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Philips Semiconductors

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TDA1562Q application note

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© Koninklijke Philips Electronics N.V. 2004. All rights reserved.

Application note

Rev. 01.02 — 05 May 2006

49 of 62

8. Driving a dual voice coil speaker

Driving a dual voice coil subwoofer with two TDA1562 amplifiers may cause a number of
fault conditions which could damage the amplifier.

The next paragraphs will explain which fault conditions may occur and give suggestions
on how the amplifiers can be protected against these fault conditions.

8.1 Pulses below substrate level at the outputs

When one of the two amplifiers is driven so hard that the lift capacitors are fully
discharged, it may occur that the other amplifier will induce voltage pulses into the output
of this amplifier, due to the cross coupling between the two loudspeaker coils.

One possible condition which has been observed is that pulses below substrate level
occur at the output of the amplifier. As soon as the voltage at the output is pulled more
than 0.7V below substrate (ground) level, a parasitic diode in the output stage (see
fig.37) will start conducting. When the current through this parasitic diode exceeds
approx.3.5A, damage to the output stage will occur.

Fig 37. One output stage of the TDA1562 with negative pulse

Parasitic

Clift

Vsupply

Pgnd

SPEAKER

0

Vpulse

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Содержание TDA1562Q

Страница 1: ...H amplifier Rev 01 02 05 May 2006 Application note Document information Info Content Keywords Car Audio Amplifier Class H High power High efficiency Abstract This document contains application information for the TDA1562Q class H amplifier ...

Страница 2: ...v 01 02 05 May 2006 2 of 62 Contact information For additional information please visit http www semiconductors philips com For sales office addresses please send an email to sales addresses www semiconductors philips com Revision history Rev Date Description 1 0 20041214 First version 1 01 20051220 First revision 1 02 20050505 Second revision ...

Страница 3: ...design of an application that will achieve the best possible performance with the device 1 2 The Class H principle Class H is basically a further development of the class G concept A class G amplifier uses two separate power supplies one with a relatively low voltage and one with a high output voltage As long as the signal is at a low level only the low supply voltage is used Only when more output...

Страница 4: ... will be driven connecting the negative terminal of the lifter capacitors C1 and C2 to ground This allows the lifter capacitors to be charged to near the supply voltage level When more output power is required transistors T7 and T8 will be shut down and transistors T5 and T6 will start conducting lifting the negative terminal of the lifter capacitors to a higher voltage The negative terminals of t...

Страница 5: ...sipation in the charging circuitry will never exceed the maximum safe level The maximum value of the charge current is approximately 5A When the power supply is lifted the lifter capacitors will provide the audio current so the power that can be delivered by the amplifier fully depends on the energy stored in the lifter capacitors Since the supply voltage of the output stage can be lifted to almos...

Страница 6: ...iconductors AN nnnnn TDA1562Q application note 12NC Koninklijke Philips Electronics N V 2004 All rights reserved Application note Rev 01 02 05 May 2006 6 of 62 1 3 Block diagram Fig 3 Block diagram of the TDA1562 ...

Страница 7: ...egative terminal of lift electrolytic capacitor 1 MODE 4 Mode select input C1 5 Positive terminal of lift electrolytic capacitor 1 PGND1 6 Power ground 1 OUT 7 Positive output DIAG 8 Diagnostic output open collector Vp1 9 Supply voltage 1 Vp2 10 Supply voltage 2 OUT 11 Negative output PGND2 12 Power ground 2 C2 13 Positive terminal of lift electrolytic capacitor 2 Vref 14 Internal reference voltag...

Страница 8: ...Philips Semiconductors AN nnnnn TDA1562Q application note 12NC Koninklijke Philips Electronics N V 2004 All rights reserved Application note Rev 01 02 05 May 2006 8 of 62 1 5 Quick reference data ...

Страница 9: ...undefined state when the mode select voltage is increased or decreased very slowly With the maximum and minimum values for the different thresholds the mode select voltage ranges where the device is guaranteed to be in a certain condition can be determined The device is guaranteed in stand by when the mode select voltage is below 1V When the mode select voltage is between 2V and 3 3V the device is...

Страница 10: ...voltages controls the Status I O voltage of all devices For example as long as one of the devices is muted all other devices will stay muted too This way all devices will switch from mute to operating at exactly the same moment When the status I O pin is not used it should be left floating 2 3 The diagnostic pin The diagnostic pin pin 8 is an open collector output pin which should be connected to ...

