TDA7498 without any input singal,but it also generate 40KHZ modulating wave output

[dengke]

Posted on September 10, 2014 at 06:06

Although there is any input singal,it still generate 40KHZ modulating wave output.

Could tell me what could cause this?

How can i solve this problem?

Testing method as fellow:

Power Supply: 24V/4Ohm

test load: cement resistor(4Ohm/100W)

#tda7498-modulating-wave-output

[Nickname1623_O]

Posted on September 10, 2014 at 06:22

hi Deng,

if you are following schematic and components value in ST datasheet, the PWM frequency of TDA7498 should be around 310Khz , then you may found some carrier freqeuncy components at speaker output when you turned on the device (even in mute status ).

so please pulled down the mute pin of TDA7498 to confirm the frequency again .

if output signal frequncy is around 300Khz , it's normal.

Thanks

[dengke]

Posted on September 10, 2014 at 08:08

Hi Zhao

   Thanks for your so quickly and professional reply.I attached my wave picture,is this noise voltage? If so could you give me some advice how to improve it. Thanks!

[Nickname1623_O]

Posted on September 10, 2014 at 08:26

hi Deng ,

according to your snap shot , the period of saw wave noise is 38.35uS , so the frequency should be around 26Khz. it's abnormal.

please confirm below items :

1) resistor value for OSC pin , normally the Rosc value should be 39K ohm

2) check the PWM output wavefrom at the IC output pin to confirm PWM operating frequency.

Thanks