L6474 datasheet(23/51 Pages) STMICROELECTRONICS

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L6474

Functional description

Doc ID 022529 Rev 2

23/51

Attention:

The overcurrent shutdown is a critical protection feature. It is

not recommended to disable it.

6.10

Undervoltage lock-out (UVLO)

The L6474 provides a motor supply UVLO protection. When the motor supply voltage falls

below the VSthOff threshold voltage, the STATUS register UVLO flag is forced low. When a

GetStatus command is sent to the IC, and the undervoltage condition has expired, the

UVLO flag is released (see paragraphs 9.1.13 and 9.2.7). Undervoltage condition expires

when the motor supply voltage goes over the VSthOn threshold voltage. When the device is

in undervoltage condition no motion can be performed. The UVLO flag is forced low by logic

reset (power-up included) even if no UVLO condition is present.

6.11

Thermal warning and thermal shutdown

An internal sensor allows the L6474 to detect when the device internal temperature exceeds

a thermal warning or an overtemperature threshold.

When the thermal warning threshold (Tj(WRN)) is reached, the TH_WRN bit in the STATUS

and a GetStatus command is sent to the IC (see paragraphs 9.1.13 and 9.2.7).

When the thermal shutdown threshold (Tj(OFF)) is reached, the device goes into thermal

shutdown condition: the TH_SD bit in the STATUS register is forced low, the power bridges

are disabled, bridges in high impedance state and the HiZ bit in the STATUS register are

raised (see paragraph 9.1.13).

Thermal shutdown condition only expires when the temperature goes below the thermal

warning threshold (Tj(WRN)).

On exiting thermal shutdown condition, the bridges are still disabled (HiZ flag high).

6.12

Reset and standby

The device can be reset and put into standby mode through a dedicated pin. When the

STBY\RST pin is driven low, the bridges are left open (High Z state), the internal charge

pump is stopped, the SPI interface and control logic are disabled, and the internal 3 V

voltage regulator maximum output current is reduced to IREG,STBY; as a result the L6474

heavily reduces the power consumption. At the same time the register values are reset to

default and all protection functions are disabled. STBY\RST input must be forced low at

least for tSTBY, min. in order to ensure the complete switch to standby mode.

On exiting standby mode, as well as for IC power-up, a delay of up to tlogicwu must be given

before applying a new command to allow proper oscillator and logic startup and a delay of

up to tcpwu must be given to allow the charge pump startup.

On exiting standby mode the bridges are disabled (HiZ flag high).

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