AN9869 Authors: Jeffrey Strang, Wittlinger, Pullen, Ivars Lauzums

The Datasheet Archive - 100 Million Datasheets from 7500 Manufacturers.

AN9869 Authors: Jeffrey Strang, Wittlinger, Pullen, Ivars Lauzums

Datasheet Thumbnail

Top Searches for this datasheet

Using HCA125ACREF Amplifier Module
AN9869
Authors: Jeffrey Strang, Wittlinger, Pullen, Ivars Lauzums
Introduction
HCA125ACREF reference design delivers 125W power into load 220W into load. Since amplifier's power efficiency greater than 90%, heatsink power supply size, weight, expense greatly reduced compared conventional class designs. amplifier module part Intersil's Cool Audioprogram. Cool Audio program supports customers' efforts achieve minimum time-to-market audio products. part program, amplifier design offered after execution Licensing Agreement. Intersil provides licensees documentation package containing: circuit description, schematics, test manufacturing information, bill materials with vendors vendor part numbers, Intersil's engineering support contacts, evaluation unit.
output devices class amplifier switching frequencies well above audio band. This switching frequency modulated audio signal that when passed through low-pass filter only audio output with some residual carrier remains. carrier does effect sound quality. result this binary on/off state, power dissipation very when compared traditional amplifiers. Higher efficiency means that designers longer limited current available from wall socket. Audio engineers don't have worry much about large heatsink into small chassis. Cost weight savings power supplies realized. System weight, therefore shipping costs, reduced. switching amplifier works employing intelligent modulator drive output MOSFETS. Depending system design, various forms feedback modulation control output signal. Older switching designs have been plagued with issues reliability, distortion, background noise. Intersil CoolAudio HCA125ACREF class amplifier module solves these problems.
POWER PASS FILTER AUDIO OUTPUT
Class Amplifier Overview
Class ("switching") amplifiers radically different from conventional audio amplifiers their operation design. Although concepts embodied class amplification have been around least since 1950s, only recent advances MOSFET integrated circuit technology that have allowed feasible, full audio bandwidth designs come market.
AUDIO INPUT MODULATOR
What Class Amplification?
Traditional class amps output devices that operating their linear region. They therefore simultaneously have both current flowing through voltage dropping across their output devices. Power dissipated output devices product current flow voltage drop. Most power consumed traditional amplifiers converted directly heat instead being used produce audio output (music). Large, heavy heatsinks needed conventional high power amplifiers operate reliable temperatures. Class amplifiers much more efficient than class amplifiers because they their output MOSFETs switches instead linear devices. When voltage across MOSFETs large (MOSFET off), current small. When current large (MOSFET fully enhanced), voltage small. result minimize power dissipation MOSFETs, which turn results dramatic improvement efficiency. Most amplifier input energy delivered loudspeaker.
OUTPUT DEVICES
POWER
FIGURE OVERVIEW CLASS AMPLIFIER SYSTEM SUCH HCA125ACREF MODULE. OUTPUT MOSFETs VERY RAPIDLY TOGGLING SWITCHES INSTEAD LINEAR ELEMENTS FOUND TRADITIONAL AMPLIFIERS.
Intersil HCA125ACREF Module?
Intersil HCA125ACREF amplifier lets you, designer, reap benefits class amplification without requiring extensive design work your part. details creating distortion, EMI/RFI compliant efficient amplifier with great sound have been taken care CoolAudio engineering team. With help this document, Intersil reference design easily modified suit almost audio application.
1-888-INTERSIL 321-724-7143 Copyright Intersil Corporation 1999 Coolaudiois trademark Intersil Corporation.
