LTC6404HUD-2#PBF Linear Technology, LTC6404HUD-2#PBF Datasheet - Page 23

• Manufacturer Part Number: LTC6404HUD-2#PBF
• Description: IC AMP/DRIVER DIFF 16-QFN
• Manufacturer: Linear Technology
• Type: ADC Driverr

Specifications of LTC6404HUD-2#PBF

• Applications: Data Acquisition
• Mounting Type: Surface Mount
• Package / Case: 16-WQFN Exposed Pad
• Current - Supply: 30.4mA
• Operating Temperature: -40°C ~ 125°C
• Output Type: Differential, Rail-to-Rail
• Number Of Circuits: 1
• Current - Output / Channel: 85mA
• Amplifier Type: Differential
• Voltage - Supply, Single/dual (±): 2.7 V ~ 5.5 V, ±1.35 V ~ 2.75 V
• -3db Bandwidth: 600MHz
• Slew Rate: 700 V/µs
• Gain Bandwidth Product: 900MHz
• Current - Input Bias: 23µA
• Voltage - Input Offset: 500µV
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
In single supply applications, where the LTC6404 is used
to interface to an ADC, the optimal common mode input
range to the ADC is often determined by the ADC’s refer-
ence. If the ADC makes a reference available for setting
the input common mode voltage, it can be directly tied
to the V
impedance presented by the V
cal Characteristics Table. This impedance can be assumed
to be connected to a mid-supply potential. If an external
reference drives the V
with a high quality 0.01μF or larger capacitor to a low
impedance ground plane to fi lter any thermal noise and
to prevent common mode signals on this pin from being
inadvertently converted to differential signals.
Output Filter Considerations and Use
Filtering at the output of the LTC6404 is often desired to
provide either anti-aliasing or improved signal to noise
ratio. To simplify this fi ltering, the LTC6404 includes an
additional pair of differential outputs (OUTF
which incorporate an internal lowpass fi lter network with
a –3dB bandwidth of 88.5MHz (Figure 6).
These pins each have a DC output impedance of 50Ω. In-
ternal capacitances are 12pF to V
plus an additional 12pF capacitor connected differentially
between the two fi ltered outputs. This resistor/capacitor
combination creates fi ltered outputs that look like a series
50Ω resistor with a 36pF capacitor shunting each fi ltered
output to AC ground, providing a –3dB bandwidth of
LTC6404
OCM
+
–
Figure 6. LTC6404 Internal Filter Topology
pin, but must be capable of driving the input
14
7
OUT
OUT
50Ω
50Ω
–
+
OCM
13
8
12pF
12pF
OUTF
OUTF
12pF
pin, it should still be bypassed
–
+
V
V
–
–
6404 F06
OCM
V
V
–
–
12
–
9
on each fi ltered output,
as listed in the Electri-
FILTERED OUTPUT
(88.5MHz)
+
and OUTF
–
)
88.5MHz, and a noise bandwidth of 139MHz. The fi lter
cutoff frequency is easily modifi ed with just a few external
components. To increase the cutoff frequency, simply add 2
equal value resistors, one between OUT
other between OUT
in parallel with the internal 50Ω resistor, lower the overall
resistance and therefore increase fi lter bandwidth. For
example, to double the fi lter bandwidth, add two external
50Ω resistors to lower the series fi lter resistance to 25Ω.
The 36pF of capacitance remains unchanged, so fi lter
bandwidth doubles. Keep in mind, the series resistance
also serves to decouple the outputs from load capacitance.
The unfi ltered outputs of the LTC6404 are designed to
drive 10pF to ground or 5pF differentially, so care should
be taken to not lower the effective impedance between
OUT
To decrease fi lter bandwidth, add two external capacitors,
one from OUTF
ground. A single differential capacitor connected between
OUTF
driven differentially it will appear at each fi ltered output
as a single-ended capacitance of twice the value. To halve
the fi lter bandwidth, for example, two 36pF capacitors
could be added (one from each fi ltered output to ground).
Alternatively, one 18pF capacitor could be added between
the fi ltered outputs, again halving the fi lter bandwidth.
Combinations of capacitors could be used as well; a three
Figure 7. LTC6404 Filter Topology Modifi ed for 2x Filter
Bandwidth (2 External Resistors)
+
+
and OUTF
LTC6404
and OUTF
+
–
+
14
+
7
to ground, and the other from OUTF
–
or OUT
49.9Ω
49.9Ω
OUT
OUT
–
can also be used, but since it is being
50Ω
50Ω
and OUTF
–
+
13
8
–
12pF
12pF
OUTF
OUTF
12pF
and OUTF
–
+
–
V
V
–
–
(Figure 7). These resistors,
6404 F07
V
V
–
–
12
9
–
+
below 25Ω.
and OUTF
LTC6404
FILTERED OUTPUT
(176MHz)
+
23
and the
–
6404f
to