ltc6404cud-2-trpbf Linear Technology Corporation, ltc6404cud-2-trpbf Datasheet - Page 11

• Manufacturer Part Number: ltc6404cud-2-trpbf
• Description: 600mhz, Low Noise, Ac Precision Fully Differential Input/output Ampli?er/driver
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Functional Description
The LTC6404-1 is a small outline, wide band, low noise,
and low distortion fully-differential amplifi er with accurate
output phase balancing. The LTC6404-1 is optimized
to drive low voltage, single-supply, differential input
14-bit to 18-bit analog-to-digital converters (ADCs). The
LTC6404-1’s output is capable of swinging rail-to-rail on
supplies as low as 2.7V, which makes the amplifi er ideal
for converting ground referenced, single-ended signals
into DC level shifted differential signals in preparation
for driving low voltage, single-supply, differential input
ADCs. Unlike traditional op amps which have a single
output, the LTC6404-1 has two outputs to process signals
differentially. This allows for two times the signal swing
in low voltage systems when compared to single-ended
output amplifi ers. The balanced differential nature of the
amplifi er also provides even-order harmonic distortion
cancellation, and less susceptibility to common mode noise
(e.g., power supply noise). The LTC6404-1 can be used as
a single ended input to differential output amplifi er, or as
a differential input to differential output amplifi er.
The LTC6404-1’s output common mode voltage, defi ned
as the average of the two output voltages, is independent
of the input common mode voltage, and is adjusted by
applying a voltage on the V
there is an internal resistive voltage divider that develops
a potential halfway between the V
this pin is not hard tied to a low impedance ground plane,
it is recommended that a high quality ceramic cap is
used to bypass the V
plane (See Layout Considerations in this document). The
LTC6404-1’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
The outputs (OUT
pable of swinging rail-to-rail. They can source or sink up
to approximately 65mA of current.
V
OUTCM
=
V
OCM
+
=
and OUT
OCM
OCM
V
OUT
pin to a low impedance ground
pin.
+
OCM
+
2
–
) of the LTC6404-1 are ca-
V
pin. If the pin is left open,
OUT
+
and V
–
–
pins. Whenever
Additional outputs (OUTF
provide fi ltered versions of the OUT
on-chip single pole RC passive fi lter bandlimits the fi ltered
outputs to a –3dB frequency of 88.5MHz. The user has a
choice of using the unfi ltered outputs, the fi ltered outputs,
or modifying the fi ltered outputs to adjust the frequency
response by adding additional components.
In applications where the full bandwidth of the LTC6404-1
is desired, the unfi ltered outputs (OUT
be used. The unfi ltered outputs OUT
designed to drive 10pF to ground (or 5pF differentially).
Capacitances greater than 10pF will produce excess peak-
ing, and can be mitigated by placing at least 25Ω in series
with the output.
Input Pin Protection
The LTC6404-1’s input stage is protected against differential
input voltages which exceed 1.4V by two pairs of back
to back diodes connected in anti-parallel series between
IN
have steering diodes to either power supply. If the input
pair is over-driven, the current should be limited to under
10mA to prevent damage to the IC. The LTC6404-1 also
has steering diodes to either power supply on the V
and ⎯ S ⎯ H ⎯ D ⎯ N pins (Pins 4 and 1) and if forced to voltages
which exceed either supply, they too, should be current
limited to under 10mA.
⎯ S ⎯ H ⎯ D ⎯ N Pin
If the ⎯ S ⎯ H ⎯ D ⎯ N pin (Pin 1) is pulled 2.1V below the positive
supply, circuitry is activated which powers down the
LTC6404-1. The pin will have the Thevenin equivalent
impedance of approximately 66kΩ to V
left unconnected, an internal pull-up resistor of 150k will
keep the part in normal active operation. Care should
be taken to control leakage currents at this pin to under
1μA to prevent inadvertently putting the LTC6404-1 into
shutdown. In shutdown, all biasing current sources are
shut off, and the output pins, OUT
+
and IN
–
(Pins 6 and 15). In addition, the input pins
+
and OUTF
+
+
and OUT
LTC6404-1
and OUT
–
+
) are available that
and OUT
+
+
and OUT
. If the pin is
–
outputs. An
–
, will each
–
) should
11
–
OCM
64041f
are
,