LT6350HMS8#TRPBF Linear Technology, LT6350HMS8#TRPBF Datasheet - Page 16

• 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
APPLICATIONS INFORMATION
Driving the input signal suffi ciently beyond the power
supply rails will cause the input transistors to saturate.
When saturation occurs, the amplifi er loses a stage of
phase inversion and the output tries to invert. Diodes D1
and D2 (Figure 5) forward bias and hold the output within
a diode drop of the input signal. With very heavy input
overdrive the output of op amp 1 could invert. To avoid
this inversion, limit the input overdrive to 0.5V beyond
the power supply rails.
OUTPUT VOLTAGE RANGE
The outputs of the LT6350 typically swing to within 55mV
of the upper and lower supply rails when driving a purely
capacitive load such as at the switched-capacitor input
stage of a SAR ADC. The LT6350 can therefore share a
single 5V supply with the SAR ADC and drive a full 8V
differential around an input common mode voltage between
2.055V and 2.945V. A modest negative supply can be
added to allow the LT6350 to swing all the way to 0V in
systems where the ADC requires a true 0V-referenced
signal or when the input common mode range of the ADC
is restricted to be lower than 2.055V. Some SAR ADCs use
2V as the input common mode voltage with a full-scale
input signal range at each input of 0V to 4V. The outputs
of the LT6350 can swing 7.78V
2V common mode voltage, which is a loss of only 0.24dB
of the full-scale range of such ADCs.
16
P-P
differentially around a
P-P
INTERFACING THE LT6350 TO A/D CONVERTERS
When driving an ADC, an additional single-pole passive
RC fi lter added between the outputs of the LT6350 and
the inputs of the ADC can sometimes improve system
performance. This is because the sampling process of ADCs
creates a charge transient at the ADC inputs that is caused
by the switching in of the ADC sampling capacitor. This
momentarily shorts the output of the amplifi er as charge is
transferred between amplifi er and sampling capacitor. For
an accurate representation of the input signal, the amplifi er
must recover and settle from this load transient before
the acquisition period has ended. An RC network at the
outputs of the driver helps decouple the sampling transient
of the ADC from the amplifi er reducing the demands on
the amplifi er’s output stage (see Figure 6). The resistors
at the inputs to the ADC minimize the sampling transients
that charge the RC fi lter capacitors.
V
IN
+
–
+ IN1
– IN1
+
–
2V
SHDN
LT6350
+ IN2
Figure 6. Driving an ADC
0.1μF
5V
V
+
–
+
V
–
0.1μF
OUT2
OUT1
R
R
FILT
FILT
C
R
R
DIFF
S
S
C
C
CM
CM
A
A
IN
IN
ADC
+
–
5V
6350 F06
6350fb