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NSD-1202

Data Sheet - D e t a i l e d D e s c r i p t i o n

7.5 Period Counter

The period counter is used to define the switching frequency of the motor. The pulse period is generated by dividing the clock input frequency by

the given period counter value.

The MSB of the high byte of the pulse counter (h) is used to enable the internal frequency doubler. This function should be used only for input

clock frequencies of 10MHz or less. At 20MHz input clock a decimal period counter value of 111 gives an output frequency of 180.18 kHz. A

period counter value of 112 results in a switching frequency of 178.75 kHz. This is equal to a maximum frequency step of 1.61 kHz. The

frequency resolution gets better for lower output frequencies, assuming a fixed input clock frequency.

The following table presents examples of the period counter and output switching frequency relationship. The values are given for 20MHz and

10MHz clock input frequency. (At 10MHz the frequency doubler can be activated, which leads to the same results.)

7.6 Pulse Counter

The pulse counter sets the number of pulses the motor should be active. Writing all zeros to the pulse counter stops the motor, even if the

previous set counter value is not completed. All outputs are then low. The same is valid for power-down mode. Bit 6 of the high byte in the pulse

counter (d) is used to set the direction of motor motion.

7.7 Output Voltage Register

This register is used to define the output voltage of the boost converter. The register value is directly transferred to the analog part. The default

value for this register set during power up or power down (XPD = LOW) is equal to 35V nominal output voltage.

Varying the output voltage can be used to vary the speed of the motor. However, if two motors are being driven, both motors use a common

output voltage and therefore one setting applies to both motors. To control the speed of two motors independently, use the Duty Cycle Register.

Period Counter Value

Typ

Unit

0110 1111

180.18

kHz

0111 0000

178.57

kHz

1000 0101

150.37

kHz

1000 0110

149.25

kHz

1000 1110

140.85

kHz

1000 1111

139.86

kHz

Pulse Counter Value

Typ

Unit

Conditions

XXXX X000 0000 0000

0

pulses

Motor is off, driver outputs are low

XXXX X100 0000 0000

1024

pulses

XXXX X111 1111 1111

2047

pulses

Maximum possible number of pulses

Output Voltage Register

Typ

Unit

Conditions

0001 0001

24.0

V

0001 0010

24.5

V

0001 1111

31.0

V

0010 0111

35.0

V

Default value

0011 0000

39.5

V

0011 0001

40.0

V