BRUSHLESS DC MOTOR CONTROLLER

2007-3-16

10/28

FSP33035

Fault Output

The open collector Fault Output (Pin 14) was designed to provide diagnostic information in the event of a system

malfunction. It has a sink current capability of 16 mA and can directly drive a light emitting diode for visual indication.

Additionally, it is easily interfaced with TTL/CMOS logic for use in a microprocessor controlled system. The Fault

Output is active low when one or more of the following conditions occur:

1) Invalid Sensor Input code

2) Output Enable at logic [0]

3) Current Sense Input greater than 100 mV

4) Undervoltage Lockout, activation of one or more of the comparators

5) Thermal Shutdown, maximum junction temperature

being exceeded

This unique output can also be used to distinguish between motor start–up or sustained operation in an overloaded

condition. With the addition of an RC network between the Fault Output and the enable input, it is possible to create

a time–delayed latched shutdown for overcurrent. The added circuitry shown in the Figure makes easy starting of

motor systems which have high inertial loads by providing additional starting torque, while still preserving

overcurrent protection. This task is accomplished by setting the current limit to a higher than nominal value for a

predetermined time. During an excessively long overcurrent condition, capacitor CDLY will charge, causing the

enable input to cross its threshold to a low state. A latch is then formed by the positive feedback loop from the Fault

Output to the Output Enable. Once set, by the Current Sense Input, it can only be reset by shorting CDLY or cycling

the power supplies.

Drive Outputs

The three top drive outputs (Pins 1, 2, 24) are open collector NPN transistors capable of sinking 50mA with a

minimum breakdown of 30 V. Interfacing into higher voltage applications is easily accomplished with the circuits

shown in two Figures below.

The three totem pole bottom drive outputs (Pins 19, 20, 21) are particularly suited for direct drive of N–Channel

MOSFETs or NPN bipolar transistors. Each output is capable of sourcing and sinking up to 100mA. Power for the

bottom drives is supplied from VC (Pin 18). This separate supply input allows the designer added flexibility in

tailoring the drive voltage, independent of VCC. A zener clamp should be connected to this input when driving

power MOSFETs in systems where VCC is greater than 20 V so as to prevent rupture of the MOSFET gates.

The control circuitry ground (Pin 16) and current sense inverting input (Pin 15) must return on separate paths to the

central input source ground.

Thermal Shutdown

Internal thermal shutdown circuitry is provided to protect the IC in the event the maximum junction temperature is

exceeded. When activated, typically at 170°C, the IC acts as though the Output Enable was grounded.

Timed Delayed Latched Over Current Shutdown

High Voltage Interface with NPN Power Transistors