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PDF AD815 Data sheet ( Hoja de datos )
| Número de pieza | AD815 | |
| Descripción | High Output Current Differential Driver | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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a
High Output Current
Differential Driver
AD815
FEATURES
Flexible Configuration
Differential Input and Output Driver
or Two Single-Ended Drivers
Industrial Temperature Range
High Output Power
Thermally Enhanced SOIC
400 mA Minimum Output Drive/Amp, RL = 10 ⍀
Low Distortion
–66 dB @ 1 MHz THD, RL = 200 ⍀, VOUT = 40 V p-p
0.05% and 0.45؇ Differential Gain and Phase, RL = 25 ⍀
(6 Back-Terminated Video Loads)
High Speed
120 MHz Bandwidth (–3 dB)
900 V/s Differential Slew Rate
70 ns Settling Time to 0.1%
Thermal Shutdown
APPLICATIONS
ADSL, HDSL, and VDSL Line Interface Driver
Coil or Transformer Driver
CRT Convergence and Astigmatism Adjustment
Video Distribution Amp
Twisted Pair Cable Driver
GENERAL DESCRIPTION
The AD815 consists of two high speed amplifiers capable of
supplying a minimum of 500 mA. They are typically configured
as a differential driver enabling an output signal of 40 V p-p on
± 15 V supplies. This can be increased further with the use of a
coupling transformer with a greater than 1:1 turns ratio. The
low harmonic distortion of –66 dB @ 1 MHz into 200 Ω
–40
VS = ؎15V
–50
G = +10
VOUT = 40V p-p
–60
–70
–80
–90
–100
RL = 50⍀
(DIFFERENTIAL)
RL = 200⍀
(DIFFERENTIAL)
–110
100
1k 10k 100k 1M 10M
FREQUENCY – Hz
Figure 1. Total Harmonic Distortion vs. Frequency
FUNCTIONAL BLOCK DIAGRAM
NC 1
24 NC
NC 2
23 NC
NC 3
22 NC
NC 4
21 NC
THERMAL
HEAT TABS
+VS*
5 AD815 20
6 TOP VIEW 19
7 (Not to Scale) 18
8 17
THERMAL
HEAT TABS
+VS*
+IN1 9
16 +IN2
–IN1 10
15 –IN2
OUT1 11
14 OUT2
–VS 12
13 +VS
NC = NO CONNECT
*HEAT TABS ARE CONNECTED TO THE POSITIVE SUPPLY.
combined with the wide bandwidth and high current drive make
the differential driver ideal for communication applications such
as subscriber line interfaces for ADSL, HDSL and VDSL.
The AD815 differential slew rate of 900 V/µs and high load drive
are suitable for fast dynamic control of coils or transformers,
and the video performance of 0.05% and 0.45° differential gain
and phase into a load of 25 Ω enable up to 12 back-terminated
loads to be driven.
The 24-lead SOIC (RB) is capable of driving 26 dBm for full
rate ADSL with proper heat sinking.
100⍀
+15V
1/2
AD815
AMP1
R1 = 15⍀
499⍀
VIN =
4Vp-p
110⍀ G = +10
VD =
40Vp-p
RL
120⍀
499⍀
100⍀
AMP2
1/2
AD815
R2 = 15⍀
1:2
TRANSFORMER
–15V
VOUT =
40Vp-p
Figure 2. Subscriber Line Differential Driver
REV. D
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties that
may result from its use. No license is granted by implication or otherwise
under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
www.analog.com
Fax: 781/461-3113 © 2015 Analog Devices, Inc. All rights reserved.
