adl5317 Analog Devices, Inc., adl5317 Datasheet - Page 11

• Manufacturer Part Number: adl5317
• Description: Avalanche Photodiode Bias Controller And Wide Range 5 Na To 5 Ma Current Monitor
• Manufacturer: Analog Devices, Inc.

APPLICATIONS
The ADL5317 is primarily designed for wide dynamic range
applications simplifying APD bias circuit architecture. Accurate
control of the bias voltage across the APD becomes critical to
maintain the proper avalanche multiplication factor as the
temperature and input power vary. Figure 21 shows how to use
the ADL5317 with an external temperature sensor to monitor
the ambient temperature of the APD. Using a look-up table and
DAC to drive VSET, it is possible to apply the correct V
the conditions. Note that Pin 9, Pin 10, and Pin 12 to Pin 15
were removed for simplification.
In this application, the ADL5317 is operating in linear mode.
The bias voltage to the APD, delivered at Pin VAPD, is
controlled by the voltage (V
VAPD is equal to 30 × V
The range of voltages available at VAPD for a given high voltage
supply is limited to approximately 33 V (or less, for V
This is because the GARD and VAPD pins are clamped to within
~40 V below VPHV, preventing internal device breakdowns.
The input current, I
precisely mirrored to Pin IPDM. This interface is optimized for
use with any of the Analog Devices translinear logarithmic
amplifiers (for example, the
precise, wide dynamic range measurement of the optical power
incident upon the APD.
If a voltage output is preferred at IPDM, a single external
resistor to ground is all that is necessary to perform the
conversion. Voltage compliance at IPDM is limited to V
V
TEMPERATURE
APD
LOOK-UP
AND DAC
SENSOR
TABLE
/3, whichever is lower.
Figure 21. Typical APD Biasing Application Using the ADL5317
SUPPLY
5V
LOGIC
FROM DC–DC
CONVERTER
VSET
FALT
VPLV
VPHV
75V
OVERCURRENT
PROTECTION
PROTECTION
THERMAL
COMM
APD
VCLH
30 × V
, is divided down by a factor of 5 and
C
SET
29 × R
R
GRD
SET
.
SET
AD8304
GARD
) at Pin VSET. The bias voltage at
CURRENT
MIRROR
5:1
VAPD
I
APD
APD
or AD8305) to offer a
IPDM
I
APD
5
TIA RECEIVER
TRANSLINEAR
LOG AMP
APD
< 41 V).
APD
PLV
OPTICAL
POWER
DATA
for
or
Rev. 0 | Page 11 of 16
SUPPLY TRACKING MODE
Some applications for the ADL5317 require a variable dc-to-dc
converter or alternative variable biasing sources to supply
VPHV. For these applications, it is necessary to configure the
ADL5317 for supply tracking mode, shown in Figure 22. In this
mode, the VSET interface is bypassed. However, the full
functionality of the precision current mirror remains available.
3V TO 5.5V
In supply tracking mode, the V
its linear operating range and effectively placed into a controlled
saturation. This is done by applying 3.0 V to 5.5 V at the VSET
pin. It is also necessary to remove the connection from VCLH,
which defines the saturation point, to VPHV. Once the ADL5317
is placed into supply tracking mode, V
below V
For those designs where it is desirable to drive VSET from the
VPLV supply, it is necessary to place a 100 kΩ resistor between
VSET and VPLV for V
limitations on the VSET pin.
TRANSLINEAR LOG AMP INTERFACING
The monitor current output, IPDM, of the ADL5317 is
designed to interface directly to an Analog Devices translinear
logarithmic amplifier, such as the AD8304, AD8305, or
ADL5306. Figure 23 shows the basic connections necessary for
interfacing the ADL5317 to the AD8305. In this configuration,
the designer is can use the full current mirror range of the
ADL5317 for high accuracy power monitoring.
4V TO 6V
10V TO 77V
5V
PHV
DC SUPPLY
VARIABLE
3
4
1
2
VSET
VPHV
.
FALT
VPLV
VPHV
OVERCURRENT
5
PROTECTION
PROTECTION
THERMAL
COMM
16
Figure 22. Supply Tracking Mode
6
VCLH
COMM
30 × V
PLV
15
29 × R
R
> 5.5 V. This is due to input current
SET
COMM
14
7
GARD
SET
COMM
amplifier is pulled up beyond
13
13
CURRENT
MIRROR
8
5:1
VAPD
APD
GARD
8V TO 75V
BIAS ACROSS APD
IPDM
NC
NC
is clamped to 2.0 V
TIA
12
11
10
9
DATA
OUT
ADL5317
LOG
RSSI