WM8956_07

w DESCRIPTION The WM8956 is a low power, high quality stereo DAC designed for portable multimedia applications. Stereo class D speaker drivers provide 1W per channel into 8Ω loads with a 5V supply. Low leakage, excellent PSRR and pop/click suppression mechanisms also allow direct battery connection to the speaker supply. Flexible speaker boost settings allow speaker output power to be maximised while minimising other analogue supply currents. A highly flexible input configuration for up to three stereo sources is integrated, with a complete microphone interface. External component requirements are drastically reduced as no separate microphone, speaker or headphone amplifiers are required. Stereo 24-bit sigma-delta DACs are used with low power oversampling digital interpolation filters and a flexible digital audio interface. The master clock can be input directly or generated internally by an onboard PLL, supporting most commonly-used clocking schemes. The WM8956 operates at analogue supply voltages down to 2.7V, although the digital supplies can operate at voltages down to 1.71V to save power. The speaker supply can operate at up to 5.5V, providing 1W per channel into 8Ω loads. Unused functions can be disabled using software control to save power. The WM8956 is supplied in a very small and thin 5x5mm QFN package, ideal for use in hand-held and portable systems. WM8956 Hi-Fi DAC with 1W Stereo Class D Speaker Drivers and Headphone Drivers FEATURES • • • • DAC SNR 99dB (‘A’ weighted), THD -87dB at 48kHz, 3.3V Pop and click suppression 3D Enhancement Stereo Class D Speaker Driver • 0.546 fs +/- 0.03dB -6dB 0.454 fs 0.546 fs -50 dB 0 0.5 fs +/- 0.03 dB 0.454 fs TEST CONDITIONS MIN TYP MAX UNIT DAC FILTERS Mode Normal Sloping Stopband Group Delay 18 / fs 18 / fs DAC FILTER RESPONSES DAC STOPBAND ATTENUATION The DAC digital filter type is selected by the DACSLOPE register bit as shown in Table 42. REGISTER ADDRESS R6 (06h) DAC Control (2) BIT 1 LABEL DACSLOPE DEFAULT 0 DESCRIPTION Selects DAC filter characteristics 0 = Normal mode 1 = Sloping stopband mode Table 42 DAC Filter Selection w PTD, July 2007, Rev 2.1 73 WM8956 M AGNITUDE(dB) 10 -10 0 -30 -50 0.02 0.04 MAGNITUDE(dB) Preliminary Technical Data 0.5 1 1.5 2 2.5 3 0.035 0.03 0.025 -70 -90 -110 -130 -150 Frequency (fs) 0.015 0.01 0.005 0 -0.005 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Frequency (fs) Figure 36 DAC Digital Filter Frequency Response (Normal Mode) M AGNITUDE(dB) 10 -10 0 -30 -50 -70 -90 -110 -130 -150 Frequency (fs) 0.5 1 1.5 2 2.5 3 Figure 37 DAC Digital Filter Ripple (Normal Mode) MAGNITUDE(dB) 0.05 0 -0.05 -0.1 -0.15 -0.2 -0.25 -0.3 -0.35 -0.4 -0.45 -0.5 Frequency (fs) 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Figure 38 DAC Digital Filter Frequency Response (Sloping Stopband Mode) Figure 39 DAC Digital Filter Ripple (Sloping Stopband Mode) w PTD, July 2007, Rev 2.1 74 Preliminary Technical Data WM8956 DE-EMPHASIS FILTER RESPONSES M AGNITUDE(dB) 0.3 MAGNITUDE(dB) 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 Frequency (Hz) 0 5000 10000 15000 20000 0.25 0.2 0.15 0.1 0.05 0 -0.05 -0.1 -0.15 Frequency (Hz) 0 2000 4000 6000 8000 10000 12000 14000 16000 18000 Figure 40 De-Emhpasis Digital Filter Response (32kHz) Figure 41 De-Emphasis Error (32kHz) M AGNITUDE(dB) 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 Frequency (Hz) 0 5000 10000 15000 20000 25000 MAGNITUDE(dB) 0.2 0.15 0.1 0.05 0 0 -0.05 -0.1 Frequency (Hz) 5000 10000 15000 20000 25000 Figure 42 De-Emhpasis Digital Filter Response (44.1kHz) Figure 43 De-Emphasis Error (44.1kHz) M AGNITUDE(dB) 0 0 -2 -4 -6 -8 -10 -12 Frequency (Hz) 5000 10000 15000 20000 25000 30000 0.1 0.15 MAGNITUDE(dB) 0.05 0 0 -0.05 5000 10000 15000 20000 25000 30000 -0.1 -0.15 Frequency (Hz) Figure 44 De-Emhpasis Digital Filter Response (48kHz) Figure 45 De-Emphasis Error (48kHz) w PTD, July 2007, Rev 2.1 75 WM8956 APPLICATIONS INFORMATION RECOMMENDED EXTERNAL COMPONENTS Preliminary Technical Data SPEAKER SELECTION For filterless operation, it is important to select a speaker with appropriate internal inductance. The internal inductance and the speaker's load resistance create a low-pass filter with a cut-off frequency of: fc = RL / 2πL e.g. for an 8Ω speaker and required cut-off frequency of 20kHz, the speaker should be chosen to have an inductance of: L = RL / 2πfc = 8Ω / 2π * 20kHz = 64µH 8Ω speakers typically have an inductance in the range 20µH to 100µH. Care should be taken to ensure that the cut-off frequency of the speaker's internal filtering is low enough to prevent speaker damage. The class D outputs of the WM8956 operate at much higher frequencies than is recommended for most speakers, and the cut-off frequency of the filter should be low enough to protect the speaker. w PTD, July 2007, Rev 2.1 76 Preliminary Technical