AN2836 datasheet(14/57 Pages) STMICROELECTRONICS

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Designing an application with L6225, L6226, L6227

AN2836

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Doc ID 15084 Rev 1

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 (typically a 100 nF÷200 nF ceramic would

suffice), since electrolytic capacitors show a poor high frequency performance. Both bulk

electrolytic and high-frequency bypass capacitors have to be connected with short tracks to

VSA, VSB and GND. On the L6225, L6226, L6227 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 resistors 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 the SENSE and OUT pins (see Section 4.2: Voltage ratings

and operating range). For the same reason the capacitors on VSA, VSB and GND should be

very close to the GND and supply pins. Refer to Section 4.5: Sensing resistors for

information on selecting the sense resistors. Traces connected to VSA, VSB, SENSEA,

SENSEB, and the four 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 heat removal, thus reducing thermal resistance.

Figure 8 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 8 prevents the recirculation current from reaching the capacitors and results in a high

voltage on the IC pins that can damage 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, also

results in a high-voltage transient since there is no capacitance to sink the recirculation

current.

Figure 8.

Two situations that must be avoided

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