a4930 Allegro MicroSystems, Inc., a4930 Datasheet - Page 7

• Manufacturer Part Number: a4930
• Description: A4930 Single Phase Fan Pre-driver
• Manufacturer: Allegro MicroSystems, Inc.

A4930
Overvoltage
diode that prevents currents from flowing back out of the fan
assembly to the 12 V supply. When the fan commutates before
the current has decayed to zero, the current charges up the VBB
bypass capacitor.
The larger the bypass capacitor, the less the voltage overshoot.
Typically, a clamp diode is required to dissipate energy from the
inductive kickback to avoid exceeding the maximum rating for
V
Layout
the application. The layout would be restricted by the placement
of the Hall element, the location of the motor connectors, and the
common requirement that all components be placed on one side
of the PCB. For optimum results, consider the following recom-
mendations:
• Place the external MOSFET bridge close to the power connec-
tor. The bridge includes two dual N-channel MOSFETs, a sense
resistor, and a power supply capacitor. This will keep the large
current flows in one area of the PCB and avoid ground loop
problems.
BB
, 36 V.
Small form factor PCBs present a layout challenge for
In a typical fan application, there is a blocking
PWM
Duty In
R1
R2
R3
0.1 μF
10 kΩ
Applications Information
PWM control using External PWM input
0.47 μF
8.2 kΩ
5 kΩ
VREG5
CPWM
PWM
SMIN
SIN
• Keep the sense connection to the power bridge as short as pos-
• Place the power traces from the MOSFETs to the motor con-
• Locate the A4930 to minimize the length of the GHx/GLx/Sx
• Connect the GND pins of the A4930 to the exposed pad. Use
External PWM
control is being used, the high voltage level is set by R1, R2, and
R3. The low voltage level is set by R1 and R3.
sible. This can be achieved by positioning the MOSFETs next to
each other, and by connecting the source of the sink side MOS-
FETs via a short trace, preferably on the surface of the PCB,
under the MOSFETs. A short trace here would minimize voltage
spikes due to inductance in the path, where currents switch at
high di/dt.
nector on the opposite side of the PCB. If possible, on that side
isolate the power traces by ground traces in order to minimize
interference with other signal traces due to the high dv/dt of the
power traces.
traces to the power stage.
vias under the IC case to connect the exposed pad to the ground
plane on the opposite face of the PCB.
Single Phase Fan Pre-Driver
+
–
Refering to the figure below, if external PWM
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
Control
Logic
7