Datasheet

21
27
25
22
6
28
1
15
24326
10kW
3kW
10kW
2 19
20
16
11
20mF
100nF
20mF
100nF
+
R
OSC
33kW
2200pF
C
OSC
68kW
R
T
3nF
C
T
BRAKE
5nF
100nF
23 8 9 10 4 5 7
2nF
2nF
2nF
100nF
10kW
5nF
240W
240W
17
18
14
13
12
3kW
2N3906
100nF
1k
4kW
TO OTHER
CHANNELS
TO OTHER
CHANNELS
10W
2N3904
10W
IRF9350
IRF532
3kW
FROM
HALL
SENSORS
VMOTOR+15V
+5V TO HALL
SENSORS
VREF
0.02
W
R
S
TO
MOTOR
0.02
W
R
D
REQUIRED
FOR
AVERAGE
CURRENT
SENSING
REQUIRED
FOR BRAKE
AND FAST
REVERSE
100mF
+
UC3625
DIR
QUAD
51kW
VREF
UC1625
UC2625
UC3625
SLUS353C –NOVEMBER 2003–REVISED JUNE 2013 www.ti.com
Figure 15. 45-V/8-A Brushless DC Motor Drive Circuit
N-Channel power MOSFETs are used for low-side drivers, while P-Channel power MOSFETs are shown for
high-side drivers. Resistors are used to level shift the UC3625 open-collector outputs, driving emitter followers
into the MOSFET gate. A 12-V zener clamp insures that the MOSFET gate-source voltage never exceeds 12 V.
Series 10-Ω gate resistors tame gate reactance, preventing oscillations and minimizing ringing.
The oscillator timing capacitor should be placed close to pins 15 and 25, to keep ground current out of the
capacitor. Ground current in the timing capacitor causes oscillator distortion and slaving to the commutation
signal.
The potentiometer connected to pin 1 controls PWM duty cycle directly, implementing a crude form of speed
control. This control is often referred to as "voltage mode" because the potentiometer position sets the average
motor voltage. This controls speed because steady-state motor speed is closely related to applied voltage.
Pin 20 (Tach-Out) is connected to pin 7 (SPEED IN) through an RC filter, preventing direction reversal while the
motor is spinning quickly. In two-quadrant operation, this reversal can cause kinetic energy from the motor to be
forced into the power MOSFETs.
A diode in series with the low-side MOSFETs facilitates PWM current control during braking by insuring that
braking current will not flow backwards through low-side MOSFETs. Dual current-sense resistors give continuous
current sense, whether braking or running in four-quadrant operation, an unnecessary luxury for two-quadrant
operation.
The 68-kΩ and 3-nF tachometer components set maximum commutation time at 140 μs. This permits smooth
operation up to 35,000 RPM for four-pole motors, yet gives 140 μs of noise blanking after commutation.
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