LT6402CUD-12#PBF Linear Technology, LT6402CUD-12#PBF Datasheet - Page 11

• Manufacturer Part Number: LT6402CUD-12#PBF
• Description: IC DIFF AMP/ADC DVR 12DB 16-QFN
• Manufacturer: Linear Technology

Specifications of LT6402CUD-12#PBF

• Amplifier Type: Differential
• Number Of Circuits: 2
• Output Type: Differential
• Slew Rate: 400 V/µs
• -3db Bandwidth: 300MHz
• Current - Input Bias: 5µA
• Voltage - Input Offset: 1000µV
• Current - Supply: 30mA
• Current - Output / Channel: 35mA
• Voltage - Supply, Single/dual (±): 4 V ~ 5.5 V, ±2 V ~ 2.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-WQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Gain Bandwidth Product: -

APPLICATIONS INFORMATION
The LT6402-12 has been designed to minimize the need
for external support components such as transformers or
AC-coupling capacitors. As an ADC driver, the LT6402-12
requires no external components except for power-supply
bypass capacitors. This allows DC-coupled operation for
applications that have frequency ranges including DC. At
the outputs, the common mode voltage is set via the V
pin, allowing the LT6402-12 to drive ADCs directly. No
output AC-coupling capacitors or transformers are needed.
At the inputs, signals can be differential or single-ended
with virtually no difference in performance. Furthermore,
DC levels at the inputs can be set independently of the
output common mode voltage. These input characteristics
often eliminate the need for an input transformer and/or
AC-coupling capacitors.
Input Impedance and Matching Networks
Calculation of the input impedance of the LT6402-12 is
not straightforward from examination of the block diagram
because of the internal feedback network. In addition, the
input impedance when driven differentially is different than
when driven single-ended.
For single-ended 50Ω applications, a 150Ω shunt match-
ing resistor to ground will result in the proper input
termination (Figure 1). For differential inputs there are
several termination options. If the input source is 50Ω
differential, then the input matching can be accomplished
by either a 67Ω shunt resistor across the inputs (Figure 3),
or equivalent 33Ω shunt resistors on each of the inputs
to ground (Figure 2). If additional AC gain is desired, an
LT6402-12
Figure 1. Input Termination for Single-Ended
50Ω Input Impedance
IF IN
Z
SINGLE-ENDED
IN
= 50Ω
150Ω
0.1μF
DIFFERENTIAL
13
14
15
16
100Ω
–INB
–INA
+INB
+INA
LT6402-12
–OUT
+OUT
8
5
SINGLE-ENDED
640212 F01
75Ω
OCM
impedance ratio transformer can also be used to better
match impedances.
Single-Ended to Differential Operation
The LT6402-12’s performance with single-ended inputs
is comparable to its performance with differential inputs.
This excellent single-ended performance is largely due
to the internal topology of the LT6402-12. Referring to
the block diagram, if the +INA and +INB pins are driven
with a single-ended signal (while –INA and –INB are tied
to AC ground), then the +OUT and –OUT pins are driven
differentially without any voltage swing needed from
amplifi er C. Single-ended to differential conversion using
more conventional topologies suffers from performance
limitations due to the common mode amplifi er.
Driving ADCs
The LT6402-12 has been specifi cally designed to interface
directly with high speed Analog to Digital Converters
(ADCs). In general, these ADCs have differential inputs, with
an input impedance of 1kΩ or higher. In addition, there is
generally some form of lowpass or bandpass fi ltering just
Figure 2. Input Termination for Differential 50Ω Input Impedance
Figure 3. Alternate Input Termination for Differential
50Ω Input Impedance
IF IN
IF IN
IF IN
IF IN
Z
DIFFERENTIAL
Z
DIFFERENTIAL
IN
IN
–
+
= 50Ω
–
+
= 50Ω
49.9Ω
49.9Ω
100Ω
13
14
15
16
13
14
15
16
–INB
–INA
+INB
+INA
–INB
–INA
+INB
+INA
LT6402-12
LT6402-12
–OUT
+OUT
–OUT
+OUT
LT6402-12
8
5
8
5
640212 F03
640212 F02
11
640212fa