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PDF ADL5315 Data sheet ( Hoja de datos )
| Número de pieza | ADL5315 | |
| Descripción | Precision Wide Range (3 nA to 3 mA) High-Side Current Mirror | |
| Fabricantes | Analog Devices | |
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Precision Wide Range (3 nA to 3 mA)
High-Side Current Mirror
ADL5315
FEATURES
Accurately mirrors input current (1:1 ratio) over 6 decades
Linearity 1% from 3 nA to 3 mA
Stable mirror input voltage
Voltage held 1 V below supply using internal reference
or can be set externally
Adjustable input current limit
2.7 V to 8 V single-supply operation
Miniature 8-lead LFCSP (2 mm × 3 mm)
APPLICATIONS
Optical power monitoring from a single photodiode
General voltage biasing with precision current monitoring
Voltage-to-current conversion
FUNCTIONAL BLOCK DIAGRAM
ADL5315
VOLTAGE
REFERENCE
4
COMM
CURRENT
LIMITING
5
RLIM
20kΩ
3
SREF
CURRENT
MIRROR
1:1
6
VPOS
VSET
2
NC
7
INPT
1
IPD
IOUT
8
IPD
Figure 1.
GENERAL DESCRIPTION
The ADL5315 is a wide input current range, precision high-side
current mirror featuring a stable and user-adjustable input
voltage. It is optimized for use with PIN photodiodes, but its
flexibility and wide operating range make it suitable for a broad
array of additional applications. Over the 3 nA to 3 mA range,
the current sourced from the INPT pin is accurately mirrored
with a 1:1 ratio and sourced from the IOUT output pin. In a
typical photodiode application, the output drives a current-
input logarithmic amplifier to produce a linear-in-dB output
representing the optical power incident upon the photodiode.
For linear voltage output, a single resistor to ground is all that is
required. The photodiode anode can be connected to a high
speed transimpedance amplifier for the extraction of the data
stream. The voltage at the INPT pin is temperature stable with
respect to the voltage at the VSET input pin, which it tracks. A
temperature stable reference voltage is provided at the SREF
pin, which, when tied to VSET, fixes the voltage at INPT 1.0 V
below VPOS. VSET can also be driven from an external source.
The VSET input has very low input current and can be driven
as low as the bottom rail, facilitating nonloading voltage-to-
current conversion as well as minimizing dark current in
photodiode applications.
The ADL5315 also features adjustable input current limiting
using an external resistor from RLIM to VPOS. The maximum
current sourced by INPT (and IOUT) can be set between 1 mA
and 16 mA, beyond which the voltage at INPT falls rapidly
from its setpoint. Connecting RLIM directly to VPOS provides
basic input short-circuit protection with the default current
limit of 16 mA typical.
The ADL5315 is available in a 2 mm × 3 mm, 8-lead LFCSP and
is specified for operation from −40°C to +85°C.
Rev. 0
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
© 2005 Analog Devices, Inc. All rights reserved.
1 page  
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
ADL5315
INPT 1
8 IOUT
VSET 2 ADL5315 7 NC
TOP VIEW
SREF 3 (Not to Scale) 6 VPOS
COMM 4
5 RLIM
NC = NO CONNECT
Figure 2. 8-Lead LFCSP
Table 3. Pin Function Descriptions
Pin No. Mnemonic Description
1 INPT
Input Current. Pin sources current only.
2 VSET Sets Voltage at INPT (Gain = 1). Range 0 V to VPOS − 1.0 V for VPOS < 6.5 V. For VPOS ≥ 6.5 V range, VPOS − 6.5 V to
VPOS − 1 V. Optional shielding of INPT trace.
3 SREF Reference Voltage for VSET. Internally generated at VPOS − 1.0 V through 20 kΩ. Can be shorted to VSET for
standard mirror operation.
4
COMM
Analog Ground.
5 RLIM External Resistor to VPOS. Sets current limit at INPT from 1 mA to 16 mA. ILIM = 48 V/(RLIM + 3 kΩ).
6 VPOS Positive Supply (2.7 V to 8.0 V).
7 N/C
Optional Shielding of IOUT Trace. No connection to die.
8 IOUT Output Current. Mirrors current at INPT with a gain of 1.0. Sources current only.
PADDLE
Internally connected to COMM, solder to ground.
Rev. 0 | Page 5 of 20
5 Page 
APPLICATIONS
The ADL5315 is primarily designed for wide dynamic range
applications, simplifying power monitoring designs where
access is only permitted to the cathode of a PIN photodiode or
receiver module. Figure 22 shows a typical application where
the ADL5315 is used to provide an accurate bias to a PIN diode
while simultaneously mirroring the diode current to be
measured by a translinear logarithmic amplifier.
In this application, the ADL5315 sets the bias voltage on the
PIN diode. This voltage is delivered at the INPT pin and is
controlled by the voltage at the VSET pin. VSET is driven by
the on-board reference VSREF, which is equal to VPOS − 1 V.
The input current, IINPT, is precisely mirrored at a ratio of 1:1 to
the IOUT pin. This interface is optimized for use with any of
ADI’s translinear logarithmic amplifiers (for example, the
AD8304 or AD8305) to offer a precise, wide dynamic range
measurement of the optical power incident upon the PIN.
If a linear voltage output is preferred at IOUT, a single external
resistor to ground is all that is necessary to perform the
conversion.
ADL5315
AVERAGE POWER MONITORING
In applications where a modulated signal is incident upon the
photodiode, the average power of the signal can be measured.
Figure 21 shows the connections necessary for using the
ADL5315 in such a measurement system.
The value of the capacitor to ground should be selected to
eliminate errors due to modulation of the ADL5315 input
current.
ADL5315
CSET
VOLTAGE
REFERENCE
4
COMM
CURRENT
LIMITING
5
RLIM
20kΩ
3
SREF
CURRENT
MIRROR
1:1
6
VPOS
VSET
2
NC
7
VPOS
INPT
1
IPD
PIN
IOUT
8
IPD
LINEAR
VOLTAGE
OUTPUT
TIA DATA PATH
Figure 21. Average Power Monitoring Using the ADL5315
NODE VOLTAGES
VSREF = VPOS – 1V
VSET = VINPT
PIN
VOLTAGE
REFERENCE
4
COMM
20kΩ
3
SREF
VSET
2
ADL5315
CURRENT
VPOS
RLIM = 48V – 3kΩ
ILIM
LIMITING
RLIM
5
RLIM ILIM = 1mA – 16mA
CURRENT
MIRROR
1:1
6
VPOS
NC
7
THIS CONNECTION IS NOT NECESSARY,
BUT REDUCES ERRORS DUE TO LEAKAGE
CURRENTS AT LOW SIGNAL LEVELS.
INPT
1
IPD
IOUT
8
IPD
VSUM
INPT
OPTICAL
POWER
TIA DATA PATH
TRANSLINEAR LOG AMP
AD8304, AD8305, ETC.
Figure 22. Typical Application Using the ADL5315
Rev. 0 | Page 11 of 20
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet ADL5315.PDF ] | |
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