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rev. 0.1 11/12 copyright ? 2012 by silicon laboratories AN726 AN726 u tility c lass -d t ool s tick u ser ? s g uide 1. introduction class-d is a switching power amplifier architecture that uses high-frequen cy pulse-width modulation (pwm) to generate the output waveform. the transistors are fully on or fully off, which means this architecture can reach very high efficiency levels, resulting in significant power savings . however, the translation from the input signal to pwm and the pwm itself can cause more distortion on the outp ut than other amplifier arch itectures. figure 1 shows a very basic class-d signal diagram. figure 1. class-d power amplifier signal diagram because the class-d amplifier transistors are fully on or fully off, the transistors lose less energy in the form of heat. this architecture, therefore, lends itself to small, cheap mosfets. th e class-d amplifier can be implemented in either analog or digital form. an analog class-d amplifier is non-trivial and typically consists of a comparator, triangle waveform generator, and several blocks to condit ion the input signal before transferring to the output mosfets. a digital class-d amplifie r requires the following: ?? pwm output (switching) frequency 10x+ faster than the highest input frequency to adequately reconstruct the input signal ?? high-resolution control of the pwm pulse width to reduce output qu antization distortion ?? method for sampling or receiving the input waveform ?? fast core for digital processing and manipulation of data ?? pins capable of driving the amplified signal since the silicon labs precision32? sim3u1xx/sim3c1xx 32-bit mcus have peripherals and fe atures capable of meeting all of these requir ements, these mcus are uniquely suited to a utility class-d power am plifier application without using many external components by directly driving the speaker using the high drive i/o. in addition to providing a development platform for class- d applications, the class-d t oolstick board serves as a lower-cost, general-purpose development platform for the sim3u1xx usb mcus. 2. relevant documents this document provides a hardware and software overvi ew for the class-d toolstick. additional documentation on the precision32 tools and mcus can be found on the silicon labs website: www.silabs.com/32bit-appnotes , www.silabs.com/32bit-software , and www.silabs.com/32bit-mcu .
AN726 2 rev. 0.1 3. using the demo the speaker in the kit connects to the jp1 1x2 header next to the green terminal block (j4). two alternate connection methods are available to support a variety of speakers: the j4 terminal block, and an output audio jack (j5). a screwdriver can be used to attach the speaker(s) of choice to j4, and each speaker should have two leads: positive (red) and negative (black). the audio jack output connects both channels of the speaker to r+ and r?, so it is not true mono. the class-d toolstick bo ard is intended for use with stereo systems. the class-d toolstick can be powered from either the debug (j3) or device (j2) usb mi ni connectors as shown in figure 2. the green power led (ds7) will light up when the board is powe red. do not touch the capacitive sensing slider during power-on, as this is when the board calibrates the slider. once the board is ready for use, the blue led (ds1) will turn on. figure 2. powering the board change the volume of the output at any time by pressing firmly and sliding on the capacitive sensing slider (cs1). the blue leds above the slider indicate the volume level. the mode button on the slider can be used to change the mode of the board: ?? mode 1 (blue led ds1): stereo jack input mode ?? mode 2 (blue led ds2): usb input/output mode ?? mode 3 (blue led ds3): play prerecorded flash mode ?? mode 4 (blue led ds4): play/record flash mode
AN726 rev. 0.1 3 3.1. stereo jack input mode the default mode of the class-d toolstick is stereo jack input mode, indicated by blue led ds1. to play sound in this mode, connect any input source (mp3 player, phone, etc.) to the j1 stereo jack. the volume level of the input device should be as high as possible without causing saturation, which the red led (ds8) indicates. 3.2. usb input/output mode in usb mode, the board plays sound from the usb host pc or records sound from the board microphone (mk1) and sends it up to the pc. to use the board in this mo de, connect the device usb connector (j2) to the host pc and press the mode button until blue led ds2 turns on. the board should appear as the utility class-d toolstick in device manager once it?s properly enumerated as a usb audio device. to select the class-d audio device as the playback or recording source in windows 7, right-click on the volume mixer icon in the system tray and select either playback devices or recording devices . in the playback tab of the dialog, select the utility class-d toolstick and press the set default button as shown in figure 3. the settings for the device can be selected using the properties button in this tab. figure 3. configuring the usb utility class-d toolstick as the playback or recording device in the recording tab of the dialog, select the utility class-d toolstick microphone and press the set default button. this will open an interface to the microphone and will display t he recorded input volume to the right of the device name. if this volume is not registering sounds, press the properties button to configure the microphone volume. once configured, any program on the pc should output to the class-d toolstick devic e. ensure that the volume levels in the program and volume mixer are set to appropriat e levels. if the device volume settings are not affecting the class-d board, click the expansion button below the speakers icon and select the speakers (utility class-d toolstick) as shown in figure 4. when recording, the red led (ds8) indicates when the microphone input saturates. note: as long as a recording interface is open (i.e. volume mixe r recording devices dialog or a recording program open), the class-d toolstick prevents the user from switching the oper ation mode. this is due to potential synchronization issues when switching between different modes and sending data up to the host pc. to switch the mode, close the volume mixer or the re cording program.
