L6722 datasheet(25/34 Pages) STMICROELECTRONICS

25 / 34 page

L6722

9 Output voltage monitor and protections

25/34

Where VoutMIN is the UVP threshold, (inductor saturation must be considered). When that

threshold is crossed, all mosfets are turned off, the FAULT pin is driven high and the device

stops working. Cycle the power supply or the INH pin to restart operation.

The maximum average current during the Constant-Current behavior results:

in this particular situation, the switching frequency for each phase results reduced. The ON time

is the maximum allowed TON(max) while the OFF time depends on the application:

The trans-conductance resistor RISENx can be designed considering that the device limits the

bottom of the inductor current ripple and also considering the additional current delivered

during the quasi-constant-current behavior as previously described in the worst case

conditions.

where

Figure 14. Constant current operation

PEAK

OCPx

OUT min

()

–

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

ON max

()

⋅

OCPx

OUT min

()

–

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

0.40

⋅

MAX tot

MAX

⋅

OCPx

PEAK

OCPx

–

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

⎝

⎠

⎛

⎞

⋅

OFF

PEAK

OCPx

–

OUT

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

⋅

ON max

()

OFF

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

ISENx

OCPx max

()

dsON max

()

⋅

OCTH min

()

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

OCPx

OUT OCP

()

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

∆I

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

–

VOUT

0.40 VIN

Constant Current (Exploded)

IOCP = N x IOCPx

(IDROOP = N x 35µA)

IOUT

UVP Threshold

Resulting Out. Char.

IMAX,tot

Limted-TON Char.

Droop Effect

TON(max)

IOCPx

IMAX

IPEAK

LS ON Skipping

Clock Cycles

TSW

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