L6759D datasheet(28/51 Pages) STMICROELECTRONICS

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Output voltage monitoring and protection

L6759D

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Doc ID 023240 Rev 1

Output voltage monitoring and protection

The L6759D 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.

Table 8.

L6759D protection at a glance

7.1

Overvoltage

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

ler 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 transition down to 250 mV on the section which

triggered the OV protection

●

The PWM 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 on-going.

This limits the output voltage excursion, protects the load and assures no undershoot is

generated (if Vout < 250 mV, the section is HiZ)

●

The PWM of the non-involved section is 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.

7.2

Overcurrent

The overcurrent threshold must be programmed to a safe value, in order to be sure that

each section doesn't enter OC during normal operation of the device. This value must take

Section

Multi-phase

Single-phase

Overvoltage

(OV)

VSEN, SVSEN = +150 mV above reference.

Action: IC latch; LS=ON & PWMx = 0 (if applicable); other section: HiZ.

Undervoltage

(UV)

VSEN, SVSEN = 400 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.

n/a

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