SABRE-LL-I datasheet(55/141 Pages) STMICROELECTRONICS

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SABRE-LL-I

Power bridges

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14.3.4

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.

14.3.5

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

side power MOS for the whole toff time. In fast decay mode the current is recirculated

through the high and low side power MOS opposite respect to those forcing current to

Table 34.

Switch truth

TSD

nReset

Low

power

mode

Enable

Current

limit

MtrXCtrl

SideA/B

PWM

OUT

XXXX

XXX

100

1010

101

1010

110

1011

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