13

Chopping Oscillator

The IM2000S contains a built-in oscillator which is

used to clock the internal pulse width modulator.

The oscillator frequency is set by an external RC

circuit.

While it is recommended to set the oscillator

frequency to approximately 20kHz to reduce

motor heating and maintain a frequency above the

audible range, the internal oscillator can accommo-

date a wide range of frequencies. Figure 3.9 shows

the relationship between the chopping frequency

and the RC resistor component values. Note that

the values shown were recorded using a fixed 1nF

capacitor.

Reset

The reset input is a Schmitt triggered input used to initialize the IM2000S. The IM2000S must be reset on power-up to

ensure proper operation. In order to initialize the IM2000S, the reset input must be held in a logic LOW state for a

minimum of 200ns.

Upon reset the IM2000S is configured such that Phase A is at 0 and Phase B is full on and in the positive half cycle. The

fault output is cleared as long as no fault condition is active on any of the protection inputs. The current reduction

output will set appoximately 1.5 seconds following the release of the reset input if no step clock input is detected.

The microstep resolution select lines and the direction input are latched on the rising edge of the reset input. This will

occur in either the buss or stand-alone mode of operation.

Exter nal Lookup Table

The IM2000S allows the use of an external lookup

table to generate the Phase A and Phase B wave-

forms. This is accomplished by the use of the RSEL

input. By using an external lookup table the user can

tailor the wave shapes to meet individual needs.

When the RSEL input is in a logic LOW state, the

internal lookup tables are selected and the sine and

cosine information is accessed internal to the

IM2000S. When RSEL is HIGH an eight bit address

is output to AD0 - AD7. This eight bit address will

then increment or decrement depending on the state

of the microstep resolution and direction inputs.

The IM2000S uses a unique approach in the genera-

tion of the address. Eight bits are used to get the full

256 positions. Only a quarter of the sine and cosine

waveforms need to be stored. The IM2000S will

automatically reconstruct the entire waveform from

this information. This means only 502 words need to

be stored to generate the entire sine and cosine

waveform for decimal resolutions. The IM2000S will

automatically generate the sign and cosine signs and

the full step output signal internally.

45

40

35

30

25

20

15

10

5

10

20

30

40

50

60

Oscillator Frequency (kHz)

Figure 3.9: Oscillator Frequency Settings

Table 3.4: External Lookup Table

Example Address Locations

p

u

k

o

o

L

l

a

n

r

e

t

x

Ep

u

k

o

o

L

l

a

n

r

e

t

x

E

p

u

k

o

o

L

l

a

n

r

e

t

x

E

p

u

k

o

o

L

l

a

n

r

e

t

x

Ep

u

k

o

o

L

l

a

n

r

e

t

x

E

e

l

p

m

a

x

E

e

l

b

a

Te

l

p

m

a

x

E

e

l

b

a

T

e

l

p

m

a

x

E

e

l

b

a

T

e

l

p

m

a

x

E

e

l

b

a

Te

l

p

m

a

x

E

e

l

b

a

T

#

p

e

t

S#

p

e

t

S

#

p

e

t

S

#

p

e

t

S#

p

e

t

S

7

D

A

-

0

D

A7

D

A

-

0

D

A

7

D

A

-

0

D

A

7

D

A

-

0

D

A7

D

A

-

0

D

A

)

x

e

H

(

l

a

m

i

c

e

D

0)

0

(

0

1

)

2

3

(

0

5

2)

4

6

(

0

0

1

3

)

6

9

(

0

5

1

4)

8

C

(

0

0

2

5

)

A

F

(

0

5

2

6)

8

C

(

0

0

2