AD8197ASTZ datasheet(29/32 Pages) AD

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Preliminary Data Sheet

AD8197

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Power Supplies

The AD8197 has five separate power supplies referenced to

two separate grounds. The supply/ground pairs are:

•

AVCC/AVEE

•

VTTI/AVEE

•

VTTO/AVEE

•

DVCC/DVEE

•

AMUXVCC/DVEE

The AVCC/AVEE (3.3 V) and DVCC/DVEE (3.3 V) supplies

power the core of the AD8197. The VTTI/AVEE supply (3.3 V)

powers the input termination (see Figure 25). Similarly, the

VTTO/AVEE supply (3.3 V) powers the output termination

(see Figure 26). The AMUXVCC/DVEE supply (3.3 V to 5 V)

powers the auxiliary multiplexer core and determines the

maximum allowed voltage on the auxiliary lines. For example,

if the DDC bus is using 5 V I2C, then AMUXVCC should be

connected to +5 V relative to DVEE.

In a typical application, all pins labeled AVEE or DVEE should

be connected directly to ground. All pins labeled AVCC,

DVCC, VTTI, or VTTO should be connected to 3.3 V, and

Pin AMUXVCC tied to 5 V. The supplies can also be powered

individually, but care must be taken to ensure that each stage of

the AD8197 is powered correctly.

Power Supply Bypassing

The AD8197 requires minimal supply bypassing. When

powering the supplies individually, place a 0.01 μF capacitor

between each 3.3 V supply pin (AVCC, DVCC, VTTI, and

VTTO) and ground to filter out supply noise. Generally, bypass

capacitors should be placed near the power pins and should

connect directly to the relevant supplies (without long inter-

vening traces). For example, to improve the parasitic inductance

of the power supply decoupling capacitors, minimize the trace

length between capacitor landing pads and the vias as shown in

Figure 34.

EXTRA ADDED INDUCTANCE

RECOMMENDED

NOT RECOMMENDED

Figure 34. Recommended Pad Outline for Bypass Capacitors

In applications where the AD8197 is powered by a single 3.3 V

supply, it is recommended to use two reference supply planes

and bypass the 3.3 V reference plane to the ground reference

plane with one 220 pF, one 1000 pF, two 0.01 μF, and one 4.7 μF

capacitors. The capacitors should via down directly to the

supply planes and be placed within a few centimeters of the

AD8197. The AMUXVCC supply does not require additional

bypassing. This bypassing scheme is illustrated in Figure 35.

Figure 35. Example Placement of Power Supply Decoupling Capacitors

Around the AD8197

AD8197ASTZ Datasheet(PDF) 29 Page - Analog Devices

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