AD8260ACPZ-RL(Rev0) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
AD8260ACPZ-RL
(Rev.:Rev0)
(Rev.:Rev0)
Analog Devices
AD8260ACPZ-RL Datasheet PDF : 32 Pages
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AD8260
1.8V OR 3.3V
ADC INP
FS INPUT
2V p-p
INN
1.8V OR 3.3V
20mA DAC
1V MAX WITH
200mA pk
50Ω 0.1µF
50Ω
0.1µF
CFB
OPTIONAL USER SELECTED
CFB REDUCES HF PEAKING
WITH CAPACITIVE LOADING
0.1µF
0V, 1.8V/3.3V
0.1µF
VMDO
VOCM INPP
32
31
30
1.5kΩ 1kΩ
1
TXEN
2
VMDI
3
VNCM
4
VMID
VPSB
3.3V
5
29
28
27
1kΩ 1.5kΩ
+
–
GM
AD8260
BIAS
0V, 1.8V/3.3V
LOW-PASS
ENBL
6
AA FILTER
0.1µF
VGAP
7
0.1µF
VGAN 8
ATTENUATOR
GM STAGES
LOGIC
9
10
11
12
13
14
26
25
×1
15
16
TXOP
24
OPTIONAL CLAMP DIODES
AND SNUBBING RESISTORS
TXOP
23
0.1µF
VPOS
22
0.1µF
VPOS
21
VPSR
20
POWERLINE
CABLE, ETC.
3.3V
VMDO
19
PRAI
18
FDBK
17
RFB1
100Ω
RFB2
100Ω
0.1µF
3.3V
Figure 64. Block Diagram and Basic Application Connections
HIGH CURRENT DRIVER AMPLIFIER
The high current driver amplifier can deliver very large output
currents suitable for driving complex impedances, such as a
power line, a 50 Ω line, or a coaxial cable. The input of the
amplifier is fully differential and intended to be driven by a
differential current-output DAC, as shown in Figure 64. The
differential input signal is amplified by 1.5× and produces a
2.25 V p-p single-ended output signal from a 1.5 V p-p input
signal. A DAC with 15 mA maximum output current into a
50 Ω load provides 1.5 V p-p of input voltage and results in
2.25 V p-p at the output. A DAC whose output is 20 mA produces
an output swing of 3 V p-p (neglecting a small gain error when
driving the parallel combination of the 50 Ω load-resistor and the
internal 1 kΩ gain resistor of the AD8260).
For a 3.3 V supply rail, the maximum limit of the output voltage
is 3 V p-p and distorts severely if exceeded. The recommended
output for optimum distortion is 2 V p-p for a 3.3 V supply.
Correspondingly, larger output swings are accommodated for
higher supply voltages such as +5 V or ±5 V.
For optimum distortion, the input drive must be controlled
such that the output swing is well within saturation levels
established by the supply rail. The output swing can be reduced
by using load resistors with values less than 50 Ω or by reducing
the amplifier gain by connecting external resistors in parallel
with the internal 1 kΩ and 1.5 kΩ resistors between Pin 27,
Pin 28, and Pin 29, and between Pin 30, Pin 31, and Pin 32.
Coincidently, noise is reduced because the gain setting resistors
are the primary noise sources of the high current driver amplifier.
The output-referred noise is 14 nV/√Hz, of which 11 nV/√Hz is
due to the gain setting resistors. Matching of the gain setting
resistors is important for good common-mode rejection and the
accuracy of the differential gain. If external resistors are used,
their accuracy should be at least ±1%. How low the resistor
values can be is primarily determined by the quality of the ac
ground at Pin VOCM; as the gain setting resistors decrease in
value, the dynamic current increases, and the quality of the
decoupling capacitors needs to increase correspondingly.
Rev. 0 | Page 21 of 32
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