MC33035
decoder can resolve the motor rotor position to within a
window of 60 electrical degrees.
prevent simultaneous conduction of the the top and bottom
power switches. In half wave motor drive applications, the
top drive outputs are not required and are normally left
disconnected. Under these conditions braking will still be
accomplished since the NOR gate senses the base voltage
to the top drive output transistors.
The Forward/Reverse input (Pin 3) is used to change the
direction of motor rotation by reversing the voltage across the
stator winding. When the input changes state, from high to
low with a given sensor input code (for example 100), the
enabled top and bottom drive outputs with the same alpha
designation are exchanged (AT to AB, BT to BB, CT to CB). In
effect, the commutation sequence is reversed and the motor
changes directional rotation.
Motor on/off control is accomplished by the Output Enable
(Pin 7). When left disconnected, an internal 25 µA current
source enables sequencing of the top and bottom drive
outputs. When grounded, the top drive outputs turn off and
the bottom drives are forced low, causing the motor to coast
and the Fault output to activate.
Dynamic motor braking allows an additional margin of
safety to be designed into the final product. Braking is
accomplished by placing the Brake Input (Pin 23) in a high
state. This causes the top drive outputs to turn off and the
bottom drives to turn on, shorting the motor–generated back
EMF. The brake input has unconditional priority over all other
inputs. The internal 40 kΩ pull–up resistor simplifies
interfacing with the system safety–switch by insuring brake
activation if opened or disconnected. The commutation logic
truth table is shown in Figure 20. A four input NOR gate is
used to monitor the brake input and the inputs to the three
top drive output transistors. Its purpose is to disable braking
until the top drive outputs attain a high state. This helps to
Error Amplifier
A high performance, fully compensated error amplifier with
access to both inputs and output (Pins 11, 12, 13) is provided
to facilitate the implementation of closed loop motor speed
control. The amplifier features a typical DC voltage gain of
80 dB, 0.6 MHz gain bandwidth, and a wide input common
mode voltage range that extends from ground to Vref. In most
open loop speed control applications, the amplifier is
configured as a unity gain voltage follower with the
noninverting input connected to the speed set voltage source.
Additional configurations are shown in Figures 31 through 35.
Oscillator
The frequency of the internal ramp oscillator is
programmed by the values selected for timing components
RT and CT. Capacitor CT is charged from the Reference
Output (Pin 8) through resistor RT and discharged by an
internal discharge transistor. The ramp peak and valley
voltages are typically 4.1 V and 1.5 V respectively. To provide
a good compromise between audible noise and output
switching efficiency, an oscillator frequency in the range of
20 to 30 kHz is recommended. Refer to Figure 1 for
component selection.
Figure 19. Representative Block Diagram
V
M
14
2
20 k
4
Fault Output
S
A
20 k
5
6
S
Sensor
Inputs
B
A
T
20 k
Rotor
Position
Decoder
S
Top
Drive
Outputs
C
1
40 k
3
B
T
Forward/Reverse
60 /120 Select
Output Enable
40 k
24
22
°
°
C
T
25 µA
7
Undervoltage
Lockout
17
V
in
V
CC
18
V
C
Reference
Regulator
9.1 V
4.5 V
21
20
19
Reference Output
8
A
B
B
Noninv. Input
Faster
11
Error Amp
Bottom
Drive
Outputs
Thermal
B
12
13
Shutdown
Latch
R
PWM
R
T
Error Amp Out
PWM Input
Q
C
B
S
Latch
10
Oscillator
S
40 k
Q
C
T
9
R
Current Sense Input
Current Sense
Reference Input
Sink Only
Positive True
15
100 mV
=
Logic With
Hysteresis
16 Gnd
23
Brake Input
9
MOTOROLA ANALOG IC DEVICE DATA
MOTOROLA [ MOTOROLA ]