Application Note 9869 Class Amplifier Output
Sonic performance demands that audio amplifiers have bandwidth greater than 20kHz. bandwidth HCA125 80kHz. special compensation technique used achieve this bandwidth still filter most carrier. However, removing carrier from output practical, some carrier reaches loudspeakers. amplitude this carrier depends upon power, generally more than 0.5VP-P power 0.5VP-P full power. carrier frequency well above audio band cannot reproduced loudspeaker. will damage speakers that rated handle power HCA125. carrier visible high-bandwidth oscilloscope small signal high frequency (>100kHz) sine wave. carrier makes difficult observe clean small square wave response HCA125. untrained eye, carrier perceived high frequency instability not. Unfortunately, most test equipment like Audio Percision (AP) test differentiate between amplifier noise carrier. carrier inaudible. noise. result, additional filtering required obtain meaningful measurements. pole 30kHz low-pass filter built into should engaged when measuring noise distortion. Similar filters required other test equipment. oscilloscope connected reading output used determine filtering adequate. carrier observed here interpreted noise. input (pin inverting input diffamp (see Figure Since modulator inverts audio signal, audio applied will maintain phase signal amplifier output. Likewise, input (pin will invert phase signal. absolute phase critical, audio should applied input, because smaller blocking capacitor used. best possible sound, blocking should polypropylene; however film capacitor also acceptable. Bipolar electrolytics used cost more important than sound quality.
Setting Amplifier Gain
HCA125ACREF module been designed have voltage gain (26dB). possible system designers modify this value. Balanced inputs provide highest possible amplifier performance. However, most systems only have provisions drive amplifier module with single-ended signal. HCA125 accommodate both types drive signals.
INPUTS
DIFFERENTIAL AMPLIFIER
GAIN AMPLIFIER
FIGURE PREAMPLIFIER STAGES INSIDE HCA125ACREF MODULE
Heat Sinking
shield supplied with HCA125 adequate heatsink operation. designed bolted additional aluminum, like back plate powered woofer chassis amplifier. Additional heatsinking required full power operation into loads. Another option cooling fan. bench testing small cooling required. cover should aluminum steel this dramatically improves thermal performance.
Single-Ended Input
Single-ended signals transmitted with wire system. wire carries signal; other ground lead. this mode operation inputs amplifier module will grounded other will carry audio. blocking must placed series with audio input line. gain amplifier adjusted using opamp second stage Figure
Gain Gain -R21
Setting Frequency Roll Phase
HCA125ACREF accept either differential single ended audio signal. Since input coupled, blocking required between preamp HCA125ACREF. Failure block potentially damage amplifier loudspeakers.
BLOCKING CAPACITOR 2.2µF 4.7µF -INPUT ROLL (-3dB) 14Hz +INPUT ROLL (-3dB) 3.5Hz
GainMod gain modulator stage. Modulator gain described below.
Balanced Inputs
lowest noise performance, balanced audio inputs recommended. identical blocking caps required, each input there chance that source material content.
MODULATOR
Application Note 9869
Input Clamp
input signal clamped avoid overdriving amplifier. This clamp clips both positive negative excursions fully adjustable changing R12.
CLAMP VOLTAGE (PEAK) 1.6V 2.6V 3.5V 4.7V 5.6V
found on-chip inside HCA125 module. recommended that each have better tolerances identical nominal values. primary reason modifying change input impedance, modifying their values will change amplifier's gain. Single-ended input impedances, with unused input grounded, determined with following relationships:
IN,Inv Input 5000 IN,NI Input 10000
clamp voltage linear approximated equation when greater than 10k: Vpeak (0.096) (R12 value 0.7V. accuracy clamp ±15%. Distortion will rise dramatically when clamps begins reduce audio input. Resistors smaller than should used. input clamp important ensures that modulator does stop switching when overdriven with large input signal.
Note that changing input impedance will affect amplifier gain reduce CMRR. best performance, adjust R14. specified optimal.
