Digital Capacitor Overview

       By controlling the input/output states of a microcontroller, you will be able to effectively switch capacitors in and out of the circuit, for as long as the circuit requires one end of the capacitor to be connected to ground when it is needed to be used. When you set a micronctorller's tristate buffer bit to be 1, it sets the pin an input and sets high impedance as if that has an open circuit. When you set microcontroller's tristate buffer bit to be 0 and then set the data bit to 0, it sets the pin an effective ground. With this kind of system you will be able to adjust the capacitance to whatever value that you want, with capacitance ranges being dictated by your choice of capacitors and the resolution being controlled by the number of MCU pins that you have made available. This system is ideal for a great number of low power circuits.

Source = http://www.budpak.com

Operation:

       The digital-display capacitor is an energy storage device, it is designed to supplement the audio amplifiers power supply during high current demand. An example of such a demand is when music hits a low bass transient. The overall bass response of an audio system will be enhanced by using this device. It is capable of storing a large amount of energy which can be discharged very fast when needed. This makes the power cap a logical addition to the audio system as automotive batteries are not designed to deliver the current required in high power car audio installations. Another feature of the digital display capacitor is its availability to filter car AC voltage induced by the amplifier's power supply. This can otherwise cause audible noise in the sound system of the car.

Installation:

       For maximum performance, the digital power capacitor should be installed as close to your amplifier as possible. The ideal location is one that allows short wiring runs while keeping the capacitor somewhat isolated from the heat created by the amplifier system. The positive wire should be kept as short as possible and should be connected to the amplifiers battery supply cable. We recommend that a High-Performance Distribution block should be used to create a splice into this cable (as shown below). No fuses should be installed in the wire between the power capacitor and the amplifier system, but make sure, that there is an appropriate fuse at the battery in the main supply cable. The ground cable for the power capacitor should be kept as short as

possible and should be connected directly to the vehicle's chassis at the bare metal surface. Do not ground the capacitor directly to the amplifier ground terminal or ground cable. (See fig.1) The positive and negative wires to the capacitor should have the same gauge as the amplifier power wires. High performance 8 or 10AWG OFC power cables are a good choice for this application. If the digital display has a remote terminal, remember to connect it with the remote terminal of your amplifier(s) using 18 to 20 AWG primary wire. (See fig.2) REM(ON/OFF)=REMOTE CONTROL Connect the Rem terminal to the automatic antenna connector of your car radio. When turning on and off your car radio, the amplifier will now automatically switch on and off. A cable diameter of 0.5mm2 is sufficient.

Source = www.maxim-ic.com

MAX1474

Miniature Electronically Trimmable Capacitor
Industry's Smallest Digitally Programmable Capacitor

Description

The MAX1474 is a fine-line (geometry) electronically trimmable capacitor (FLECAP) programmable through a simple digital interface. There are 32 programmable capacitance values ranging from 6.4pF to 13.3pF in 0.22pF increments (see Table 1). The quartz dielectric capacitance is highly stable and exhibits a very low voltage coefficient. It has virtually no dielectric absorption and has a very low temperature drift coefficient (<33ppm/°C). The MAX1474 is programmed through two digital interface pins, which have Schmidt triggers and pulldown resistors to secure capacitance programming.

Key Features

• Tiny SC70 Package (1.1mm x 2.2mm x 2.4mm)
• High-Performance Electronically Trimmable Capacitance
• Very Simple Digital Interface
• Eliminates the Need for Mechanical Tuning
• Enabling Technology for Low-Cost Production Line Automation
• Fully Static Operation After Programming (No Switching)

Applications/Uses

• Accelerometer Measurements
• Automotive Sensors
• Cell Phones
• Force Sensors
• Humidity Sensors
• Industrial Sensor Transmitters/Transducers
• Industrial Sensor Transmitters/Transducers
• Mobile Radios
• Piezoresistive Transducers
• Temperature Sensing and Monitoring