Страница 11: ...ps between the voltages at the three pins Figure 4 contains all information about the relationship between the status I O pin and the mode select pin When the amplifier is switched on by means of the mode select voltage the reference voltage Vref at pin 14 will rise gradually to Vp 2 When the status I O pin is used as an output the voltage at this pin will remain low until Vref reaches the thresho...

Страница 12: ...When a load was detected during switching on the diagnostic pin will stay high while the device is muted During clipping the diagnostic output will be low as long as the output signal is clipping so the width and frequency of the pulses at the diagnostic pin depend on the signal frequency and how far the amplifier is driven into clipping When one of the outputs is shorted either to ground or to th...

Страница 13: ...its when the status I O pin is open When the status I O pin is forced high the class H circuits will not be disabled and the amplifier will continue working in class H mode This type of operation is risky since the class H circuits will now be stressed more severely than they were meant to be When the status I O pin is left floating or it is used as a diagnostic output the voltage at the status I ...

Страница 14: ...puts A symmetrical input has the advantage that common mode interference that is picked up in the input lines is effectively suppressed Especially in an automotive application where there is much interference by external sources the suppression of noise is very important 3 Switch on off behavior When the amplifier is switched on it should be kept in the mute condition long enough to ensure that th...

Страница 15: ...to mute Mute Mute to operating Mode select pin Low 0V 0V to 3V 3V for 200ms dependent on input capacitors Increase voltage gradually from 3V to above 4 5V after Status I O is released Status I O pin Low 0V Low 0V Low 0V Release floating When the amplifier is switched off it should be muted as fast as possible in order to minimize the risk of switching noise from circuits in front of the amplifier ...

Страница 16: ... 2 after the supply voltage has returned to its normal value When the amplifier is in stand by mode the internal circuitry which prevents the negative terminals being pulled below substrate level will not work So despite the amplifier being switched off this may still cause plops during engine start In this condition plops can be prevented by connecting Schottky diodes between the negative termina...

Страница 17: ...y damage the device Examples of double faults are Short circuit of one of the outputs to ground while the power ground is disconnected also known as loss of ground condition Short circuit of one of the outputs to the supply while the supply is disconnected During operation at supply voltages higher than 16V the charge circuits for the lifter capacitors and the voltage lifting circuits will heat up...

Страница 18: ... device is connected to ground However when either pin 5 or pin 13 is shorted to an adjacent pin the charge remaining in the lifter capacitors may cause damage When in extreme conditions the supply voltage drops rapidly and this voltage drop exceeds 1V the negative terminals of the lifter capacitors will be pulled down to voltages below the substrate level When this occurs the amplifier can be tem...

Страница 19: ...xception of the components connected to pins 3 and 5 and 13 and 15 it is the schematic of any class AB BTL amplifier with a symmetrical input In this paragraph the different components in the application will be discussed Rload C lift C lift Csup2 Csup1 Vsupply P Gnd 1k diag led 100k 1k 10k P gnd Cin 2 Cin 1 22uF P gnd M S pin Input signal Cref Sig gnd 17 2 15 13 14 3 8 4 1 7 10 9 5 12 6 11 P Gnd ...

Страница 20: ...ilm capacitors for this purpose since any DC leakage at the inputs will result in a DC offset at the outputs Electrolytic capacitors usually have a relatively high DC leakage current so they should not be used as input capacitors As already mentioned the TDA1562 has a symmetrical input In order to achieve the highest possible suppression of common mode interference the two input capacitors should ...

Страница 21: ...g on of the amplifier it is used as a timing device A recommended value for this capacitor is 10µF Using a smaller capacitor than this may result in worse supply voltage ripple rejection and possibly malfunction of the load detection circuit during start up The supply decoupling capacitors Csup1 and Csup2 Csup1 is the supply decoupling electrolytic capacitor This capacitor acts as a buffer in orde...

Страница 22: ...700µF C Low ESR electrolytic capacitors 10000µF Fig 10 The influence of ESR and capacitance of the lift capacitors on the output power When the ESR is high the power losses in the capacitors will be high too resulting in a reduction of output power In fig 10 it is visible that using Low ESR capacitors instead of standard multi purpose electrolytics will result in a considerably higher output power...

Страница 23: ...t when the diagnostic is activated the LED will light up The mode select circuit The mode select pin pin 4 is connected to the supply through a switch and an RC circuit which ensures that the voltage at the mode select pin rises gradually ensuring a plop free switch on The EMI filtering capacitors C emi and Boucherot Zobel networks In many applications small capacitors 1 10nF to ground are are pla...

Страница 24: ...igher than 5V the charge current will increase to it s maximum value of 5A This has been done to limit the dissipation and heat production in the charge circuitry to prevent overheating of the charge circuits This figure also shows the limitations of the charge circuit When the lift capacitors are fully discharged it will take some time in the case of 10000µF capacitors approx 60ms for the voltage...

