AN1625 STMicroelectronics, AN1625 Datasheet - Page 6

• Manufacturer Part Number: AN1625
• Description: L6235 THREE PHASE BRUSHLESS DC MOTOR DRIVER
• Manufacturer: STMicroelectronics

AN1625 APPLICATION NOTE
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.
Both bulk electrolytic and high frequency bypass capacitors have to be connected with short tracks to V
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-
itors on V
section for information on selecting the sense resistors. Traces that connect to V
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.
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Logic Supply
3.3 ÷ 5 V
+
-
SA
, V
Custom Logic
SB
V
and GND pins should be very close to the GND and supply pins. Refer to the Sensing Resistors
µC
ref
or
= 0 ÷1V
R1
C1
H1
H2
H3
FWD/REV
BRAKE
TACHO
DIAG
EN
OUT
C2
1
OUT
V
r ef
2
R2
OUT
3
RC
OFF
Brushless
DC Motor
3-Phase
C3
L6235
V
BOOT
R3
D1
RC
C5
R4
PULSE
CP
C4
GND
D2
GND
V
SA
GND
SENSE
SENSE
V
GND
SB
C8
A
B
R5
SA
C6
, V
SB
, SENSE
C7
A
, SENSE
V
S
= 8 ÷ 52 V
+
-
SA
B
, V
, and
SB