L6717ATR datasheet(46/57 Pages) STMICROELECTRONICS

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Output voltage monitoring and protections

L6717A

46/57

DocID024465 Rev 1

G34 design flow is the following:

–

Define the maximum total output current (I

OC_TOT

) according to system

requirements: I

OC_TOT

= 120% x IddTDC (Typ)

–

Design Per-Phase OC and R

resistor in order to have I

INFOx

= I

OC_TH

(35

μA)

when I

OUT

is 120% higher than the IddSpike current. It results:

where N is the number of phases and DCR the DC resistance of the inductors.

should be designed in worst-case conditions.

–

Design the total current OC and R

ILIM

in order to have the ILIM pin voltage to

OC_TOT

at the desired maximum current I

OC_TOT

. It results:

where V

OC_TOT

is typically 2.5 V and I

OC_TOT

= 120% x IddTDC is the Total

Current OC threshold desired.

–

Provide filtering capacitor for ILIM pin in order to properly filter IddSpike (1.5 mSec

Typ time-constant).

–

Adjust the defined values according to bench-test of the application.

8.4.3

NB section

NB Section performs per-phase over current: its maximum information current (I

INFO_NB

) is

internally limited to I

OCTH_NB

(35

μA typ). If the current information for the NB phase exceeds

the end-of-scale current (i.e. if I

INFO_NB

> I

OCTH_NB

), the device will turn-on the Low-Side

MOSFET, also skipping clock cycles, until the threshold is re-crossed (i.e. until I

INFO_NB

OCTH_NB

). After exiting the OC condition, the low-side MOSFET is turned off and the high-

side is turned on with a duty cycle driven by the PWM comparator.

Design R

G_NB

resistor in order to have I

DROOP_NB

= I

OCTH_NB

(35

μA) at the I

OC_NBmax

current. It results:

Note:

DRP_ADJ command from power manager I2C does not alter the current information used

for Per-Phase OC.

1.2

I ddSpike

⋅

() DCR

⋅

OC T H

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

ILIM

OC_TOT

⋅

OC_TOT

DC R

⋅

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

OC_TOT

⋅

1.2

I ddTD C

D C R

⋅⋅

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

LI M

DC R

------------- I

OU T

⋅





OC_NBmax

DC R

⋅

OCTH_NB

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

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