AN2937 datasheet(32/41 Pages) STMICROELECTRONICS

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Representative waveforms

AN2937

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Doc ID 15418 Rev 1

11.1.3

Fault management: overvoltage and undervoltage

The PM6686 provides fault protection for the switching section against undervoltage and

overvoltage.

Figure 21 shows the undervoltage fault management. If, during regulation, the output

voltage drops below 70% of the nominal value, an undervoltage latched fault is detected.

The controller performs a soft-end procedure. The undervoltage fault is reset by toggling the

EN pin or by cycling the VIN (this action performs triggers a power on reset [POR]).

Figure 21.

Undervoltage protection (UVP) management

The PM6686 provides latched overvoltage protection (OVP). If the output voltage rises

above the +111% (typ.) from the nominal value for section 1 and above the +116% typ. for

section 2, latched OVP protection is activated. The controller attempts to pull down the

output voltage to 0 V, working in PWM. The current is limited by the negative current limit.

The low-side MOSFET is kept on when the output voltage is about 0 V. This management

prevents high negative undervoltage of the output rail that may damage the load (

Figure 22).

If the EN signal is pulled low, the low-side MOSFET is still high, keeping the output to

ground, thus preventing any damage to the load if the cause of the overvoltage is still

present (

Figure 23).

The protection is latched and this fault is cleared by toggling the EN pin of the section, or

cycling the VIN.

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