AN4355 datasheet(19/25 Pages) STMICROELECTRONICS

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AN4355

Protections

The relation between the voltage threshold which is programmed into the device register

and the actual load current is defined by Equation 1:

Equation 1

IOCDth = VOCDth × Rds(ON)

Where Rds(ON) is the ON resistance of the external MOSFET. Considering that the on

resistance value varies with temperature and gate voltage, the VCC value and the operative

temperature of the power stage must be considered when the threshold value is defined.

5.3

Gate drivers undervoltage

The undervoltage protection avoids the gate driving circuitry of the device to operate with

a supply voltage below a programmed value. This way a minimum gate-source voltage for

the external MOSFET is guaranteed.

At power-up the device is in undervoltage status: the power stage is kept disabled until the

VCC voltage is below the turn-on threshold. In this condition all the commands enabling the

bridges (e.g.: Move, Run, GoTo, HardStop, etc.) are ignored and the UVLO failure flag is

forced low.

When the turn-on threshold is reached the power stage is operative. The UVLO flag is kept

low until it is released through a GetStatus command.

The device returns in undervoltage status if the supply voltage falls below the turn-off

threshold.

Figure 14. Undervoltage protection

Two possible threshold values can be set through the UVLOVAL bit in the CONFIG register.

AN4355 Datasheet(PDF) 19 Page - STMicroelectronics