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PDF AD8390A Data sheet ( Hoja de datos )
| Número de pieza | AD8390A | |
| Descripción | High Output Current Differential Amplifier | |
| Fabricantes | Analog Devices | |
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Data Sheet
Low Power, High Output Current
Differential Amplifier
AD8390A
FEATURES
Voltage feedback amplifier
Ideal for ADSL and ADSL2+ central office (CO) and
customer premises equipment (CPE) applications
Enables high current differential applications
Low power operation
Single- or dual-supply operation from 10 V (± 5 V)
up to 24 V (± 12 V)
5.5 mA total quiescent supply current for full power ADSL
and ADSL2+ CO applications
Adjustable supply current to minimize power
consumption
High output voltage and current drive
400 mA peak output drive current
44 V p-p differential output voltage
Low distortion
−70 dBc MTPR, 26 kHz to 1.1 MHz
−65 dBc MTPR, 1.1 MHz to 2.2 MHz
High speed: 260 V/μs differential slew rate
FUNCTIONAL BLOCK DIAGRAM
VCC
INP AD8390A
VCC
56kΩ
56kΩ
OUTN
VCOM
56kΩ
VEE
56kΩ
OUTP
INN
VEE
Figure 1.
APPLICATIONS
ADSL/ADSL2+ CO and CPE line drivers
xDSL line drivers
High current differential amplifiers
GENERAL DESCRIPTION
The AD8390A is a high output current, low power consumption
differential amplifier. It is particularly well suited for the central
office (CO) driver interface in digital subscriber line systems
such as ADSL and ADSL2+. In full bias operation, the driver
delivers 20.4 dBm output power into low resistance loads while
compensating for hybrid and transformer insertion losses and
back termination resistors.
The AD8390A is available in a thermally enhanced LFCSP
package (16-lead LFCSP). Significant control and flexibility
in bias current have been designed into the AD8390A.
Four power modes are selectable via two digital inputs, PD0 and
PD1, providing three levels of driver bias and one power-down
state. In addition, the IADJ pin is available for fine quiescent
current trimming to tailor the performance of the AD8390A.
The low power consumption, high output current, high output
voltage swing, and robust thermal packaging enable the
AD8390A to be used as the central office line driver in ADSL,
ADSL2+, and proprietary xDSL systems, as well as in other high
current applications requiring a differential amplifier.
Rev. B
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. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
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
©2013 Analog Devices, Inc. All rights reserved.
Free Datasheet http://www.datasheet4u.com/
1 page  
Data Sheet
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
AD8390A
INP 1
PD1 2
PD0 3
INN 4
PIN 1
INDICATOR
AD8390A
TOP VIEW
(Not to Scale)
12 OUTN
11 VEE
10 VCC
9 OUTP
NOTES
1. NC = NO CONNECT.
2. NO ELECTRICAL CONNECTION. CONNECT THE
EXPOSED PAD TO A SOLID EXTERNAL PLANE
WITH LOW THERMAL RESISTANCE.
Figure 3. Pin Configuration
Table 4. Pin Function Descriptions
Pin No. Mnemonic Description
1 INP
Amplifier Noninverting Input.
2 PD1
Power Mode Control.
3 PD0
Power Mode Control.
4 INN
Amplifier Inverting Input.
5 NC
No Connection.
6
DGND
Ground.
7 IADJ
Bias Current Adjustment.
8 NC
No Connection.
9
OUTP
Amplifier Noninverting Output.
10 VCC
Positive Power Supply.
11 VEE
Negative Power Supply.
12 OUTN Amplifier Inverting Output.
13 NC
No Connection.
14 NC
No Connection.
15 VCOM Common-Mode Voltage.
16 NC
No Connection.
EPAD
Exposed pad. No electrical connection. Connect the exposed pad to a solid external plane with low thermal
resistance.
Rev. B | Page 5 of 12
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5 Page 
Data Sheet
ADSL AND ADSL2+ APPLICATIONS
In a typical ADSL/ADSL2+ application, a differential line driver
drives the signal from the analog front end (AFE) onto the
twisted pair telephone line. Referring to the typical circuit
representation in Figure 17, the differential input appears at
VIN+ and VIN− from the AFE. The differential output is
transformer-coupled to the telephone line at tip and ring. The
common-mode operating point, generally midway between the
supplies, is set through VCOM.
In ADSL/ADSL2+ applications, it is common practice to
conserve power by using positive feedback (R3 in Figure 17) to
synthesize the output resistance, lowering the required value of
the line matching resistors, RM.
VCC
0.1µF
10µF
R2
R3
R1
+IN
0.1µF
VCOM
R1 0.1µF
–IN
VEE
0.1µF
10µF
RADJ
–OUT RM
+OUT
R3
RM
R2
1:N
+
RL VOUT, DM
–
Figure 17. ADSL/ADSL2+ Application Circuit
The differential input impedance to the circuit is 2 × R1.
R1 is chosen by the designer to match system requirements.
The synthesized value of the back termination resistor is given
by the following equation.
RM
=
k×
RL
2×N2
where RL is the line impedance, and N is the turns ratio of the
transformer.
The factor k defines the relationship between the negative and
positive feedback resistors and is given by
k =1
−
R3
R2
Commonly used values for k are between 0.1 and 0.25. Values
less than 0.1 can lead to instability and are not recommended.
AD8390A
Assuming low values for back termination resistor RM, R3 is
approximated as
R3 ≅ R1× 2× k × AV
where AV is the voltage gain.
R2 is given by
R2
=
R3
1−k
With RM, R3, and R2 calculated, the closest 1% resistors are
chosen and the gain rechecked with the following equation:
AV
=
R1 [R M
R2 × R3
+ R2(k + 1) − R3]
Table 6 compares the results of the exact values, the simplified
approximation, and the closest 1% resistor value calculations. In
this example, R1 = 1.0 kΩ, AV = 10, and k = 0.1.
Note that decreasing the value of the back termination resistors
attenuates the receive signal by approximately 1/k. Advances in
low noise receive amplifiers permit the use of k values as small
as 0.1.
The line impedance, turns ratio, and k factor specify the output
voltage and current required from the AD8390A. To accom-
modate higher crest factors or lower supply rails, the turns ratio,
N, may need to be increased. Because higher turns ratios and
smaller k factors both attenuate the receive signal, a large
increase in N may require an increase in k to maintain the
desired noise performance. Any particular design process
requires that these trade-offs be addressed.
Table 6. Resistor Selection
Component
Exact
Value
R1 (Ω)
1000
R2 (Ω)
2246.95
R3 (Ω)
2022.25
RM (Ω)
5
Actual AV
Actual k
10.000
0.1
Approximate
Calculation
1000
2222.22
2000
5
9.889
0.1
Standard 1%
Resistor Value
1000
2210
2000
4.99
10.138
0.095
LIGHTNING AND AC POWER FAULT
When the AD8390A is an ADSL/ADSL2+ line driver, it is
transformer-coupled to the twisted pair telephone line. In this
environment, the AD8390A is subject to large line transients
resulting from events such as lightning strikes or downed power
lines. Additional circuitry is required to protect the AD8390A
from damage due to these events.
Rev. B | Page 11 of 12
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