LTC6401CUD-26#PBF Linear Technology, LTC6401CUD-26#PBF Datasheet - Page 11

• Manufacturer Part Number: LTC6401CUD-26#PBF
• Description: IC ADC DRIVER DIFF 16-QFN
• Manufacturer: Linear Technology
• Type: ADC Driverr

Specifications of LTC6401CUD-26#PBF

• Applications: Data Acquisition
• Mounting Type: Surface Mount
• Package / Case: 16-WQFN Exposed Pad
• No. Of Amplifiers: 1
• Input Offset Voltage: 2.5mV
• Gain Db Max: 26dB
• Bandwidth: 1.6GHz
• Slew Rate: 3300V/µs
• Supply Voltage Range: 2.85V To 3.5V
• Supply Current: 45mA
• Amplifier Case Style: QFN
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

APPLICATIONS INFORMATION
The LTC6401-26 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 LTC6401-26 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 LTC6401-26 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
Figure 3. Input Termination for Single-Ended 50Ω Input
Impedance
+
–
V
+
–
0.1μF
1/2 R
1/2 R
37.4Ω
V
V
50Ω
150Ω
=
R
IN
IN
S
R
S
S
T
V
V
0.1μF
0.1μF
OUT
13
14
15
16
IN
Figure 4. Calculate Differential Gain
+IN
+IN
–IN
–IN
13
14
15
16
=
+IN
+IN
–IN
–IN
R
25Ω
25Ω
1000
S
+
25Ω
25Ω
IN+
IN–
50 25
IN+
IN–
•
500Ω
500Ω
OUT–
OUT+
500Ω
500Ω
R
+
L
R
OUT–
OUT+
L
12.5Ω
12.5Ω
50Ω
50Ω
12.5Ω
12.5Ω
LTC6401-26
50Ω
50Ω
2.7pF
+OUTF
–OUTF
LTC6401-26
+OUT
–OUT
640126 F04
2.7pF
+OUTF
–OUTF
640126 F03
+OUT
–OUT
8
7
6
5
1/2 R
1/2 R
V
OUT
8
7
6
5
L
L
The internal low pass fi lter outputs at +OUTF/–OUTF have
a –3dB bandwidth of 590MHz. External capacitors 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 ca-
pacitors and 16nH inductor create a bandpass fi lter with
165MHz center frequency, –3dB frequencies at 138MHz
and 200MHz.
Output Common Mode Adjustment
The LTC6401-26’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 voltage disturbance. The V
to a DC bias voltage with a 0.1μF bypass capacitor. When
interfacing with 3V A/D converters such as the LTC22xx
families, the V
of the ADC.
Driving A/D Converters
The LTC6401-26 has been specifi cally designed to interface
directly with high speed A/D converters. Figure 7 shows the
LTC6401-26 with 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
Figure 5. LTC6401-26 Internal Filter Topology Modifi ed for Low
Filter Bandwidth (Three External Capacitors)
13
14
15
16
+IN
+IN
–IN
–IN
OCM
25Ω
25Ω
IN+
IN–
pin, which is a high impedance input. The
OCM
500Ω
500Ω
OCM
pin can be connected to the V
OUT–
OUT+
pin and is aimed to reduce com-
12.5Ω
12.5Ω
50Ω
50Ω
LTC6401-26
LTC6401-26
2.7pF
OCM
+OUTF
–OUTF
640126 F05
+OUT
–OUT
pin should be tied
8
7
6
5
OCM
8pF
12pF
8pF
FILTERED OUTPUT
(87.5MHz)
control is
11
CM
640126f
OCM
OCM
pin