Data Sheet

ADL5308

PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS

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Rev. 0 | 6 of 22

Figure 3. Pin Configuration

Table 5. Pin Function Descriptions

Pin Number

Mnemonic

Description

1, 4

SUM

Guard Pins. The SUM pins are used to shield the input current lines to INP and IREF.

2

INP

Photocurrent Input. INP is connected to the PD anode (current flows into INP).

3

IREF

Reference Current Input. IREF can optionally be connected to a reference current or a second PD for log ratio

measurements (optical gain).

5

SDA

I2C Interface Data Input/Output.

6

SCL

I2C Interface Clock Input.

7

CREF

Comparator Reference Level. Comparator output is high when the VLOG voltage exceeds the voltage applied to this pin.

When left open, the reference level is set by an internal I2C programmable digital-to-analog converter (DAC) if the CREF

register content is not zero.

8

CMP

Comparator Output Voltage.

9

GND

Analog Ground.

10

VLOG

Logarithmic Output. The voltage at this pin changes logarithmically with the current applied to INP and IREF.

11

FB

Feedback Pin of Output Amplifier. Can be used to change the logarithmic slope with two external resistors.

12

HYST

Hysteresis. The voltage at the pin controls the amount of hysteresis in the comparator output. A voltage greater than 2.0 V

applied to this pin enables the latch function.

13

VCC

Positive Power Supply. Decoupling with 1 nF and 4.7 μF capacitors to ground is recommended at this pin.

14

PDB

PD Bias. PDB can be connected to the PD cathode to provide adaptive bias control. A series network of 10 Ω and 220 pF

to ground is recommended at this pin if the PD capacitance is higher than 3 pF. For lowest PD cathode to anode offset at

low input currents, avoid resistive loading at this pin.

15

SUM

One of the exposed pads on the underside of the device, Pin 15, is internally connected to SUM for improved shielding of

the input pins. Connect all SUM pins together and leave floating.

16

GND

One of the exposed pads on the underside of the device, Pin 16, is internally connected to ground and requires good

thermal and electrical connection to the ground of the PCB. Connect all ground pins to a low impedance ground plane.