L6207 datasheet(16/53 Pages) STMICROELECTRONICS

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AN1762 APPLICATION NOTE

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be bigger than tRCRISE for allowing a good current regulation by the PWM stage. Furthermore, the on time tON

can not be smaller than the minimum on time tON(MIN).

tRCRISE = 600 · COFF

3.11.1 Off-time Selection and minimum on-time (L6207 ONLY)

Figure 16 also shows the lower limit for the on time tON for having a good PWM current regulation capacity. It

has to be said that tON is always bigger than tON(MIN) because the device imposes this condition, but it can be

smaller than tRCRISE - tDT. In this last case the device continues to work but the off time tOFF is not more con-

stant.

So, small COFF value gives more flexibility for the applications (allows smaller on time and, therefore, higher

switching frequency), but, the smaller is the value for COFF, the more influential will be the noises on the circuit

performance.

Figure 16. Off-time selection and minimum on-time (L6207 ONLY).

ON MIN

()

>1.5

µs (typ. value)

RCRISE

–







0.1

100

1 . 10

Coff [nF]

0.1

100

Coff [nF]

R = 20 k

Ω

R = 47 k

Ω

R = 100 k

Ω

L6207 Datasheet(PDF) 16 Page - STMicroelectronics