L6701TR datasheet(31/44 Pages) STMICROELECTRONICS

31 / 44 page

L6701

13 Output voltage Monitor and Protections

31/44

Figure 14. Feedback Disconnection

13.5

PGOOD (Only for VR9 and K8 Modes)

It is an open-drain signal set free after the soft-start sequence has finished. It is pulled low

when the output voltage drops below -230mV of the programmed voltage.

13.6

Over Current Protection

Output current in each phase is monitored by L6701 through RISEN and so, programming the

value of these resistors, it is possible to set the OCP to the desired value. The Over Current

threshold has to be programmed to a safe value, in order to be sure that the device doesn't

enter OCP during normal operation of the device. This value must take into consideration also

the extra current needed during the Dynamic VID Transition ID-VID and, since the device reads

across MOSFETs RDS(on), the process spread and temperature variations of these sensing

elements. Moreover, since also the internal threshold spreads, the Rg design has to consider

the minimum value IOCTH(min) of the threshold as follow:

where IOCPx is the current measured by the current reading circuitry when the device enters

Quasi-Constant-Current.

Since the device reads the current across Low Side MOSFETs, it limits the bottom of the

inductor current entering in constant current until setting UVP as below explained. IOCPx must

be calculated starting from the corresponding output current value IOUT(OCP) as follow (ID-VID

must also be considered when D-VID are supported) since the device holds the valley current

information:

where IOUT(OCP) is still the output current value at which the device enters Quasi-Constant-

Current, IPP is the inductor current ripple in each phase and ID-VID is the additional current

required by D-VID (when applicable). In particular, since the device limits the valley of the

DCR1

DCR2

DCR3

RD RD

PHASE3

PHASE2

PHASE1

VOUT

IINFO

CS_DROOP+

CS_DROOP-

IDROOP

x 3

RFB

COMP

VSEN

FBR

FBG

VID

FB_DISCONNECTED

OC Px m ax

() RdsON max

()

⋅

OCTH m in

()

------------------------------------------------------------------

OCPx

OU T O CP

()

----------------------------

∆I

------------

DVID

–

------------------

–

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