AN4243

Designing an application with the L6230

Doc ID 024199 Rev 1

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PCB, the right package should be chosen considering the power dissipation. Heat sinking

can be achieved using copper on the PCB with proper area and thickness.

Otherwise, using a Power-SO package with copper slug soldered on a 1.5 mm copper

is about 35 °C/W.

Using a multi-layer board with vias to a ground plane, the thermal impedance can be

reduced down to 15 °C/W.

2.12

Brake

In general, motor braking can be achieved making a short-circuit across the windings: the

BEMF forces a current, proportional to the braking torque that flows in the opposite direction

than in normal running mode. For high BEMF and inertia moment, the current may reach

very high values: a power resistor is often used to reduce the maximum braking current and

dissipate the motor energy.

In the L6230, brake function can be achieved to quickly stop the motor while it is running:

providing a high logic level to the three IN pins all the high-side DMOS switch on, making a

short-circuit across the motor windings.

A power resistor is not used: while the motor is braking, both thermal and overcurrent

protections still work, avoiding BEMF to cause a current exceeding the device's maximum

ratings. Using a RC network (see Section 2.10) a disable time between each overcurrent

event can be set, reducing the maximum RMS value of the current.

Figure 17 shows what happens if the current exceeds the OCD threshold while the motor is

braking: as soon as the current, in one of the three motor phases, reaches the OCD

threshold (2.8 A typ.), the open-drain MOSFET internally connected to the DIAG-EN pin

discharges the external capacitor; the DIAG-EN pin voltage falls to GND and all the bridges

of the device are disabled for a time that depends on the RC network values. During this

disable time, the current, forced by the BEMF decreases and so the braking torque; when

the current becomes zero (because the motor inductances have been fully discharged), if

the BEMF is less than the supply voltage there is no braking effect (since the freewheeling

diodes cannot be turned on) until the disable time expires and all the high-side power DMOS

turn on again.