L8229 datasheet(18/42 Pages) STMICROELECTRONICS

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L6219_8 mode

L8229

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L6219_8 mode

A second configuration of the device is achieved when PROG1 and PROG2 pins (pin 7 and

18) are asserted to 01. The device is now configured into the L6219_8 configuration. This

device mode function is similar to L6219_HI, but with the possibility of using 8 current levels

instead of 4, to implement a more accurate microstepping function and with the possibility to

set a mixed decay for recirculation current. The remaining functionalities are identical to

L6219_HI mode.

7.1

8 Level Current Setting

This setting is achieved by using pin 8 (STB) as a strobe for latching the current setting

control inputs. The rising edge of STB will latch the I01, I11 and I12 inputs for decoding

current levels settings for Bridge 1. Similarly the falling edge will latch the I01, I11 and I12

inputs for decoding current levels settings for Bridge 2.

In order to allow a good similitude to sine drive, the levels set by the input pins are not

equally spaced but are choosen to approximate a sinusoidal wave.

On power up, the device is by default into a no current drive state for both H Bridges and will

start driving only upon the rising or falling edges of STB.

7.2

Mixed Decay

VREFCOM input (pin 15) is the reference voltage for both bridges while VREFDEC input

(pin 11) is a voltage reference for decay control. When the current setting is set from an

higher level to a lower level, the device can be set to perform:

Slow decay (current is recirculated throught the low side drivers) when VREFDEC > 0.94Vcc.

A mix of Fast followed by Slow decay when 0.33Vcc < VREFDEC < 0.94Vcc.

Fast decay (current is recirculated from Sense to Vs) when VREFDEC < 0.33Vcc.

In case 2, VREFDEC voltage is compared with the RC discharging voltage during the Toff

duration. Until the RC voltage is above VREFDEC there will be fast decay: the bridge

outputs will be driven to enable recirculation from Rsense to VS. For RC voltages below

VREFDEC, the bridges will be driven to recirculate through the low side drivers. (see

Figure 8)

Table 12.

Current levels

STB

I01

I11

I12

Current level

Bridge1

Bridge 2

No current

IOUT / Imax=0.22

IOUT / Imax=0.42

IOUT / Imax=0.61

IOUT / Imax=0.77

IOUT / Imax=0.87

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