LM2696: Why min on time and off time is needed in LM2696?

Yi Dou

Intellectual 545 points

Part Number: LM2696

Hi expert,

Why are both min on time &min off time needed in COT mode? WHat are the purposes?

(not due to current sensing blanking time, because min on time is much higher than blanking time 165ns)

So that When Vin and fsw are fixed, output voltage Vo_min and Vo_max should be limited by these two parameters, right?

over 4 years ago

0 Andy Chen over 4 years ago

TI__Mastermind 27355 points

Hi Dou,

Ton_min limit the high step down ratio (small duty cycle) conversion for higher Vin to lower Vout, The converter switching freq can be set higher with smaller Ton_min.

Toff_min limit the high duty cycle conversion when Vin is close to Vout.

B R

Andy

0 Yi Dou over 4 years ago in reply to Andy Chen

Intellectual 545 points

Understood, but why do we need these two parameters for duty cycle limitation, instead of 0 and 100%?

0 Andy Chen over 4 years ago in reply to Yi Dou

TI__Mastermind 27355 points

actually the feature of maximum duty cyle like 98% is sated on some converter data sheet, but it maybe just for Fsw=200KHz condition, the user need to check max duty cycle at target Fsw based on Toff-min spec., for same reason, user can check possible highest Fsw for target Vin/Vout with Ton-min spec.

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LM2696: Why min on time and off time is needed in LM2696?