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Hi all, In the motorola app. brief to design a class D amplifier, the author states that to work out the PWM value register, the following formula applies: PWM Value = (Input Data Sample) x (PWM Modulus) However, in the 56f80x user's manual, it is stated then whenever the PWM Value is greater than or equal to the PWM Modulus, the output of the PWM will be 0 permanently (which makes sense). When using above formula, the PWM value will always be more than the PWM modulus except when the input data samples = 0. (The input data samples is from a audio CODEC which have a 16 bit resolution). Obviously I am reading the formula incorrectly. Can someone please shed more light on this subject for me. Thank you in advance... Roelof Oelofsen Telkom Development Laboratory Telkom SA

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Using fractional math, if the input data sample is a FRACT16 number, the formula holds true. I believe you will want to deal with the sign of the sample separately, as to which output to enable. -----Original Message----- From: Roelof Oelofsen [mailto:] Sent: Tuesday, February 12, 2002 2:21 AM To: Subject: [motoroladsp] Application brief BR1544/D Hi all, In the motorola app. brief to design a class D amplifier, the author states that to work out the PWM value register, the following formula applies: PWM Value = (Input Data Sample) x (PWM Modulus) However, in the 56f80x user's manual, it is stated then whenever the PWM Value is greater than or equal to the PWM Modulus, the output of the PWM will be 0 permanently (which makes sense). When using above formula, the PWM value will always be more than the PWM modulus except when the input data samples = 0. (The input data samples is from a audio CODEC which have a 16 bit resolution). Obviously I am reading the formula incorrectly. Can someone please shed more light on this subject for me. Thank you in advance... Roelof Oelofsen Telkom Development Laboratory Telkom SA _____________________________________ /groups.php3 <http://www.dsprelated.com/groups.php3 > .

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Thank you, Jerry (It is Jerry I assume?) It's much clearer now. There is another problem though. If I have a PWM output stage switching at 1Mhz, the maximum resolution will be 40 if you use an 56807 running at 40MIPS. Am I correct? Thanks again Roelof Oelofsen Telkom Development Laboratories Telkom SA >>> "Johnson, Jerry" <> 02/13/02 04:31PM >>> Using fractional math, if the input data sample is a FRACT16 number, the formula holds true. I believe you will want to deal with the sign of the sample separately, as to which output to enable. -----Original Message----- From: Roelof Oelofsen [mailto:] Sent: Tuesday, February 12, 2002 2:21 AM To: Subject: [motoroladsp] Application brief BR1544/D Hi all, In the motorola app. brief to design a class D amplifier, the author states that to work out the PWM value register, the following formula applies: PWM Value = (Input Data Sample) x (PWM Modulus) However, in the 56f80x user's manual, it is stated then whenever the PWM Value is greater than or equal to the PWM Modulus, the output of the PWM will be 0 permanently (which makes sense). When using above formula, the PWM value will always be more than the PWM modulus except when the input data samples = 0. (The input data samples is from a audio CODEC which have a 16 bit resolution). Obviously I am reading the formula incorrectly. Can someone please shed more light on this subject for me. Thank you in advance... Roelof Oelofsen Telkom Development Laboratory Telkom SA _____________________________________ /groups.php3 <http://www.dsprelated.com/groups.php3 > .

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