LM6584

www.ti.com

SNOSA44C – MAY 2003 – REVISED MARCH 2013

APPLICATION NOTES

CIRCUIT DESCRIPTION

GENERAL & SPEC

The LM6584 is a bipolar process operational amplifier. It has an exceptional output current capability of 330mA.

The part has both rail to rail inputs and outputs. It has a

−3dB bandwidth of 24MHz. The part has input voltage

noise of 23nV/

√Hz, and 2nd and 3rd harmonic distortion of −53dB and −40dB respectively.

INPUT SECTION

The LM6584 has rail to rail inputs and thus has an input range over which the device may be biased of V− minus

0.5V, and V+ plus V. The ultimate limit on input voltage excursion is the ESD protection diodes on the input pins.

The most important consideration in Rail-to-Rail input op amps is to understand the input structure. Most Rail-to-

Rail input amps use two differential input pairs to achieve this function. This is how the LM6584 works. A

conventional PNP differential transistor pair provides the input gain from 0.5V below the negative rail to about

one volt below the positive rail. At this point internal circuitry activates a differential NPN transistor pair that

allows the part to function from 1 volt below the positive rail to 0.5V above the positive rail. The effect on the

inputs pins is as if there were two different op amps connected to the inputs. This has several unique

implications.

•

The input offset voltage will change, sometimes from positive to negative as the inputs transition between the

two stages at about a volt below the positive rail. this effect is seen in the VOS vs. VCM chart in the Typical

Performance Characteristics section of this datasheet.

•

The input bias currents can be either positive or negative. Do not expect a consistent flow in or out of the

pins.

•

The part will have different specifications depending on whether the NPN or PNP stage is operating.

•

There is a little more input capacitance then a single stage input although the ESD diodes often swamp out

the added base capacitance.

•

Since the input offset voltages can change from positive to negative the output may not be monotonic when

the inputs are transitioning between the two stages and the part is in a high gain configuration.

It should be remembered that swinging the inputs across the input stage transition may cause output distortion

and accuracy anomalies. It is also worth noting that anytime any amps inputs are swung near the rails THD and

other specs are sure to suffer.

OUTPUT SECTION

Current Rating

The LM6584 has an output current rating, sinking or sourcing, of 300mA. The LM6584 is ideally suited to loads

that require a high value of peak current but only a reduced value of average current. This condition is typical of

driving the gate of a MOSFET. While the output drive rating is 300mA peak, and the output structure supports

rail-to-rail operation, the attainable output current is reduced when the gain and drive conditions are such that the

output voltage approaches either rail.

Output Power

Because of the increased output drive capability, internal heat dissipation must be held to a level that does not

increase the junction temperature above its maximum rated value of 150° C.

Power Requirements

The LM6584 operates from a voltage supply, of V+ and ground, or from a V− and V+ split supply. Single-ended

voltage range is +5V to +13V and split supply range is ±2.5V to ±6.5V.

Copyright © 2003–2013, Texas Instruments Incorporated

Submit Documentation Feedback

11

Product Folder Links: LM6584