STDRIVE102BH datasheet(37/56 Pages) STMICROELECTRONICS

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The time constant of the rising transient is:

Equation 6

τEN= REN∙RPD,EN

REN+RPD,EN∙CEN

(6)

Using the values calculated in Eq. (5) and in Eq. (6), it is possible to find the delay time required to re-arm the

power MOSFETs, after a FAULT condition:

Equation 7

tdelay,EN=τEN∙ln VEN,ℎigℎ−Vrelease

VEN,ℎigℎ−VIH

(7)

According to Eq. (5), the value of REN should be chosen to be several times smaller than RPD,EN to avoid an

excessive drop of the high level on the EN pin (VEN,high). In this hypothesis, it is possible to approximate Eq. (7)

as:

Equation 8

tdelay,EN≅REN∙CEN∙ln VDD−Vrelease

VDD−VIH

(8)

5.6.2

FLAG pin (STDRIVE102BH only)

Unlike the UVLO protection on the VCC, the warning on the VCC supply does not disable or limit the drivers and

the device functionalities. The only effect is that the FLAG pin is forced low. The external microcontroller can

detect this condition and manage it by modifying the control algorithm of the driver.

In case a hardwired solution is required to disable the drivers at a higher threshold than the VCC UVLO threshold,

connect together the EN and the FLAG pins.

A capacitor can be added as shown in Figure 27 to provide an extra delay for the enabling of the drivers: the

delay is determined by the time constant

τFLAG≅RFLAG∙CFLAG,explainedinthepreviousSection5.6.1.

Figure 27. FLAG and EN management

FLAG

GPIO

MCU

STDRIVE102

VDD

configuration

open drain

RFLAG

CFLAG

5.7

Device power-up

The power-up sequence starts at the rising edge of the main supply applied on the VS pin, supposing that the

nSTBY pin is forced high. In case the VM and VS pins are supplied by different voltage sources, the VM voltage

must be applied before the VS voltage. This sequence is not important if the nSTBY pin is kept low and it is raised

after the supplies are stable.

The internal 5 V regulator begins to charge the capacitor on the LGC_CAP pin. When the POR threshold is met,

the internal logic starts to operate and initialize all the internal circuits. During this phase the nFAULT signal is

kept low.

Then, the regulators are enabled and they can charge their external bypass capacitors: most of the time required

by the device to be operative is due to the charge of the external bypass capacitor. Depending on the capacitor

value and the current capability of the LDO regulators and the charge pump, this time can last hundreds of

microseconds.

STDRIVE102BH, STDRIVE102H

Device description

DS14545 - Rev 1

page 37/56

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