AN1625 APPLICATION NOTE

6/39

Figure 5. Typical Application and Layout suggestions.

High current GND tracks (i.e. the tracks connected to the sensing resistor) must be connected directly to the neg-

ative terminal of the bulk capacitor. A good quality, high-frequency bypass capacitor is also required (typically a

100 nF÷200 nF ceramic would suffice), since electrolytic capacitors show a poor high frequency performance.

and GND. On the L6235 GND pins are the Logic GND, since only the quiescent current flows through them. Logic

GND and Power GND should be connected together in a single point, the bulk capacitor, to keep noise in the

Power GND from affecting Logic GND. Specific care should be paid layouting the path from the SENSE pins

through the sensing resistor to the negative terminal of the bulk capacitor (Power Ground). These tracks must be

as short as possible in order to minimize parasitic inductances that can cause dangerous voltage spikes on

SENSE and OUT pins (see the Voltage Ratings and Operating Range section); for the same reason the capac-

the three OUT pins must be designed with adequate width, since high currents are flowing through these traces,

and layer changes should be avoided. Should a layer change prove necessary, multiple and large via holes have

to be used. A wide GND copper area can be used to improve power dissipation for the device.

Figure 6 shows two typical situations that must be avoided. An important consideration about the location of the

bulk capacitor is the ability to absorb the inductive energy from the load, without allowing the supply voltage to

exceed the maximum rating. The diode shown in Figure 6 prevents the recirculation current from reaching the

capacitors and will result in a high voltage on the IC pins that can destroy the device. Having a switch or a power

connection that can disconnect the capacitors from the IC, while there is still current in the motor, will also result

in a high voltage transient since there is no capacitance to absorb the recirculation current.

+

-

EN

BRAKE

F WD/REV

H3

H2

H1

GND

GND

GND

GND

CP

D1

D2

R1

R2

R3

R4

R5

C1

C2

C3

C4

C7

C8

C5

C6

L6235

µC

or

Custom Logic

3-Phase

Brushless

DC Motor

+

-

Logic Supply

3.3 ÷ 5 V

DIAG

TACHO