LMC8101BPX NSC [National Semiconductor], LMC8101BPX Datasheet - Page 7

• Manufacturer Part Number: LMC8101BPX
• Description: Rail-to-Rail Input and Output, 2.7V Op Amp in micro SMD package with Shutdown
• Manufacturer: NSC [National Semiconductor]

Application Notes
Conversion Boards:
In order to ease the evaluation of tiny packages such as the
micro SMD, there is a conversion board (LMC8101CONV)
available to board designers. This board converts a micro
SMD device into an 8 pin DIP package (see Figure 2 , Con-
version Board Pin out diagram) for easier handling and
evaluation. This board can be ordered from National Semi-
conductor by contacting http://www.national.com .
Increased Output Current:
Compared to the LMC7101, the LMC8101 has an improved
output stage capable of up to three times larger output
sourcing and sinking current. This improvement would allow
a larger output voltage swing range compared to the
LMC7101 when connected to relatively heavy loads. For
lower supply voltages this is an added benefit since it in-
creases the output swing range. For example, the LMC8101
can typically swing 2.5Vpp with 2mA sourcing and sinking
output current (Vs = 2.7V) whereas the LMC7101 output
swing would be limited to 1.9Vpp under the same conditions.
Also, compared to the LMC7101 in the SOT23 package, the
LMC8101 can dissipate more power because both the
MSOP and the micro SMD packages have 40% better heat
dissipation capability.
Lower 1/f noise:
The dominant input referred noise term for the LMC8101 is
the input noise voltage. Input noise current for this device is
of no practical significance unless the equivalent resistance
it looks into is 5M
The LMC8101’s low frequency noise is significantly lower
than that of the LMC7101. For example, at 10Hz, the input
referred spot noise voltage density is 85 nV
pared to about 200nV
quency range of 0.1Hz to 100Hz, the total noise of the
LMC8101 will be approximately 60% less than that of the
LMC7101.
Lower THD:
When connected to heavier loads, the LMC8101 has lower
THD compared to the LMC7101. For example, with 5V sup-
ply at 10KHz and 2Vpp swing (Av = −2), the LMC8101 THD
(0.2%) is 60% less than the LMC7101’s. The LMC8101 THD
can be kept below 0.1% with 3Vpp at the output for up to
10KHz (refer to the Typical Characteristics Plots).
Improving the Cap load drive capability:
This can be accomplished in several ways:
The Phase Margin increases with increasing load (refer to
the Typical Characteristics Plots). When driving capacitive
loads, stability can generally be improved by allowing some
output current to flow through a load. For example, the cap
•
FIGURE 2. micro SMD Conversion Board pin-out
Output resistive loading increase:
or higher.
for the LMC7101. Over a fre-
(Continued)
DS101240-89
as com-
7
load drive capability can be increased from 8200pF to
16000pF if the output load is increased from 5K
(Av = +10, 25% overshoot limit, 10V supply).
•
This resistor will isolate the feedback path (where excessive
phase shift due to output capacitance can cause instability)
from the capacitive load. With a 10V supply, a 100 isolation
resistor allows unlimited capacitive load without oscillation
compared to only 300pF without this resistor (Av = +1).
•
Operating the LMC8101 at higher supply voltages allows
higher cap load tolerance. At 10V, the LMC8101’s low supply
voltage cap load limit of 300pF improves to about 600pF (Av
= +1).
•
As with all Op Amps, the capacitive load tolerance of the
LMC8101 increases with increasing closed loop gain. In ap-
plications where the load is mostly capacitive and the resis-
tive loading is light, stability increases when the LMC8101 is
operated at a closed loop gain larger than +1.
Isolation resistor between output and cap load:
Higher supply voltage:
Closed loop gain increase:
www.national.com
to 600