lmh6551qmmx National Semiconductor Corporation, lmh6551qmmx Datasheet - Page 13

• Manufacturer Part Number: lmh6551qmmx
• Description: Differential, High Speed Op Amp
• Manufacturer: National Semiconductor Corporation

SINGLE SUPPLY OPERATION
The input stage of the LMH6551Q has a built in offset of 0.7V
towards the lower supply to accommodate single supply op-
eration with single ended inputs. As shown in
input common mode voltage is less than the output common
voltage. It is set by current flowing through the feedback net-
work from the device output. The input common mode range
of 0.4V to 3.2V places constraints on gain settings. Possible
solutions to this limitation include AC coupling the input signal,
using split power supplies and limiting stage gain. AC cou-
pling with single supply is shown in
In
=V
differential operation V
measured differentially. This means that gain is really 1/2 or
6 dB less when measured on either of the output pins sepa-
rately. Additionally, note that the input signal at R
V
V
I
ICM
) is 1/2 of V
Figure 5
S
/ 2, as long as R
= Input common mode voltage = (V
closed loop gain = V
S
when R
M
I
T
is measured single ended while V
<< R
is chosen to match R
G
. Note that in single ended to
O
/ V
Figure
I
≊
FIGURE 5. Single Ended In to Differential Out
I1
+V
R
6.
F
I2
/ R
S
) / 2.
Figure
to R
T
G
(labeled as
, where V
IN
.
5, the
O
is
I
13
FIGURE 6. AC Coupled for Single Supply Operation
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