L6460 datasheet(63/139 Pages) STMICROELECTRONICS

63 / 139 page

L6460

Power bridges

Doc ID 17713 Rev 1

63/139

14.1.4

Switch configuration

Each bridge can be configured to be used as 2 independent switches that connects the

output to supply or to ground. It is also possible to parallel the two switches and use them as

a single super switch.

All resulting switches will behave according to the following truth table.

Note:

When “low power mode” bit is active the bridge will reduce its biasing thus contributing to the

whole power saving.

When a current limit event occurs this event will be latched and the bridge will remain in high

impedance state for the toff time.

14.1.5

Bipolar stepper configuration

The bridges 3 and 4 can be configured to be used as a micro-stepping, bidirectional driver

for bipolar stepper motors.

The primary features of the driver are the following:

–

Internal PWM current control.

–

Micro stepping.

–

Fast, mixed and slow current decay modes.

Each H-bridge is controlled with a fixed and selectable off-time PWM current control circuit

that limits the load current to a value set by choosing VSTEPREF voltage by means of the

internal DAC and an the external RSENSE value.

The max current level could be calculated using the formula:

IMAX=VSTEPREF/RSENSE

To obtain the best current profile, the user can choose three different current decay modes:

slow, fast and mixed. Initially, during Ton, a diagonal pair of source and sink power MOS is

enabled and current flows through the motor winding and the sense resistor. When the

voltage across the sense resistor reaches the programmed DAC output voltage, the control

logic will change the status of the bridge according to the selected decay mode (slow, fast or

mixed). In slow decay mode the current is recirculated through the path including both high

Table 20.

Switch truth table

TSD

nReset

Low

power

mode

Enable

Current

limit

MtrXCtrl

SideA/B

PWM

OUT

XXX

011

010

100

010

101

010

101

010

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