TB6556F/FG

2005-01-19

11

Functional Description

1.

Basic operation

The motor is driven by the square-wave turn-on signal based on a positional signal. When the positional

signal reaches number of rotations f

= 5 Hz or higher, the rotor position is estimated according to the

positional signal and a modulation wave is generated. The modulation wave and the triangular wave are

compared; then the sine-wave PWM signal is generated and the motor is driven.

From start to 5 Hz: When driven by square wave (120° turn-on) f

2.

Select drive function

This function can select drive mode.

SS pin

HIGH or OPEN = Sine-wave PWM drive (180

° turn-on mode)

LOW = Square-wave drive (120

° turn-on mode)

Note: If the position sensing signal is f = 5 Hz or lower, the driver is 120

° turn-on mode even when SS =

HIGH.

3.

(1)

Turns off output (gate protection)

(2)

When the voltage command signal is input at 1.0 V

< Ve <= 2.1 V:

Turns on the lower transistor at the regular (carrier) cycle. (ON duty is approx. 8%.)

(3)

When the voltage command signal is input at Ve

> 2.1 V:

During sin-wave drive, outputs drive signal as it is. During square-drive, forcibly turns on the lower

transistor at regular (carrier) cycle. (ON duty is approx. 8%)

Note: At startup, turn the lower transistor on for a fixed time with 1.0 V

< Ve <= 2.1 V to charge the upper

transistor gate power supply.

4.

Dead time function: upper/lower transistor output off-time

When the motor is driven by sine-wave PWM, dead time is digitally generated in the IC to prevent a

short circuit caused by the simultaneous turning on of upper and lower external power devices. When a

square wave is generated in full-duty cycle mode, the dead time function is turned on to prevent a short

circuit.

Td Pin

Internal Counter

HIGH or OPEN

1.9

µs

LOW

3.8

µs

= 4.19 MHz.

(1)

(2)

(3)

100%

2.1 V

1.0 V

5.4 V

Ve

PWM Duty