SCT0 PWM rise time settings

[mohit2904]

Hello All & @Alice_Yang ,

             I am using LPC845 in my project and implementing 4 complementary PWM but my PWM output rise time is high 25 usec but we need around 120 nsec can you please help us to know how we can change PWM rise time as shown in attached image "trise".

using SCT @ 18MHz and configure SCT as BIDIR mode

Rise time its coming around= 25 micro sec 

but we need in our application rise time = 125 nsec or lower

[Alice_Yang]

Hello @mohit2904 

The rise time is related to pin drive capacity and the load, we can't control it by software.

You can consider add a Pre-Drive after PWM pin.

BR

Alice

[mohit2904]

Not Clear because in datasheet (attached image) it is mentioned around (3ns -5ns IO pins rise time) & ( 6ns max SCTimer/PWM output skew time) then why in our case it is coming too high please help is it because of we split timer as below in our application?

SCT0->CONFIG |= (1 << 17); // split timers, auto limit
SCT0->CTRL_ACCESS16BIT.CTRLL |= (1 << 4); // configure SCT1 as BIDIR*/

[mohit2904]

attachment++

Not Clear because in datasheet (attached image) it is mentioned around (3ns -5ns IO pins rise time) & ( 6ns max SCTimer/PWM output skew time) then why in our case it is coming too high please help is it because of we split timer as below in our application?

SCT0->CONFIG |= (1 << 17); // split timers, auto limit
SCT0->CTRL_ACCESS16BIT.CTRLL |= (1 << 4); // configure SCT1 as BIDIR*/

[Alice_Yang]

Hello @mohit2904 

To get the value on DS, need meet conditions:

BR

Alice