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AN1451 APPLICATION NOTE

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

negative terminal of the bulk capacitor. A good quality, high-frequency bypass capacitor is also required (typi-

cally a 100nF÷200nF ceramic would suffice), since electrolytic capacitors show a poor high frequency perfor-

mance. Both bulk electrolytic and high frequency bypass capacitors have to be connected with short tracks to

them. Logic GND and Power GND should be connected together in a

noise in the Power GND from affecting Logic GND. Specific care should be paid layouting the path from the

tracks must be as short as possible in order to minimize parasitic inductances that can cause dangerous voltage

spikes on

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 capacitors 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.

Figure 6. Two situations that must be avoided.

GND

GND

GND

GND

R5

C7

C6

L6208

DON’T connect the Logic GND here

Voltage drop due to current in sense

path can disturb logic GND.

DON’T put a diode here!

Recirculating current cannot flow into the

bulk capacitor and causes a high voltage

spike that can destroy the IC.

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