6

ATA6830

4575C–BCD–05/03

Stepping Motor Driver

Figure 5. H-bridge Driver Stage

Figure 5 shows the diagram of one H-bridge driver stage. It consists of two NMOS and

two PMOS power transistors. An external shunt is used for measuring the current flow-

ing through the motor coil. Additional comparators and current sensing circuitry is

integrated for error detection.

Data Communication

The circuit receives all commands for the stepping motor via a single wire bus. In idle

mode the bus pin is pulled up by an internal current source near to VBAT voltage. Dur-

ing the transmission the external transmitter has to pull down the bus level to send

information about data and clock timing. The used baud rate has to be about 2400 baud.

Because of oscillator tolerances a synchronization sequence has to be sent at the

beginning of data transfer.

Figure 6 shows the pattern used for this sequence. The circuit uses the 1-0-1-0

sequences for adjusting the internal bit time. Later on during data transfer every 1-0-1-0

sequence coming up randomly is used for resynchronization. Thus all tolerances that

occur during operation will be eliminated.

To obtain a synchronization of up to 15% oscillator tolerance the pattern has to be sent

at least 4 times.

Shunt

VBAT

SM1x

SM2x

SRx

Vref

Stepper Motor Control

Temperature

Warning

Temperature

Shutdown

Clk

Reset

Error Signals

Driver Logic

Temp. Shutdown

Temp. Warning