LTC6400CUD-26#PBF Linear Technology, LTC6400CUD-26#PBF Datasheet - Page 11

• Manufacturer Part Number: LTC6400CUD-26#PBF
• Description: IC ADC DRIVER DIFF 16-QFN
• Manufacturer: Linear Technology
• Type: ADC Driverr

Specifications of LTC6400CUD-26#PBF

• Applications: Data Acquisition
• Mounting Type: Surface Mount
• Package / Case: 16-WQFN Exposed Pad
• No. Of Amplifiers: 1
• Input Offset Voltage: 2mV
• Gain Db Max: 26dB
• Bandwidth: 1.9GHz
• Slew Rate: 6670V/µs
• Supply Voltage Range: 2.85V To 3.5V
• Supply Current: 85mA
• Amplifier Case Style: QFN
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
The LTC6400-26 is unconditionally stable, i.e. differential
stability factor Kf>1 and stability measure B1>0. However,
the overall differential gain is affected by both source
impedance and load impedance as shown in Figure 4:
The noise performance of the LTC6400-26 also depends
upon the source impedance and termination. A trade-off
between gain and noise is obvious when constant noise
fi gure circle and constant gain circle are plotted within
the same input Smith Chart, based on which users can
choose the optimal source impedance for a given gain
and noise requirement.
Output Impedance Match and Filter
The LTC6400-26 can drive an ADC directly without external
output impedance matching. Alternatively, the differential
output impedance of 25Ω can be made larger, e.g. 50Ω,
by series resistors or LC network.
A
V
IN
V
+
–
–
+
=
1/2 R
1/2 R
V
37.4Ω
IN
Figure 3. Input Termination for Single-Ended
50Ω Input Impedance
50Ω
150Ω
R
S
V
S
S
R
T
V
OUT
IN
13
14
15
16
0.1μF
0.1μF
Figure 4. Calculate Differential Gain
+IN
+IN
–IN
–IN
=
13
14
15
16
R
25Ω
25Ω
+IN
+IN
–IN
–IN
1000
S
+
IN+
IN–
25Ω
25Ω
50 25
IN+
IN–
•
500Ω
500Ω
OUT–
OUT+
R
500Ω
500Ω
+
L
R
OUT–
OUT+
L
12.5Ω
12.5Ω
50Ω
50Ω
LTC6400-26
12.5Ω
12.5Ω
50Ω
50Ω
2.7pF
+OUTP
–OUTF
+OUT
–OUT
640026 F04
LTC6400-26
2.7pF
+OUTF
–OUTF
8
7
6
5
640026 F03
+OUT
–OUT
1/2 R
1/2 R
V
OUT
L
L
8
7
6
5
The internal low pass fi lter outputs at +OUTF/–OUTF
have a –3dB bandwidth of 590MHz. External capacitor
can reduce the low pass fi lter bandwidth as shown in
Figure 5. A bandpass fi lter is easily implemented with
only a few components as shown in Figure 6. Three
39pF capacitors and a 16nH inductor create a bandpass
fi lter with 165MHz center frequency, –3dB frequencies at
138MHz and 200MHz.
Output Common Mode Adjustment
The LTC6400-26’s output common mode voltage is set
by the V
output common mode voltage is capable of tracking V
in a range from 1V to 1.6V. Bandwidth of V
typically 15MHz, which is dominated by a low pass fi lter
connected to the V
mon mode noise generation at the outputs. The internal
common mode feedback loop has a –3dB bandwidth of
400MHz, allowing fast rejection of any common mode
output disturbance. The V
bias voltage with a 0.1μF bypass capacitor. When interfac-
ing with A/D converters such as the LTC22xx families, the
V
Driving A/D Converters
The LTC6400-26 has been specifi cally designed to interface
directly with high speed A/D converters. Figure 7 shows the
LTC6400-26 with a single-ended input driving the LTC2208,
which is a 16-bit, 130Msps ADC. Two external 5Ω resistors
help eliminate potential resonance associated with bond
wires of either the ADC input or the driver output. V
of the LTC6400-26 is connected to V
at 1.25V. Alternatively, a single-ended input signal can be
OCM
13
14
15
16
Figure 5. LTC6400-26 Internal Filter Topology Modifi ed
for Low Filter Bandwidth (Three External Capacitors)
+IN
+IN
–IN
–IN
pin can be connected to the V
OCM
25Ω
25Ω
pin, which is a high impedance input. The
IN+
IN–
500Ω
500Ω
OCM
OUT–
OUT+
pin and is aimed to reduce com-
OCM
12.5Ω
12.5Ω
50Ω
50Ω
pin should be tied to a DC
LTC6400-26
2.7pF
LTC6400-26
+OUTF
–OUTF
640026 F05
+OUT
–OUT
CM
CM
8
7
6
5
pin of the ADC.
of the LTC2208
8.2pF
12pF
8.2pF
OCM
FILTERED OUTPUT
(87.5MHz)
control is
11
640026fa
OCM
OCM