EMI/EMC Compliance Issues
HCA125ACREF module designed incorporated into larger amplifier chassis, powered speaker, other audio product. Special care must taken ensure that systems using HCA125 amplifier module follow best-practice guidelines. shield important part amplifier's system. remove Additional shielding required pass specifications. important that chassis into which HCA125 installed provide least 40dB shielding effectiveness. This means that must closed with holes greater than inch length (i.e., metal chassis with plastic front plate effective shield). addition, 1000pF leaded ceramic chassis feed through capacitors should installed points where amplified audio signals leave chassis (such positive speaker binding posts). Ground returns audio signals should connected common point chassis preferably same point that safety earth ground wire present) connected chassis. powered speakers where there metal chassis, shielded speaker wires required. amplifier should attached aluminum steel plate, 1000pF ceramic bypass (npo) needed between audio input this plate, located right plate. Twisting power supply return wires around there source recommended. capacitor across input line along with power entry module with filtering required pass conducted emission tests. Significant changes should made board layout inside shield. board been very carefully engineered minimum Electro Magnetic emission changes increase radiated conducted interference with EMI-susceptible products. However, product design engineer wishes connector other than card-edge design embodied reference amplifier, acceptable change connector style outside shielded enclosure.
Modulator Gain
frequency modulator gain determined from following relationship:
Gain
When amplifier assembled using reference part values, modulator's gain 8.70. changed modify modulator gain. Changing other resistors will effect amplifiers stability frequency response. This should attempted without guidance from cool audio engineers. best noise performance, adjust gain modulator. Adjust gain with non-inverting opamp stage. full power, output non-inverting opamp should between peak.
High Frequency Roll
form pass filter that useful trimming high-frequency response. When amplifier assembled using reference part values 2200pF 681s R19, high-frequency pole those components 106kHz. pole calculated other component values
Pole
Setting Input Impedance
Figure shows differential input amplifier associated external components R14. resistors
Application Note 9869 Start Issues
ENABLE module provides quiet startup shutdown amplifier. best keep ENABLE during power cycling prevent transient noises through loudspeakers. Capacitor sets startup delay time follows:
Startup 80000
input. example, signal, would cause surge each half period example just given.
Multiple Channel Systems (Note Caution)
Systems using multiple HCA125ACREF modules have various power supply protection fuse configurations. Designers elect fuse ±Bus supply each module independently need extreme caution. Each module must include additional blocking diode +V12FLOAT supply (see Figure Should module fail (-VBUS fuse opens), this diode 200V, 0.5W) protects other modules from failure preventing floating supply's negative reference point (-VBUS) approaching ground. multiple channel systems where only fuse used voltage protection, diode required.
+V12FLOAT DIODES ADDED -VBUS HCA125ACREF
With reference design value 1µF, startup delay time 80ms. startup delay needs increased, increase value Power sequence important with exception. -Bus energized before +Bus amplifier start. Simultaneous, power both +BUS -BUS desired recommended. Since almost supplies work this way, this minor issue that usually only observed when using bench supplies power evaluate board.
HCA125ACREF
Power Supply Specifications
Voltages greater than ±85V will activate overvoltage shutdown circuit. This will latch amplifier until power recycled. Very large overvoltage transients will damage amplifier. important operate amplifier full power close possible specified ±60VDC voltage rating. module under voltage protection that keeps from switching when voltages less than about ±45VDC. Unregulated supplies fine switching supplies. Switching supplies should operate range 100-200kHz minimize interference with amplifier. power supply capacitance determined minimum frequency operation, power speaker load impedance. Half bridge amplifiers source current into power supplies, this action causes supply voltage rise (pump up). This energy must stored power supply capacitance. stereo applications this effect minimized inverting input output channel. Most recordings mastered such that bass signals phase. inverting channel, each channel compensates other. Pump issue when amplifier bridged. Pump given load, frequency power easy calculate. Roughly load current each sinusoidal half period will tend charge power supply capacitance. load, peak current HCA125 8As. 10Hz sine wave drives full power, half period 0.05 seconds. power supply capacitance 10,000µF rail, then supply will rise during this half cycle. Fortunately, full power unregulated supplies droop more than This effect becomes serious when very frequencies applied
-VBUS HCA125ACREF -VBUS
FIGURE
Soft Clipping
When traditional class amplifiers clip, sound very harsh. poor sound many early designs this clipping. Soft clipping prevents 100% modulation. output never reaches rail, sound during clipping actually pleasant only order harmonics produced. Soft clipping engages fixed percentage voltage rails cannot modified. This feature reason Cool Audio amplifiers sound better than competition. drawback soft clipping that distortion begins rise before amplifier output reaches rail. result that cool audio 125W amplifier will sound louder better than competitor's Class 125W amplifier.
