Page 13

• Manufacturer Part Number: LMC6681
• Description: Low Voltage / Rail-To-Rail Input and Output CMOS
• Manufacturer: National Semiconductor

Application Information
1.0 Input Common-Mode Voltage
Range
The LMC6681/2/4 has a rail-to-rail input common-mode volt-
age range. Figure 1 shows an input voltage exceeding both
supplies with no resulting phase inversion on the output.
The absolute maximum input voltage at V
beyond either supply rail at room temperature. Voltages
greatly exceeding this absolute maximum rating, as in Figure
2 , can cause excessive current to flow in or out of the input
pins, possibly affecting reliability. The input current can be
externally limited to
in Figure 3 .
FIGURE 1. An Input Signal Exceeds the LMC6681/2/4
Power Supply Voltages with No Output Phase
FIGURE 2. A
Voltages Exceeding the Supply Voltage
FIGURE 3. Input Current Protection for
Causing No Phase Inversion Due to R
Exceeds the 3V Supply in Figure 3 ,
±
5 mA, with an input resistor, as shown
±
7.5V Input Signal Greatly
Inversion
+
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= 3V is 300 mV
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I
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13
2.0 Rail-to-Rail Output
The approximated output resistance of the LMC6681/2/4 is
50
output swing can be estimated as a function of load using the
calculated output resistance.
3.0 Low Voltage Operation
The LMC6682 operates at supply voltages of 2.2V and 1.8V.
These voltages represent the End of Discharge voltages of
several popular batteries. The amplifier can operate from 1
Lead-Acid or Lithium Ion battery, or 2NiMH, NiCd, or
Carbon-Zinc batteries. Nominal and End of Discharge of
Voltage of several batteries are listed below.
At V
common-mode voltage range. Figure 4 shows an input volt-
age extending to both supplies and the resulting output.
The amplifier is operational at V
put common-mode voltage range, output swing, and CMRR
specs. Figure 5 shows the response of the LMC6681/2/4 at
V
NiMH
NiCd
Lead-Acid
Silver Oxide
Carbon-Zinc
Lithium
Battery Type
S
= 1.8V.
S
sourcing, and 50
Range Extends to Both Supplies at V
FIGURE 4. The Input Common-Mode Voltage
= 2.2V, the LMC6681/2/4 has a rail-to-rail input
FIGURE 5. Response of the LMC6681/2/4
Nominal Voltage
2.6V–3.6V
at V
sinking at V
1.2V
1.2V
1.6V
1.5V
2V
S
= 1.8V
S
= 1.8V, with guaranteed in-
S
= 3V. The maximum
End of Discharge
1.7V–2.4V
Voltage
S
1.8V
1.3V
1.1V
1V
1V
= 2.2V
www.national.com
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