Страница 25: ...e sine wave is not clipping yet The voltage across the lift capacitor is shown for the positive output so during the positive half of the sinewave Vlift drops and it is visible that current is drawn from the lift capacitor Icharge going negative During the negative half of the sinewave the lift capacitor is recharged Fig 12 Charge current output signal and lift capacitor voltage at Po 40W f 30Hz V...

Страница 26: ...le the output signal is clipping It is visible now that the charge current is at it s maximum value almost all the time during the recharging of the lift capacitor The lift capacitor voltage almost drops to 5V In this situation the charge circuit is only just able to maintain the charge in the lift capacitor Fig 14 Charge current output signal and lift capacitor voltage while lift capacitor is ful...

Страница 27: ... been discharged Condition 1 shows that it is important that the amount of energy which can be stored in the lift capacitors should be sufficient When the amplifier should mainly drive low frequency signals the lift capacitors should be large enough to store sufficient energy for the expected signal For frequencies down to 20Hz a capacitance of 22000µF is recommended Condition 2 shows that driving...

Страница 28: ...is 4Ω When a lower impedance than 3 2Ω is connected to the TDA1562 the current protection will activate frequently causing severe distortion Also no guarantee can be given for the long term reliability of the device since reliability guarantees are given for operation with the nominal load impedance Prolonged operation with a lower load impedance may eventually result in overstress of parts 5 4 Re...

Страница 29: ...capacitor Lower value Worse SVRR Csup2 100nF SMD NPO or X7R material HF decoupling of the supply Lower value possibly oscillations in the supply Cref 10µF 16V Electrolytic capacitor Decoupling of internal reference voltage timing for load detection circuit Lower value Worse SVRR and possibly malfunction of load detection circuit Clift 4700µF 16V Electrolytic capacitor Supply lift capacitors Lower ...

Страница 30: ... to the PCB Star grounding It must be prevented that high supply currents will run through signal ground or reference ground tracks since ripple on these tracks will cause unnecessary distortion The high frequency decoupling capacitor 100 nF should be mounted as close as possible to the supply pins Keep the tracks of the and inputs and the signal ground pin as close together as possible this way t...

Страница 31: ...pplication note 12NC Koninklijke Philips Electronics N V 2004 All rights reserved Application note Rev 01 02 05 May 2006 31 of 62 a Bottom side component view b Bottom side copper layer Fig 16 Bottom view of the TDA1562Q PCB as seen from above ...

Страница 32: ...t would be at approximately 10W The power dissipation will then be approximately 10W An 80W amplifier will have a worst case power dissipation with sine wave signal of approximately 40W A rule of thumb is that the power dissipation with a music signal is 50 of the worst case power dissipation measured with a sine wave signal For an 80W amplifier this would then be approximately 20W These rules onl...

Страница 33: ...e TDA1562Q and the normal class AB amplifier The curve for the class AB amplifier is the characteristic curve for such a device The power dissipation rises steeply at low output powers and slowly reduces after the maximum power dissipation has been reached at approximately 33W For the TDA1562Q the situation is different Up to output power levels of 11W the amplifier behaves like a single channel B...

Страница 34: ...late an appropriate heatsink for the amplifier it is necessary to know the power dissipation As already mentioned for class AB amplifiers this is usually done by measuring the worst case power dissipation with a sine wave signal and then taking 50 of that value as a value for the power dissipation with music From fig 18 we can see that in this case the worst case power dissipation for the class AB...

Страница 35: ...will be used as criterion for the calculations a TDA1562Q b Class AB amplifier Fig 20 Thermal equivalent circuits for calculation of the external heatsink For this calculation we have assumed the thermal resistance from junction to case Rth j c for both devices to be 0 5K W and thermal resistance from the case to the external heatsink Rth c hs to be 0 1K W thermal compound used When we assume that...

Страница 36: ...size as is illustrated in figure 21 Figure 21 shows a standard heatsink Fischer Elektronik SK178 which can be used for cooling an amplifier To achieve a thermal resistance of 5 8K W the heatsink needs to have a length of approximately 50mm To achieve a thermal resistance of 4 25K W the length of the heatsink should be approximately 100mm so the class AB amplifier would need a heatsink twice the si...

Страница 37: ...utput will no longer be symmetrical The following figures show that the sine wave is expanded upwards so that the top half of the sine wave will become sharper than the bottom half of the sine wave However when the signal is measured across the load between the two outputs The distortion will be compensated and the signal between the two outputs will still be a sine wave Fig 22 Output signals befo...

