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L6258EP

3

FUNCTIONAL DESCRIPTION

The circuit is intended to drive both windings of a bipolar stepper motor or two DC motors.

The current control is generated through a switch mode regulation.

With this system the direction and the amplitude of the load current are depending on the relation of phase and

duty cycle between the two outputs of the current control loop.

The L6258EP power stage is composed by power DMOS in bridge configuration as it is shown in figure 4, where

driven to ground with a low level at the same inputs .

The zero current condition is obtained by driving the two half bridge using signals IN_A and IN_B with the same

phase and 50% of duty cycle.

ground, but keeping the differential voltage across the load equal to zero.

In figure 4A is shown the timing diagram of the two outputs and the load current for this working condition.

Following we consider positive the current flowing into the load with a direction from OUT_A to OUT_B, while

we consider negative the current flowing into load with a direction from OUT_B to OUT_A.

Now just increasing the duty cycle of the IN_A signal and decreasing the duty cycle of IN_B signal we drive pos-

itive current into the load.

In this way the two outputs are not in phase, and the current can flow into the load trough the diagonal bridge

there will be a current recirculation into the higher side of the bridge, through T1 and T2, when both the outputs

are at Vs and a current recirculation into the lower side of the bridge, through T3 and T4, when both the outputs

are connected to ground.

Since the voltage applied to the load for recirculation is low, the resulting current discharge time constant is high-

er than the current charging time constant during the period in which the current flows into the load through the

diagonal bridge formed by T1 and T4. In this way the load current will be positive with an average amplitude

depending on the difference in duty cycle of the two driving signals.

In figure 4B is shown the timing diagram in the case of positive load current

On the contrary, if we want to drive negative current into the load is necessary to decrease the duty cycle of the

IN_A signal and increase the duty cycle of the IN_B signal. In this way we obtain a phase shift between the two

outputs such to have current flowing into the diagonal bridge formed by T2 and T3 when the output OUT_A is

driven to ground and output OUT_B is driven to Vs, while we will have the same current recirculation conditions

of the previous case when both the outputs are driven to Vs or to ground.

So, in this case the load current will be negative with an average amplitude always depending by the difference

in duty cycle of the two driving signals.

In figure 4C is shown the timing diagram in the case of negative load current .

Figure 5 shows the device block diagram of the complete current control loop.

3.1 Reference Voltage

The voltage applied to VREF pin is the reference for the internal DAC and, together with the sense resistor val-

ue, defines the maximum current into the motor winding according to the following relation:

I

MAX

0.5 V

REF

⋅

R

S

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

1

FI

-----

V

REF

R

S

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

⋅

==