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TDA9855 Datasheet(PDF) 11 Page - NXP Semiconductors |
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TDA9855 Datasheet(HTML) 11 Page - NXP Semiconductors |
11 / 52 page 1997 Nov 04 11 Philips Semiconductors Product specification I2C-bus controlled BTSC stereo/SAP decoder and audio processor TDA9855 SUBWOOFER; SURROUND SOUND CONTROL The subwoofer or the surround mode can be activated with the control bit SUR (see Table 6). A low bit provides an output signal 1 ⁄2(L + R) in subwoofer mode, a high bit selects surround mode and provides an output signal 1 ⁄2(L − R). The signal is fed through a volume control stage with a range from +14 to −14 dB in 2 dB steps on top of the main channel control to the output pin OUTS. The last setting is the mute position (see Table 11). The capacitor C35 at pin SW provides a 230 Hz low-pass filter in subwoofer mode. In surround mode this capacitor should be disconnected. If balance is not in mid position the selected left and right output levels will be combined. MUTE The mute function can be activated independently with the last step of volume or subwoofer/surround control at the left, right or centre output. By setting the general mute bit GMU via the I2C-bus all audio part outputs are muted. All channels include an independent zero-crossing detector. The zero-crossing mute feature can be selected via bit TZCM: TZCM = 0: forced mute with direct execution TZCM = 1: execution in time with signal zero-crossing. In the zero-crossing mode a change of the GMU bit is activated but not executed. The execution is enabled at the next zero-crossing of the signal. To avoid a large delay of mute switching, when very low frequencies are processed, or the output signal amplitude is lower than the DC offset voltage, the following I2C-bus transmissions are needed: A first transmission for mute execution A second transmission approximately 100 ms later, which must switch the zero-crossing mode to forced mute (TZCM = 0) A third transmission to reactivate the zero-crossing mode (TZCM = 1). This transmission can take place immediately, but must follow before the next mute execution. Adjustment procedure COMPOSITE INPUT LEVEL ADJUSTMENT Apply the composite signal (from the FM demodulator) with 100% modulation (25 kHz deviation) L + R; fi = 300 Hz. Set input level control via the I2C-bus monitoring line output (500 mV ±20 mV). Store the setting in a non-volatile memory. Adjustment of the spectral and wideband expander is performed via the stereo channel separation adjust. AUTOMATIC ADJUSTMENT PROCEDURE • Capacitors of external inputs EIL and EIR must be grounded • Composite input signal L = 300 Hz, R = 3.1 kHz, 14% modulation for each channel; volume gain +16 dB via the I2C-bus; to avoid annoying sound level set GMU bit to logic 1 during adjustment procedure • Effects, AVL, loudness off • Selector setting SC0, SC1 and SC2 = 0, 0, 0 (see Table 12) • Line out setting bits: STEREO = 1, SAP = 0 (see Table 21) • Start adjustment by transmission ADJ = 1 in register ALI3; the decoder will align itself • After 1 second, stop alignment by transmitting ADJ = 0 in register ALI3 read the alignment data by an I2C-bus read operation from ALR1 and ALR2 (see Chapter “I2C-bus protocol”) and store it in a non-volatile memory; the alignment procedure overwrites the previous data stored in ALI1 and ALI2 • Disconnect the capacitors of external inputs from ground. MANUAL ADJUSTMENT Manual adjustment is necessary when no dual tone generator is available (e.g. for service). • Spectral and wideband data have to be set to 10000 (middle position for adjustment range) • Composite input L = 300 Hz; 14% modulation • Adjust channel separation by varying wideband data • Composite input L = 3 kHz; 14% modulation • Adjust channel separation by varying spectral data • Iterative spectral/wideband operation for optimum adjustment • Store data in non-volatile memory. After every power-on, the alignment data and the input level adjustment data must be loaded from the non-volatile memory. TIMING CURRENT FOR RELEASE RATE Due to possible internal and external spreading, the timing current can be adjusted via the I2C-bus (see Table 25) as recommended by dbx. |
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