L7203S datasheet(10/13 Pages) STMICROELECTRONICS

10 / 13 page

PHS on = tsys * 4 * Nphase

where: tsys = 50ns if fsys = 20MHz

The resulting PHASE SHIFT value is:

PHASE SHIFT = Nphase(8:3) x 10 +

Nphase(2:0) x 1.25

For istance if Nphase = 00011 110

PHASE SHIFT = 3 x 10 + 6 x 1.25 = 37.5

Low Voltage Detector

This circuit detects if VCC is lower than a fixed

threshold. If this event happens the internal logic

is resetted and the output FETS are forced in

High impedance.

Slew Rate Control Circuit

This circuit fixes the slew rate for the output stage

in order to reduce EMI.

A reference current is generated by means of an

internal reference voltage and an external resis-

tor.

The ISRC is used to fix slew rate with a linear law:

SLEW RATE = RSLR/ISRC

⋅

VREF

REXT

Rext recommended value >10K

Ω

Prescaler Pin

The PRS Pin should be forced to ground when

the FSYS frequency is lower (or equal) than

20MHz and should be forced to VCC when FSYS

frequency is higher than 20MHz, in order to set

the correct timing during the inductive sense,

start up and resynchronization phases.

Example of different phase shift settings are

shown in the following pictures.

PHS on

NPhase

Phase Shift (degree)

time

µs

decimal

bit

56.0

56.2

56.4

56.6

56.8

57.0

57.2

57.4

> 57.6

280

281

282

283

284

285

286

287

288

100011 000

100011 001

100011 010

100011 011

100011 100

100011 101

100011 110

100011 111

100100 000

350

351.25

352.50

353.75

355.00

356.25

357.50

358.75

Table 1. (continued)

VREF

ISRC =

SRC

Rext

Figure 12.

Hall sensor

OUT V

OUT U

OUT W

Figure 13. Phase relation between OUTPUT

sinusoidal voltage (PWM_IN > 50%)

and Hall sensor signal writin Phase

shift = 0° (default value)

Hall sensor

OUT V

OUT U

OUT W

30°

Figure 14. Phase relation between OUTPUT

sinusoidal voltage (PWM_IN > 50%)

and Hall sensor signal writing Phase

shift = 30°

Hall sensor

30°

OUT V

OUT U

OUT W

Figure 15. Phase relation between OUTPUT

sinusoidal voltage (PWM_IN > 50%)

and Hall sensor signal writing Phase

shift = 330°

L7203

10/13

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