LT6350HMS8#TRPBF Linear Technology, LT6350HMS8#TRPBF Datasheet - Page 12

• Manufacturer Part Number: LT6350HMS8#TRPBF
• Description: IC DIFF CONVERT/ADC DRIVER 8MSOP
• Manufacturer: Linear Technology
• Type: ADC Driverr

Specifications of LT6350HMS8#TRPBF

• Applications: Data Acquisition
• Mounting Type: Surface Mount
• Package / Case: 8-MSOP, Micro8™, 8-uMAX, 8-uSOP,
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

LT6350
OPERATION
The LT6350 is a low noise single-ended to differential
converter /ADC driver. It converts a high or low impedance,
single-ended input signal to a low impedance, balanced
differential output suitable for driving high performance
differential sucessive approximation register (SAR) ADCs.
The closed loop –3dB bandwidth for the typical gain-of-two
confi guration is 33MHz.
The LT6350 uses a two op amp topology as shown in
the Block Diagram: at the input is one fully uncommitted
op amp with both inputs and output brought out to pins.
This is followed by an op amp internally hardwired and
optimally compensated as a unity-gain inverter with its
input connected to the output of the fi rst op amp. The
noninverting input of the inverting op amp is brought out to
a pin and is used to set the output common mode voltage
level. The outputs of the two op amps are therefore 180°
out-of-phase and provide a low impedance differential
drive for differential-input analog to digital converters.
The outputs of the LT6350 can swing rail-to-rail and can
source or sink a transient 45mA of current. The outputs
are designed to drive 40pF to ground or 20pF differentially.
Load capacitances larger than 40pF should be decoupled
from each output with at least 25Ω of series resistance.
The LT6350 features very low noise op amps to support
signal-to-noise ratios >110dB.
BASIC CONNECTIONS
A typical use of the LT6350 is to convert a high impedance,
single-ended input signal into a low impedance differential
output. The confi guration for such an application is shown
in Figure 2. Here, the input op amp is wired as a non-
inverting buffer with a high input impedance at +IN1. At
the outputs, V
an inverted copy of V
of two. The input op amp has a rail-to-rail input stage, and
both outputs are rail-to-rail, typically swinging to within
55mV of the rails at each output in this confi guration
allowing 8V
This provides a simple interface to differential input ADCs
that accept a mid-rail input common mode voltage.
12
P-P
OUT1
differential outputs from a single 5V rail.
follows the input, and V
OUT1
for an overall differential gain
OUT2
provides
DESIGN EQUATIONS AND ALTERNATIVE CONNECTIONS
Because the input op amp presents its output and both
its inputs to LT6350 pins, alternative confi gurations are
possible. Consider the general confi guration shown in
Figure 3.
Ordinary op amp analysis gives the equations for V
and V
If we defi ne the differential and common mode output
voltages as:
and
then combining the expressions for V
the defi nitions gives the resulting differential and common
mode output voltages:
V
V
V
V
V
V
V
V
+
–
OUT1
OUT1
OUT2
OUTDIFF
OUTCM
OUTDIFF
OUTDIFF
OUTCM
V
OUT2
V
0.5V-4.5V
IN
IN
4.5V
= V
= V
= –V
0.5V
given the input voltages V1, V2, V
≡ (V
= V2
= 2 • (V
≡ V
= 2 • (V
A
IN
• (1+R
OUT1
• (1+R
OUT1
OUT1
Figure 2. Basic Connections
+ IN1
– IN1
+
–
IN
+ 2 • V2
A
– V
+ V
F
• (1+R
• (1+R
F
/R
/R
2.5V
SHDN
OUT2
OUT2
G
LT6350
+ IN2
G
) + V1
) – V1 • (R
F
F
/R
)/2,
/R
5V
0.1μF
V
G
G
–
+
+
)–V1 • (R
) + V1 – V2)
V
–
F
OUT1
0.1μF
/R
OUT2
OUT1
G
F
)
/R
and V
G
IN
)–V2) (1)
and V
OUT2
0.5V
4.5V
V
V
OUT2
OUT1
0.5V
4.5V
6350 F02
OUT1
with
6350fb
A
(2)
(3)
: