TAS5548/58 Modulation Index Limit

Sadanori Kato

Hi,

Could you please give us your advice for the modulation index limit ?
For example, the pwm minimum width is 16 DCLK, then pwm maximum duty is 96.88%(100-16/512*100) if setting on the default.
However, the modulation index limit is 93.70%.
How should we consider the modulation index limit ?
So, please tell us the way of thinking.

Best regards,
Kato

over 8 years ago

0 Diego Melendez over 8 years ago

TI__Guru 57800 points

Hi Kato-San,

The modulation limit of this device can be configured for each channel pair on registers 0x16, 0x17, 0x18 and 0x19. You should consider the value configured on this register as the actual modulation limit.

Regards,

-Diego Meléndez López
Audio Applications Engineer

0 Sadanori Kato over 8 years ago in reply to Diego Melendez

Guru 36490 points

Hi Diego-san,

Thank you for your response.
Could you please tell us the difference between the modulation index limit and the pwm maximum duty since I understand how to set the modulation index limit ?

Best regards,
Kato

0 Justin Bohr over 8 years ago in reply to Sadanori Kato

TI__Mastermind 27850 points

Hi Kato-san,

The equation for calculating the modulation index from DCLKs is the following:

DCLKs(1/DCLK rate) = time1

[1-time1(1/PWM rate)]*100 = Duty Cycle

(Duty Cycle) - (1 - Duty Cycle) = Modulation index

Using 196.61 MHz as DCLK rate, and 384 kHz as PWM rate we get the following:

16(1/196.61 MHz) = 81.3 nS

[1-81.3 nS/(1/384 kHz)]*100 = 96.87%

(0.9687) - (1 - 0.9687) = 0.9375 or 93.75%

Justin

Audio

Audio forum

TAS5548/58 Modulation Index Limit