AN2836 datasheet(37/57 Pages) STMICROELECTRONICS

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AN2836

Application example (L6227)

Doc ID 15084 Rev 1

37/57

Application example (L6227)

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

≅ 32 V. A 50 V capacitor is

used. Allowing a voltage ripple of 200 mV, the capacitor ESR should be lower than 200 mV /

0.5 A = 400 m

Ω. The AC current capability should be about 0.5 A.

Providing a reference voltage of 0.5 V, a sensing resistor of 1

Ω is needed.

Loading the input data on the power dissipation and thermal analysis section, the resulting

switching frequency is 11.9 kHz. The on-time is tON = (1 / fSW) - tOFF ≅ 70 µs, which is far

from the minimum allowed (1.5 µs), so slow decay can be used. The duty cycle is D

≅ 78%.

The sense resistors’ power rating is about PR ≅ Irms

2 · R

SENSE · D ≅ 0.25 W.

Ω - 0.25 W - 1% resistor is used. The charge pump uses recommended components

(1N4148 diodes and ceramic capacitors).

R = 18 k

Ω, C = 1.2 nF are connected to the RC pins, obtaining t

OFF ≅ 16 µs. On the EN pins

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

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 1 µs, and tDISABLE ≅ 240 µs.

Table 2.

Application data

Value

Rotation speed

300 rpm (fCK=1 kHZ)

Winding peak current

0.5 A

Maximum ripple

50 mA

Supply voltage

24 V

± 5 %

Sequence

Wave mode

OFF time

15 µs

Table 3.

Motor data

Value

Winding resistance

6.6

Winding inductance

7.9 mH

Step angle

1.8

° / step

Maximum BEMF at 300 rpm

15 V

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