Data WM8956 Figure 46 Speaker Equivalent Circuit PCB LAYOUT CONSIDERATIONS The efficiency of the speaker drivers is affected by the series resistance between the WM8956 and the speaker (e.g. inductor ESR) as shown in Figure 47. This resistance should be as low as possible to maximise efficiency. VDD Class D output Switching Losses VMID GND Losses due to resistance between WM8956 and speaker (e.g. inductor ESR) This resistance must be minimised in order to maximise efficiency. Figure 47 Speaker Connection Losses The distance between the WM8956 and the speakers should be kept to a minimum to reduce series resistance, and also to reduce EMI. Further reductions in EMI can be achieved by additional passive filtering and/or shielding as shown in Figure 48. When additional passive filtering is used, low ESR components should be chosen to minimise series resistance between the WM8956 and the speaker, maximising efficiency. LC passive filtering will usually be effective at reducing EMI at frequencies up to around 30MHz. To reduce emissions at higher frequencies, ferrite beads placed as close to the device as possible will be more effective. w PTD, July 2007, Rev 2.1 77 WM8956 Preliminary Technical Data Figure 48 EMI Reduction Techniques w PTD, July 2007, Rev 2.1 78 Preliminary Technical Data WM8956 PACKAGE DRAWING FL: 32 PIN QFN PLASTIC PACKAGE 5 X 5 X 0.9 mm BODY, 0.50 mm LEAD PITCH DM033.D D D2 25 32 L 24 EXPOSED GROUND 6 PADDLE A 1 DETAIL 1 4 INDEX AREA (D/2 X E/2) E2 E 17 8 2X 9 B b 1 bbb M C A B 2X aaa C aaa C 16 e 15 BOTTOM VIEW ccc C A3 A 0.08 C 5 TOP VIEW R = 0.3MM EXPOSED GROUND PADDLE C SEATING PLANE SIDE VIEW A1 DETAIL 2 W T A3 H b Exposed lead G DETAIL 1 Half etch tie bar DETAIL 2 Symbols A A1 A3 b D D2 E E2 e G H L T W MIN 0.80 0 0.18 3.30 3.30 Dimensions (mm) NOM MAX NOTE 0.90 1.00 0.02 0.05 0.20 REF 1 0.25 0.30 5.00 3.45 5.00 3.45 0.50 BSC 0.213 0.1 0.40 0.1 0.2 3.55 3.55 2 2 0.30 0.50 Tolerances of Form and Position aaa bbb ccc REF: 0.15 0.10 0.10 JEDEC, MO-220, VARIATION VHHD-5. NOTES: 1. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.15 mm AND 0.30 mm FROM TERMINAL TIP. 2. FALLS WITHIN JEDEC, MO-220, VARIATION VHHD-5. 3. ALL DIMENSIONS ARE IN MILLIMETRES. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JEDEC 95-1 SPP-002. 5. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. 6. REFER TO APPLICATION NOTE WAN_0118 FOR FURTHER INFORMATION REGARDING PCB FOOTPRINTS AND QFN PACKAGE SOLDERING. 7. THIS DRAWING IS SUBJECT TO CHANGE WITHOUT NOTICE. w PTD, July 2007, Rev 2.1 79 WM8956 IMPORTANT NOTICE Preliminary Technical Data W olfson Microelectronics plc (“Wolfson”) products and services are sold subject to Wolfson’s terms and conditions of sale, delivery and payment supplied at the time of order acknowledgement. Wolfson warrants performance of its products to the specifications in effect at the date of shipment. Wolfson reserves the right to make changes to its products and specifications or to discontinue any product or service without notice. Customers should therefore obtain the latest version of relevant information from Wolfson to verify that the information is current. Testing and other quality control techniques are utilised to the extent Wolfson deems necessary to support its warranty. Specific testing of all parameters of each device is not necessarily performed unless required by law or regulation. In order to minimise risks associated with customer applications, the customer must use adequate design and operating safeguards to minimise inherent or procedural hazards. Wolfson is not liable for applications assistance or customer product design. The customer is solely responsible for its selection and use of Wolfson products. Wolfson is not liable for such selection or use nor for use of any circuitry other than circuitry entirely embodied in a Wolfson product. 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Reproduction of information from Wolfson datasheets is permissible only if reproduction is without alteration and is accompanied by all associated copyright, proprietary and other notices (including this notice) and conditions. Wolfson is not liable for any unauthorised alteration of such information or for any reliance placed thereon. Any representations made, warranties given, and/or liabilities accepted by any person which differ from those contained in this datasheet or in Wolfson’s standard terms and conditions of sale, delivery and payment are made, given and/or accepted at that person’s own risk. Wolfson is not liable for any such representations, warranties or liabilities or for any reliance placed thereon by any person. ADDRESS: W olfson Microelectronics plc 26 Westfield Road Edinburgh EH11 2QB United Kingdom Tel :: +44 (0)131 272 7000 Fax :: +44 (0)131 272 7001 Email :: sales@wolfsonmicro.com w PTD, July 2007, Rev 2.1 80