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audio switching amplifier ad1994 rev. 0 information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent rights of analog devices. trademarks and registered trademarks are the property of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781.329.4700 www.analog.com fax: 781.461.3113 ?2006 analog devices, inc. all rights reserved. features integrated stereo modulator and power stage <0.005% thd + n 105 db dynamic range (a-weighted) 2 25 w output power (6 , 10% thd + n) 1 50 w output power (3 , 10% thd + n) r ds-on < 0.3 (per transistor) psrr > 65 db on-off-mute pop noise suppression emi optimized modulator short-circuit protection overtemperature protection low cost dmos process applications advanced televisions compact multimedia systems minicomponents general description the ad1994 is a 2-channel, bridge tied load (btl), switching audio power amplifier with integrated - modulator. the modulator accepts a single-ended, analog input signal and converts it to a switching waveform to drive speakers directly. one of the two modulators can control both output stages providing twice the current and almost twice the efficiency for single-channel applications. both modulators can also control external power devices for arbitrarily high output power. a digital, microprocessor-compatible interface provides control of reset, mute, and pga gain, as well as feedback signals for thermal and overcurrent error conditions. the output stage can operate over a power supply voltages range of 8 v to 20 v. the analog modulator and digital logic operate from a 5 v supply. functional block diagram b2 b1 a2 a1 outl+ level shifter and dead time control h-bridge pgnd outl? outr+ dctrl2 dctrl1 dctrl0 outr? d2 d1 c2 c1 nfr+ nfr? nfl+ nfl? mute reset err2 err1 err0 - modulator order reducer - modulator pga pga oscillator voltage reference mode control logic and pop/click suppression agnd clki clko ref_filt ainr mod_filt ainl pv dd av dd dv dd pga1 pga0 feedback network feedback network ad1994 0 5775-001 figure 1.
ad1994 rev. 0 | page 2 of 24 table of contents features .............................................................................................. 1 applications ....................................................................................... 1 general description ......................................................................... 1 functional block diagram .............................................................. 1 revision history ............................................................................... 2 specifications ..................................................................................... 3 absolute maximum ratings ............................................................ 5 esd caution .................................................................................. 5 pin configuration and function descriptions ............................. 6 typical performance characteristics ............................................. 8 theory of operation ...................................................................... 15 overview ...................................................................................... 15 - modulator ............................................................................ 15 mute and reset ..................................................................... 15 mono mode ................................................................................. 16 modulator mode ........................................................................ 16 gain structure ............................................................................. 16 power stage ................................................................................. 17 clocking ....................................................................................... 18 protection circuits and error reporting ................................ 19 application circuits ....................................................................... 20 outline dimensions ....................................................................... 21 ordering guide .......................................................................... 21 revision history 2/06revision 0: initial version
ad1994 rev. 0 | page 3 of 24 specifications test conditions, unless otherwise specified. table 1. parameter ratings supply voltages av dd 5 v dv dd 5 v pv dd 12 v ambient temperature 25c load impedance 6 clock frequency 12.288 mhz pga gain 0 db measurement bandwidth 20 hz to 20 khz table 2. parameter min typ max unit test conditions/comments r ds-on per high-side transistor 260 355 m t = 25c per low-side transistor 210 265 m t = 25c maximum current through outx 5 a peak thermal warning active 135 c die temperature thermal shutdown active 150 c die temperature restore temperature after thermal shutdown 120 c die temperature table 3. performance specifications parameter typ unit test conditions/comments total harmonic distortion and noise (thd + n) 0.003 % pga = 0 db, p o = 1 w, 1 khz 0.006 % pga = 6 db, p o = 1 w, 1 khz 0.01 % pga = 12 db, p o = 1 w, 1 khz 0.02 % pga = 18 db, p o = 1 w, 1 khz signal-to-noise ratio (snr) 105 db 1 khz, a-we ighted, 0 db referred to 1% thd + n output dynamic range (dnr) 105 db 1 khz, a-weighted, ?60 db referred to 1% thd + n output crosstalk (left-to-right or right-to-left) ?100 db pga = 0 db, p o = 5 w, 1 khz table 4. dc specifications parameter typ unit test conditions/comments input impedance 20 k ainl, ainr input pins output dc offset 4 mv independent of pga setting
ad1994 rev. 0 | page 4 of 24 table 5. power supplies parameter min typ max unit test conditions/comments analog supply, av dd 4.5 5.0 5.5 v digital supply, dv dd 4.5 5.0 5.5 v power transistor supply, pv dd 6.5 8 to 20 22.5 v reset/power-down current reset held low av dd 0.6 1 a 5 v dv 7.5 11 a 5 v dd pv 19 40 a 12 v dd quiescent current inputs grounded, nonoverlap = minimum av 20 ma 5 v dd dv 5.5 ma 5 v dd pv 30 ma 12 v dd operating current v in = 1 v rms, r l = 6 , p o = 1 w av 20 27 ma 5 v dd dv 5.5 7 ma 5 v dd pv 218 260 ma 12 v dd table 6. digital i/o parameter min typ max unit test conditions/comments input logic high 2.0 v input logic low 0.8 v output logic high 2.4 v @ 4 ma output logic low 0.4 v @ 4 ma leakage current on digital outputs 10 a table 7. digital timing parameter typ unit test conditions/comments t md 10 s delay after mute is asserted until output stops switching t ud 34 s delay after mute is deasserted until output starts switching mute outx t ud t md 05775-002 figure 2. mute and unmute delay timing
ad1994 rev. 0 | page 5 of 24 absolute maximum ratings table 8. parameter rating stresses above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. avdd, dvdd to agnd, dgnd ?0.3 v to +6.5 v pvddx to pgndx ?0.3 v to +30.0 v 1 agnd to dgnd to pgndx ?0.3 v to +0.3 v avdd, to dvdd ?0.5 v to +0.5 v operating temperature range C40c to +85c storage temperature range C65c to +150c maximum junction temperature 150c thermal resistance 19.2c/w ja jc (at the exposed pad surface) 0.9c/w (on jedec standard pcb) 9.7c/w jb 1 including any induced voltage due to inductive load. esd caution esd (electrostatic discharge) sensitive device. electros tatic charges as high as 4000 v readily accumulate on the human body and test equipment and can discharge wi thout detection. although this product features proprietary esd protection circuitry, permanent dama ge may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality.
ad1994 rev. 0 | page 6 of 24 pin configuration and fu nction descriptions pin 1 indicator 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 err2 err1 modl/err0 modr/dctrl2 dctrl1 dctrl0 dgnd dvdd dvdd dgnd clki clko mute reset pga1 pga0 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 mono_en nfl+ nfl? nc ainl nc mod_filt avdd agnd ref_filt nc ainr nc nfr? nfr+ mod_en 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 pgnd1 pgnd1 pgnd1 outl+ outl+ outl+ pvdd1 pvdd1 pvdd1 pvdd1 outl? outl? outl? pgnd1 pgnd1 pgnd1 nc = no connect pgnd2 pgnd2 pgnd2 outr+ outr+ outr+ pvdd2 pvdd2 pvdd2 pvdd2 outr? outr? outr? pgnd2 pgnd2 pgnd2 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 ad1994 top view (not to scale) 05775-003 figure 3. pin configuration table 9. pin function descriptions pin no. nemonic in/out description 1, 2, 3 pgnd1 negative power supply. used for the a2 and b2 high power transistors. 4, 5, 6 outl+ o output of transistor pair a1 and a2. 7, 8, 9, 10 pvdd1 positive power supply. used for the a1 and b1 high power transistors. 11, 12, 13 outl? o output of transistor pair b1 and b2. 14, 15, 16 pgnd1 negative power supply. used for the a2 and b2 high power transistors. 17 err2 o active low thermal shutdown. 18 err1 o active low thermal warning error output. 19 modl/ err0 o active low overcurrent error output/modulator output left. 20 modr/dctrl2 i/o nonoverlap time setting msb/modulator output right. 21 dctrl1 i nonoverlap time setting. 22 dctrl0 i nonoverlap time setting lsb. 23, 26 dgnd negative power supply for low power digital circuitry. 24, 25 dvdd positive power supply for low power digital circuitry. 27 clki i clock input for 256 f s audio modulator clock. 28 clko o inverted version of clki for use with an external xtal oscillator. 29 mute i active low mute input. 30 reset i active low reset input. 31 pga1 i pga gain control msb. 32 pga0 i pga gain control lsb. 33, 34, 35 pgnd2 negative power supply for high power transistors c2 and d2. 36, 37, 38 outr? o output of transistor pair d1 and d2. 39, 40, 41, 42 pvdd2 positive power supply for high power transistors c1 and d1. 43, 44, 45 outr+ o output of transistor pair c1 and c2. 46, 47, 48 pgnd2 negative power supply for high power transistors c2 and d2. 49 mod_en i modulator mode enable pin when pulled to logic high.
ad1994 rev. 0 | page 7 of 24 pin no. mnemonic in/out description 50 nfr+ i right channel negative feedbacknoninverting input. 51 nfr? i right channel negative feedbackinverting input. 52 nc no connectionshould be left floating. 53 ainr i analog input for right channel. 54 nc no connectionshould be left floating. 55 ref_filt o filter pin for band gap referenceshould be bypassed to agnd. 56 agnd negative power supply for low power analog circuitry. 57 avdd positive power supply for low power analog circuitry. 58 mod_filt o modulator filter pinused to set time constant of modulator order reduction circuit. 59 nc no connectionshould be left floating. 60 ainl o analog input for left channel. 61 nc no connectionshould be left floating. 62 nfl? i left channel negative feedbackinverting input. 63 nfl+ i left channel negative feedbacknoninverting input. 64 mono_en i mono mode enable pinwhen pulled up to logic high.
ad1994 rev. 0 | page 8 of 24 frequency (khz) power (dbfs: 0db = power at which thd = 1% (13.8w)) typical performance characteristics 0 ?160 02 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 2 4 6 8 1012141618 0 5775-004 frequency (khz) power (dbfs: 0db = power at which thd = 1% (10.1w)) figure 4. 1 w output power into 4 load 0 ?160 02 0 ?20 ?40 ?60 ?80 ?100 ?120 ?140 2 4 6 8 1012141618 0 5775-005 frequency (khz) power (dbfs: 0db = power at which thd = 1% (7.9w)) figure 5. 1 w output power into 6 load 0 ?160 02 0 5775-006 0 ?160 02 0 frequency (khz) power (dbfs: 0db = power at which thd = 1% (13.8w)) ?20 ?40 ?60 ?80 ?100 ?120 ?140 2 4 6 8 1012141618 ?20 ?40 ?60 ?80 ?100 ?120 ?140 24681012141618 0 figure 6. 1 w output power into 8 load 0 5775-007 0 ?160 02 0 frequency (khz) power (dbfs: 0db = power at which thd = 1% (10.1w)) figure 7. ?60 dbfs output power into 4 load ?20 ?40 ?60 ?80 ?100 ?120 ?140 2 4 6 8 1012141618 0 5775-008 0 ?160 02 0 frequency (khz) power (dbfs: 0db = power at which thd = 1% (7.9w)) figure 8. ?60 dbfs output power into 6 load ?20 ?40 ?60 ?80 ?100 ?120 ?140 2 4 6 8 1012141618 5775-009 0 figure 9. ?60 dbfs output power into 8 load
ad1994 rev. 0 | page 9 of 24 20 ?140 10k frequency (hz) power (db, relative to 500mw) (output power in the 19k and 20k tones) 0 ?20 ?40 ?60 ?80 ?100 ?120 100 1k 0 5775-010 0 0.0001 10k frequency (hz) thd (%) 100 1k ? 40 ?120 thd (db, relative to fundamental) ?50 ?60 ?70 ?80 ?90 ?100 ?110 0.1 0.01 0.001 0 5775-013 figure 10. imd for 19 khz/20 khz twin-tone stimulus with 1 w total output power figure 13. thd vs. frequency, 1 w output power into 4 load, pvdd = 12 v 40 0 10k frequency (hz) amplifier gain (db) 100 1k 35 30 25 20 15 10 5 pga gain = 18db pga gain = 12db pga gain = 6db pga gain = 0db 0 5775-011 0 0.0001 10k frequency (hz) thd (%) 100 1k ? 40 ?120 thd (db, relative to fundamental) ?50 ?60 ?70 ?80 ?90 ?100 ?110 0.1 0.01 0.001 0 5775-014 figure 11. amplifier gain vs. frequency, 6 load, pvdd = 12 v figure 14. thd vs. frequency, 1 w output power into 6 load, pvdd = 12 v 0 ?120 10k frequency (hz) signal in idle channel (db, relative to driven channel signal) 100 1k ?20 ?40 ?60 ?80 ?100 l channel driven, r channel idle l channel idle, r channel driven 0 5775-012 0 0.0001 10k frequency (hz) thd (%) 100 1k ? 40 ?120 thd (db, relative to fundamental) ?50 ?60 ?70 ?80 ?90 ?100 ?110 0.1 0.01 0.001 0 5775-015 figure 12. channel separation vs. frequency, driven channel has 1 w output power into 6 load figure 15. thd vs. frequency, 1 w output power into 8 load, pvdd = 12 v
ad1994 rev. 0 | page 10 of 24 100 10 0.001 10 output power (w) thd or thd + n (%) 0.1 1 0 ?100 thd or thd + n (db, relative to fundamental) ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 1 0.1 0.01 thd + n thd 0 5775-016 100 10 0.001 10 output power (w) thd or thd + n (%) 0.1 1 0 ?100 thd or thd + n (db, relative to fundamental) ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 1 0.1 0.01 thd + n thd 0 5775-019 figure 19. thd and thd + n vs. output power, 1 khz sine, 4 load, pvdd = 15 v figure 16. thd and thd + n vs. output power, 1 khz sine, 4 load, pvdd = 12 v 100 10 0.001 10 output power (w) thd or thd + n (%) 0.1 1 0 ?100 thd or thd + n (db, relative to fundamental) ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 1 0.1 0.01 thd + n thd 0 5775-020 100 10 0.001 10 output power (w) thd or thd + n (%) 0.1 1 0 ?100 thd or thd + n (db, relative to fundamental) ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 1 0.1 0.01 thd + n thd 0 5775-017 figure 17. thd and thd + n vs. output power, 1 khz sine, 6 load, pvdd = 12 v figure 20. thd and thd + n vs. output power, 1 khz sine, 6 load, pvdd = 15 v 100 10 0.001 10 output power (w) thd or thd + n (%) 0.1 1 0 ?100 thd or thd + n (db, relative to fundamental) ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 1 0.1 0.01 thd + n thd 0 5775-018 100 10 0.001 10 output power (w) thd or thd + n (%) 0.1 1 0 ?100 thd or thd + n (db, relative to fundamental) ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 1 0.1 0.01 thd + n thd 0 5775-021 figure 21. thd and thd + n vs. output power, 1 khz sine, 8 load, pvdd = 15 v figure 18. thd and thd + n vs. output power, 1 khz sine, 8 load, pvdd = 12 v
ad1994 rev. 0 | page 11 of 24 1 100 10 0.001 10 output power (w) thd or thd + n (%) 0.1 0 ?100 thd or thd + n (db, relative to fundamental) ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 1 0.1 0.01 thd + n thd 0 5775-022 100 10 0.001 10 output power (w) thd or thd + n (%) 0.1 1 0 ?100 thd or thd + n (db, relative to fundamental) ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 1 0.1 0.01 thd + n thd 0 5775-025 figure 22. thd and thd + n vs. output power, 1 khz sine, 4 load, pvdd = 18 v figure 25. thd and thd + n vs. output power, 1 khz sine, 4 load, pvdd = 20 v 100 10 0.001 10 output power (w) thd or thd + n (%) 0.1 1 0 ?100 thd or thd + n (db, relative to fundamental) ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 1 0.1 0.01 thd + n thd 0 5775-023 100 10 0.001 10 output power (w) thd or thd + n (%) 0.1 1 0 ?100 thd or thd + n (db, relative to fundamental) ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 1 0.1 0.01 thd + n thd 0 5775-026 figure 23. thd and thd + n vs. output power, 1 khz sine, 6 load, pvdd = 18 v figure 26. thd and thd + n vs. output power, 1 khz sine, 6 load, pvdd = 20 v 100 10 0.001 10 output power (w) thd or thd + n (%) 0.1 1 0 ?100 thd or thd + n (db, relative to fundamental) ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 1 0.1 0.01 thd + n thd 0 5775-024 100 10 0.001 10 output power (w) thd or thd + n (%) 0.1 1 0 ?100 thd or thd + n (db, relative to fundamental) ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 1 0.1 0.01 thd + n thd 0 5775-027 figure 27. thd and thd + n vs. output power, 1 khz sine, 8 load, pvdd = 20 v figure 24. thd and thd + n vs. output power, 1 khz sine, 8 load, pvdd = 18 v
ad1994 rev. 0 | page 12 of 24 pvdd voltage (v) output power per channel (w) 50 0 82 0 45 40 35 30 25 20 15 10 5 10 12 14 16 18 thd = 10% thd = 1% 0 5775-028 pvdd voltage (v) output power per channel (w) figure 28. maximum power vs. pvdd, stereo mode, 4 load 50 0 82 0 45 40 35 30 25 20 15 10 5 10 12 14 16 18 thd = 10% thd = 1% 0 5775-029 pvdd voltage (v) output power per channel (w) figure 29. maximum power vs. pvdd, stereo mode, 6 load 50 0 82 0 5775-030 100 0 82 0 pvdd voltage (v) output power (w) 90 80 70 60 50 40 30 20 10 thd = 10% thd = 1% 10 12 14 16 18 45 40 35 30 25 20 15 10 5 10 12 14 16 18 thd = 10% thd = 1% 0 figure 30. maximum power vs. pvdd, stereo mode, 8 load 0 5775-031 100 0 82 0 pvdd voltage (v) output power (w) figure 31. maximum power vs. pvdd, mono mode, 2 load 90 80 70 60 50 40 30 20 10 thd = 10% thd = 1% 10 12 14 16 18 0 5775-032 100 0 82 0 pvdd voltage (v) output power (w) figure 32. maximum power vs. pvdd, mono mode, 3 load 90 80 70 60 50 40 30 20 10 thd = 10% thd = 1% 5775-033 10 12 14 16 18 0 figure 33. maximum power vs. pvdd, mono mode, 4 load
ad1994 rev. 0 | page 13 of 24 100 0 10 output power per channel (w) power efficiency (%) 0.1 1 90 80 70 60 50 40 30 20 10 2 x8 ? load 2 x6 ? load 2 x4 ? load 0 5775-034 100 0 10 output power (w) power efficiency (%) 0.1 1 90 80 70 60 50 40 30 20 10 1 x4 ? load 1 x3 ? load 1 x2 ? load 0 5775-037 figure 34. power efficiency vs. output power, stereo mode, pvdd = 12 v figure 37. power efficiency vs. output power, mono mode, pvdd = 12 v 4.0 0 20 output power per channel (w) on-chip power dissipation per channel (w) 0 2 x8 ? load 2 x6 ? load 2 x4 ? load 3.5 3.0 2.5 2.0 1.5 1.0 0.5 24681012141618 0 5775-035 8 0 40 output power (w) on-chip power dissipation (w) 0 7 6 5 4 3 2 1 5 101520253035 1 x4 ? load 1 x3 ? load 1x2 ? load 0 5775-038 figure 35. on-chip power dissipation vs. output power, stereo mode, pvdd = 12 v figure 38. on-chip power dissipation vs. output power, mono mode, pvdd = 12 v 250 0 100 05775-036 mosfet on-resistance (m ? ) count 200 150 100 50 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 p-type 25c n-type 25c p-type 130c n-type 130c 20 ?140 ?130 ?120 ?110 ?100 ?90 ?80 ?70 ?60 ?50 ?40 ?30 ?20 ?10 20 20k frequency (hz) psrr (db) 0 10 10050 200 500 1k 2k 5k 10k 0 5775-039 figure 36. power supply rejectio n ratio (psrr) vs. frequency figure 39. histogram showing manufacturing variation of r of the output mosfets at 25c and 130c ds-on
ad1994 rev. 0 | page 14 of 24 100 0 10 output power per channel (w) power efficiency (%) 0.1 1 90 80 70 60 50 40 30 20 10 2 x6 ? load 2 x8 ? load 2 x4 ? load 0 5775-040 20 0 80 output power (w) on-chip power dissipation (w) 0 10 20 30 40 50 60 70 18 16 14 12 10 8 6 4 2 1x2 ? load 1 x4 ? load 1 x3 ? load 0 5775-043 figure 40. power efficiency vs. output power, stereo mode, pvdd = 18 v figure 42. on-chip power dissipation vs. output power, mono mode, pvdd = 18 v 10 0 40 output power per channel (w) on-chip power dissipation per channel (w) 0 5 101520253035 9 8 7 6 5 4 3 2 1 2 x8 ? load 2 x6 ? load 2x4 ? load 0 5775-041 100 0 10 output power (w) power efficiency (%) 0.1 1 90 80 70 60 50 40 30 20 10 1 x4 ? load 1 x3 ? load 1 x2 ? load 0 5775-042 figure 41. on-chip power dissipation vs. output power, stereo mode, pvdd = 18 v figure 43. power efficiency vs. output power, mono mode, pvdd = 18 v
ad1994 rev. 0 | page 15 of 24 theory of operation overview the ad1994 is a 2-channel, high performance, switching, audio power amplifier. each of the two - modulators converts a single-ended analog input into a 2-level pulse stream that controls the differential, full h-bridge, power output stage. the combination of an - modulator and a switching power stage provides an inherently linear and efficient means of amplifying the entire range of audio frequencies. the ad1994 also offers warning and protection circuits for overcurrent and over- temperature conditions, as well as silent turn-on and turn-off transitions. - modulator the ad1994 is a switching type, also known as a class-d, audio power amplifier. this class of amplifiers maximizes efficiency by only using its power output devices in full-on or full-off states. while most class-d amplifiers use some variation of pulse-width modulation (pwm), the ad1994 uses - modulation to determine the switching pattern of the output devices. this provides a number of important benefits. - modulators do not produce a sharp peak with many harmonics in the am frequency band as pulse-width modulators (pwm) often do. in addition, the 1-bit quantizer produces excellent linearity across the full amplitude range. - modulators require feedback to generate an error signal with respect to the input. the feedback voltages for the ad1994 modulators come from the outputs of the power devices and before the passive low-pass filters (see figure 45 ). this compensates for nonlinear behavior in the power stage, such as nonoverlap time, mismatched rise and fall times, and propagation delays. it also reduces sensitivity to both dc and transient changes of the power supply voltage. - modulators operate in discrete time. as with all time- quantized systems, the nyquist frequency is equal to half of the sampling frequency and input signals above that point aliases back into the base band. the ad1994 sampling frequency (master clock) is equal to half the frequency of the input clock, approximately 6 mhz, so images only alias for input frequencies above approximately 3 mhz. this is far enough above the audio band that bandwidth and aliasing are not a problem in real applications. the ad1994 implements a seventh-order, - modulator with a 1-bit quantizer. traditionally, higher-order designs such as this are not suitable for driving a class-d amplifier because of stability problems at higher modulation factors. the modulator design of the ad1994 is unusual in that it is stable to 90% modulation. to allow the amplifier to drive even further, the ad1994 dynamically reverts from seventh order to second order above a fixed modulation threshold. the second-order modulator is unconditionally stable, including during prolonged voltage clipping conditions, enabling stable operation at full modulation. the dynamic-order reduction circuit uses the high-order modulator, except during the crests of the highest waveform peaks. during these peaks, the quantization noise increases, but the snr is still quite high. these modulator order transitions are fast and smooth enough to avoid audible artifacts. the modulator has a noise shaping effect, and snr is increased in the audio band by shifting the quantization noise upward in frequency. for a nominal input clock frequency of 12.288 mhz, the noise floor rises sharply above 20 khz. the actual clock frequency used in an applicatio n circuit can deviate from this rate by as much as 10%, and the corner frequency of the noise scales proportionately. the frequency at which the quantization noise dominates the output determines the amplifiers practical bandwidth. the expected transition rate at the output of a typical seventh- order, - modulator would be high enough to negate much of the efficiency benefit of a switching amplifier. however, the ad1994 incorporates a proprietary, dynamic, switching rate, reduction scheme that lowers that average switching frequency by approximately a factor of four. this results in slightly increased output energy between 450 khz and 500 khz and efficiency on par with other class-d amplifiers. this low-q spectral boost is an artifact of the noise shaping and is in no way related to the carrier frequency visible in the spectrum of pwm class-d amplifiers. mute and reset when power is applied and the reset pin remains asserted, the ad1994 is in its lowest power consumption mode. the analog modulator is not running, and the power stage is tri- stated. on deasserting the reset pin, the modulator begins a start-up sequence that includes initialization of the modulator, the protection circuits, and other functions. once the start-up sequence is complete, the amplifier is in a state in which the modulator is running, but the output stage is not driven. when mute is deasserted, the output is started using a soft-start sequence that avoids any audible pop or click noise in the output signal. the output power transistors do not switch while mute remains asserted. unlike the analog mute circuits found on some amplifiers that can be limited in their attenuation by the control logic or crosstalk, the mute attenuation on the ad1994 is greater than its dynamic range. the noise floor of the output signal also drops while in mute because the output transistors are not switching.
ad1994 rev. 0 | page 16 of 24 power-up sequencing when the load impedance is substantially less than 4 , the system would be current limited if configured for normal stereo operation, and the amplifier would enter the overcurrent error state when a nominal input signal is applied. under these conditions, the amount of real power delivered to the load increases in mono mode. the minimum recommended impedance in mono mode is 2 (as compared to 4 for stereo operation), so the effective power delivered to a single channel can be as much as twice the maximum achievable in stereo mode. careful power-up is necessary when using the ad1994 to ensure correct operation and to avoid possible latch-up issues. the ad1994 should be powered up with reset mute and held low until all the power supplies have stabilized. once the supplies have stabilized, bring the ad1994 out of reset by bringing reset high. mute begin the soft unmute sequence by bringing high at least 1 sec after the reset rising edge. the amplifier produces audio using a shorter start-up sequence (as shown in for reactive loads, the impedance can only be below the recommended threshold over a small portion of the amplifiers bandwidth. in these cases, the amplifier can enter overcurrent shutdown in response to even small input signals in those frequency bands. when designing a system, use the minimum load impedance over the entire range of amplified frequencies when calculating current output rather than the average or nominal load impedance ratings often cited by loudspeaker driver manufacturers. table 7 ), but the amplifier can produce an audible pop or click noise as the output starts switching. this is because the ac coupling capacitors at the analog input have a long time constant. if mute is deasserted substantially less than 1 sec after deasserting reset , then these capacitors may not have charged to a steady state. they need ample time to settle at a bias voltage of v ref , the reference voltage for the single-ended inputs, or the amplifier starts with a slight dc offset. modulator mode mono mode the ad1994 is capable of operating as a modulator for controlling external power devices. when mod_en (pin 49) is logic level high at the rising edge of the power supply voltage and the limited current that the output transistors can source combine to dictate that maximum total output power of the ad1994. for higher impedance loads, the system is voltage limited, and for lower impedance loads, the system is current limited. in normal stereo operation, each output is driven by four mosfet devices arranged in a full h-bridge configuration, also known as bridge-tied load (btl). this provides the maximum differential output voltage swing, equal to twice the voltage of the power supply. however, operating in mono mode doubles the maximum achievable output current. reset , both the left and right internal power stages are disabled. the error output flags ( when mono_en (pin 64) is logic level high at the rising edge of reset , the right channel modulator is disabled, and the left channel modulator is used to drive both the left and right output stages in parallel. when using mono mode, connect outl+ directly to outr+, connect outl? directly to outr?, and use the combined differential pair to a drive a single load. connect the feedback pair to the positive and negative feedback input of the left modulator. the right channel feedback pins are unused in mono mode. the r ds-on of the power fets drops to half of its value in stereo operation because the devices are in parallel, and the ad1994 delivers its full current capability to a single channel. note that the practical effect of mono mode depends greatly on the load impedance. if the load is 4 or greater, the efficiency of the amplifier increases due to the reduced effective resistance of power fets, and the amplifier dissipates less heat. however, the amount of real power delivered to the load does not increase because the system is voltage limited (that is, the output waveform voltage clips before current limiting occurs). err2 err1 , , and err0 ) and the nonoverlap delay inputs (dcntl2, dcntl1, and dcntl0) no longer have meaning because they apply only to the internal power stages. the logic level outputs from the two modulators appear on pin 19 (modl) and pin 20 (modr). gain structure analog input levels the ad1994 has single-ended inputs for the left and right channels. the analog input section uses an internal amplifier to bias the input signal to the reference level, v ref , which is nominally equal to av /2. a dc-blocking capacitor, as shown in figure 44 dd , prevents this bias voltage from affecting the signal source. in combination with the nominal 20 k input impedance, the value of this capacitor should be large enough to produce a flat frequency response at the lowest input frequency of interest. note that the amplifier is capable of dc-coupled operation if the circuit includes some means to account for this bias voltage. ainl/ ainr 0 v + 0 5775-044 figure 44. ac-coupled input signal
ad1994 rev. 0 | page 17 of 24 setting the modulator gain programmable gain amplifier (pga) the - modulator itself requires a fixed gain for a given value of pv the ad1994 modulator uses a combination of the input signal and feedback from the power output stage to calculate its two- state output pattern. the feedback input nodes are part of the internal analog circuit that operates from the av dd to maintain optimal stability. this gain can be appropriate, but many applications require more gain to account for low source signal levels. the ad1994 includes a programmable gain amplifier (pga) to boost the overall amplifier gain. pga1 (pin 31) and pga0 (pin 32) select one of four pga gain values, as shown in dd (nominal 5 v) power supply. because the voltage measured at the power outputs is nominally between 0 v and pv dd , and thus beyond the 0 v to av table 11 . dd range, a voltage divider is required to scale the feedback to an appropriate level. tale 11. pga gain settings resistor voltage dividers should sense the voltage on each side of the differential output and provide these feedback signals to the modulator, as shown in pga1 pga0 pga gain (db) 0 0 0 figure 45 . external components r1 r3 cc ll r l d2 d4 d1 d3 outx+ outx? r2 r4 pv dd pv dd nfx+ nfx? pgnd pgnd 05775-045 figure 45. h-bridge configuration the resistor values should satisfy the following equation to maintain modulator stability. 635.34 43 2 21 dd pv r rr r rr gain = + = + = selecting a gain that meets this criterion ensures that the modulator remains in a stable operating condition. the ratio of the resistances sets the gain rather than the absolute values. however, the dividers provide a path from the high voltage supply to ground; therefore, the values should be large enough to produce negligible loss due to quiescent current. the chip contains a calibration circuit to minimize voltage offsets at the speaker, which helps to minimize clicks and pops when muting or unmuting. optimal performance is achieved for the offset calibration circuit when the feedback divider resistors sum to 6 k, that is, (r1 + r2) = 6 k, and (r3 + r4) = 6 k. tale 10. recommended feed ack resistor values pv dd (v) r1 (k) r2 (k) gain 12 4.2 1.8 3.3 (+10.4 db) 15 4.55 1.45 4.1 (+12.3 db) 18 4.8 1.2 5.0 (+14.0 db) 20 4.91 1.09 5.5 (+14.8 db) 0 1 6 1 0 12 1 1 18 the ad1994 incorporates a single-ended-to-differential converter for each channel in the analog front-end section. the pga is also part of this analog front-end, and it affects the analog input signal before it enters the - modulator. the pga1 and pga0 pins are continuously monitored and allow the gain to be changed at any time. power stage the h-bridge the output stage of the ad1994 includes four integrated mosfet devices arranged in a full h-bridge, as shown in figure 45 . the p-type, high-side transistor of one leg and the n-type, low-side transistor of the opposite leg switch on and off as a pair producing a total voltage swing across the load of ?pv dd to +pv dd . the drive is floating and differential, and it is important that neither output terminal be shorted to ground. the power supply for the output stage of the ad1994, pv dd , should be in the 8 v to 20 v range and should be capable of supplying enough current to drive the load. connect the power supply across the pvdd and pgnd pins. the feedback pins, nfr+, nfr?, nfl+, and nfl?, supply negative feedback to the modulator as described in the setting the modulator gain section.
ad1994 rev. 0 | page 18 of 24 output transistor nonoverlap time - modulator as mentioned in the section, the modulator has a noise-shaping effect such that snr is increased within the audio band by shifting modulator quantization noise upward in frequency. for external clock frequency of 12.288 mhz, the modulators noise-shaping works in a manner that results in a flat noise floor at the amplifier output for frequencies 20 khz and below. above 20 khz, the amplifier noise rises due to the spectral shaping of the modulator quantization noise. at very high frequencies, the noise floor levels off and decreases due to poles in the modulator noise-transfer function and in the external lc filter. the ad1994 allows the user to select from one of eight different nonoverlap times, as shown in figure 46 . nonoverlap time prevents or minimizes the period during which both the high- side and low-side devices are on simultaneously due to propagation delays and nonzero rise and fall times. if both the upper and lower portions of a half-bridge conduct simultaneously, there is a path directly from the power supply to ground and an induced current flow known as shoot-through. however, introducing this delay increases distortion by pushing the switching pattern further from an ideal two-state waveform. selecting the nonoverlap delay requires a compromise between distortion and efficiency. the logic levels on the three delay control pins, dctrl2, dctrl1, and dctrl0, set the nonoverlap time according to the clock frequency does not have to be exactly equal to 12.288 khz and can vary by up to 10%. for other rates, the noise corner scales linearly with frequency. when the modulator runs at a rate lower than nominal, the average power stage switching frequency decreases, the efficiency increases slightly, and the noise floor begins to rise at a slightly lower frequency. likewise, a faster clock gives slightly increased bandwidth and slightly lower efficiency. table 12 . the state of dctrl[2:0] is read on the rising edge of reset and should not be changed while reset is logic high. tale 12. nonoverlap time settings dctrl2 dctrl1 dctrl0 nonoverlap time (ns) 1 using a crystal oscillator 0 0 0 62 the ad1994 can use a crystal connected to the clki and clko pins as a master clock source, as shown in 0 0 1 49 figure 47 . the clki and clko pins connect to an internal inverter to create a full resonator. the typical values shown work in many applications, but the crystal manufacturer should provide the exact type and value of the capacitors and the resistor. 