Datasheet

V
+
V
-
I
P
R
P
+
-
I
CC
SET BLOCK
5k:
LMH6732
www.ti.com SNOSA47B –FEBRUARY 2003–REVISED MARCH 2013
Table 1. Device Parameters Related to Supply Current
Specification Effect as I
CC
Increases
Bandwidth Increases
Rise Time Decreases
Enable/ Disable Speed Increases
Output Drive Increases
Input Bias Current Increases
Input Impedance Decreases (see Source impedance Discussion)
Both the Electrical Characteristics pages and the TYPICAL PERFORMANCE CHARACTERISTICS section
illustrate these effects to help make the supply current vs. performance trade-off. The supply current is adjustable
over a continuous range of more than 10 to 1 with a single resistor, R
P
, allowing for easy trade-off between
power consumption and speed. Performance is specified and tested at I
CC
= 1mA, 3.4mA, and 9mA. (Note:
Some test conditions and especially the load resistances are different for the three supply current settlings.) The
performance plots show typical performance for all three supply currents levels.
When making the supply current vs. performance trade-off, it is first a good idea to see if one of the standard
operating points (I
CC
= 1mA, 3.4mA, or 9mA) fits the application. If it does, performance ensured on the
specification pages will apply directly to your application. In addition, the value of R
P
may be obtained directly
from the Electrical Characteristics pages.
BEYOND 1GHz BANDWIDTH
As stated above, the LMH6732 speed can be increased by increasing the supply current. The −3dB Bandwidth
can even reach the unprecedented value of 1.5GHz (A
V
= +2, V
OUT
= 0.25V
PP
). Of course, this comes at the
expense of power consumption (i.e. supply current). The relationship between −3dB BW and supply current is
shown in Figure 48 to Figure 50. The supply current would nominally have to be set to around 10mA to achieve
this speed. The absolute maximum supply current setting for the LMH6732 is 14mA. Beyond this value, the
operation may become unpredictable.
The following discussion will assist in selecting I
CC
for applications that cannot operate at one of the
specified supply current settlings.
Use the typical performance plots for critical specifications to select the best I
CC
. For parameters containing
Min/Max ratings in the data sheet tables, interpolate between the values of I
CC
in the plots & specification tables
to estimate the max/min values in the application.
The simplified schematic for the supply current setting path (I
P
) is shown below in Figure 61.
Figure 61. Supply Current Control's Simplified Schematic
The terminal marked "R
P
" is tied to a potential through a resistor R
P
. The current flowing through R
P
(I
P
) sets the
LMH6732's supply current. Throughout the data sheet, the voltages applied to R
P
and V
−
are both considered to
be −5V. However, the two potentials do not necessarily have to be the same. This is beneficial in applications
where non-standard supply voltages are used or when there is a need to power down the op amp via digital logic
control.
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