FET Input Analog Front End

with ADC Driver

Data Sheet

ADA4350

Rev. B

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FEATURES

Low noise, low input bias current FET input amplifier

Very low input bias current: ±0.25 pA typical at 25°C

Low input voltage noise

92 nV/√Hz typical at 10 Hz at 5 V

5 nV/√Hz typical at 100 kHz at ±5 V

Gain bandwidth product: 175 MHz

Input capacitance

3 pF typical, differential mode

2 pF typical, common mode

Integrated gain switching

Sampling and feedback switch off leakage: ±0.5 pA typical

Integrated analog-to-digital converter (ADC) driver

Differential mode and single-ended mode

Adjustable output common-mode voltage

−5 V to +3.8 V typical for ±5 V supply

Wide output voltage swing: ±4.8V minimum for ±5 V supply

Linear output current: 18 mA rms typical for ±5V supply

SPI or parallel switch control of all functions

Wide operating range: 3.3 V to 12 V

Quiescent current: 8.5 mA typical (±5 V full system)

APPLICATIONS

Current to voltage (I to V) conversions

Photodiode preamplifiers

Chemical analyzers

Mass spectrometry

Molecular spectroscopy

Laser/LED receivers

Data acquisition systems

GENERAL DESCRIPTION

The ADA4350 is an analog front end for photodetectors or other

sensors whose output produces a current proportional to the

sensed parameter or voltage input applications where the system

requires the user to select between very precise gain levels to

maximize the dynamic range.

The ADA4350 integrates a FET input amplifier, a switching network,

and an ADC driver with all functions controllable via a serial

peripheral interface (SPI) or parallel control logic into a single

IC. The FET input amplifier has very low voltage noise and current

noise making it an excellent choice to work with a wide range of

photodetectors, sensors, or precision data acquisition systems.

Its switching network allows the user individual selection of up

to six different, externally configurable feedback networks; by

using external components for the feedback network, the user

can more easily match the system to their desired photodetector or

sensor capacitance. This feature also allows the use of low thermal

drift resistors, if required.

The design of the switches minimizes error sources so that they

add virtually no error in the signal path. The output driver can

be used in either single-ended or a differential mode and is

ideal for driving the input of an ADC.

The ADA4350 can operate from a single +3.3 V supply or a dual

±5 V supply, offering user flexibility when choosing the polarity of

the detector. It is available in a Pb-free, 28-lead TSSOP package and

is specified to operate over the −40°C to +85°C temperature range.

Multifunction pin names may be referenced by their relevant

function only.

FUNCTIONAL BLOCK DIAGRAM

VOUT2

ADC DRIVER

SWITCHING NETWORK

FET AMP

IN-P

VOUT1

SPI INTERFACE

IN-N

ADA4350

3

26

25

23

2

28

1

27

4

5

6

7

8

9

22

21

20

19

17

16

13

12

11

10

S0

S1

S2

S6

S7

S8

S3

S4

S5

S9

S10

S11

M1

P1

Figure 1.