L6235Q datasheet(13/33 Pages) STMICROELECTRONICS

Part #	L6235Q

Description	Tacho output for speed loop

PDF	33 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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13 / 33 page

L6235Q

Circuit description

Doc ID 018997 Rev 2

13/33

Figure 12 shows the lower limit for the ON time tON for having a good PWM current

regulation capacity. It should be mentioned 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 constant.

Therefore, a small COFF value gives more flexibility to the applications (allows smaller ON

time and, therefore, higher switching frequency), but, the smaller the value for COFF, the

more influential the noises on the circuit performance.

Figure 11.

tOFF vs. COFF and ROFF

ON MIN

()

RCRISE

–

⎩

⎪

⎨

⎪

⎧

1.5

μstyp

()

RCRISE

600 C

OFF

⋅

0.1

100

1 .10

Coff [nF]

Roff = 100kΩ

Roff = 47kΩ

Roff = 20kΩ

L6235Q Datasheet(PDF) 13 Page - STMicroelectronics