1/7 AN1643 application note january 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. sam261 board: sam261 is a bash@6.1 (6x50w + 1x100w) amplifier utilizing the sta530 ic. this board is specifically designed for multi-channel implementation in dvd - htib systems, multi - media systems, mini and micro systems and set top boxes. sam261 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: 5 x 50 w @ 8 ohm load (left / right/ rear-left /rear- right/ centre) 1 x 100w @ 4 ohm load (subwoofer) control software figure 1. by luigi pagotto & marco motta 6 ch volume controller plus sam261 bash amplifier in this document is explained how to connect the audio processor tda7448 to the board bash sam261, in order to obtain a complete amplifier with the volume controlled via i 2 c bus.
AN1643 application note 2/7 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. C 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.
3/7 AN1643 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 sam261 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 sam261 : (connector j9) sam261 module utilize two supply voltages: C signal supply voltage +/-vs: +/- 24vdc / 100ma C power section voltage +/-dc: +50v /3.0a 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 sta530 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 sam261 module it is necessary to connect a wire to the pin.9 of the connector j8: C when pin.9 open : sam261 module is muted C when pin.9 is at 15v : sam261 module is in play. all the 7 channels are configurated in btl and completely separated among them and isolated from the rest of the system.
AN1643 application note 4/7 C interfacing tda7448 to bash@sam261 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
5/7 AN1643 application note bash@sam261 module 6.1 configuration: figure 4. block diagram system specification table 1. parameter rating notes output power sats @8ohm C 50w@thd10% see graphs thd+n <0.05% @ 40w <0.05% @ 75w measured @ 1khz snr -102db (relative to full power) -110db (a-weighted) ch 5 terminated sensitivity 1vrms crosstalk -87db ch 5 @ 10w ,1khz, 8 ohm ch 3 input terminated main power supply 50v / 3a max voltage is 50v min. voltage is 40v aux power supply +/- 24v / 100ma sam261 is a bash? 6.1 amplifier implementation utilizing the sta530 integrated circuit. sta530 4 x 50watts sta530 1 x 100watts 2 x 50watts stabp01 converter 50vdc 8 ohm loads 4 ohm load +/- 24vdc 50ma for each sta530 audio inputs audio inputs the sta530 is a 4 x 50 watt amplifier configurable for 2, 3 of 4 channels of operation. all full range channels are configured for 8 ohms, sub in configured 4 ohms. sam261 is a bash? 6.1 amplifier implementation utilizing the sta530 integrated circuit. sta530 4 x 50watts sta530 1 x 100watts 2 x 50watts stabp01 converter 50vdc 8 ohm loads 4 ohm load +/- 24vdc 50ma for each sta530 audio inputs audio inputs the sta530 is a 4 x 50 watt amplifier configurable for 2, 3 of 4 channels of operation. all full range channels are configured for 8 ohms, sub in configured 4 ohms.
AN1643 application note 6/7 power - on-off sequences: in order to avoid damages to the sam261 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 satellite channels figure 6. thd +noise vs. output power subwoofer channel distortion vs. output power tda7448 + sam261 output1 rl= 8 ohm solid cyan line f=1 khz dash green line = 10 khz dot red line = 100 hz 0.01 10 0.02 0.05 0.1 0.2 0.5 1 2 5 % 100m 60 200m 500m 1 2 5 10 20 w distortion vs. output power tda7448 + sam261 output s ubwoofer rl= 4 ohm solid line green f=1 khz dot line yellow = 100 hz 0.01 10 0.02 0.05 0.1 0.2 0.5 1 2 5 % 600m 100 12 51020 50 w
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 7/7 AN1643 application note
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