L6758ATR datasheet(27/42 Pages) STMICROELECTRONICS

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L6758A

Output voltage monitoring and protection

The L6758A monitors the regulated voltage of both sections through pin VSEN and SVSEN

in order to manage OV and UV. The device shows different thresholds when in different

operative conditions but the behavior in response to a protection event is still the same as

described below.

Protection is active also during soft-start while it is properly masked during DVID transitions

with an additional delay to avoid false triggering.

7.1

Overvoltage

When the voltage sensed by VSEN and/or SVSEN overcomes the OV threshold, the

controller acts in order to protect the load from excessive voltage levels avoiding any

possible undershoot. To reach this target, a special sequence is performed as per the

following list:

–

The reference performs a DVID_Fast transition down to 250 mV on the section

which triggered the OV protection.

–

The PWMs of the section which triggered the protection are switched between HiZ

and zero (ENDRV is kept high) in order to follow the voltage imposed by the

DVID_Fast on-going. This limits the output voltage excursion, protects the load

and assures no undershoot is generated (if V

OUT

< 250 mV, the section is HiZ).

–

The PWMs of the non-involved section are set permanently to HiZ (ENDRV is kept

low) in order to realize a HiZ condition.

–

OSC/ FLT pin is driven high.

–

Power supply or EN pin cycling is required to restart operations.

If the cause of the failure is removed, the converter ends the transition with all PWMs in HiZ

state and the output voltage of the section which triggered the protection lower than 250 mV.

Table 12. L6758A protection at a glance

Section

Multi-phase

Single-phase

Overvoltage (OV)

VSEN, SVSEN = +175 mV above reference.

Action: IC Latch; DVIDFast to 250 mV, LS=ON & PWMx = 0 if required to keep

the regulation to 250 mV; other section: HiZ.

Undervoltage (UV)

VSEN, SVSEN = 500 mV below reference. Active after Ref > 500 mV

Action: IC Latch; both sections HiZ.

Overcurrent (OC)

Current monitor across inductor DCR.

Dual protection, per-phase and average.

Action: UV-Like.

Dynamic VID

Protection masked with additional delay to prevent from false triggering.

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