(question) TBA820M audio amplifier

[nandax]

I build the audio circuit using speaker connected to ground according to datasheet

http://www.datasheetcatalog.org/data...cs/mXqzurv.pdf

it worked perfectly ,
but the problem now i dont understand the relation between the pin description and the connection of the circuit,
for example how can I set the gain setting there? why should I put the certain value of resistor and capacitor?
can somebody give me the information about the function of each pin and how to assign it?

[pacificblue]

Pin 1: Frequency compensation. Cb and Rf determine a low pass filter, with which you determine the upper frequency limit. Select Cb according to Rf from Figure 7 on page 4 of the datasheet.

Pin 2: Gain Setting (Inverting Input). The gain is set by Rf and R5. R5 is 6k and inside the IC, look at the schematic on page 2. Choose Rf according to your needs.

Pin 3: Non-inverting input.
Pin 4: Ground.
Pin 5: Output.
Pin 6: Supply Voltage.

Pin 7: Bootstrap. Used to maintain the output signal symmetric. Refer to Figure 1 or 2 on page 1 for the correct connection.

Pin 8: Ripple Rejection. Add a capacitor there, if you hear hum or buzz through your speaker that is not caused by ground loops.

[nandax]

Originally posted by pacificblue
Pin 1: Frequency compensation. Cb and Rf determine a low pass filter, with which you determine the upper frequency limit. Select Cb according to Rf from Figure 7 on page 4 of the datasheet.

Pin 2: Gain Setting (Inverting Input). The gain is set by Rf and R5. R5 is 6k and inside the IC, look at the schematic on page 2. Choose Rf according to your needs.

Pin 3: Non-inverting input.
Pin 4: Ground.
Pin 5: Output.
Pin 6: Supply Voltage.

Pin 7: Bootstrap. Used to maintain the output signal symmetric. Refer to Figure 1 or 2 on page 1 for the correct connection.

Pin 8: Ripple Rejection. Add a capacitor there, if you hear hum or buzz through your speaker that is not caused by ground loops.

thanks for the reply..
I still dont get about pin 1 frequency compensation,
u said that it depend on Cb and Rf
but if i follow this scjhemtaic
http://www.electronica.ro/audio/TBA820M.shtml
Cb= 220 pF and Rf= 120 Ohms
so upper frequency limit is 6 Mhz
so hat is the relation with frequency compensation?

[mjf]

hello.
please look at fig.8(frequencyresponse):recommended vaues are c=220pf and r=120 ohm for standardoperation(this will work up to 20 kilohertz,not 6 mhz -i think you have made an error when looking at fig.7).
if you want to alter the voltagegain,you have to change rf and find in the diagram the value of cb that fits.
cb is for hf-stability(the ic will not begin to oscillate...)
greetings............

[nandax]

Originally posted by mjf
hello.
please look at fig.8(frequencyresponse):recommended vaues are c=220pf and r=120 ohm for standardoperation(this will work up to 20 kilohertz,not 6 mhz -i think you have made an error when looking at fig.7).
if you want to alter the voltagegain,you have to change rf and find in the diagram the value of cb that fits.
cb is for hf-stability(the ic will not begin to oscillate...)
greetings............

thanks for the reply..
but what is the function of C1 in figure 2?
is it also influence the gain?
and what is relation between C5 and bootstrap pin?

[mjf]

this is an amp with a single-supply,it means that there must be some caps built in to isolate the dc-current from ground.here is it c1 and c5.they influence the gain of the bass,to small values will cut the bass of............
c5 is a bootstrapcap,it is a kind of technic to give some (power)ic`s better properties (or performance).
greetings.............

[poynton]

Bootstrapping is an active load technique to increase the available output voltage swing. so more power from a small ic.

Andy

[nandax]

Originally posted by poynton
Bootstrapping is an active load technique to increase the available output voltage swing. so more power from a small ic.

Andy

thanks for the reply..
but can u explain it easier with example maybe what is bootstrapping in that schematic is?
in figure 2 it use C7 and C5 also R3

[pacificblue]

Originally posted by nandax
but can u explain it easier with example maybe what is bootstrapping in that schematic is?
in figure 2 it use C7 and C5 also R3

In figure 2 the bootstrap circuit is formed by R3 and C7. Without the bootstrap capacitor the voltage swing would be unsymmetric. The bootstrap capacitor loads the transistors for the positive cycle so that the voltage swing becomes symmetric again and you can make best use of the available supply voltage.

C5 is the DC blocking cap. Without it DC would pass through your speakers and could destroy them. It forms a high pass filter together with the speaker with a roll-off at f = 1 / (2*PI*C*Rl). E. g. 220 µF with an 8 Ohm speaker would give you a lower f(-3) at ~90 Hz. With a 4 Ohm speaker ~180 Hz.

[nandax]

Originally posted by pacificblue


In figure 2 the bootstrap circuit is formed by R3 and C7. Without the bootstrap capacitor the voltage swing would be unsymmetric. The bootstrap capacitor loads the transistors for the positive cycle so that the voltage swing becomes symmetric again and you can make best use of the available supply voltage.

C5 is the DC blocking cap. Without it DC would pass through your speakers and could destroy them. It forms a high pass filter together with the speaker with a roll-off at f = 1 / (2*PI*C*Rl). E. g. 220 µF with an 8 Ohm speaker would give you a lower f(-3) at ~90 Hz. With a 4 Ohm speaker ~180 Hz.

how can i determine the input impedance of that circuit?