L6984 datasheet(22/34 Pages) STMICROELECTRONICS

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Device description

L6984

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DocID025378 Rev 3

3.8

Overvoltage protection

The overvoltage protection monitors the FB pin and enables the low-side MOSFET to

discharge the output capacitor if the output voltage is 20% over the nominal value. A new

soft-start takes place after the OVP event ends.

Figure 16. Overvoltage operation

The OVP feature is a second level protection and should never be triggered in normal

operating conditions if the system is properly dimensioned. In other words, the selection of

the external power components and the dynamic performance should guarantee an output

voltage regulation within the overvoltage threshold even during the worst case scenario in

term of load transitions.

The protection is reliable and also able to operate even during normal load transitions for

a system whose dynamic performance is not in line with the load dynamic request. As

a consequence the output voltage regulation would be affected.

In Figure 16 the PGOOD output is driven in low impedance (refer to Section 3.7) as long as

the OVP event is present (VFB = VCC, that is an internal resistor divider for VOUT = 3.3 V).

3.9

Thermal shutdown

The shutdown block disables the switching activity if the junction temperature is higher than

a fixed internal threshold (150 °C typical). The thermal sensing element is close to the

power elements, ensuring fast and accurate temperature detection. A hysteresis of

approximately 20 °C prevents the device from turning ON and OFF continuously. When the

thermal protection runs away a new soft-start cycle will take place.

L6984 Datasheet(PDF) 22 Page - STMicroelectronics