Страница 38: ...ng as is illustrated in figs 23 and 24 Fig 23 Output signals at low level lifting f 1kHz Fig 24 Output signals at high lifting level f 1kHz Figure 23 shows the shape of the signals at both outputs when the amplifier just starts lifting the supply It is visible that the tops of the sine waves are becoming slightly sharper and it is also visible that the bottom part of the sinewaves starts flattenin...

Страница 39: ...low signal frequencies the tops of a clipping signal will slope down fig 26 This sloping down of the signal is caused by the energy being drained from the lift capacitors As long as not too much energy is drained from the lift capacitors the voltage will be sustained At low signal frequencies much energy is drained from the lift capacitors which will cause the voltage across the lift capacitors to...

Страница 40: ... AN nnnnn TDA1562Q application note 12NC Koninklijke Philips Electronics N V 2004 All rights reserved Application note Rev 01 02 05 May 2006 40 of 62 Fig 26 Waveforms during clipping at low frequencies 40Hz OUT 1 OUT 2 Vload ...

Страница 41: ...ted thus lifting the voltage at the positive terminal Figure 27 shows the waveforms at the and terminals of one of the lift capacitors during lifting The lowest voltage level at the terminal is slightly above 0V which is the saturation voltage of transistors T7 and T8 see fig 1 The lowest voltage level at the terminal will be approximately one diode forward voltage below the supply voltage due to ...

Страница 42: ...rms when the lift capacitors are drained f 40Hz 8200µF capacitors Figures 30 to 32 show the currents in the terminal of the lift capacitors In figure 30 the amplifier is lifting moderately at a signal frequency of 1kHz The charging of the capacitor takes place while the other channel is lifting In this case at an output power of 40W the charge current I charge does not exceed 2 5A As soon as the o...

Страница 43: ...Electronics N V 2004 All rights reserved Application note Rev 01 02 05 May 2006 43 of 62 Fig 30 Current waveform during lifting Po 40W f 1kHz 1 Fig 31 Current waveform during clipping Po 55W f 1kHz 0V Vp 0A 5A 5A I charge I audio Clift Clift Clift Clift I charge I audio 5A 5A 0A Vp 0V ...

Страница 44: ...ned Fig 32 Current waveform during hard clipping At an output level of 75W 1kHz the charge current for the lift capacitors reaches the maximum value of 5A As long as sufficient energy can be stored in the lift capacitors the amplifier will be able to sustain a continuous sine wave signal At low frequencies the lift capacitors must deliver much more energy than at higher frequencies so at low frequ...

Страница 45: ...ected with a properly designed application A f 1kHz B f 100Hz C f 10kHz Fig 33 Output power vs THD at a supply voltage of 14 4V with a 4Ω load The Po vs THD curves show the performance of the TDA1562 at frequencies of 100Hz 1kHz and 10kHz The bump at 10W output powers shows the level at which the lifting circuitry becomes active The notch in the 100Hz and 1kHz curves is caused by internal circuitr...

Страница 46: ...1562 behaves like any class AB BTL amplifier The THD noise increases with the signal frequency as a result of crossover distortion Below 10W most of the THD noise figures are caused by noise and crossover distortion Since these are constant numbers the THD noise ratio decreases as the output power increases Above 10W artifacts from the lifter circuitry are responsible for increased THD numbers THD...

Страница 47: ...C Koninklijke Philips Electronics N V 2004 All rights reserved Application note Rev 01 02 05 May 2006 47 of 62 A THD 10 B THD 0 5 Fig 35 Pout vs Vp at constant THD levels Pout vs Vp 10 20 30 40 50 60 70 80 5 10 15 20 Vp V Po W A B f 1kHz Rl 4ohms Clift 8200uF 16V ...

Страница 48: ...on note 12NC Koninklijke Philips Electronics N V 2004 All rights reserved Application note Rev 01 02 05 May 2006 48 of 62 Fig 36 Supply voltage ripple rejection SVRR vs Freq 80 70 60 50 40 0 1 1 10 F kHz SVRR dB Vp 14 4V Rload 4ohms Rin 0 Vripple 2Vp p ...

Страница 49: ...ts When one of the two amplifiers is driven so hard that the lift capacitors are fully discharged it may occur that the other amplifier will induce voltage pulses into the output of this amplifier due to the cross coupling between the two loudspeaker coils One possible condition which has been observed is that pulses below substrate level occur at the output of the amplifier As soon as the voltage...

