A6986I datasheet(23/62 Pages) STMICROELECTRONICS

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This 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 determined by the compensation network should guarantee an output voltage regulation within the

overvoltage threshold even during the worst-case scenario in terms of load transitions.

Figure 25 shows the overvoltage operation during a negative steep load transient and designed with a not

optimized compensation network. This can be considered as an example for a system with dynamic performance

not in line with the load request.

The A6986I device implements a 1.9 A typ. negative current limitation to limit the maximum reversed switch

current during the overvoltage operation.

Moreover, the overvoltage protection also activates the internal pull-down on the RST pin. Once OVP is

deactivated, the A6986I releases the RST (Figure 25). The release of the RST pin can be delayed by connecting

a capacitor to the DELAY pin (pin 9). For the selection of the capacitance value, equation (28) can be used.

Figure 25. Overvoltage operation

5.11

Thermal shutdown

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

threshold (165°C typical). The thermal sensing element is close to the power elements, ensuring fast and

accurate temperature detection. A hysteresis of approximately 30°C prevents the device from turning ON and

OFF continuously. When the thermal protection runs away a new soft-start cycle takes place.

A6986I

Thermal shutdown

DS13481 - Rev 2

page 23/62

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