Datasheet
SLUS318B – APRIL 1999 – REVISED JANUARY 2002
17
www.ti.com
APPLICATION INFORMATION
Figure 17 illustrates a simple 175-V, 2-A, two-quadrant velocity controller using the UCC3626. The power stage
is designed to operate with a rectified off-line supply using IR2210s to provide the interface between the low
voltage control signals and the power MOSFETs. The power topology illustrated in Figure 13c is implemented
in order to provide braking capability.
UDG–99061
11 IOUT
+
–
13 PWM_I
CURRENT
ERROR
AMPLIFIER
+
–
U6
+
–
SIGN/MAGNITUDE CONVERTER
21 DIRU7
CURRENT SIGN
3 TACH_OUT
+
–
U2
TACHOMETER
FILTER
2N7002
8 DIR_OUT
+
–
U3
BIPOLAR
TACH GAIN
+
–
U1
CURRENT
MAGNITUDE
U5
U8
10 kΩ
10 kΩ
10 kΩ 10 kΩ
10 kΩ
10 kΩ
4.99 kΩ 4.99 kΩ
10 kΩ
VELOCITY
COMMAND
± 5 V
Figure 16. Four-Quadrant Control Loop
The controller’s speed command is set by potentiometer R30, while the speed feedback signal is obtained by
low-pass filtering and buffering the TACH_OUT signal using R11 and C9. Small signal compensation of the
velocity control loop is provided by amplifier U5A, whose output is used to control the PWM duty cycle. The
integrating capacitor, C8, places a pole at 0 Hz and a zero in conjunction with R10. This zero can be used to
cancel the low-frequency motor pole and to cross the loop-over with a –20 dB gain response.
Four-quadrant applications require the control of motor current. Figure 16 illustrates a sign/magnitude current
control loop within an outer bipolar velocity loop using the UCC3626. U1 serves as the velocity loop error
amplifier and accepts a ± 5-V command signal. Velocity feedback is provided by low-pass filtering and scaling
the TACH_OUT signal using U2. The direction output switch, DIR_OUT, and U3 set the polarity of the
tachometer gain according to the direction of rotation. The output of the velocity error amplifier, U1, is then
converted to sign/magnitude form using U5 and U6. The sign portion is used to drive the DIR input while the
magnitude commands the current error amplifier, U8. Current feedback is provided by the internal current sense
amplifier via the IOUT pin.