Changing Voltage
There number components amplifier that must modified change operating voltage. This recommended. need real, consult cool audio technical expertise.
Operating from Current Power Supply
possible, desired, amplifier control circuitry from positive negative current voltage power supplies instead deriving operating voltages from main power bus. regulated ±12V available, then these changes recommended: populate R36, R17, R16, R37. Instead populate
Application Note 9869
supply external positive negative supply voltages through card-edge connector pins respectively. Page HCA125ACREF schematic shows these connections. calculations presented previous section, replaces parallel combination R17. replaces parallel combination R37. ease use, suggested resistor values operation shown table below.
TABLE RESISTOR VALUES LOW-VOLTAGE SUPPLY OPTION SUPPLY VOLTS ±12V ±15V 75mW 0.10W 180/ 0.15W 330/ 0.25W 510/ 50mW 900/ 0.10W 0.10W 0.10W 160/ 0.15W 330/ 0.25W 270/ 0.10W 560/ 0.20W
Current sensing accomplished sensing voltage drop across MOSFETs. This means current limit will engage earlier MOSFETs their rDS(ON) rises. card-edge connector board supplied with evaluation amplifier modules includes that lights when current limiting active. lights power level, values need modified according equations above. These resistors also constrained over voltage under voltage points below.
Current Limit Time-out Capacitor
Capacitor controls amount time that amplifier current limit before automatically latching off. Latch-off time determined
Latchoff 80000
NOTE: edge connector supplied with does support this mode operation.
Current Limiting System
There three modes current limiting built into HCA8001 control When amplifier encounters hard short output stage (such shorted output terminals), amplifier will shut down. situations where current demanded output stage more than amplifier safely handle, determined ratio control will "throttle back" output. stays current limited mode long current limit time-out capacitor, discussed below), amplifier will shut down. circuit automatically reset shutdown latch restart amplifier presented "Enable Circuit" section this application note. control built-in current limiting circuitry protect output stage amplifier module. current limit, size that 200µA current flows through them when amplifier running chosen voltage:
200x10
listed reference Bill Materials, capacitor therefore yields latch-off time 80ms. should always least times value (R28 R29) ensure proper functioning current limiting circuitry. supplied reference design, 2.15 times value (R28 R29). this guideline followed, amplifier damaged outputs shorted.
Setting Overvoltage Under Voltage Points
over undervoltage trip points HCA8001. discussed previously, HCA8001 expects nominal 200µA current through sizing overvoltage trip voltage increased. This provides less current sensors HCA8001 when running nominal operating voltage. Setting allow only 190µA instead 200µA flow will increase overvoltage shutdown point significantly. Note that current sensors HCA8001 only accurate within 15%, further changes should take that into consideration. under voltage shutdown occurs when currents through drop below 100µA. Startup during power-on-reset event won't take place until least 150µA flows. That hysteresis allows smooth amplifier startup shutdown. MOSFETs used bridge have 200V limitation. Overvoltage must ±85V, amplifier vulnerable overvoltage transients.
