AD8605/AD8606/AD8608

Rev. D | Page 15 of 20

V+

V–

4

2

3

8

1

AD8605

200mV

Figure 48. Snubber Network Configuration

TIME (10

µs/DIV)

Figure 49. Capacitive Load Drive with Snubber

Table 5 summarizes a few optimum values for capacitive loads.

Table 5.

500

100

1,000

1,000

70

1,000

2,000

60

800

An alternate technique is to insert a series resistor inside the

feedback loop at the output of the amplifier. Typically, the value

of this resistor is approximately 100 Ω. This method also

reduces overshoot and ringing but causes a reduction in the

maximum output swing.

LIGHT SENSITIVITY

The AD8605ACB (MicroCSP package option) is essentially

a silicon die with additional post fabrication dielectric and

intermetallic processing designed to contact solder bumps on

the active side of the chip. With this package type, the die is

exposed to ambient light and is subject to photoelectric effects.

Light sensitivity analysis of the AD8605ACB mounted on

standard PCB material reveals that only the input bias current

directly by high intensity light. No degradation in electrical

performance is observed due to illumination by low intensity

with increasing wavelength and intensity of incident light;

shown in Figure 50 are not normal for most applications, i.e.,

When the MicroCSP package is assembled on the board with

the bump-side of the die facing the PCB, reflected light from the

PCB surface is incident on active silicon circuit areas and results

illumination of the backside (substrate) of the AD8605ACB.

The AD8605ACB is particularly sensitive to incident light with

wavelengths in the near infrared range (NIR, 700 nm to 1000

nm). Photons in this waveband have a longer wavelength and

lower energy than photons in the visible (400 nm to 700 nm)

and near ultraviolet bands (NUV, 200 nm to 400 nm); therefore,

they can penetrate more deeply into the active silicon. Incident

light with wavelengths greater than 1100 nm has no photo-

electric effect on the AD8605ACB because silicon is trans-

parent to wave lengths in this range. The spectral content of

conventional light sources varies: sunlight has a broad spectral

range, with peak intensity in the visible band that falls off in the

NUV and NIR bands; fluorescent lamps have significant peaks

in the visible but not in the NUV or NIR bands.

Efforts have been made at a product level to reduce the effect

of ambient light; the under bump metal (UBM) has been

designed to shield the sensitive circuit areas on the active side

(bump-side) of the die. However, if an application encounters

any light sensitivity with the AD8605ACB, shielding the bump

side of the MicroCSP package with opaque material should

eliminate this effect. Shielding can be accomplished using

materials such as silica filled liquid epoxies that are used in

flip chip underfill techniques.

WAVELENGTH (nm)

3500

0

350

2500

3000

2000

500

1000

1500

450

550

650

750

850

4000

4500

5000

Figure 50. AD8605ACB Input Bias Current Response to Direct Illumination of

Varying Intensity and Wavelength

MICROCSP ASSEMBLY CONSIDERATIONS

For detailed information on MicroCSP PCB assembly and

reliability, refer to ADI Application Note AN-617 on the ADI

website www.analog.com.