ADL5317

Rev. 0 | Page 11 of 16

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

the conditions. Note that Pin 9, Pin 10, and Pin 12 to Pin 15

were removed for simplification.

OVERCURRENT

PROTECTION

THERMAL

PROTECTION

COMM

FALT

VSET

VPLV

VPHV

VCLH

GARD

VAPD

IPDM

CURRENT

MIRROR

5:1

30

× V

SET

5

R

29

× R

LOGIC

SUPPLY

LOOK-UP

TABLE

AND DAC

TEMPERATURE

SENSOR

5V

OPTICAL

POWER

TRANSLINEAR

LOG AMP

APD

TIA RECEIVER

75V

FROM DC–DC

CONVERTER

DATA

Figure 21. Typical APD Biasing Application Using the ADL5317

In this application, the ADL5317 is operating in linear mode.

The bias voltage to the APD, delivered at Pin VAPD, is

The range of voltages available at VAPD for a given high voltage

This is because the GARD and VAPD pins are clamped to within

~40 V below VPHV, preventing internal device breakdowns.

precisely mirrored to Pin IPDM. This interface is optimized for

use with any of the Analog Devices translinear logarithmic

amplifiers (for example, the AD8304 or AD8305) to offer a

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

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.

OVERCURRENT

PROTECTION

THERMAL

PROTECTION

FALT

VSET

VPLV

VPHV

VPHV

VCLH

GARD

VAPD

IPDM

CURRENT

MIRROR

5:1

30

× V

SET

R

29

× R

5V

COMM

16

COMM

15

COMM

14

COMM

13

1

2

3

4

5

6

7

8

11

10

9

NC

GARD

VARIABLE

DC SUPPLY

10V TO 77V

TIA

8V TO 75V

BIAS ACROSS APD

DATA

OUT

LOG

RSSI

3V TO 5.5V

4V TO 6V

12

13

NC

Figure 22. Supply Tracking Mode

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

For those designs where it is desirable to drive VSET from the

VPLV supply, it is necessary to place a 100 kΩ resistor between

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.