AN1625 datasheet(33/39 Pages) STMICROELECTRONICS

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AN1625 APPLICATION NOTE

Motor Data

Winding Resistance (2 phases):

Ω

Winding Inductance (2 phases):

800

µH

Supply Voltage:

24 V +/- 5%

Polar Couples:

Referring to approximated formulae in Figure 24, it's possible to calculate the Duty Cycle (D), the Switching Fre-

quency (fSW), the Current Ripple (∆I). With a 8 µs off-time, we will have:

≅ 61%, fSW ≅ 49 kHz, ∆I ≅ 320 mA.

The on-time is tON = D / fSW ≅ 12.5 µs, which is far from the minimum allowed (1.5 µs).

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

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

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

Ω; the AC current

capability should be about 1.5 A (worst case).

Providing a reference voltage of 0.5 V, 0.33

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

≅ Irms2 · RSENSE · D ≅ 0.37 W. Three 1 Ω / 0.25 W - 1% resistors in parallel are used. The charge pump

uses recommended components (1N4148 diodes, ceramic capacitors and a 100

Ω resistor to reduce EMI).

R = 24 k

Ω, C = 470 pF are connected to the RC pins, obtaining tOFF ≅ 7.8 µs. On the EN pin a 5.6 nF has been

placed, and the pin is driven by the

µC through a 100 kΩ resistor.

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.

Figure 36. Application Example.

Referring to Figure 23, Figure 24, Figure 25, the dissipating power is about 2.37 W. If the ambient temperature

is lower than 50 °C, with 5 cm2 of copper area on the PCB, a ground layer and a PowerSO36 package, the

estimated junction temperature is about 97 °C.

VS = 24 V

Vref = 0.5 V

BRAKE

CW/CCW

Vref

RCPULSE

RCOFF

GND

SENSEA

SENSEB

VSA

VSB

VBOOT

OUT3

OUT1 OUT2

1N4148

100 k

Ω

24 k

Ω

100

Ω

0.25W

5.6 nF

Ceramic

47nF

Ceramic

470 pF

Ceramic

100nF 50V

Ceramic

220nF 35V

Ceramic

10nF 50V

Ceramic

100µF 50V

ESR<200m

Ω

L6235

µC

Custom Logic

3-Phase

Brushless DC Motor

3 X

Ω, 0.25 W, 1%

2 k

Ω 0.25 W

18 k

Ω 0.25 W

Logic Supply

5 V

TACHO

DIAG

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