LMH6643MMX datasheet(16/22 Pages) NSC

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Application Notes

CIRCUIT DESCRIPTION:

The LMH664X family is based on National Semiconductor’s

proprietary VIP10 dielectrically isolated bipolar process.

This device family architecture features the following:

•

Complimentary bipolar devices with exceptionally high f

(

∼8GHz) even under low supply voltage (2.7V) and low

bias current.

•

A class A-B “turn-around” stage with improved noise,

offset, and reduced power dissipation compared to simi-

lar speed devices (patent pending).

•

Common Emitter push-push output stage capable of

75mA output current (at 0.5V from the supply rails) while

consuming only 2.7mA of total supply current per chan-

nel. This architecture allows output to reach within milli-

volts of either supply rail.

•

Consistent performance from any supply voltage (3V-

10V) with little variation with supply voltage for the most

important specifications (e.g. BW, SR, I

OUT, etc.)

•

Significant power saving (

∼40%) compared to competi-

tive devices on the market with similar performance.

Application Hints:

This Op Amp family is a drop-in replacement for the AD805X

family of high speed Op Amps in most applications. In addi-

tion, the LMH664X will typically save about 40% on power

dissipation, due to lower supply current, when compared to

competition. All AD805X family’s guaranteed parameters are

included in the list of LMH664X guaranteed specifications in

order to ensure equal or better level of performance. How-

ever, as in most high performance parts, due to subtleties of

applications, it is strongly recommended that the perfor-

mance of the part to be evaluated is tested under actual

operating conditions to ensure full compliance to all specifi-

cations.

With 3V supplies and a common mode input voltage range

that extends 0.5V below V

−, the LMH664X find applications

in low voltage/low power applications. Even with 3V sup-

plies, the −3dB BW (@ A

V = +1) is typically 115MHz with a

tested limit of 80MHz. Production testing guarantees that

process variations with not compromise speed. High fre-

quency response is exceptionally stable confining the typical

-3dB BW over the industrial temperature range to ±2.5%.

As can be seen from the typical performance plots, the

LMH664X output current capability (

∼75mA) is enhanced

compared to AD805X. This enhancement, increases the

output load range, adding to the LMH664X’s versatility.

Because of the LMH664X’s high output current capability

attention should be given to device junction temperature in

order not to exceed the Absolute Maximum Rating.

This device family was designed to avoid output phase

reversal. With input overdrive, the output is kept near supply

rail (or as closed to it as mandated by the closed loop gain

setting and the input voltage). See Figure 1:

However, if the input voltage range of −0.5V to 1V from V

+ is

exceeded by more than a diode drop, the internal ESD

protection diodes will start to conduct.The current in the

diodes should be kept at or below 10mA.

Output overdrive recovery time is less than 100ns as can be

seen from Figure 2 plot:

20018542

FIGURE 1. Input and Output Shown with CMVR

Exceeded

20018543

FIGURE 2. Overload Recovery Waveform

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