L6717ATR datasheet(45/57 Pages) STMICROELECTRONICS

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L6717A

Output voltage monitoring and protections

OC_TOT

, the device detects an OC and immediately latches with all the MOSFETs

of all the sections OFF (HiZ).

Typical design considers the intervention of the total current OC before the Per-Phase OC,

leaving this last one as an extreme-protection in case of hardware failures in the external

components. Typical design flow is the following:

–

Define the maximum total output current (I

OC_TOT

) according to system

requirements

–

Design Per-Phase OC and R

resistor in order to have I

INFOx

= I

OC_TH

(35

μA)

when I

OUT

is about 10% higher than the I

OC_TOT

current. It results:

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

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 2.5V and I

OC_TOT

is the total current OC threshold

desired.

–

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

–

An additional capacitor in parallel to R

ILIM

can be considered to add a delay in the

protection intervention.

Note:

What previously listed is the typical design flow. Custom design and specifications may

require different settings and ratios between the Per-Phase OC threshold and the total

current OC threshold. Applications with huge ripple across inductors may be required to set

Per-Phase OC to values different than 110%: design flow should be modified accordingly.

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

for Per-Phase OC and total current OC.

8.4.2

IddSpike and IddTDC support

L6717A supports G34 processors and as a consequence, allows dual level OCP supporting

IddSpike and IddTDC (refer to CPU related documents for details about IddSpike and

IddTDC levels).

Proper design of the per-phase and Total Current OC is required to meet these

specifications:

–

per-phase OC is used to face with IddSpike: set to 120% (Typ) of IddSpike;

–

Total current OC is used to face with IddTDC: set to 120% (Typ) of IddTDC and

provide proper filtering.

1.1

OC_TOT

⋅

() DCR

⋅

OC T H

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

ILIM

OC_TOT

⋅

OC_TOT

DC R

⋅

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

LI M

DC R

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

OU T

⋅





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