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L6258E

The formula defining the gain of the load considering the Bemf of the stepper motor becomes:

we can see that the Bemf influences only the gain of the load block and does not introduce any other additional

pole or zero, so from the stability point of view the effect of the Bemf of the motor is not critical because the

phase margin remains the same.

Practically the only effect of the Bemf is to limit the gain of the total Aloop with a consequent variation of the

bandwidth of the system.

5

APPLICATION INFORMATION

A typical application circuit is shown in Fig.12.

Note: For avoid current spikes on falling edge of DISABLE a "DC feedback" would be added to the ERROR

Amplifier. (R1-R2 on Fig. 12).

5.1 Interference

Due to the fact that the circuit operates with switch mode current regulation, to reduce the effect of the wiring

inductance a good capacitor (100nF) can be placed on the board near the package, between the power supply

line (pin 13,31) and the power ground (pin 1,36,18,19) to absorb the small amount of inductive energy.

It should be noted that this capacitor is usually required in addition to an electrolytic capacitor, that has poor

performance at the high frequencies, always located near the package, between power supply voltage (pin

13,31) and power ground (pin 1,36,18,19), just to have a current recirculation path during the fast current decay

or during the phase change.

The range value of this capacitor is between few

µF and 100µF, and it must be chosen depending on application

parameters like the motor inductance and load current amplitude.

A decoupling capacitor of 100nF is suggested also between the logic supply and ground.

The EA_IN1 and EA_IN2 pins carry out high impedance lines and care must be taken to avoid coupled noise

on this signals. The suggestion is to put the components connected to this pins close to the L6258E, to surround

them with ground tracks and to keep as far as possible fast switching outputs of the device. Remember also an

1 Mohm resistor between EA_INx and EA_OUTx to avoid output current spike during supply startup/shutdown.

A non inductive resistor is the best way to implement the sensing. Whether this is not possible, some metal film

resistor of the same value can be paralleled.

The two inputs for the sensing of the winding motor current (SENSE_A & SENSE_B) should be connected di-

rectly on the sensing resistor Rs terminals, and the path lead between the Rs and the two sensing inputs should

be as short as possible.

ACload

Vsense

Vout

----------------------

V

S

Bemf

–

()

R

S

R

L

R

S

+

---------------------

⋅

V

S

-----------------------------------------------------------

==

Acload

V

S

Bemf

–

V

S

----------------------------

R

S

R

L

R

S

+

---------------------

⋅

=

ACload

dB

20

V

S

Bemf

–

V

S

----------------------------

R

S

R

L

R

S

+

---------------------

⋅







log

⋅

=