Datasheet

LTC6405
13
6405fb
For more information www.linear.com/6405
applications inForMation
Figure 1. DC Test Circuit
–
+
1
SHDN
5 6
–IN
7
+OUT
8
+OUTF
16 15
+IN
V
TIP
NC
14
–OUT
13
–OUTF
V
–OUTF
R
F
C
F
V
+OUTF
V
–OUT
V
+OUT
2
V
+
3
V
–
V
+
V
–
V
+
V
–
4
V
OCM
V
SHDN
V
VOCM
V
OCM
12
V
–
11
V
+
10
V
+
9
V
–
V
–
V
–
V
–
C
F
V
–
V
–
6405 F01
LTC6405
SHDN
0.1µF
0.01µF
V
CM
R
F
R
I
R
I
R
BAL
100k
R
BAL
100k
+
–
V
INP
–
+
V
INM
V
–IN
V
+IN
V
OUTCM
V
+
0.1µF
V
–
0.1µF
0.1µF
0.1µF
1.25pF
1.25pF
1.25pF
0.1µF
0.01µF
50Ω
50Ω
(R
I
, R
F
: 0.1% RESISTORS)
*TO OPTIMIZE THE HIGH FREQUENCY PERFORMANCE FOR THE PIN CONFIGURATION OF THE LTC6405
IN THE SMALL MSOP PACKAGE, A FEEDBACK RESISTANCE OF AT LEAST 300Ω IS RECOMMENDED.
PACKAGE
MSOP*
QFN
DEFAULT VALUES
C
F
1.0pF
1.8pF
R
I
300Ω
200Ω
R
F
300Ω
200Ω
Functional Description
The LTC6405 is a small outline, wideband, low noise, and
low distortion fully-differential amplifier with accurate
output phase balancing. The LTC6405 is optimized to
drive low voltage, single-supply, differential input analog-
to-digital converters (ADCs). The LTC6405 input common
mode range is rail-to-rail, while the output common mode
voltage is independently adjustable by applying a voltage
on the V
OCM
pin. The output voltage swing extends from
near-ground to 4V, to be compatible with a wide range of
ADC converter input requirements. This makes the LTC6405
ideal for level shifting signals with a wide common mode
range for driving 12-bit to 16-bit single supply, differential
input ADCs. The differential output allows for twice the
signal swing in low voltage systems when compared to
single-ended output amplifiers. The balanced differential
nature of the amplifier also provides even-order harmonic
distortion cancellation, and less susceptibility to common
mode noise (like power supply noise). The LTC6405 can be
used as a single ended input to differential output amplifier,
or as a differential input to differential output amplifier.
The LTC6405 output common mode voltage, defined as
the average of the two output voltages, is
independent of
the input common mode voltage, and is adjusted by apply-
ing a voltage on the V
OCM
pin. If the pin is left open, there
is an internal resistive voltage divider, which develops a
potential of 2.5V (if the supply is 5V). It is recommended
that a high quality ceramic cap is used to bypass the V
OCM
pin to a low impedance ground plane. The LTC6405’s
internal common mode feedback path forces accurate
output phase balancing to reduce even order harmonics,
and centers each individual output about the potential set
by the V
OCM
pin.
V
OUTCM
= V
OCM
=
V
+OUT
+
V
–OUT
2