VBUS VSHUNT magnitude voltage shunt voltage (7.0V this control IC), respectively. sized proportionally depending minimum load impedance which amplifier will used. ensure that current limiting enabled when driving load, follows:
0.894
other load impedances, following equality must satisfied:
ILrms2xr MOSFET -Bus
Application Note 9869 Bridging Amplifier Modules
system designer wishes increase power output system using HCA125ACREF module, possible "bridge" modules. differential amplifier that first stage each module makes such connection very easy. module connected inverting amplifier other non-inverting amplifier. taking speaker output across positive terminals both modules, output voltage delivered speaker twice that single module. Since output power function square output voltage, output power will four times that single module. 0.1% bridged modules will produce 500W into load nearly 800W into load. Figure below, depicts wiring required bridge amplifiers. Note that modules must changed slightly from reference value prevent interaction between oscillators. Since current higher, should adjusted that current limit instead Each module will dissipate twice power heatsink must re-evaluated.
DIFF (PIN AUDIO DIFF(PIN HCA125 MODULE 680pF +12V +20V
CARD EDGE CONNECTOR
1/2U1
1/2U1
SPEAKER
FIGURE OPTIONAL EXTERNAL CONTROLLER CIRCUIT SCHEMATIC TABLE EXTERNAL CONTROLLER CIRCUIT COMPONENT VALUES COMPONENT VARIABLE SPEED Open 90.9K 90.9K Open 0.1µF 1.0µF 0.1µF CA358 RFD3055M 155µA/355µA WITH HYSTERESIS 23.2k 95.3K 1.5K Open Open 0.1µF Open 0.1µF CA358 RFD3055M 350µA/285µA
DIFF (PIN DIFF(PIN HCA125 MODULE 560pF
FIGURE BRIDGING HCA125ACREF AMPLIFIER MODULES
built with factory part values, each module voltage gain 26dB.
Control Other Thermal Issues
Although HCA125 more than efficient, still does generate some waste heat. Some users will want cool amplifiers with fan. Presented below optional external control circuit that uses control (pin HCA125 card edge connector) control ways. variable speed using components from center column following table. also controlled on/off device with some temperature hysteresis using component values from right-hand column following table.
ON/OFF
Application Note 9869 ENABLE Circuit
ENABLE
There ENABLE signal HCA125 card edge connector. When amplifier operating properly, this signal weakly pulled approximately +5VDC. resistor capacitor form circuit that slows pull-up ENABLE amplifier turn-on quiet startup. shuts down fault other reason, ENABLE signal will ground potential. power-on reset will reset internal latches that have pulled ENABLE deactivated amplifier. accomplished pulling four power supplies HCA8001 (VDDA, VDDD, VEEA, VEED) below approximately 5VDC. HCA8001 powered through dropping resistors from main power busses shipped evaluation form), main power must turned power supply caps that connected amplifier must allowed drain before event will take place. ENABLE also serves control input amplifier. needs muted deactivated, pull ENABLE ground. time constant ENABLE ensures quiet startup. ensure quiet shutdown, recommended that ENABLE pulled down ground before shutting down voltage floating supplies. However, long ENABLE pulled within seconds after power busses floating supply low, turn-off transients should occur. ENABLE pins each board system should only tied together using diodes isolate different amps' ENABLE pins. Connect cathode diode each ENABLE anode each diode control circuit that pulls ENABLE low. This hookup will prevent entire amplifier from shutting down when only single channel problem, thus making troubleshooting easier amplifier's user. figure below depicts circuit that used make amplifier re-start after fault condition. MUTE-N HCA8001 connects ENABLE card edge connector through combination
VDDA UF/15 NDC7002 MUTE-N UF/15 1N4148 VDDD
NDC7002
FIGURE OPTIONAL CIRCUIT RESET AMPLIFIER ONCE FAULT LATCH BEEN
HCA8001 Pinout Description
following table describes connections HCA8001 control found HCA125ACREF amplifier module. information presented system troubleshooting. Intersil does this time provide support third-party designs using HCA8001 integrated circuit.
