1/6 AN1656 application note february 2003 before to start the description we summarize what are the characteristic of the two boards. tda7448 board: with this board is possible to obtain the independent volume control for six channels in 1.0db steps, the volume attenuation ranges from 0 to -79db. all functions are programmable via serial bus (i 2 c). the board is feed with a supply voltage ranging from 4.75 to10v. it will be also described how to use the control sw. sam351 board: sam351 is a bash@5.1 (6x100w) amplifier utilizing the sta575 ic. this board is specifically designed for multi-channel implementation in dvd - htib systems, multi - media systems, av receivers. sam351 is dimensioned to provide the maximum output power (@ thd= 10%) on two channels and 1/ 3 max pout on the remaining outputs, this assumption is important to define the main power supply size (+50v). in this document we describe an application configuration where the used loads are: 6 x 100w @ 6 ohm control software figure 1. by luigi pagotto & marco motta 6 ch volume controller plus sam351 bash amplifier in this document is explained how to connect the audio processor tda7448 to the board bash sam351, in order to obtain a complete amplifier with the volume controlled via i 2 c bus.
AN1656 application note 2/6 once installed, the control software will appear as shown in fig.1, here below is explained how to work with it. step 1: clicking on the "parallel port" icon it will appear the following image. figure 2. the program automatically detects the printer ports installed in the system and enables them. select the port connected to the device evaluation board through the appropriate interface. to verify if the device is working, press the button with the binocular . the program scans all possible device address and stops when it receives the acknowledge. to restore default device address press the button with the default value. the clock frequency slider allows the user to vary the communication speed. three buttons set the bus operating mode: C ack detection. it toggles ack detection on/off. if the ack detection is on and the device is not acknowledging the commands, the button is red , signaling that ack error occurred on last command. incremental mode. it toggles incremental bus on/off .when incremental bus is active all the pre- set commands are sent by using incremental bus mode (i.e. the message is made by the first sub- address and then all the data bytes follow. the device automatically increments the destination ad- dress internally). the send button acts as well C block mode. it toggles block mode on/off . when block mode is on , any variation in volume is not sent to the device in real time. commands are sent all together either when user click on send command or block mode is turned to off. step 2: push the button 0 in order to load the default reset condition. it is possible now to increment /decrement the volume attenuation acting on the sliders command or pushing the buttons that allow to attenuate by one step. it is possible to save 4 settings for the volume pressing the buttons [14] + shift.
3/6 AN1656 application note additional features: acting on the button is shown the registers' table, where is shown the current value of all the de- vice's registers. it is real time updated as the user modifies any parameter. it is possible to entry directly a value in binary , hexadecimal or decimal notation by clicking on the correspondent cell and inserting a new value. the send command refresh all registers of the device with current settings. it may use the incremental mode it is enabled. pcb and components layout in fig.2 is shown how to connect the two boards tda7448 and sam351 in order to have a complete am- plification system with volume control via i 2 c. to complete the application it is necessary to provide the correct power supply for the two boards as fol- lows: tda7448 : (connector j6) the supply voltage to be used can range from +5 up to +10v sam351 : (connector j9) sam351 module utilize two supply voltages: C signal supply voltage +/-vs: +/- 24vdc / 100ma C power section voltage +/-dc: +50v /4.0a in the dimensioning of the power section is important to know that the module is able to provide the max- imum power (@thd=10%) on two channels and instantaneously 1/3 max pout on the remaining outputs or continuously 1/8 of max. pout. the two supply voltages are completely separated between them: the signal vs is splitted (+/-24v) and its central point (a-gnd) is the reference ground for the sta575 circuits (inputs, stand-by, etc.), while the power dc is a single supply and its reference must be completely isolated from a-gnd . in order to implement the mute function for the sam351 module it is necessary to connect a wire to the pin.9 of the connector j8: C when pin.9 open : sam351 module is muted C when pin.9 is at 15v : sam351 module is in play. all the 6 channels are configurated in btl and completely separated among them and isolated from the rest of the system.
AN1656 application note 4/6 C interfacing tda7448 to bash@sam351 figure 3. connector audio signals i2c bus a udio n put s ignals vcc power supply connector speakers connectors connector description gnd out6 out5 out4 out3 out2 out1 j4 9 8 7 6 5 4 3 2 1 j8 nc 4dc- 3dc+ 2vs- 1vs+ 50v -24v +24v j9 +15v play openmute gnd to supply
5/6 AN1656 application note bash@sam351 module 6.1 configuration: figure 4. block diagram system specification table 1. parameter rating notes output power sats @6ohm C 100w@thd10% see graphs thd+n <0.05% @ 40w <0.05% @ 75w measured @ 1khz snr -104db (relative to full power) -113db (a-weighted) sensitivity 1.3vrms amplifier crosstalk -76db (relative to 10w) 1khz, 8 ohms main power supply 60v / 4a max voltage is 60v min. voltage is 50v aux power supply +/- 24v / 100ma v s supply input board supplied to facilitate sta575 sta575 2 x 100watts 2 x 100watts sta575 sta575 2 x 100watts 2 x 100watts stabp01 stabp01 converter converter 60vdc 6 ohm loads +/- 24vdc 50ma for each sta530 audio inputs audio inputs sta575 sta575 2 x 100watts 2 x 100watts audio inputs sta575 sta575 2 x 100watts 2 x 100watts sta575 sta575 2 x 100watts 2 x 100watts stabp01 stabp01 converter converter 60vdc 6 ohm loads +/- 24vdc 50ma for each sta530 audio inputs audio inputs sta575 sta575 2 x 100watts 2 x 100watts audio inputs
information furnished is believed to be accurate and reliable. however, stmicroelectronics assumes no responsibility for the co nsequences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. no license is granted by implication or otherwise under any patent or patent rights of stmicroelectronics. specifications mentioned in this publicati on are subject to change without notice. this publication supersedes and replaces all information previously supplied. stmicroelectronics prod ucts are not authorized for use as critical components in life support devices or systems without express written approval of stmicroelectro nics. the st logo is a registered trademark of stmicroelectronics ? 2003 stmicroelectronics - all rights reserved stmicroelectronics group of companies australia - brazil - canada - china - finland - france - germany - hong kong - india - israel - italy - japan -malaysia - malta - morocco - singapore - spain - sweden - switzerland - united kingdom - united states. http://www.st.com 6/6 AN1656 application note power - up sequences: in order to avoid damages to the sam351 board it is important to follow these sequences: at power-on apply in the first the auxiliary power supply (24v) and after the main power supply (+50v) , in this condition the system is in "mute state" and it can move in "play state" with the switch present on the pcb. at power-off is better to bring the sam module in "mute state" and after that to follow this order: switch- off the main supply voltage (+50v) and subsequently the auxiliary power supply. (24v) . figure 5. thd +noise vs. output power 0.01 10 0.02 0.05 0.1 0.2 0.5 1 2 5 % 0 110 10 20 30 40 50 60 70 80 90 100 w 0.01 10 0.02 0.05 0.1 0.2 0.5 1 2 5 % 0 110 10 20 30 40 50 60 70 80 90 100 w
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