TDA7391 MUTE and SYNC pins

leon2 · ‎2015-05-10

Posted on May 11, 2015 at 02:41

The TDA7391 (

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00000162.pdf

) has two pins that are named MUTE and SYNC. SYNC is supposed to be connected to ground through a resistor (named R2), and MUTE is supposed to be connected to a capacitor (named C3). The datasheet notes that: ''The values of C3 and R2 determine the time required to bias the amplifier.''

The datasheet has an example circuit (Figure 3 in the datasheet) which shows R2 as 56 kOhm and C3 as 33 F. I think that last number must be a typo.

Does anyone know what a good value for C3 is? Does anyone know how exactly the values of C3 and R2 determine the time required to bias the amplifier? Is it just the RC time?

For what it's worth, the

http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/DM00051686.pdf

(a similar device) has a R2 of 220 kOhm and a C3 of 2.2 uF in its example circuit. That datasheet also notes: ''The suggested values of C3 and R2 define the correct timing in order to switch on/off the amplifier without any pop noise.'' However, the datasheet still does not say how R2 and C3 were chosen.

Nickname1623_O · ‎2015-05-10

Posted on May 11, 2015 at 03:39

Hi Inmaurer ,

for TDA7391 , the mute pin capacitor value should be 33uF .

the R2 value had been used to adjust charge current for C3 , so you can also use the configuration for TDA7391LV .

Thanks

leon2 · ‎2015-05-11

Posted on May 11, 2015 at 18:56

Hello zhao.yun tao,

Thank you for your response. I have two more questions:

1) Do you know what happens to C3? For example, should it charge until it reaches Vs? Should the charging happen on the timescale of C3 * R2? (See below.)

2) Can you say any more about how R2 and C3 are chosen? Assuming it's an RC time, 33 uF * 56 kOhm = 1.8 s, and 2.2 uF * 220 kOhm = 0.5 s.

(I'm asking because I'm trying to troubleshoot a TDA7391 circuit. Anything I can learn about its behaviour is useful.)

Nickname1623_O · ‎2015-05-12

Posted on May 12, 2015 at 09:43

hi Inmaurer ,

the time constant is not simply R*C, the R2 value will be relavent with C3 charging current .

you may monitor the output DC level and mute pin DC level ramp up with different R2 value , let's say 100K ohm and 220K ohm , then you can get relation between charging current and setting resistor .

Thanks