IRS2452AM self-oscillating frequency calculation

[PhilGood_82]

Hi 

With IRS2452AM, application notes and examples describe 400kHz switching frequency (IRAUDAMP23 for exemple). How modify values to get self-oscillation frequency higher (around 600kHz or 700kHz) ?

Thank you

[Shiva_C]

Hi,

The highest self-oscillating frequency is limited by the propagation delay (300+ ns). 500kHz is the practical max frequency. Note that deadtime needs to be increased for higher frequencies as the inductor ripple reduces.” Unfortunately, we can’t recommend switching higher than 500kHz.

BR,

SC

[PhilGood_82]

Hi SC

Thank you for the answer. Furthermore, if controlled by external clock, can the IRS2452AM work over 500Khz? In IRS2452AM datasheet, the maximum frequency clock is announced at 800Khz, so why working over 500KHz is not possible ? 

I have an other question regarding the IRS2452 ; how is made the relation between the signal input level and the duty cycle of the PWM ; we have a problem on our prototype : when increasing the audio input signal, the output PWM signal becomes irregular and we have broken the output power stage.

The last question : we currently have made a prototype with IRS2452AM + GanDriver 1EDN7116GXTMA1 + Gan Fet (EPC2207). Do you think that 1EDN7116 is necessary or do you think that driving the Gan Fet with a bipolar totem-pole stage is possible (including regulation of the totem-pole supply for voltage limitation on the gate of the Gan Fet) ? 

Thank you

[Shiva_C · Accepted solution]

Hi,

1. The self-oscillating PWM will change the frequency with changes in input signal by its nature.   Can you share more detail on the issue, maybe some pictures?

2. We are driving Infineon GaN devices (IGT40R070D1 E8220) in EVAL_AUDAMP24 without a GaN driver or totem pole. 

BR,

SC

[Shiva_C]

Hi,

“The gate driver stage from COMP to HO/LO is capable of operating 1MHz. The OCP works well up to 800kHz, depending on load current phase angle. What stops making it work at >500kHz is the 330ns propagation delay when the device is used in a self-oscillating PWM topology. As far as using a self-oscillating PWM as shown in the typical application diagram, the loop cannot run at higher than 500kHz. The datasheet is not assuming self-oscillating PWM as device can be used in different topologies.”

BR,

SC

[喜马拉雅之雪]

Hi Philgood_82:

Thanks for your comments.

For audio system, best performance is from balance and she will fouce on customer favorites. For example PCB layout, most experience told us(class-A, class-AB and ClassD AMP), one SCH to different PCB layout, it will be out different sound(tone colour).

For normal application，400kHz PWM is best for system lever.

For Gan FET, IRS2452AM can direct drive it.

[喜马拉雅之雪]

Hi Philgood:

For 600/700 kHz, if only on switching, it is soo easy. Most customer use it with 40kHz sin waveform power piezoceramics drive. There PWM is about 800kHz. But for audio, it is look like disastrous.

[喜马拉雅之雪]

For self-oscillating frequency, it is semicircular trajectory with output pressure difference ratio（VDC- Vpk of audio/Vdc*100%).

If Vpk is near the DC BUS, the switching frequency will been down. So best audio systen need set a buffer for best voice.