[ARM] LPC1769 Dead time control problem

[chitikivenu]

Hai all..
I am using LPC1769 to generate PWM with dead time using MCPWM peripheral. The problem is normal PWM is max duty cycle is 48% , inverted PWM should be max duty cycle 48%. But inverted PWM is getting minimum 52% duty cycle. Dead time is 2usec. Can any one help me?

 

[D.A.(Tony)Stewart]

Define your drivers , switches and load ESR.

Skew occurs when Ciss rises with lower RdsOn for each stage.

I assume lpc1769 output RdsOn is 25 Ohm from recollection of Vol/Iol. See end of spec for actual values, and show schematic and waveforms with load ESR.

 

[chitikivenu]

I am not using any drivers, just absorbed wave forms in scope. see the attached image.
pwm switching frequency = 10khz
dead time = 2usec
yellow color = PWM
Blue color = Inverted PWM

 

[D.A.(Tony)Stewart]

Good, now show output pins and how this complementary output is generated with load/no load.

Asymmetric delays are often created with series R and //diode to input Ciss for asymmetric delays to enhance deadtime. Driver Chips do this internally with single ended inputs.

 

[chitikivenu]

LPC1769 has MCPWM peripheral. so, it will also generate complementary output. The complementary out put will get at GPIO pins.

 

[D.A.(Tony)Stewart]

Oh , ok, but they don't satisfy your need for deadtime, so try something else and contact OEM, your purchasing and/or Distributor support with an Incident Report.

Consider a bridge driver chip after you define the load specs.