0 1 0 37 0 1 1 24 1 0 0 15 1 0 1 13.5 1 1 0 12 1 1 1 9 clki clko 22pf 22pf x t a l 47 ? 05775-047 values are typical and are not production tested. 1 high-side gate drive low-side gate drive t nol t nol 05775-046 figure 47. crystal connection using an external clock source figure 46. half-bridge nonoverlap delay timing if a clock signal of the appropriate frequency already exists in the application circuit, connect it directly to clki and leave clko floating. the logic levels of the square wave should be compatible with those defined in the shortest setting (dctrl[2:0] = 111) or the second shortest setting (dctrl[2:0] = 111) is recommended for most applications. these two settings allow a small trade-off between efficiency and distortion. longer nonoverlap times generally increase distortion while providing little or no decrease in shoot- through current. specifications section. large amounts of jitter on the clock input degrade performance. whenever possible, avoid passing the clock signal though programmable logic and other circuits with unknown or variable propagation delay. in general, clock signals suitable for audio adcs or dacs are also appropriate for use with the ad1994. clocking the ad1994 - modulator requires an external clock source with a nominal frequency of 12.288 mhz. this clock can come from a crystal or from an existing clock signal in the application circuit. the discrete time portions of the modulator run internally at 6.144 mhz, corresponding to 128 f , where f s s = 48 khz.
ad1994 rev. 0 | page 19 of 24 clocking multiple am plifiers in parallel if there are multiple ad199x family amplifiers connected to the same pv dd supply, use the same clock source (or synchronous derivatives) for each amplifier as previously described. avoid clocking amplifiers from similar but asynchronous clocks if they use the same power supply because this can result in beat frequencies. protection circuits and error reporting thermal protection the ad1994 features thermal protection. when the die temperature exceeds approximately 135c, the thermal warning error output ( err1 ) is asserted. if the die temperature exceeds approximately 150c, the thermal shutdown error output ( err2 ) is asserted. if this occurs, the part shuts down to prevent damage to the part. when the die temperature drops below approximately 120c, the part returns to normal operation automatically and negates both error outputs. overcurrent protection the ad1994 features over current or short-circuit protection. if the current through any power transistors exceeds approximately 4 a, the part enters a mute state and the overcurrent error output ( err0 ) is asserted. this is a latched error and does not clear automatically. restore normal operation and clear the error condition by either asserting and then negating reset or by asserting and then negating mute .
ad1994 rev. 0 | page 20 of 24 application circuits outr+ nfr+ outr? nfr? 0.1f 0.1f 0.1f 1000f pv dd l c r1 r2 outl+ nfl+ l r1 r2 outl? nfl? c pv dd pv dd l c r1 r2 l r1 r2 c pv dd pv dd err0 overcurrent err1 thermal warning err2 thermal shutdown ainl ainl mod_filt 6.8f 10k ? ref_filt 4.7f 47f 47f 10f 10f 0.1f reset mute dctrl0 dctrl1 dctrl2 clki clko pga1 pga0 0.1f 1000f pv dd av dd dv dd ad1994 + + + + + + + + r1 = 4.2k ? r2 = 1.8k ? l = 18h c = 1f load = 6 ? digital inputs avdd dvdd pvdd1 pvdd2 agnd dgnd pgnd1 pgnd2 05775-048 figure 48. typical stereo circuit
ad1994 rev. 0 | page 21 of 24 outline dimensions 0.25 min compliant to jedec standards mo-220-vmmd-4 pin 1 indicator top view 8.75 bsc sq 9.00 bsc sq 1 64 16 17 49 48 32 33 0.45 0.40 0.35 0.50 bsc 0.20 ref 12 max 0.80 max 0.65 typ 1.00 0.85 0.80 7.50 ref 0.05 max 0.02 nom 0.60 max 0.60 max exposed pad (bottom view) 0.30 0.25 0.18 seating plane pin 1 indicator 7.25 7.10 sq 6.95 122105-0 figure 49. 64-lead lead frame chip scale package [lfcsp_vq] 9 mm 9 mm body, very thin quad (cp-64-3) dimension shown in millimeters ordering guide model temperature range package description package option ad1994acpz ?40c to +85c 64-lead lead frame chip scale package (lfcsp_vq) cp-64-3 1 ad1994acpzrl ?40c to +85c 64-lead lead frame chip scale package (lfcsp_vq), 13 tape and reel cp-64-3 1 ad1994acpzrl7 ?40c to +85c 64-lead lead frame chip scale package (lfcsp_vq), 7 tape and reel cp-64-3 1 eval-ad1994eb evaluation board 1 z = pb-free part.
ad1994 rev. 0 | page 22 of 24 notes
ad1994 rev. 0 | page 23 of 24 notes
ad1994 rev. 0 | page 24 of 24 notes ?2006 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. d05775-0-2/06(0)

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