AN726 4 rev. 0.1 figure 4. selecting the usb utility class-d toolstick in volume mixer 3.3. play prer ecorded flash mode in prerecorded flash mode, the class-d toolstick will output ~7 seconds of sound from an array saved to flash. enter the mode by pressing the mode button until blue led ds3 turns on. press the play slider button on the board to start the waveform, and press the play slider button again to stop it before it completes. the blue led (ds6 ) will indicate when a play operation is in progress. this mode provides an alternative sound input source when no sources are available and provides an indication of what sound effects would sound like. 3.4. play/record flash mode the play/record flash mode records compressed sound to th e flash of the mcu. enter the mode by pressing the mode button until blue led ds4 turns on. press the rec slider button to start recording, and press the rec slider button again to stop recording. the blue led (ds5) will indicate when a record op eration is in progress. multiple recordings will a ppend to the full recording in flash. once the flash is full, the mcu will indicate no additional reco rdings can be made by turning on and immediately turning off the blue record led. to record additional sound, press the erase slider button to erase the flash. the blue ds5 led will turn on while the erase operation is in progress. wh en recording, the red led (ds8) indicates when the microphone input saturates. press the play slider button on the board to start the waveform, and press the play slider button again to stop it before it completes. the blue led (ds6) will indicate when a play operation is in progress.
AN726 rev. 0.1 5 4. class-d toolstick hardware overview the class-d toolstick board enables class-d applicati on development on the sim3u164 mcu. in addition to providing a development platform for class-d applications, the class-d toolstick board serves as a low-cost, general-purpose development platform for the sim3u1xx usb mcus. figure 5 shows the utility class-d toolstick board feat ures. full schematics for th e board can be found in 7. "schematics?" on page 22 figure 5. utility class-d toolstick board features 4.1. push-button switches and leds (s1-2, ds1-ds8) the class-d toolstick board has two push-button switches and eight leds summarized in table 1. the switches connect to pb0.6 (s1) and pb0.7 (s2) and are currently unused in the class-d firmware. the switches are normally open and pull the pin voltage to ground when pressed. port pins pb0.1, pb0.2, pb0.4, pb0.5, pb0.10, and pb0 .11 connect to six blue le ds (ds1-ds6). pin pb3.3 connects to the red led (ds8). the green led, power (ds7), turns on when usb power is applied to the board from either usb connector. the leds connec t to vio through a current limiting resistor. table 1. class-d toolstick switches and leds gpio pin switch or led pb0.6 push-button switch (s1) pb0.7 push-button switch (s2) pb0.1 blue led (ds1) pb0.2 blue led (ds2) pb0.4 blue led (ds3) toolstick debug adapter audio inputs stereo jack and microphone gain/bias capacitive sensing slider and led user interface class-d output filters and speaker header testpoint pin access for general-purpose development optional high power components
AN726 6 rev. 0.1 4.2. class-d output ne twork, terminal (j4), he ader (jp1), and jack (j5) the four high drive i/o pins on the sim3u164 40-pin qf n package connect to the j4 terminals after going through the class-d output network, allowing these pins to direct ly drive the speaker(s). the jp1 1x2 header connects to r+ and r? to interface with the kit speaker. the output jack (j5) connects r+ and r? to both channels and does not provide true mono sound. to create a mono output, connect the l_in and r_in test points together in the stereo jack and microphone gain/bias section of the board. the output network consists of a ferrite bead, lc, and gr ounding caps for each pair of channels, r+/r? and l+/l?. these components should be tuned for the specific app lication speaker as discussed in 6. "tuning the class-d output network?" on page 18. 4.3. toolstick debug adapter (u3) the class-d toolstick board features a debug adapt er via the mini-b usb connector (j3) labeled debug . this debug adapter can be used with the precision32 (1.0.2 and higher) and arm uvision ides (4.54 and higher). when using an older version of the ides, the debug ada pter dlls in the ide directories must be replaced to support the toolstick debug adapter. contact technical support (?contact information? section) for more information. 4.4. usb connection options (j2) the class-d toolstick board features a usb connecti on via the mini-b usb connector (j2) labeled device . this usb connector provides the usb audio features of the board and facilitates ge neral-purpose us b development on the sim3u164 device. pb0.5 blue led (ds4) pb0.10 blue led (ds5) pb0.11 blue led (ds6) pb3.3 red led (ds8) ? green power led (ds7) table 2. terminal block pin descriptions (j4) pin i/o 1 pb4.0 / r+ 2 pb4.1 / r? 3 pb4.2 / l+ 4 pb4.3 / l? table 1. class-d toolstick switches and leds (continued) gpio pin switch or led
