LM6211

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SNOSAH2C – FEBRUARY 2006 – REVISED MARCH 2013

APPLICATION NOTES

ADVANTAGES OF THE LM6211

High Supply Voltage, Low Power Operation

The LM6211 has performance ensured at supply voltages of 5V and 24V. The LM6211 is ensured 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 ranging from portable instrumentation to

industrial control systems.

Low Input Referred Noise

The LM6211 has very low flatband input referred voltage noise, 5.5 nV/

√Hz. 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/

√Hz). 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

currents (2 pA) and extremely low input referred current noise (0.01 pA/

√Hz). 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 M

Ω. 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, required 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 amplifiers, 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

especially 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 susceptible 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

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