PBM 3960/1

6

Where (L

grammed in channel 2’s level register.

(D

and old values of DA-Data2.

The two level registers, LEVEL1 and

LEVEL2, consist of three flip flops each

and they are compared against the

three most significant bits of the DA-

Data value, sign bit excluded.

DA

These are the two outputs of DAC1 and

DAC2. Input to the DACs are internal

data bus (Q

Reference Voltage V

Ref

V

DACs. Special care in layout, gives a

very low voltage drop from pin to

resistor. Any V

can be applied, but output might be non-

linear above 3.0 V.

Power-on Reset

This function automatically resets all

internal flip flops at power-on. This

results in V

outputs and all digital outputs.

Figure 10. Table showing how data is transfered inside PBM 3960/1.

Figure 9. Motor current dragging at high

step rates and current decay influence.

Fast current decay will make it possible

for the current to follow the ideal sine

curve. Output shown without sign shift.

Figure 8b. An example of accessible

positions with a given torque deviation/

fullstep. Note that 1:st

µstep sets highest

resolution. Data points are exaggerated

for illustration purpose.

TNom = code 127.

Where (D

sent to DA-Data1 and (Q

Data1’s old value. (L

three bits for setting the current decay

level at LEVEL1.

The logic definition of CD

CD

CD

NOT{[(D

AND[(D

Reset

If Reset is not used, leave it disconnec-

ted. Reset can be used to measure

leakage currents from V

Applications Information

How Many Microsteps?

The number of true microsteps that can

be obtained depends upon many

different variables, such as the number

of data bits in the Digital-to-Analog

converter, errors in the converter,

acceptable torque ripple, single- or

double-pulse programming, the motor’s

electrical, mechanical and magnetic

characteristics, etc. Many limits can be

found in the motor’s ability to perform

properly; overcome friction, repeatability,

torque linearity, etc. It is important to

realize that the number of current levels,

not the number of steps

available. 128 is the number of current

levels (reference voltage levels)

available from each driver stage.

Combining a current level in one winding

with any of 128 other current levels in

the other winding will make up 128

current levels. So expanding this, it is

possible to get 16,384 (128 • 128)

combinations of different current levels in

the two windings. Remember that these

16,384 micro-positions are not all useful,

the torque will vary from 100% to 0%

and some of the options will make up the

same position. For instance, if the

current level in one winding is OFF (0%)

you can still vary the current in the other

winding in 128 levels. All of these

combinations will give you the same

position

but a varying torque.

Typical Application

The microstepper solution can be used

in a system with or without a micro-

processor.

Without a microprocessor, a counter

addresses a ROM where appropriate

step data is stored. Step and Direction

are the input signals which represent

clock and up / down of counter. This is

the ideal solution for a system where

there is no microprocessor or it is heavily

loaded with other tasks.

With a microprocessor, data is stored

in ROM / RAM area or each step is

successively calculated. PBM 3960/1 is

connected like any peripheral addressa-

ble device. All parts of stepping can be

tailored for specific damping needs etc.

T

[mNm]

1

T

[mNm]

2

max

T

nom

T

min

T

DA output [V]

t

Current dragging

Time

CD

CS

A0

A1

Data Transfer

0

0

0

D7 —> Sign1, (D6—D0) —> (Q61—Q01), New value —> CD1

0

0

1

(D6—D4) —> (L61—L41)

0

1

0

D7 —> Sign2, (D6—D0) —> (Q62—Q02), New value —> CD2

0

1

1

(D6—D4) —> (L62—L42)

1

X

X

No Transfer

I [mA]

1

I [mA]

2

I

Figure 8a. Assuming that torque is

proportional to the current in resp.

winding it is possible to draw figure 8b.