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PDF LM6211 Data sheet ( Hoja de datos )
| Número de pieza | LM6211 | |
| Descripción | RRO Operational Amplifier | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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May 2006
LM6211
Low Noise, RRO Operational Amplifier with CMOS Input
and 24V Operation
General Description
The LM6211 is a wide bandwidth, low noise op amp with a
wide supply voltage range and a low input bias current. The
LM6211 operates with a single supply voltage of 5V to 24V,
is unity gain stable, has a ground-sensing CMOS input
stage, and offers rail-to-rail output swing.
The LM6211 is designed to provide optimal performance in
high voltage, low noise systems. The LM6211 has a unity
gain bandwidth of 20 MHz and an input referred voltage
noise density of 5.5 nV/
at 10 kHz. The LM6211
achieves these specifications with a low supply current of
only 1 mA. The LM6211 has a low input bias current of
2.3 pA, an output short circuit current of 25 mA and a slew
rate of 5.6 V/us. The LM6211 also features a low common-
mode input capacitance of 5.5 pF which makes it ideal for
use in wide bandwidth and high gain circuits. The LM6211 is
well suited for low noise applications that require an op amp
with very low input bias currents and a large output voltage
swing, like active loop-filters for wide-band PLLs. A low total
harmonic distortion, 0.01% at 1 kHz with loads as high as
600Ω, also makes the LM6211 ideal for high fidelity audio
and microphone amplifiers.
The LM6211 is available in the small SOT package, allowing
the user to implement ultra-small and cost effective board
layouts.
Features
(Typical 24V supply unless otherwise noted)
n Supply voltage range
5V to 24V
n Input referred voltage noise
5.5 nV/
n Unity gain bandwidth
20 MHz
n 1/f corner frequency
400 Hz
n Slew rate
5.6 V/µs
n Supply current
1.05 mA
n Low input capacitance
5.5 pF
n Temperature range
-40˚C to 125˚C
n Total harmonic distortion
0.01% @ 1 kHz, 600Ω
n Output short circuit current
25 mA
Applications
n PLL loop filters
n Low noise active filters
n Strain gauge amplifiers
n Low noise microphone amplifiers
Typical Application
20120303
20120304
© 2006 National Semiconductor Corporation DS201203
www.national.com
1 page  
Typical Performance Characteristics Unless otherwise specified, TA = 25˚C, VS = 24V, V+ = VS,
V− = 0 V, VCM = VS/2.
Supply Current vs. Supply Voltage
VOS vs. Supply Voltage
VOS vs. VCM
20120318
VOS vs. VCM
20120319
Input Bias Current vs. VCM
20120320
Input Bias Current vs. VCM
20120321
20120350
5
20120351
www.national.com
5 Page 
Application Notes
ADVANTAGES OF THE LM6211
High Supply Voltage, Low Power Operation
The LM6211 has performance guaranteed at supply volt-
ages of 5V and 24V. The LM6211 is guaranteed to be
operational at all supply voltages between 5V and 24V. In
this large range of operation, the LM6211 draws a fairly
constant supply current of 1 mA, while providing a wide
bandwidth of 20 MHz. The wide operating range makes the
LM6211 a versatile choice for a variety of applications rang-
ing from portable instrumentation to industrial control sys-
tems.
Low Input Referred Noise
The LM6211 has very low flatband input referred voltage
noise, 5.5 nV/
. The 1/f corner frequency, also very low,
is about 400 Hz. The CMOS input stage allows for an
extremely low input current (2 pA) and a very low input
referred current noise (0.01 pA/
). This allows the
LM6211 to maintain signal fidelity and makes it ideal for
audio, wireless or sensor based applications.
Low Input Bias Current and High Input Impedance
The LM6211 has a CMOS input stage, which allows it to
have very high input impedance, very small input bias cur-
rents (2 pA) and extremely low input referred current noise
(0.01 pA/
). This level of performance is essential for op
amps used in sensor applications, which deal with extremely
low currents of the order of a few nanoamperes. In this case,
the op amp is being driven by a sensor, which typically has a
source impedance of tens of MΩ. This makes it essential for
the op amp to have a much higher impedance.
Low Input Capacitance
The LM6211 has a comparatively small input capacitance for
a high voltage CMOS design. Low input capacitance is very
beneficial in terms of driving large feedback resistors, re-
quired for higher closed loop gain. Usually, high voltage
CMOS input stages have a large input capacitance, which
when used in a typical gain configuration, interacts with the
feedback resistance to create an extra pole. The extra pole
causes gain-peaking and can compromise the stability of the
op amp. The LM6211 can, however, be used with larger
resistors due to its smaller input capacitance, and hence
provide more gain without compromising stability. This also
makes the LM6211 ideal for wideband transimpedance am-
plifiers, which require a wide bandwidth, low input referred
noise and low input capacitance.
RRO, Ground Sensing and Current Limiting
The LM6211 has a rail-to-rail output stage, which provides
the maximum possible output dynamic range. This is espe-
cially important for applications requiring a large output
swing, like wideband PLL synthesizers which need an active
loop filter to drive a wide frequency range VCO. The input
common mode range includes the negative supply rail which
allows direct sensing at ground in a single supply operation.
The LM6211 also has a short circuit protection circuit which
limits the output current to about 25 mA sourcing and 38 mA
sinking, and allows the LM6211 to drive short circuit loads
indefinitely. However, while driving short circuit loads care
should be taken to prevent the inputs from seeing more than
±0.3V differential voltage, which is the absolute maximum
differential input voltage.
Small Size
The small footprint of the LM6211 package saves space on
printed circuit boards, and enables the design of smaller and
more compact electronic products. Long traces between the
signal source and the op amp make the signal path suscep-
tible to noise. By using a physically smaller package, the
LM6211 can be placed closer to the signal source, reducing
noise pickup and enhancing signal integrity
STABILITY OF OP AMP CIRCUITS
Stability and Capacitive Loading
The LM6211 is designed to be unity gain stable for moderate
capacitive loads, around 100 pF. That is, if connected in a
unity gain buffer configuration, the LM6211 will resist oscil-
lation unless the capacitive load is higher than about 100 pF.
For higher capacitive loads, the phase margin of the op amp
reduces significantly and it tends to oscillate. This is because
an op amp cannot be designed to be stable for high capaci-
tive loads without either sacrificing bandwidth or supplying
higher current. Hence, for driving higher capacitive loads,
the LM6211 needs to be externally compensated.
20120337
FIGURE 1. Gain vs. Frequency for an Op Amp
An op amp, ideally, has a dominant pole close to DC, which
causes its gain to decay at the rate of 20 dB/decade with
respect to frequency. If this rate of decay, also known as the
rate of closure (ROC), remains at 20 dB/decade at the unity
gain bandwidth of the op amp, the op amp is stable. If,
however, a large capacitance is added to the output of the op
amp, it combines with the output impedance of the op amp to
create another pole in its frequency response before its unity
gain frequency (Figure 1). This increases the ROC to
40 dB/decade and causes instability.
In such a case a number of techniques can be used to
restore stability to the circuit. The idea behind all these
schemes is to modify the frequency response such that it
can be restored to a ROC of 20 dB/decade, which ensures
stability.
11 www.national.com
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| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet LM6211.PDF ] | |
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