AN726 rev. 0.1 7 4.5. capacitive sensing buttons and slider (cs1) four capacitive sensing buttons and one slider comprised of six segments are included on the board to provide the user interface. six gpio pins are connected to the slider as shown in table 3. the gpio pins are connected to the slider in descending order from the location labeled mode to the location labeled play on the board. the test points above the slider fa cilitate adding grounde d or shrouded c onnectors to meas ure the capacitive sensing pins. 4.6. analog audio inputs (j1 and mk1) the stereo jack on the board (j1) allows the board to measure stereo inputs from an input source. the microphone (mk1) enables the device to measure voice data directly. these signals are conditioned by a bias and gain circuit provided by a quad op-amp ic (u1), resistors, and capaci tors to a range appropriate for the sim3u164 saradc modules. table 3. capacitive sensing gpio connections location pin mode pb1.1 ? pb1.0 erase pb0.15 ? pb0.14 rec pb0.13 play pb0.12
AN726 8 rev. 0.1 5. class-d toolstick firmware overview 5.1. system overview the system is configured for 48 mhz ahb and apb to maximize the output resolu tion of the epca. in all modes, the epca0 operates continuously and out puts the pwm signal to the speaker. this waveform generation is never interrupted. the saradc modules operate in 12-bit mode at the maximum sar clock frequency in order to complete conversions as quickly as possible . the usb internal oscillator provides the 48 mhz system clock, which in conjunction with the pll0 module, provides the precise timing required in the different modes to recreate the audio waveforms. 5.1.1. sim3u164 module usage the modules used by the class-d toolstick firmware are: ?? saradc0 : measures the right stereo jack channel and the microphone input ?? saradc1 : measures the left stereo jack channel ?? vref0 : provides the 2.4 v reference for the adcs ?? flashctrl0 : writes recorded micr ophone data to flash ?? epca0 : generates class-d pwm waveforms (four channels) ?? capsense0 : provides button and slider user interface ?? timer0 : generates ~20 ms capacitive sensing scan timer ?? timer1 : generates mode timing (e.g. 48 khz in usb) and handles led pwm updates ?? pca0 and crossbar : generates led pwm waveforms for the six blue leds (one channel) ?? usb0 : provides the usb audio input/output interface ?? pll0 : provides the precise timing for the system and spectrum spreading to reduce emissions appbuilder generates the init ialization code for all modules except for the usb0 module. this appbuilder project is included in the utility class-d toolstick software package. note: exporting code from version 1.1.1 of appbui lder will overwrite the project file asso ciated with the cla ss-d toolstick firm- ware. this project file includes manual changes to include the si32library that will be removed when appbuilder exports the code. a saved version of the project file ( save.project ) is available in the class-d toolstick firmware package in case this project file is overwritten. to rest ore the project file, simp ly copy the contents of save.project to the .project file. 5.1.2. firmware organization the class-d toolstick code follows the appbuilder code organization scheme. the application-specific code for each peripheral is in the src folder in the my- files, and the generated files from appbuilder are in a generated folder below the src folder. additional application-specific files are in the src folder with names associated with the functions in the file, lik e mulaw or led_control. ?? class_d : includes the main class-d loop and any control not handled by the timer1l interrupt handler. ?? led_control : blue and red led update functions; handles the shifting of the pca channel on the crossbar. ?? mulaw : implements the law companding algorithms. ?? myapplication : implements the system in itialization code before pa ssing control to class_d. ?? mybuildoptions : required for si32library. ?? mydataplanein : si32library callback functions for the usb in transactions (recording). ?? mydataplaneout : si32library callback functions for the usb out transactions (playing). ?? myusbaudiodevice : usb audio descriptors and audio-specific si32library function calls. ?? myusb0 : non-audio usb si32library func tions calls for the application. ?? pre_recorded_array : law compressed prerecorded flash data. ?? volume : handles the volume decoding and control from either the usb interface or the capacitive sensing slider. ?? my- files : implement application code associated with the particular peripheral. ?? g- files : appbuilder generated initialization code associated with the particular peripheral.
