ADA4352-2ACPZ-R7 datasheet(33/47 Pages) AD

33 / 47 page

Data Sheet

ADA4352-2

analog.com

Rev 0

33 of 47

Additional voltage headroom is required due to IR drop through the switch resistance. A conservative estimate of

the maximum available linear output voltage swing considering these headroom requirements is given by the

following equation:

��,�� =

�� − ��

1 +

��

where:

VHR is the output stage headroom.

RON is the resistance of the switch inside the loop.

RFX is the gain resistor in the selected loop.

Consequently, the PGTIA maximum linear input current can be calculated by the following equation:

��,�� =

��,��

��

For instance, if VHR = 0.1 V, and RON = 19 Ω over process corners, the resulting maximum linear output voltage VO,MAX

from the above equation is 4.62 V for RF0= 315 Ω and 4.9 V for RF3= 450 kΩ. The maximum linear input current that

can be pulled from the amplifier in this case is 14.7 mA for RF0= 315 Ω and 10.9 µA for RF3= 450 kΩ. Table 8 shows

maximum linear currents and voltages for various gain settings and supply conditions. Note that the value of the

gain resistors can vary by ±11%, which is considered in the Table 8 values.

The previous example assumed no resistive load, and thus, no IR drop across the switch on the right side in Figure

73. If the PGTIA needs to drive a resistive load, there is an IR drop through the right-side switch outside the loop.

Careful consideration of these effects is essential to achieve the highest signal path accuracy with maximum

available output swing.

The ADA4352-2 also can be used in the applications with photodiodes pushing current into the PGTIA summing

node at the inverting input (−IN). The ADA4352-2 input requires 1.5 V headroom from the positive supply to

maintain specified linearity. Therefore, linear output voltage swing and linear input current are lower for this

configuration (see Table 8).

Table 8. Maximum Linear Output Currents and Voltages

RF0 = 315 Ω

RF1 = 3.5 kΩ

RF2 = 40.2 kΩ

RF3 = 450 kΩ

VS = 5 V VS = 3 V VS = 5 V VS = 3 V VS = 5 V

VS = 3 V

VS = 5 V VS = 3 V

Sensor pulls

current out

VO,MAX (V)

4.65

2.65

4.88

2.88

4.90

2.90

4.90

2.90

IPULL (mA)

13.41

7.64

1.27

0.75

0.11

0.065

0.01

0.006

Sensor

pushes

current in

VO,MAX (V)

3.22

1.28

3.38

1.39

3.40

1.40

3.40

1.40

IPUSH (mA)

9.30

3.69

0.88

0.36

0.077

0.031

0.07

0.003

ESD Protection

The ADA4352-2 is fabricated on a low-voltage CMOS process. To protect the device from electrostatic discharge

(ESD), all pins have reverse-biased ESD protection diodes, as shown in Figure 74. The ADA4352-2 also has several

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