AD8191 Analog Devices, AD8191 Datasheet - Page 23

• Manufacturer Part Number: AD8191
• Description: 4:1 DVI/HDMI Switch with Equalization Preliminary Data Sheet (Rev. PrJ, 8/2006)
• Manufacturer: Analog Devices

Preliminary Technical Data
and the corresponding outputs as illustrated in Figure 12. The
AD8191 does not buffer the auxiliary signals, therefore, the
input traces, output traces, and the connection through the
AD8191 all must be considered when designing a PCB to meet
HDMI/DVI specifications. The unselected auxiliary inputs of the
AD8191 are placed into a high impedance mode when the device
is powered up. To ensure that all of the auxiliary inputs of the
AD8191 are in a high impedance mode when the device is
powered off, it is necessary to power the AMUXVCC supply as
illustrated in Figure 13.
In contrast to the auxiliary signals, the AD8191 buffers the
TMDS signals, allowing a PCB designer to layout the TMDS
inputs independently of the outputs.
POWER SUPPLIES
The AD8191 has five separate power supplies referenced to
two separate grounds. The supply/ground pairs are:
AVCC/AVEE, VTTI/AVEE, VTTO/AVEE, DVCC/DVEE,
and AMUXVCC/DVEE.
The AVCC/AVEE (3.3 V) and DVCC/DVEE (3.3 V) supplies
power the core of the AD8191. The VTTI/AVEE supply (3.3 V)
powers the input termination (see Figure 10). Similarly, the
VTTO/AVEE supply (3.3 V) powers the output termination
(see Figure 11). 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,
Rev. PrJ | Page 23 of 29
if the DDC bus is using 5 V I
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 AD8191 is powered correctly.
POWER SUPPLY BYPASSING
The AD8191 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.
In applications where the AD8191 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
AD8191. The AMUXVCC supply does not require additional
bypassing.
2
C, then AMUXVCC should be
AD8191