AN726 rev. 0.1 9 5.2. algorithms the class-d toolstick uses two algorithms to manipulate data: exponentially weighted moving average (ewma) and law. this section also describes remainder-weighted dithering as an optional algorithm. 5.2.1. exponentially weighted moving average (ewma) the ewma is a form of exponential aver aging that creates a low-pa ss filter. this filter performs noise shaping to help move the quantization noise out of the audible range. the class-d toolstick firmware uses this form of averaging to filter the adc results. the ewma takes the form: in this equation, y(n) is the current out put, y(n-1) is the previous output, x(n) is the current input sample, and m is the weight of the average. the weight determines how heavy the average of the ewma is. the smaller weights (m = 1, 2) use more of the new sample and react more quickly to dramatic changes in the input. larger weights (m = 4, 5) use more of the previous output and provide more smoothing. the ewma has several advantages over other forms of averaging: ?? quick to calculate (two shifts, an addition, and a subtraction) ?? only saving the previous value ?? contains history from every sample in time, which wo uld take lots of memory in a traditional average ?? the weight can be dynamically adjusted easily in firmware depending on the circumstances without dramatically changing the computational time the ewma is a form of iir filter, which means it can be come unstable if the cumulative error becomes too large. 5.2.2. remainder-weighted dithering the firmware quantizes the 12-bit adc results or 16-bi t signed usb data to a 9-bit epca pwm value. remainder- weighted dithering is an optional algorithm that allows the class-d toolstick firmware to recover some of the energy lost in the lsbs during this conversion in a random, inaudible way. this algorithm captures the lsbs of the original 12- or 16-bit data, shifts the data to the final 9-bit size, and compares against a random value of the same magnitude as the lsbs shifted away. if the original data was positive and the lsbs are greater than the random valu e, then the lsb of the 9-bit data is incremented by 1. similarly, if the original data was negative and the lsbs are less than the random value, the lsb is decremented by 1. otherwise, the data remains unchanged. figure 6. remainder-weighted dithering example yn ?? yn 1 ? ?? yn 1 ? ?? 2 m -------------------- ? xn ?? 2 m ----------- + = 12-bit to 9-bit (3 bits): output_value = 1931 = 0x078b output_lsb = 0x78b & 0x7 = 3 output_value = 1931 >> 3 = 241 random_lsb = 1 epca overflows 241 242 random_lsb = 6 random_lsb = 4 random_lsb = 0 random_lsb = 3 output code
AN726 10 rev. 0.1 the example in figure 6 assumes a original 12-bit si gned data value of 1931 and shows how the average energy increases. in this particular example, the data remains the same for each epc a overflow for simplicity, but this will not necessarily be the case in the operation of the algorithm. 5.2.3. law (or mulaw) the law companding algorithm has long been used in telephony and other voice applications. this algorithm takes advantage of the behavior of the human ear by rese rving most of the compressio n bins for low volume levels where the ear is most sensitive. usin g this algorithm, the class-d firmware can store more data in flash with no noticeable degradation in audio quality. this algorithm takes a 14-bit signed number and adds 32 to the magnitude, which ensures that a 1 occurs in bits 5? 12 of the value. this means the valid input range is ?8 160 to 8159. this value is then converted to an 8-bit compressed result as shown in figure 7, where s is the sign bit. finally, the 8-bit value is complemented. figure 7. law algorithm table figure 8 shows the plot of the 14-bit signed inputs versus the 8-bit compressed output. figure 8. law algorithm plot 00000001 abcd x 0000001 abcd xx 000001 abcd xxx 00001 abcd xxxx 0001 abcd xxxxx 001 abcd xxxxxx 01 abcd xxxxxxx 1 abcd xxxxxxxx s s s s s s s s 000 abcd 001 abcd 010 abcd 011 abcd 100 abcd 101 abcd 110 abcd 111 abcd s s s s s s s s 14-bit signed input data 8-bit law encoded data input data compressed output -8000 -4000 50 -6000 -2000 8000 4000 6000 2000 100 -50 -100
