L6207 datasheet(32/53 Pages) STMICROELECTRONICS

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AN1762 APPLICATION NOTE

32/53

APPLICATION EXAMPLE (L6207)

Application Data

Motor Data

Rotation Speed:

300 rpm (fCK = 1kHz)

Winding Resistance:

6.6

Ω

Winding peak Current: 1A

Winding Inductance:

7.9mH

Maximum Ripple:

50mA

Step Angle:

1.8°/step

Supply Voltage:

24V ±5%

Maximum BEMF at 300rpm: 15V

Sequence:

Wave Mode

4.1 Decay mode, sensing resistors and reference voltage.

Referring to approximated formulae in Figure 32, it's possible to calculate the Duty-Cycle (D), the Switching Fre-

quency (fSW), the Current Ripple (∆I). With a 15 µs off-time, we will have:

≅ 63%, fSW ≅ 25kHz, ∆I ≅ 29mA. The on-time is tON = D / fSW ≅ 25µs, which is far from the minimum allowed

(1.5µs), so slow decay can be used.

The bulk capacitor need to withstand at least 24V + 5% + 25%

≅ 32V. A 50V capacitor will be used. Allowing a

voltage ripple of 200mV, the capacitor ESR should be lower than 200mV / 1A = 200m

Ω; the AC current capa-

bility should be about 1A.

Providing a reference voltage of 0.5V, 0.5

Ω sensing resistor are needed. The resistors power rating is about PR

≅ Irms2 · RSENSE · D ≅ 0.32W. Two 1Ω - 0.25W - 1% resistors in parallel are used. The charge pump uses rec-

ommended components (1N4148 diodes, ceramic capacitors and a 100

Ω resistor to reduce EMI).

R = 18k

Ω, C = 1.2 nF are connected to the RC pins, obtaining tOFF ≅ 16µs. On the EN pins 5.6nF capacitors

have been placed, and the pins are driven by the µC through 100k

Ω resistors. With these values, in case of

short circuit between two OUT pins or an OUT pin and GND, the PowerDMOS turns off after about 1µs, and

tDISABLE ≅ 240µs.

Figure 34. Application Example.

With Wave Drive selected, referring to Figure 31 to Figure 33, the dissipating power is about 1.36 W. If the am-

bient temperature is lower than 50°C, with 4cm2 of copper area on the PCB and a SO24 package, the estimated

junction temperature is about 123°C. Using more copper area or a PowerDIP package will reduce the junction

temperature.

VS = 24 V

Vref = 0.5 V

ENB

IN2B

IN2A

IN1B

IN1A

VrefA

VrefB

RCA

RCB

GND

SENSEA

SENSEB

VSA

VSB

VBOO T

OUT1B OUT2B

OUT1A OUT2A

1N4148

100 k

Ω

1.2 nF

Ceramic

18 k

Ω

100

Ω

0.25W

5.6 nF

Ceramic

47nF

Ceramic

18 k

Ω

1.2 nF

Ceramic

100nF 50V

Cera mi c

220nF 50V

Ceramic

10nF 50V

Ceramic

100µF 50V

ESR<200m

Ω

L6207

µC

Custom Logic

2-Phase

Stepper Motor

4 X

Ω, 0.25 W, 1%

2 k

Ω 0.25 W

18 k

Ω 0.25 W

Logic Supply

5 V

ENA

100 k

Ω

5.6 nF

Cera mi c

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