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
t
(
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
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
20018542
FIGURE 1. Input and Output Shown with CMVR
Exceeded
20018543
FIGURE 2. Overload Recovery Waveform
LMH6642/6643/6644
www.national.com
16