L8229 datasheet(15/42 Pages) STMICROELECTRONICS

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L8229

L6219_HI mode

15/42

L6219_HI mode

The device will be set into the L6219_HI mode by asserting PROG1 and PROG2 pins (pin 7

and 18) to 00.

In the L6219_HI mode, the device is pin and function compatible with the ST L6219 device.

Please note that while ST L6219 allows good power dissipation by simply connecting to gnd

the center pins because of the batwing frame, the L8229 power dissipation will be good only

by connecting the exposed pad to a proper heat sink.

The circuit is intended to drive both windings of a bipolar stepping motor. The peak current

control is made through switch mode regulation. There is a choice of three different current

levels with the two logic inputs I01 and I11 for winding 1 and I02 and I12 for winding 2. The

current can also be completely switched off.

6.1

Input Logic (I0 and I1)

The current level in the motor winding is selected with these inputs (see Figure 1). If any of

the logic inputs is left open, the circuit will treat it as a high level input.

6.2

Phase

This input pin determines the direction of current flow in the windings, depending on the

motor connections. The signal is fed through a Schmitt trigger for noise immunity, and

through a time delay in order to guarantee that no cross conduction occurs in the output

stage during phase-shift. High level on the PHASE input causes the motor current to flow

from OutA through the motor winding to OutB.

6.3

Current Sensing

This part contains a low pass filter for the external current sensing resistor (Rs) and three

comparators. Only one comparator is active at a time: it is activated by the input logic

according to the current level chosen with signals I0 and I1.

The motor current flows through the sensing resistor Rs and when the current has increased

so that the voltage across Rs becomes higher than the reference voltage on the other

comparator input, the comparator output goes high, triggering the pulse generator.

The max peak current Imax can be defined by:

Imax = Vref / 10 Rs

Table 11.

Input Logic (I0 and I1)

I0X

I1X

Current Level

No Current

Low Current:

1/3 Io max

Medium Current:

2/3 Io max

Maximum Current: Io max

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