TABLE HCA8001 CONTROL PINOUT SIGNAL DESCRIPTION NAME VDDA ONDEL CLAMP DIFF+ DIFFDIFOUT OPIN+ OPINOPOUT AGND COMP VEEA VEED +7VDC Sawtooth Ramp Ground voltage clamp resistor Audio input signal ground Audio input signal ground Audio output signal from opamp Audio signal Ground Audio output signal from opamp Ground ±10mV Ripple Triangle sawtooth wave -7VDC -7VDC NORMAL SIGNAL DESCRIPTION Positive analog power supply shunt regulator input. time constant connected this sets dead time. Digital control signal ground. Clamp prevent overdriving Non-inverting input differential amplifier. Inverting input differential amplifier. Output from differential amplifier. Non-inverting input uncommitted opamp. Inverting input uncommitted opamp. Output from uncommitted opamp. Analog control signal ground. Integrator input. Integrator output. Negative analog power supply shunt regulator input. Negative digital power supply shunt regulator input.
Application Note 9869
TABLE HCA8001 CONTROL PINOUT SIGNAL DESCRIPTION (Continued) NAME SFCLIP CLIMIT CLTO CLPHASE PGND TEMP MUTE-N VDDD NORMAL SIGNAL Normally ground; pulses during soft clipping activity. Normally ground; pulses during current limiting activity. Normally ground; slowly charges during current limiting situation. -0.7VDC Square Wave +0.7VDC Ground Square Wave Square Wave Hi-Z (TEMP +7VDC (TEMP 2V). inversely proportional temperature. during operation; ground when shut down. +7VDC DESCRIPTION Soft clipping indicator output. Current limiting indicator output. When CLTO reaches threshold, HCA8001 shuts down current limit time-out operation. Current limit sensing input. Feedback Current limit sensing input. Power ground point. Lower gate drive signal. Upper gate drive signal. Signal used drive external fan. thermistor voltage divider circuit drives this pin. Indicates whether amplifier active; also pulled disable amplifier. Positive digital power supply shunt regulator input.
Optimizing Amplifier Various Load Impedances
Speaker impedance varies with frequency. design HCA125 optimized Special techniques employed prevent peaking high load impedances early roll impedances. amplifier stable into generic amplifiers, design already optimized. powered speakers, parameters changed optimize circuit desired response. advice CoolAudio engineer recommended before attempting this optimization.
capacitors should used only power supply pass. voltage coefficient these capacitors will introduce significant distortion. specifies capacitors that signal path. substitutions these capacitors will compromise sound should avoided.
Board Configurations
samples built with edge connector power supply connections. gold plating pins this connector cost board. gerber files HCA125 with cheaper connector available from cool audio.
Optimizing Sound Capacitor Selection
specifies 1.5µF mylar capacitance output filter, C95. sound HCA125 enhanced polypropylene. additional cost should weighed against incremental cost. specifies integrator capacitor, C17. Sound improved polypropylene, teflon polystyrene. Since this capacitor small, incremental cost small. Gerber files with footprint such available from cool audio.
References
Intersil documents available internet, site http://www.intersil.com/ Intersil AnswerFAX (321) 724-7800 Intersil Digital-5 Memo Compliance www.tecknit.com. EMI/EMC Design Information
Intersil semiconductor products manufactured, assembled tested under ISO9000 quality systems certification.
Intersil semiconductor products sold description only. Intersil Corporation reserves right make changes circuit design and/or specifications time without notice. Accordingly, reader cautioned verify that data sheets current before placing orders. Information furnished Intersil believed accurate reliable. However, responsibility assumed Intersil subsidiaries use; infringements patents other rights third parties which result from use. license granted implication otherwise under patent patent rights Intersil subsidiaries.
information regarding Intersil Corporation products, site www.intersil.com

AN9869 Authors: Jeffrey Strang, Wittlinger, Pullen, Ivars Lauzums

Top Searches for this datasheet

Other recent searches