AD8305ACPZ-RL7 Analog Devices Inc, AD8305ACPZ-RL7 Datasheet

IC, LOGARITHMIC AMP, 20mV, LFCSP-16

AD8305ACPZ-RL7

Manufacturer Part Number
AD8305ACPZ-RL7
Description
IC, LOGARITHMIC AMP, 20mV, LFCSP-16
Manufacturer
Analog Devices Inc
Type
Logarithmic Converterr
Datasheet

Specifications of AD8305ACPZ-RL7

No. Of Amplifiers
1
Dynamic Range, Decades
5
Scale Factor V / Decade
0.2
Supply Voltage Range
3V To 12V
Amplifier Case Style
LFCSP
Supply Current
5.4mA
Input Offset Voltage
20mV
Design Resources
Interfacing ADL5315 to Translinear Logarithmic Amplifier (CN0056) Interfacing ADL5317 High Side Current Mirror to a Translinear Logarithmic Amplifier in an Avalanche Photodiode Power Detector
Applications
Fiber Optics
Mounting Type
Surface Mount
Package / Case
16-LFCSP
Rohs Compliant
Yes
Number Of Channels
1
Number Of Elements
3
Power Supply Requirement
Single/Dual
Single Supply Voltage (typ)
5V
Dual Supply Voltage (typ)
±3/±5V
Power Dissipation
500mW
Rail/rail I/o Type
Rail to Rail Output
Single Supply Voltage (min)
3V
Single Supply Voltage (max)
12V
Dual Supply Voltage (min)
±1.5V
Dual Supply Voltage (max)
±6V
Operating Temp Range
-40C to 85C
Operating Temperature Classification
Industrial
Mounting
Surface Mount
Pin Count
16
Package Type
LFCSP EP
Lead Free Status / RoHS Status
Lead free / RoHS Compliant
Lead Free Status / RoHS Status
Lead free / RoHS Compliant, Lead free / RoHS Compliant
Other names
AD8305ACPZ-RL7