AN726 rev. 0.1 11 5.3. epca0 class-d output in all modes, the epca0 module runs in center-aligned pw m mode with an upper limit of 256. this means that the channels operate in the range of 0?511, since the channe ls count in half clocks. when the positive channel is on longer than the negative channel, the resulting equivalent energy is positive (above zero). when the negative channel is on longer than the positive channel, the resultin g equivalent energy is negative (below zero). combined with the components on the output, this pwm scheme gener ates the output waveform on the speaker as shown in figure 9. figure 9. class-d output example note: the output network configuration in figure 9 is the configuration in revision 1.0 of the hardware. an alternate output net- work discussed in 6. "tuning the class- d output network?" on page 18 may pr ovide better performance than the original configuration. 5.4. volume control the volume control on the class-d toolstick board uses the current-limiting feature of the high drive i/o to adjust the output power. this has the additional benefit of allowin g the pwm to always operate at full range, even at lower volumes, which reduces firmware size and improves sound quality. ch0 (r+) ch1 (r-) differential pb4.0 (r+) pb4.1 (r-) fb fb l l c c g c g
AN726 12 rev. 0.1 5.5. stereo jack input mode in stereo jack input mode, the goal is to sample at an even division of the epca0 update frequency to provide the lowest distortion attainable. the data from the adcs is 12-bit unsigned. figure 10. stereo jack input mode block diagram this mode measures the input source from the stereo ja ck (j1) using both saradc modules, performs the ewma algorithm, quantizes the data to 9 bits, and outputs th e pwm waveform on the epca0 module. figure 11 shows the data flow for the stereo input jack mode. the class-d toolstick board automatically biases the inpu t waveform to vref/2. on hardware that does not do this, an additional dc offset adjustment algorithm may be required. figure 11. stereo jack input mode flow diagram sim3u1xx saradc0 epca saradc1 r l class-d rd board sim3u1xx hardware gain stage hardware gain stage saradc0 saradc1 ewma remainder- weighted dither 9-bit quantization adjusting dc offset algorithm epca r l
AN726 rev. 0.1 13 5.6. usb input/output mode in usb input/output mode, the system samples and outputs data at 48 khz. the usb data is 16-bit signed data. figure 12. usb input/output mode block diagram for playing (from pc to the board), the board receives data from the usb interface using the si32library usb audio component and outputs the pwm waveform on the epca0 module. for recording (from board to the pc), the firmware measures the microphone (mk1) using one saradc module and sends the data to the pc using the si32library usb audio component. figure 13 shows the data flow for the usb input/output mode. figure 13. usb input/output mode flow diagram class-d rd board sim3u1xx saradc0 epca usb r l mic host pc sound software sim3u1xx hardware gain stage saradc0 remainder- weighted dither shift from 12 bits unsigned to 16 signed epca 9-bit quantization usb0 host pc sound software mic r l
AN726 14 rev. 0.1 5.7. play prer ecorded flash mode in play prerecorded flash mode, the system outputs data from the flash at 9.6 khz. figure 14. play prerecorded flash mode block diagram the firmware reads the compressed data from the flash, decompresses the data using law, performs the ewma algorithm, quantizes the data to 9 bits, and outputs the pwm waveform on the epca0 module. the remainder- weighted dithering algorithm is not us ed at all in this mode since the data lsbs will often be 0s from the compression algorithm. figure 15 shows the data flow for the play prerecorded flash mode. figure 15. play prerecorded flash mode flow diagram class-d rd board sim3u1xx flash epca r l sim3u1xx flash 12-bit quantization 9-bit quantization law decompression 8 bits to 14 (signed) epca ewma r l
AN726 rev. 0.1 15 5.8. play/record flash mode in play/record flash mode, the system samples and outputs data at 9.6 khz. figure 16. play/record flash mode block diagram for playing, the firmware reads the compressed data fr om the flash, decompresses the data using law, performs the ewma algorithm, quantizes the data to 9 bits, and outputs the pwm waveform on the epca0 module. the remainder-weighted ditheri ng algorithm is not used at all in this mode since the data lsbs will often be 0?s from the compression algorithm. for recording, the firmware measures the microphone (mk1) using one saradc module, compresses the data using law, and stores the data in flash. figure 17 shows the data flow for the play/record flash mode. figure 17. play/record flash mode flow diagram class-d rd board sim3u1xx saradc0 epca flash r l mic sim3u1xx flash 12-bit quantization 9-bit quantization law decompression 8 bits to 14 (signed) epca ewma hardware gain stage saradc0 convert from 12 bits unsigned to 14 signed law compression 14 bits to 8 (signed) r l mic