Страница 50: ... visible in fig 38 A and B The energy contained in the negative pulse is an important factor As long as the current in the parasitic diode doesn t flow for more than 50µs the current may be much higher a No damage to TDA1562 b Damage to TDA1562 Fig 38 Current through the parasitic diode To protect the parasitic diode from too high currents a schottky diode can be connected externally between the o...

Страница 51: ...y diode The schottky diode will conduct most of the current thus protecting the parasitic diode Fig 40 shows the current distribution between the schottky diode and the parasitic diode The yellow trace shows the current through the parasitic diode at 5A division and the magenta trace shows the current through the schottky diode at 10A division Schottky ROHM RSX301L Parasitic Clift Vsupply Pgnd SPE...

Страница 52: ...p was tested for 4 hours with a pulse signal with a pulse duration of 50ms and a duty cycle of 50 After the test the device was still undamaged The conclusion of this test is that a 3A schottky diode should be sufficient to protect the device against negative voltage pulses 8 2 Positive voltage pulses at the outputs Beside negative voltage pulses at the outputs it is also possible that positive pu...

Страница 53: ... voltage pulses at the outputs can be done by connecting a diode from each output to the supply rail In the TDA1562 this method cannot be applied because during normal operation the output voltage can exceed the supply voltage Since in most cases the terminal of the lift capacitors is the connection with the highest voltage in the application the most effective way to protect the output against po...

Страница 54: ...v 01 02 05 May 2006 54 of 62 Finally adding a 50mΩ resistor between the output and the diode gave some more improvement The total circuitry needed for optimum reliability in dual voice coil applications is shown in fig 43 1 Fig 42 Protection against positive pulses at the output Parasitic Clift Vsupply Pgnd SPEAKER 1N4007 Schottky ROHM RSX301L ...

Страница 55: ...ed in a tight feedback loop that instantaneously adjusts the audio input level or Hard Limits the maximum output volume The Hard Limiter will slow the THD from growing and also will prevent the Lifting Capacitors from ever fully discharging If one of the lifting capacitors starts to ratchet down in voltage due to peculiar music content the THD will fire the clip detector and hold the audio input l...

Страница 56: ... reference voltage used by the audio op amp that inputs the audio signal into the TDA1562 The Source of the FET is connected to the Input of the audio op amp and therefore is DC biased up to the reference voltage 4V Since the FET is an N channel depletion mode FET it is always fully ON and needs to be biased OFF By raising the Source pin to the reference voltage 4V and referencing the GATE through...

Страница 57: ...h determines it s recovery time 8 3 2 OVP circuit Fig 45 OVP circuit When the battery voltage Vp reaches a level of 15 1V then Q3 will conduct and connects the status I O pin 16 of the TDA1562 via diode D2 to zener diode D5 This results in a voltage of about 3 2V on the status I O pin which means that the TDA1562 is forced into class AB mode preventing the amplifier of going into class H mode The ...

Страница 58: ...milli Henry s If these kind of subwoofers are connected to the TDA1562 one should use an extra external circuit to get a proper load detection at the DIAG pin This external circuit creates a short time correction between the outputs of the amplifier during enabling of the mode pin so when the amplifier is starting up It is only active for a very short time so no negative side effects occur during ...

Страница 59: ...ers Now if the voltage swing on the output exceeds the level of 100mV the SR flip flop is reset and a no load detect situation occurs no mather if a load is connected to the outputs or not unless the voltage crosses 30mV after the positive voltage swing Then the SR flip flop is set again It is seen that a voltage swing of 100mV can occur on the output when a large dual voice coil subwoofer is conn...

Страница 60: ...ts an amplifier equipped with the TDA1562 can deliver high power and very good performance with a high reliability The class H configuration enables customers to build a high power car amplifier without the need to use DC DC converters to increase the supply voltage Thanks to the high efficiency of the amplifier the heatsink needed for such an amplifier can be considerably smaller that that of a c...

Страница 61: ...nd overstress conditions 16 5 Application description 18 5 1 Application schematic 18 5 2 Dimensioning of the Class H application 23 5 3 Minimum load impedance 28 5 4 Recommendations 28 5 5 Used components 29 5 6 PCB lay out 30 5 7 Thermal behavior 32 5 7 1 Power dissipation 32 5 7 2 Power dissipation curves 33 5 7 3 Heatsink calculation 35 6 Typical waveforms 37 7 Measurement curves 45 8 Driving ...

Страница 62: ...ation presented in this document does not form part of any quotation or contract is believed to be accurate and reliable and may be changed without notice No liability will be accepted by the publisher for any consequence of its use Publication thereof does not convey nor imply any license under patent or other industrial or intellectual property rights Date of release 5 May 2006 Document order nu...

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