L6740L datasheet(31/44 Pages) STMICROELECTRONICS

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L6740L

Output voltage monitoring and protections

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Output voltage monitoring and protections

L6740L monitors the regulated voltage of both sections through pin VSEN and NB_VSEN in

order to manage OV, UV and PWRGOOD. 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.

Protections are active also during soft-start (See Section 6.10) while they are masked dur-

ing OTF-VID transitions with an additional delay to avoid false triggering.

Table 12.

L6740L protection at a glance.

7.1

Programmable over voltage

Once VCC crosses the turn-ON threshold and the device is enabled (EN = 1), L6740L pro-

vides an Over Voltage Protection for both the sections: when the voltage sensed by VSEN

and/or NB_VSEN overcomes the OV threshold, the controller:

–

Permanently sets the PWM of the involved section to zero keeping ENDRV of that

section high in order to keep all the Low-Side MOSFETs on to protect the load of

the Section in OV condition.

Protection

Section

CORE

NORTH BRIDGE

Over voltage

(OV)

SVI / PVI: Programmable threshold according to OVP pin.

V_FIX: Fixed to 1.8V; OVP pin is externally shorted to SGND.

Action: PWMx = 0 & ENDRVx = 1; Other Section (SVI only): PWMx = HiZ;

ENDRVx = 0; FLT driven High.

Under voltage

(UV)

VSEN, NB_VSEN = VID -400mV. Active after Ref > 500mV

Action: All PWMx = HiZ; ENDRVx = 0; FLT Driven High.

PWRGOOD

PWRGOOD is the logic AND between internal CORE and NB PGOOD in SVI

mode while is the CORE section PGOOD in PVI mode.

Each PGOOD is set to zero when the related voltage falls below the

programmed reference -250mV.

Action: Section(s) continue switching, PWRGOOD driven low.

VSEN, NB_VSEN

Disconnection

Set when VSEN > CS1- +600mV.

Action: UV-Like

µA Pull-Up from NB_VSEN to set

OV (SVI Only).

Action: OV-Like

FBG, NB_FBG

Disconnection

Internal Comparator across the opamp to recover from GND losses.

Action: UV-Like

Over current (OC)

Current Monitor across Inductor DCR.

Dual Protection, per-phase and average.

Action: UV-Like

Current Monitor across LS RdsON.

Constant Current, Valley CLimit.

Action: UV-Like

On-The-Fly VID

Masked with the exception of OC with additional 16 clock delay to prevent from

false triggering (both SVI and PVI).

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