AN726 16 rev. 0.1 5.9. build configurations the precision32 and uvision projects include two bu ild configurations each: release and debug. these configurations change the code optimization settings. in addition, each configuration sets a flag to allow the firmware to automatically detect the current build configur ation and ide. this enables the firmware to modify the play/record flash mode array size to appropriate settings based on the code size. the approximate sizes for each build configuration are shown in table 4. to change the active build configuration in the precision32 ide, right-click on the project name in the project view and select build configurations ? set active ? debug or release . figure 18. setting the active precision32 ide build configuration table 4. build code size comparisons ide build code size (bytes) precision32 debug 68200 release 47200 uvision4 debug 40200 release 34700
AN726 rev. 0.1 17 to change the active build configurat ion in uvision4, select the configuration from the drop-down menu shown in figure 19. figure 19. setting the active uvision4 ide build configuration 5.10. si32 hal version the class-d toolstick firmware was orig inally developed for v1.1.1 of the hal or later. compiling against previous versions of the ha l will generate errors.
AN726 18 rev. 0.1 6. tuning the class-d output network 6.1. revision 1.0 configuration class-d is an extension of a single-ended, single-pin sp eaker drive, where one side of the speaker is driven directly (perhaps with a ferrite bead) and one side is grounded. this output method works very well with sim3u1xx devices. the full class-d output network consists of ferrite beads, inductor-capacitor (lc) filters, and grounding capacitors (c g ). figure 20 shows the output network configuration used by the revision 1.0 hardware. an alternate output network shown in figure 21 may provide better pe rformance than the original configuration. figure 20. revision 1.0 hardware class-d output network?direct drive the ferrite beads dissipate pad switching noise as heat fo r emi purposes, the lc components filter the pwm noise, and the grounding capacitors provide additional filtering in conjunction wit h the speaker reactance. in almost all applications, the ferrite beads should be pop ulated on the board. however, the other components may or may not be populated, depending on the speaker used an d the cost requirements of the application. if either the l or the c are installed, both should be populated to ensure lower power consumption. in most cases, the easiest method of determining whether to install the components and the values for these components is through physical experimentation. the perceived quality can be determined by the following characteristics: ?? loudness ?? changes in loudness across bandwidth ?? bandwidth ?? noise harmonics across bandwidth ?? hiss at low and high volumes other factors to consider are the application?s sound source (i.e. usb data versus sampled adc data) and the maximum power consumption of the boar d in the application, which will dete rmine how much data processing can occur and if external mosfets are appropriate. the class-d board provides 0 ? resistor pads to bypass the series components, if desired. pb4.0 (r+) pb4.1 (r-) fb fb l l c c g c g
AN726 rev. 0.1 19 6.2. alternate configuration figure 20 shows the output network configuration used by the revision 1.0 hardware. an alternate output network shown in figure 21 may provide better pe rformance than the original configuration. figure 21. alternate class-d output network?direct drive for the alternate configuration, the recommended components for the board are shown in table 5. table 5. class-d toolstick alternate output network recommended components reference value l ~3.3 h, 1.5 a c~2.2f c g ~20 pf c b ~0.47 f pb4.0 (r+) pb4.1 (r-) c g c g fb l c b l fb c c placed as close to the device as possible placed as close to the speaker connectors as possible
AN726 20 rev. 0.1 6.3. revision 1.0 hi gh power configuration instead of directly driving the speaker, the high-dri ve i/o can interface with external mosfets as shown in figure 22, enabling higher-power applic ations. the board includes footprin ts for these external mosfets to enable development wit h this configuration. the pull- up and pull-down resistors (~100 k ? ) ensure that the tristate reset state of the high drive i/o does not cause the fe ts to accidentally conduct current. when using these external mosfets, uninstall the r32, r35, r38, and r41 0 ? resistors. figure 23 illustrates an alternate full -bridge high-power out put network. the diode and rc circuits on the mosfet gates ensure that the tw o devices will not both be conducting simultaneously. figure 22. half-bridge class-d output network?external mosfets the revision 1.0 hardware provides footprints to a 9 v dc adapter connector and high power ldo. these components can be populated to provide a higher current source to the external mosfet transistors and viohd. alternatively, an external supply can connect to the transistors alone by removing the r48 0 ? resistor and placing the positive terminal on the p_pwr test point. fb fb l l c c g c g viohd pb4.0 (r+) pb4.1 (r-)