Available stocks

Company
Part Number
Manufacturer
Quantity
Price
Part Number:
AD8305ACPZ-RL7
Manufacturer:
AD
Quantity:
12 459
FEATURES
Optimized for fiber optic photodiode interfacing
Measures current over 5 decades
Single- or dual-supply operation (3 V to 12 V total)
Full log-ratio capabilities
Nominal slope of 10 mV/dB (200 mV/decade)
Nominal intercept of 1 nA (set by external resistor)
Complete and temperature stable
Rapid response time for a given current level
Miniature 16-lead chip scale package
Low power: ~5 mA quiescent current
APPLICATIONS
Optical power measurement
Wide range baseband logarithmic compression
Measurement of current and voltage ratios
Optical absorbance measurement
GENERAL DESCRIPTION
The AD8305
optimized for determining optical power in fiber optic systems. It uses
an advanced implementation of a classic translinear (junction based)
technique to provide a large dynamic range in a versatile and easily
used form. A single-supply voltage of between 3 V and 12 V is
adequate; dual supplies may optionally be used. The low quiescent
current (typically 5 mA) permits use in battery-operated applications.
The input current, I
collector current of an optimally scaled NPN transistor, which converts
this current to a voltage (V
second such converter is used to handle the reference current (I
applied to pin I
(0.5 V). This is generally acceptable for photodiode applications where
the anode does not need to be grounded. Similarly, this bias voltage is
easily accounted for in generating I
front end is available at Pin VLOG.
The basic logarithmic slope at this output is nominally 200 mV/decade
(10 mV/dB). Thus, a 100 dB range corresponds to an output change of
1 V. When this voltage (or the buffer output) is applied to an ADC that
permits an external reference voltage to be employed, the AD8305
voltage reference output of 2.5 V at Pin VREF can be used to improve
the scaling accuracy. Suitable ADCs include the
AD7823
values of the logarithmic slope can be provided using a simple external
resistor network.
1
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.
Trademarks and registered trademarks are the property of their respective owners.
Protected by U.S. Patent No. 5,519,308.
Law conformance 0.1 dB from 10 nA to 1 mA
Optional adjustment of slope and intercept
(LFCSP 3 mm × 3 mm)
(serial 8-bit), and
1
is an inexpensive microminiature logarithmic converter
REF
. These input nodes are biased slightly above ground
PD
, of 10 nA to 1 mA applied to the INPT pin is the
BE
AD7813
) with a precise logarithmic relationship. A
REF
(parallel, 8-bit or 10-bit). Other
. The output of the logarithmic
AD7810
(serial 10-bit),
REF
)
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
Fax: 781.461.3113
The logarithmic intercept (also known as the reference current) is
nominally positioned at 1 nA by the use of the externally generated
current, I
between VREF, at 2.5 V, and the reference input, IREF, at 0.5 V. The
intercept can be adjusted over a wide range by varying this resistor.
The AD8305 can also operate in a log ratio mode, with the numerator
current applied to INPT and the denominator current applied to IREF.
A buffer amplifier is provided for driving a substantial load, for use in
raising the basic slope of 10 mV/dB to higher values, as a precision
comparator (threshold detector), or in implementing low-pass filters.
Its rail-to-rail output stage can swing to within 100 mV of the positive
and negative supply rails, and its peak current sourcing capacity is
25 mA.
It is a fundamental aspect of translinear logarithmic converters that the
small signal bandwidth falls as the current level diminishes, and the
low frequency noise-spectral density increases. At the 10 nA level, the
bandwidth of the AD8305 is about 50 kHz and increases in proportion
to I
amplifier, the increase in noise level at low currents can be addressed by
using it to realize lowpass filters of up to three poles.
The AD8305 is available in a 16-lead LFCSP package and is specified
for operation from −40°C to +85°C.
100 dB Range (10 nA to 1 mA)
200kΩ
V
PD
BIAS
up to a maximum value of about 15 MHz. Using the buffer
VRDZ
VREF
VSUM
IREF
I
INPT
PD
REF
, of 10 μA, provided by a 200 kΩ resistor connected
FUNCTIONAL BLOCK DIAGRAM
0.5V
0.5V
Logarithmic Converter
©2003–2010 Analog Devices, Inc. All rights reserved.
20kΩ
COMM
VNEG
Q2
Q1
80kΩ
Figure 1.
+
V
2.5V
V
BE2
VPOS
BE1
COMPENSATION
TEMPERATURE
V
GENERATOR
P
BIAS
COMM
14.2kΩ
6.69kΩ
I
LOG
AD8305
0.20 log
www.analog.com
451Ω
COMM
SCAL
BFIN
10
1nA
VOUT
VLOG
I
PD

Related parts for AD8305ACPZ-RL7

AD8305ACPZ-RL7 Summary of contents

Page 1

FEATURES Optimized for fiber optic photodiode interfacing Measures current over 5 decades Law conformance 0.1 dB from Single- or dual-supply operation ( total) Full log-ratio capabilities Nominal slope of 10 mV/dB ...

Page 2

AD8305 TABLE OF CONTENTS Features .............................................................................................. 1 Applications ....................................................................................... 1 Functional Block Diagram .............................................................. 1 General Description ......................................................................... 1 Revision History ............................................................................... 2 Specifications ..................................................................................... 3 Absolute Maximum Ratings ............................................................ 4 ESD Caution .................................................................................. 4 Pin Configuration and Function Descriptions ...

Page 3

SPECIFICATIONS 25° 200 kΩ, and VRDZ connected to VREF, unless otherwise noted REF Table 1. Parameter INPUT INTERFACE Specified Current Range Input Current ...

Page 4

AD8305 ABSOLUTE MAXIMUM RATINGS Table 2. Parameter Supply Voltage V − Input Current Internal Power Dissipation 1 θ JA Maximum Junction Temperature Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering 60 sec) 1 With package die ...

Page 5

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS Table 3. Pin Function Descriptions Pin No. Mnemonic Function 1 VRDZ Top of a Resistive Divider Network that Offsets V may also be connected to ground when bipolar outputs are to be provided. 2 VREF ...

Page 6

AD8305 TYPICAL PERFORMANCE CHARACTERISTICS 200 kΩ 25°C, unless otherwise noted REF A 1 –40°C, 0°C, +25°C, +70°C, +85° 1.4 ...

