BRUSHLESS DC MOTOR CONTROLLER

2007-3-16

7/28

FSP33035

FUNCTION DESCRIPTION

Rotor Position Decoder

An internal rotor position decoder monitors the three sensor inputs (Pins 4, 5, 6) to provide the proper sequencing of

the top and bottom drive outputs. The sensor inputs are designed to interface directly with open collector type Hall

Effect switches or opto slotted couplers. Internal pull–up resistors are included to minimize the required number of

external components. The inputs are TTL compatible, with their thresholds typically at 2.2 V. The FSP33035 series is

designed to control three phase motors and operate with four of the most common conventions of sensor phasing. A

60°/120° Select (Pin 22) is conveniently provided and affords the FSP33035 to configure itself to control motors

having either 60°, 120°, 240° or 300° electrical sensor phasing. With three sensor inputs there are eight possible

input code combinations, six of which are valid rotor positions. The remaining two codes are invalid and are usually

caused by an open or shorted sensor line. With six valid input codes, the decoder can resolve the motor rotor

position to within a window of 60 electrical degrees.

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),

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 k: 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 Table below. 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 prevent simultaneous conduction of the

top and bottom power switches. In half wave motor drive applications, the top drive outputs are not required and are

normally left disconnected.

Three Phase, Six Step Commutation Truth Table (Note 1)

NOTES: 1. V = Any one of six valid sensor or drive combinations X = Don’t care.

2. The digital inputs (Pins 3, 4, 5, 6, 7, 22, 23) are all TTL compatible. The current sense input (Pin 9) has a

100 mV threshold with respect to Pin 15. A logic 0 for this input is defined as < 85 mV, and a logic 1 is >

115 mV.

3. The fault and top drive outputs are open collector design and active in the low (0) state.