AN726 rev. 0.1 21 6.4. alternate high power configuration the revision 1.0 hardware uses a half -bridge configuration shown in figu re 22. this configuration can lead to higher distortion. figure 23 illustrates an alternate full-bridge high-power output ne twork. the diode and rc circuits on the mosfet gates ensure th at the two devices will not both be conduc ting simultaneously. the value of these components should be tuned for the gate capacitance of the fets. figure 23. full-bridge class-d output network?external mosfets c g c g fb l c b l fb c c placed as close to the drivers as possible placed as close to the speaker connectors as possible viohd viohd pb4.0 (r+) pb4.1 (r-)
AN726 22 rev. 0.1 7. schematics left_ch virtual_gnd right_ch virtual_gnd virtual_gnd virtual_gnd adc_vref +3.3v_vdd adc_vref adc_in_jack_2 adc_in_jack_1 r15 21 r4 2.74k c2 0.47uf + - v+ v- u1a mc33204 3 2 1 11 4 c1 10uf r14 5.11k r18 100k r8 4.99k j1 audio jack 1 3 2 c8 0.47uf r17 470k r10 470k + - u1c mc33204 10 9 8 r1 2k r11 10k c4 0.1uf r19 280k mgain- c3 10uf r9 100 mgain+ r2 21 l_in c6 0.47uf + - u1b mc33204 5 6 7 mk1 microphone 1 2 c7 2.2uf r13 280k r5 200k c5 2.2uf r16 100 r7 21 r6 24.9k r12 100k r3 470k + - u1d mc33204 12 13 14 r_in figure 24. utility class-d toolstick board schematic (1 of 3)?revision 1.0
AN726 rev. 0.1 23 mode play rec erase utility class-d toolstick www.silabs.com/toolstick led2 led3 led2 led1 resetb swdio resetb swclk uart0_rx uart0_tx uart0_rx swdio i2s_rx_ws i2s_rx_sck i2s_rx_sd i2s_rx_sck i2s_rx_sd i2s_rx_ws adc_in_jack_1 adc_in_jack_1 led0 led0 led1 led3 swclk uart0_tx +3.3v_vdd usb_5.0v_device usb_5.0v_debug +3.3v_vdd usb_5.0v_device usb_5.0v_debug vregin_device +3.3v_vdd viohd +3.3v_vdd +3.3v_vdd +3.3v_vdd +3.3v_vdd +3.3v_vdd +3.3v_vdd vdd_debug adc_vref vregin_device viohd vdd_debug vdd_debug +3.3v_vdd +3.3v_vdd +3.3v_vdd +3.3v_vdd 5.0v_wall 5.0v_wall adc_in_mic r+ r- l+ l- adc_in_jack_1 r26 100 c16 4.7uf s1 vout vin gnd u4 mc7805abd2tg 1 3 4 c19 0.1uf r28 750 cs slider 1 2 3 4 5 6 u2 sim3u164-b-gm pb4.3 1 vsshd 2 viohd 3 pb4.2 4 pb4.1 5 pb4.0 6 pb3.3 7 pb3.2 8 pb3.1 9 pb3.0 10 pb1.3 11 pb1.2 12 vio 13 vss 14 pb1.1 15 pb1.0 16 pb0.15 17 pb0.14 18 pb0.13 19 pb0.12 20 pb0.11 21 pb0.10 22 swdio 23 swclk 24 pb0.9 25 pb0.8 26 pb0.7 27 pb0.6 28 pb0.5 29 pb0.4 30 pb0.3 31 pb0.2 32 pb0.1 33 pb0.0 34 vdd 35 vregin 36 vbus 37 d+ 38 d- 39 reset 40 r49 1k c21 4.7uf u3 cf326-sx0261gm gpio 1 gnd 2 d+ 3 d- 4 vio 5 vdd 6 regin 7 vbus 8 rstb/c2ck 9 c2d 10 suspend 11 led_stop 12 nc 13 nc 14 nc 15 nc 16 nc 17 led_run 18 nc 19 nc 20 nc 21 gpio/cts 22 gpio/rts 23 tdo/swo/rx 24 tdi/tx 25 tms/swdio 26 nsrst 27 tck/swclk 28 epad 29 r22 100 c17 0.1uf l1 0.68uh j2 cn-usb-otg device +v d- d+ id gnd sh sh sh sh ds7 green r21 100 ds8 red pb3.3 c12 0.1uf ds1 blue d4b d3 sp0503baht r29 1k r20 1k r27 0 r23 100 ds5 blue viohd c24 1uf ds3 blue r42 750 j6 power jack 3 2 1 r44 1k r45 0 c25 0.1uf c10 0.1uf c23 0.1uf r24 100 c33 4.7uf c32 0.33uf d1 sp0503baht c9 4.7uf c15 0.1uf c11 4.7uf r50 0 r25 100 c22 4.7uf ds6 blue j3 cn-usb-otg debug +v d- d+ id gnd sh sh sh sh c20 0.1uf ds4 blue c14 4.7uf d4a s2 ds2 blue c13 0.1uf c18 4.7uf figure 25. utility class-d toolstick board schematic (2 of 3)?revision 1.0
AN726 24 rev. 0.1 r+ r- l+ l- p_power p_power p_power r+ r- r+ r- viohd viohd l- l+ r- r+ c27 2.2uf c29 0.022uf r+ l- fb4 600 ohm l-_pin l+_i l3 3.3uh l- p j5 audio jack 1 3 2 q1 ntr4170nt1g c30 2.2uf c31 0.022uf l4 3.3uh l-_i jp1 r46 47k r38 0 r- p l+ r34 0 l5 3.3uh r40 0 l+_pin q2 ntr4170nt1g r47 47k r+_i r32 0 p_pwr fb1 600 ohm r41 0 r+ n j4 analog header 1 3 2 4 r-_pin c26 0.022uf r- fb2 600 ohm ls1 speaker r48 0 m2 ntr4171pt1g r+_pin r-_i l+ n r31 0 c28 0.022uf r35 0 fb3 600 ohm r37 0 l2 3.3uh m1 ntr4171pt1g figure 26. utility class-d toolstick board schematic (3 of 3)?revision 1.0
AN726 rev. 0.1 25 8. bill of materials table 6. utility class-d toolstick board bill of materials reference part number source description c1, c3 c0603x5r6r3-106m venkel 10 f, 6.3 v r% x5r 0603 c2, c6, c8 c0603x7r250-474k venkel 0.47 f, 25 v 10% x7r 0603 c24 c0603x7r100-105k venkel 1 f, 10 v 10% x7r 0603 c26, c28, c29, c31 c1608x7r1h223m tdk corporation 0.022 f, 50 v 20% x7r 0603 c4, c10, c12, c13, c15, c17, c19, c20, c23, c25 c0603x7r100-104k venkel 0.1 f, 10 v 10% x7r 0603 c5, c7 c0603x7r100-225k venkel 2.2 f, 10 v 10% x7r 0603 c9, c11, c14, c16, c18, c21, c22 c0603x5r6r3-475k venkel 4.7 f, 6.3 v 10% x5r 0603 d1, d3 sp0503bahtg littlefuse usb diodes 300 mw, 20 v tvs sot143 d4 rb550eatr rohm semiconductor diode 700 ma , ? 