Page 7

I (A) REF Figure 9. V vs. I for Multiple Values of I LOG REF mA) ...

Page 8

AD8305 10 10nA 100nA 0 –10 –20 1mA –30 1µA –40 –50 100 1k 10k 100k FREQUENCY (Hz) Figure 15. Small Signal AC Response (5% Sine Modulation), from for I in Decade Steps from 10 nA ...

Page 9

MEAN + 3σ 0 MEAN – 3σ –0.5 –1.0 –1.5 –2.0 1n 10n 100n 1µ 10µ I (A) PD Figure 21. Law Conformance Error Distribution (3σ to Either Side of Mean) 2.0 1.5 MEAN + 3σ ...

Page 10

AD8305 MEAN + 3σ –2 MEAN – 3σ –4 –6 –8 –10 –40 –30 –20 – TEMPERATURE (°C) Figure 27. Slope Drift vs. Temperature (3σ to Either Side of ...

Page 11

GENERAL STRUCTURE The AD8305 addresses a wide variety of interfacing conditions to meet the needs of fiber optic supervisory systems, and is also useful in many nonoptical applications. These notes explain the structure of this unique style of translinear log ...

Page 12

AD8305 required to accommodate this situation (see the Using A Negative Supply section). The voltage generated by applying I LOG resistance of 4.55 kΩ, formed by the parallel combination of a 6.69 kΩ resistor to ground and ...

Page 13

C bypassing capacitor on VSUM. If board space limits the amount of external circuitry to the AD8305 it is possible to eliminate the transistor in Figure 34 is the recommended and connect the resistor divider ...

Page 14

AD8305 APPLICATIONS The AD8305 is easy to use in optical supervisory systems and in similar situations where a wide ranging current converted to its logarithmic equivalent, which is represented in decibel terms. Basic connections for measuring a ...

Page 15

CALIBRATION The AD8305 has a nominal slope and intercept of 200 mV/decade and 1 nA, respectively. These values are untrimmed, and the slope alone may vary as much as 7.5% over temperature. For this reason recommended that a ...

Page 16

AD8305 USING A NEGATIVE SUPPLY Most applications of the AD8305 require only a single supply of 3 5.5 V. However, to provide further versatility, dual supplies may be employed, as illustrated in Figure 37. 5V VPOS VRDZ BIAS ...

Page 17

LOG-RATIO APPLICATIONS It is often desirable to determine the ratio of two currents, for example, in absorbance measurements. These are commonly used to assess the attenuation of a passive optical component, such as an optical filter or variable optical attenuator. ...

Page 18

AD8305 REVERSING THE INPUT POLARITY Some applications may require interfacing to a circuit that sources current rather than sinks current, such as connecting to the cathode side of a photodiode. Figure 40 shows the use of a current mirror circuit. ...

Page 19

CHARACTERIZATION METHODS During the characterization of the AD8305, the device was treated as a precision current-input logarithmic converter, because it is not practical for several reasons to generate accurate photocurrents by illuminating a photodiode. The test currents are generated by ...

Page 20

AD8305 The setup shown in Figure 44 was used for frequency response measurements of the logarithmic amplifier section. The AD8138 output is offset to 1 and modulated to a depth frequency chosen (over ...

Page 21

EVALUATION BOARD An evaluation board is available for the AD8305, the schematic for which is shown in Figure 49. It can be configured for a wide variety of experiments. The buffer gain is factory-set to unity, providing a slope of ...

Page 22

AD8305 Figure 47. Component Side Layout Figure 48. Component Side Silkscreen Rev Page ...

Page 23

R20 OPEN R17 VRDZ OPEN R7 0Ω R18 VREF OPEN R1 200kΩ IREF OPEN R13 1kΩ 1nF 2 SC-STYLE PD 3 INPT LK1 R9 C11 OPEN 1nF VSUM COMM COMM COMM COMM ...

Page 24

... AD8305ACP-R2 −40°C to +85°C AD8305ACP-REEL7 −40°C to +85°C AD8305ACPZ-R2 −40°C to +85°C AD8305ACPZ-RL7 −40°C to +85°C AD8305-EVALZ RoHS Compliant Part; # denotes lead-free product may be top or bottom marked. ©2003–2010 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners ...

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