Specifications

ELECTRICAL CONSIDERATIONS

In order to ensure proper operation of the IS4920’s electrical system, care must

be taken to ensure the following requirements are met.

Power Supply *

The IS4920 is powered from the host device via the VIN and GND pins of the ZIF

connector on the decode board. This voltage must be maintained within the

specified voltage range (see electrical specs) at the decode board. Thus, voltage

drops in the flex cable must be taken into account. In addition, this power must

be clean and heavily decoupled in order to provide a stable power source. Note,

that when the illumination LEDs are enabled, the input current will increase

considerably (see current waveforms) thus, the power supply must be able to

handle dynamic current loads.

Host Flex Cable

The host flex cable is used to carry power and data signals between the IS4920

and the host system. As indicated in the previous section, this cable should

allow for minimal voltage drop and maintain good ground connection between the

host and the IS4920 engine. In terms of grounding and voltage drop, a shorter

cable is better.

In addition to power, this cable will also carry the digital signals required for

communication. The cable design is especially important in the case of USB due

to the relative high speed of the USB signals. As such, the impedance of the

cable should match, or close as possible to, the impedance of the USB driver

(approximately 45 ohms per trace).

In addition to cable length and trace geometry, the routing of this cable also plays

a critical role in system design. This cable should be routed away from high

frequency devices as these frequencies can couple onto the flex cable and cause

potential data corruption or unwanted EMI.

Power Sequencing*

The IS4920 is powered from the VIN power signal on the ZIF connector on the

decode board. Most of the host signals (signals present on the ZIF connector)

are relative to this voltage. Not all of these signals are overvoltage tolerant thus;

care must be taken to ensure that the relationship between VIN and the host

signals are always met (see electrical characteristics).

See page 41 for additional information on electrical specifications.

See pages 41 and 47 for additional information on the engine and flex cable pinouts.