ADA4356ABCZ datasheet(35/61 Pages) AD

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Data Sheet

ADA4356

analog.com

Rev. 0

35 of 61

APPLICATIONS INFORMATION

Power and Power Control

The 12mm × 6mm CSP_BGA has multiple balls designated to support the ADA4356 power requirements, with 12 balls

assigned to VCC, and one ball each to VEA, VED, and VLD. The ADA4356 has internal 0.1µF bypass capacitors on all

supplies, so additional external supply decoupling is not required.

VCC is a 3.3V supply that powers the ADA4356’s analog core and internal LDO. Connect all VCC balls (A3, C3 to C5, D3

to D5, F3 to F6, and F8) to a clean 3.3V supply.

VLD (F12) is the internal 1.8V LDO’s output. This LDO is provided as one option to power the internal ADC’s analog

and digital supplies. To enable this LDO, pull VLDEN (F7) high.

VEA (E10) and VED (E12) are the analog and digital supply balls, respectively, for the internal ADC. These balls should

be connected to a clean 1.8V supply. To power the ADC via the internal 1.8V LDO, connect VLD to both VEA and VED,

and enable VLDEN (see Figure 3).

To use an external 1.8V supply to power the internal ADC instead of the provided LDO, disable the internal LDO by

pulling VLDEN low, and connect VEA and VED to an external 1.8V supply (see Figure 4).

The ADA4356 has 32 balls assigned as GND. There is no connection between the GND balls inside the package.

Therefore, connect all GND balls to a low-impedance GND plane on the PCB.

Transimpedance Amplifier Input

The performance of the TIA inside the ADA4356 is affected by the total capacitance CS present at the INPUT ball.

Higher CS reduces TIA bandwidth and increases noise.

CS is the sum of the input photodiode capacitance (usually the largest), the TIA’s own input capacitance (2.0pF),

stray capacitance from the board layout, and any other capacitances present at INPUT (E1).

For more details on how to reduce the board layout capacitance at the TIA input, see the PCB Design Tips section.

Extending Input Current Range

The linear current input range of the ADA4356 is limited by saturation of the TIA’s output. Given the input bias at

1.65V and supply of 3.3V, assuming current is being sunk into the photodiode, the output of the TIA can swing

approximately 1.5V above the bias voltage before reaching nonlinearity and saturating.

For the lowest gain of TZ = 4.54kΩ, the output saturates at an input current of 1.5V/4.54kΩ, or about 330µA.

Similarly, TZ = 11kΩ saturates 136µA, and TZ = 133kΩ saturates at 11.3µA.

Table 9 lists recommended maximum input currents for linear TIA operation, along with the corresponding input-

referred current noise iN with no filtering or averaging and a total input capacitance of 5pF.

Table 9. Recommended Maximum Input Current for Linear TIA Operation

GAIN RANGE (kΩ)

MAXIMUM LINEAR INPUT CURRENT (µA)

INPUT REFERRED CURRENT NOISE, Cs = 5pF,

FSEL = 0

4.54

300

68nA rms

100

33nA rms

133

8.4nA rms

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