REP015: Tuning dual-channel CDMA PA to achieve high linearity

This reference design (RD) shows how a cellular-band, CDMA linear power amplifier (PA) can be tuned for high linearity and narrowband CDMA. This RD features the MAX2264 RF power amplifier which is designed for IS-98-based CDMA, PDC , and IS-136 TDMA. Schematics and test setup are shown.

Schematic PCB

Create an audio preamplifier with an attenuator using the DS1802 push-button digital potentiometer

This application note discusses how to best bias the AC signal to within the DC supply range and how to use digital potentiometers in circuits designed for mechanical potentiometers. This understanding is crucial to effectively using the DS1802 in a pushbutton-controlled audio preamplifier circuit.

Isolated power supplies for telecom applications

Simple easy to use high side current sense amps protects power supplies as a result of irregular supply voltage caused by short-circuit conditions.

Provides +5V and +3.3V power to portable devices from USB port

A portable device using the circuit of Figure 1 derives power from the USB bus. The MAX1811 uses USB power charges a lithium-ion (Li+) battery at, USB compatible, 100mA or 500mA rates. Battery power is then stepped up with the MAX1797 to create the 5V supply rail. The 5V supply rail is then stepped down with the MAX1837 to create the 3.3V supply rail. The circuit includes a low battery shutdown to protect the Li+ battery and offers a convenient charging LED.

Driving LEDs in Battery-Powered Applications: Efficiently Control Brightness Power

White light-emitting diode (WLED) drivers provide high efficiency and brightness matching for LCD backlighting in displays. To control brightness, these drivers regulate current going into LEDs that are arranged in either serial or parallel configuration. Charge pumps drive parallel LEDs whose currents are regulated with individual regulators or simple ballast resistors. Inductor-based converters deliver current to a string of LEDs, inherently equal. Both configurations aim to drive LEDs efficiently for cell phones, PDAs, and digital still cameras.

Extending high-side current detector operating voltage to 1kV using optocouplers

This application note describes the use of a current-sense amplifier along with an optocoupler to extend the operating voltage range up to 1,000 volts for high-voltage applications. The circuit relies on the optocoupler's isolation barrier to separate the high-side and grounded side of the 1,000V system. Op amps are used to eliminate photodiode non-linearity and drift and provide an accurate output voltage proportional to the load on the 1kV supply.

High performance 1-Wire network driver

This document describes a microcontroller-based 1-Wire® master interface for reliable operation of small, medium, and large 1-Wire networks. This is accomplished using careful impedance matching, intelligent (software-controlled) active pullup, and slew-rate control. Software flow charts are included to assist the user in generating the correct 1-Wire timing for reset pulse, presence detect, write one, write zero, and read time slots using any suitable microcontroller. Scope traces illustrate the timing performance of the driver as well as transmission line effects as they appear with long cables.

CNC sine wave generator

Flexible system fault protection circuit design

When it is necessary to plug in a board into a system that is currently powered, it is critical to control the inrush current to prevent damage/system fault conditions. This application provides a simple circuit to achieve this function as well as an easy method for resetting the system and monitoring against temperature issues.

Lower cost, improved performance HDTV active reconstruction filters

In order to preserve the quality of HDTV and progressive DVD video, a bank of three (RGB/YPbPr), 5-pole reconstruction filters are used to set the 30MHz bandwidth and to provide the >40dB selectivity required by EIA770-3.

Application of 3V DAC in ±10V

Many modern systems have the majority of their electronics powered by 3.3V or lower, but must drive external loads with ±10V, a range that is still very common in industrial applications. There are digital to analog converters (DACs) available that can drive loads with ±10V swings, but there are reasons to use a 3.3V DAC and amplify the output voltage up to ±10V.

Flexible fault protection

A flexible circuit is shown that limits current or removes power in response to a command from the user or other fault-indicating signal. It accommodates manual-reset (MR), over-temperature, and protection in hot-swap applications. Residing on either the backplane/host side or the removable-card/remote-device side of the backplane connectors, it guards against start-up faults when a card or board is inserted into a rack or host with the main power supply turned on.

Step-down/inverting 3A, ±5V power supply with all-ceramic capacitor design

A MAX8538 dual synchronous buck controller supplies both +5V and -5V outputs at 3A. One controller operates as a synchronous rectified step-down (buck) converter while the second controller runs a transformer driven inverter. The circuit also features soft start and soft stop .

Designing robust, fault-tolerant motion control feedback systems

This article reviews basic servo systems and development of the fault-tolerant feedback systems for servo systems. Controller receiver circuit design, proper PC-board receiver circuit layout, and the encoder's signal cable and termination are discussed. Additionally, various types of industrial feedback encoders are presented, along with the various types of faults that can develop in a servo feedback system.

Power supplies that meet AMD K8 low-power mobile processor specifications

This application note describes a two-phase, synchronous, step-down converter that is fully compliant with the AMD® K8 Low-Power Mobile Specification. It includes details of the circuit operation, schematic, bill of materials, and a 1.2 volt, 27.3 Amp reference design with test data.

Charge battery via USB

Many devices with rechargeable batteries use USB power to recharge the batteries while they are connected. This application note describes the power available from USB and how it can be used to charge batteries, including circuits and some hints.

Active video filter

Originally, video filters were passive LC circuits surrounded by amplifiers. Smaller, more efficient designs can currently be achieved by combining the amplifier with an RC filter. Sensitivity analysis and predistortion methods developed in the 1960s have, moreover, overcome the poor performance that gave early video filters a bad reputation.

Use of MAX4090 with reconstruction filter

In most video applications, the video signal generated from the DAC requires a reconstruction filter to smooth out the signal and attenuate the sampling aliases. The MAX4090 is a direct, DC-coupled output driver, which can be used after the reconstruction filter to drive the video signal. The driving load from the video DAC can be varied from 75Ω to 300Ω. A low input impedance (< 100Ω) is required by the MAX4090 in normal operation, special care must be taken when a reconstruction filter is used in front of the MAX4090.

Provides three-channel, ±5% stable output high-efficiency PoE (Power over Ethernet) power supply

This note describes a triple-output, high efficiency, POE (Power over Ethernet) power supply with synchronous rectification. The supply has ±5% regulation an all outputs and meets all the IEEE802.3af requirements. The topology for the dc-dc converter is a continuous current flyback. The switching frequency for the primary PWM is 275 Khz.

Positive temperature coefficient compensation for PT100 temperature sensor

This article reviews the basic characteristics of common temperature sensors, describes the RTD PT100 temperature transducer, and explains a simple analog approach for linearizing and conditioning the output of that device.