AN2269 datasheet(7/25 Pages) STMICROELECTRONICS

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AN2269 - Application Note

Emergency Deactivation/Fault Detection

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Emergency Deactivation/Fault Detection

ST8024 is equipped with a fault detection circuitry which monitors the following conditions

(see

Figure 1 on page 1):

●

VDD undervoltage,

●

Fault on card removal,

●

VCC Short circuit protection,

●

VDDP drop, and

●

Over-Temperature protection.

3.1

PORADJ VDD Undervoltage without External Resistor Bridge

The ST8024 logic circuitry is supplied by VDD. In order to avoid voltage spikes that could

cause damage, or malfunction of the device and/or card, a voltage supervisor block is

embedded (see

Figure 1). This block monitors VDD and when it gets lower than VTH2

(Falling Threshold Voltage on VDD, 2.45V, typ), the supervisor immediately starts the

deactivation sequence and VCC goes low.

As VDD goes higher than VTH2 + VHYS2, (VHYS2 is the Hysteresis of threshold voltage,

100mV, typ), after a certain amount of time (tw + tdebounce, where tw is the internal power-on

reset pulse width, 8ms typ, see

Figure 5 on page 8), CMDVcc goes low. The activation

sequence starts and VCC goes high. The PORADJ pin can be left floating, but connecting it

to GND to avoid noise capture is recommended.

Note: See

Fault On Card Removal on page 12 for tdebounce feature details.

AN2269 Datasheet(PDF) 7 Page - STMicroelectronics