Precision Wide Range (3 nA to 3 mA)
High-Side Current Mirror
ADL5315
Rev. 0
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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
VOLTAGE
REFERENCE
CURRENT
LIMITING
COMM
VSET NC
INPT
I
PD
CURRENT
MIRROR
1:1
ADL5315
4
2 7
SREF
3
1
6
VPOS
20kΩ
5
RLIM
8
IOUT
I
PD
05694-001
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.