30 v ? dual ? schottky ? sot5n ds1, ds2, ds3, ds4, ds5, ds6 lb q39g-l2n2-35-1 osram opto semiconductors inc blue 15 ma, 2.85 v smt, chipled 0603 ds7 sml-lx0603sugw lumex inc green 25 ma 0603 ds8 sml-lx0603iw lumex inc red 30 ma 0603 fb1, fb2, fb3, fb4 mpz1608s601a tdk corporation 600 ? , 1 a smt 0603 j1, j5 sj1-3543n cui inc stereo audio jack j2, j3 ux60-mb-5st hirose usb mini connector b j4 1729144 phoenix contact 1x4 terminal block jp1 tsw-102-07-t-s samtec 1x2 jumper header l1 nlv25t-r68j-pf tdk 0.68 h, 300 ma 5% gp l2, l3, l4, l5 84332c murata 3.3 h, 1.5 a 20% unshielded ls1 ga0571h alc speaker 1 w max mk1 cma-4544pf-w cui inc microphone mic-2.5x9.7mm-rad r1 cr0603-10w-2001f venkel 2 k ? , 1/10 w 1% thickfilm 0603 r11, r18 cr0603-10w-1003f venkel 100 k ? , 1/10 w 1% thickfilm 0603 r12, r19 cr0603-16w-2803f venkel 280 k ? , 1/16 w 1% thickfilm 0603 r13 cr0603-10w-1002f venkel 10 k ? , 1/10 w 1% thickfilm 0603 r14 cr0603-8w-5111f venkel 5.11 k ? , 1/8 w 1% thickfilm 0603 r2, r7, r15 cr0603-16w-21r0f venkel 21 ? , 1/16 w 1% thickfilm 0603 r20, r29, r44, r49 cr0603-10w-1001f venkel 1 k ? , 1/10 w 1% thickfilm 0603 r28, r42 cr0603-16w-7500f venkel 750 ? , 1/10 w 1% thickfilm 0603
AN726 26 rev. 0.1 r3, r10, r17 cr0603-10w-4703f venkel 470 k ? , 1/10 w 1% thickfilm 0603 r31, r32, r34, r35, r37, r38, r40, r41, r48 cr0603-16w-000 venkel 0 ? , 1 a thickfilm 0603 r4 cr0603-16w-2741f venkel 2.74 k ? , 1/16 w 1% thickfilm 0603 r5 cr0603-10w-2003f venkel 200 k ? , 1/10 w 1% thickfilm 0603 r6 cr0603-10w-2492f venkel 24.9 k ? , 1/10 w 1% thickfilm 0603 r8 cr0603-16w-4991f venkel 4.99 k ? , 1/16 w 1% thickfilm 0603 r9, r16, r21, r22, r23, r24, r25, r26 cr0603-10w-1000f venkel 100 ? , 1/10 w 1% thickfilm 0603 s1, s2 evq-pad04m panasonic corp mom entary tactile switch 6.5x4.5 sc1, sc2, sc3, sc4 nss-4-4-01 richco plastic co 4-40 hdw so1, so2, so3, so4 2397 spc technology standoff hdw u1 mc33204dr2 on semiconductor quad op-amp u2 sim3u164-b-gm silicon la boratories sim3u16 4-b-gq mcu qfn40 m6x6 p0.5 u3 cf326-sx0261gm silicon laboratories toolstick debug adapter mcu components not installed c27, c30 c0603x7r100-225k venkel 2.2 f, 10 v 10% x7r 0603 not installed (ni) c32 c0603x7r100-334k venkel 0.33 f, 10 v 10% x7r 0603 not installed (ni) c33 c0603x5r6r3-475k venkel 4.7 f, 6.3 v 10% x7r 0603 not installed (ni) j6 rapc722x switchcraft inc. 3-pin po wer jack 5a barrel not installed (ni) m1, m2 ntr4171pt1g on semiconductor ?3.5 a, ?30 v pchan sot23 not installed (ni) q1, q2 ntr4170nt1g on semiconductor 3.2 a, 30 v nchan sot23 not installed (ni) r27, r45, r50 cr0603-16w-000 venkel 0 ? , ? 1 a thickfilm 0603 not installed (ni) r46, r47 cr0603-16w-4702f venkel 47 k ? , 1/16 w 1% thickfilm 0603 not installed (ni) u4 mc7805abd2tg on semiconductor 1 a max ldo d2pak not installed (ni) table 6. utility class-d toolstick board bill of materials (continued) reference part number source description
AN726 rev. 0.1 27 n otes :
AN726 28 rev. 0.1 c ontact i nformation silicon laboratories inc. 400 west cesar chavez austin, tx 78701 please visit the silicon labs technical support web page: http://www.silabs.com/support and register to submit a technical support request. patent notice silicon labs invests in research and development to help our cust omers differentiate in the market with innovative low-power, s mall size, analog- intensive mixed-signal soluti ons. silicon labs' extensive pat ent portfolio is a testament to our unique approach and world-clas s engineering team. silicon laboratories and silicon labs are trademarks of silicon laboratories inc. other products or brandnames mentioned herein are trademarks or registered trademarks of their respective holders. the information in this document is believed to be accurate in all respects at the time of publ ication but is subject to change without notice. silicon laboratories assumes no responsibili ty for errors and omissions, and disclaim s responsibility for any consequences resu lting from the use of information included herein. a dditionally, silicon laboratorie s assumes no responsibility for the functioning of und escribed fea- tures or parameters. silicon laboratories reserves the right to make changes without further notice. silicon laboratories makes no warran- ty, representation or guarantee regarding t he suitability of its products for any par ticular purpose, nor does silicon laborato ries assume any liability arising out of the application or use of any product or circuit, and specif ically disclaims any and all liability, in cluding without limitation consequential or incidental damages . silicon laboratories products are not designed, intended, or authorized for use in applica tions intend- ed to support or sustain life, or for any other application in which the failure of the silicon laboratories product could crea te a situation where personal injury or death may occur. should buyer purchase or us e silicon laboratories products for any such unintended or unaut horized application, buyer shall indemnify and hold silicon laboratories harmle ss against all claims and damages.

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