1 page  
AD815–Typical Performance Characteristics
20
15
10
5
0
0 5 10 15 20
SUPPLY VOLTAGE – ؎Volts
Figure 4. Input Common-Mode Voltage Range vs. Supply
Voltage
36
34
VS = ؎15V
32
30
28
26
VS = ؎5V
24
22
20
18
–40 –20 0 20 40 60 80 100
JUNCTION TEMPERATURE – ؇C
Figure 7. Total Supply Current vs. Temperature
40 80
30 60
NO LOAD
20
RL = 50⍀
40
(DIFFERENTIAL)
RL = 25⍀
(SINGLE-ENDED)
10 20
00
0 5 10 15 20
SUPPLY VOLTAGE – ؎Volts
Figure 5. Output Voltage Swing vs. Supply Voltage
33
TA = +25؇C
30
27
24
21
18
0
2
4 6 8 10 12
SUPPLY VOLTAGE – ؎Volts
14 16
Figure 8. Total Supply Current vs. Supply Voltage
30 60
VS = ؎15V
25 50
20 40
15 30
10 20
VS = ؎5V
5 10
00
10 100 1k 10k
LOAD RESISTANCE – (Differential – ⍀) (Single-Ended – ⍀/2)
Figure 6. Output Voltage Swing vs. Load Resistance
10
SIDE A, B
+IB
0
VS = ؎15V, ؎5V
–10
–20
VS = ؎5V
–30
SIDE B
–40 –IB
SIDE A
–50
–60
–70
–80
–40
SIDE B
SIDE A –IB
VS = ؎15V
–20 0
20 40
60
JUNCTION TEMPERATURE – ؇C
80
100
Figure 9. Input Bias Current vs. Temperature
–4– REV. D
5 Page 
AD815
SIDE A
SIDE B
G = –1
RF = 562⍀
RL = 100⍀
Choice of Feedback and Gain Resistors
The fine scale gain flatness will, to some extent, vary with
feedback resistance. It therefore is recommended that once
optimum resistor values have been determined, 1% tolerance
values should be used if it is desired to maintain flatness over
a wide range of production lots. Table I shows optimum values
for several useful configurations. These should be used as
starting point in any application.
1V 20ns
Figure 42. 4 V Step Response, G = –1
THEORY OF OPERATION
The AD815 is a dual current feedback amplifier with high
(500 mA) output current capability. Being a current feedback
amplifier, the AD815’s open-loop behavior is expressed
as transimpedance, ∆VO/∆I–IN, or TZ. The open-loop
transimpedance behaves just as the open-loop voltage gain
of a voltage feedback amplifier, that is, it has a large dc value
and decreases at roughly 6 dB/octave in frequency.
Since RIN is proportional to 1/gM, the equivalent voltage gain is
just TZ × gM, where the gM in question is the transconductance
of the input stage. Using this amplifier as a follower with gain,
Figure 43, basic analysis yields the following result:
( )VO = G ×
TZ S
( )VIN TZ S + G × RIN + RF
where:
G = 1 + RF
RG
RIN = 1/gM ≈ 25 Ω
RF
RG
RN
RIN
VOUT
VIN
Table I. Resistor Values
RF (⍀) RG (⍀)
G = +1 562
–1 499
+2 499
+5 499
+10 1 k
ϱ
499
499
125
110
PRINTED CIRCUIT BOARD LAYOUT
CONSIDERATIONS
As to be expected for a wideband amplifier, PC board parasitics
can affect the overall closed-loop performance. Of concern are
stray capacitances at the output and the inverting input nodes. If
a ground plane is to be used on the same side of the board as
the signal traces, a space (5 mm min) should be left around the
signal lines to minimize coupling.
POWER SUPPLY BYPASSING
Adequate power supply bypassing can be critical when optimizing
the performance of a high frequency circuit. Inductance in the
power supply leads can form resonant circuits that produce
peaking in the amplifier’s response. In addition, if large current
transients must be delivered to the load, then bypass capacitors
(typically greater than 1 µF) will be required to provide the best
settling time and lowest distortion. A parallel combination of
10.0 µF and 0.1 µF is recommended. Under some low frequency
applications, a bypass capacitance of greater than 10 µF may be
necessary. Due to the large load currents delivered by the
AD815, special consideration must be given to careful bypassing.
The ground returns on both supply bypass capacitors as well as
signal common must be “star” connected as shown in Figure 44.
+VS
+IN
Figure 43. Current Feedback Amplifier Operation
Recognizing that G × RIN << RF for low gains, it can be seen to
the first order that bandwidth for this amplifier is independent
of gain (G).
Considering that additional poles contribute excess phase at
high frequencies, there is a minimum feedback resistance below
which peaking or oscillation may result. This fact is used to
determine the optimum feedback resistance, RF. In practice
parasitic capacitance at the inverting input terminal will also add
phase in the feedback loop, so picking an optimum value for RF
can be difficult.
Achieving and maintaining gain flatness of better than 0.1 dB at
frequencies above 10 MHz requires careful consideration of
several issues.
–10–
RG
(OPTIONAL)
RF
RF
–IN
–VS
+OUT
–OUT
Figure 44. Signal Ground Connected in “Star”
Configuration
REV. D
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet AD815.PDF ] | |
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