L6713ATR datasheet(42/64 Pages) STMICROELECTRONICS

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Soft-start

L6713A

42/64

Soft-start

L6713A implements a soft-start to smoothly charge the output filter avoiding high in-rush

currents to be required to the input power supply. The device increases the reference from

zero up to the programmed value in different ways according to the selected operative mode

and the output voltage increases accordingly with closed loop regulation.

The device implements soft-start only when all the power supplies are above their own turn-

on thresholds and the OUTEN pin is set free.

At the end of the digital soft-start, SS_END/PGOOD signal is set free. Protections are active

during this phase; under voltage is enabled when the reference voltage reaches 0.6 V while

over voltage is always enabled with a threshold dependent on the selected operative mode

or with the fixed threshold programmed by ROVP (See “Over voltage and programmable

OVP” Section).

Figure 15.

Soft-start

16.1

Intel mode

Once L6713A receives all the correct supplies and enables, and Intel mode has been

selected, it initiates the soft-start phase with a T1 = 1 ms(min) delay. After that, the reference

ramps up to VBOOT = 1.081 V (1.100V - 19mV) in T2 according to the SS/LTBG/AMD settings

and waits for T3 = 75 μsec(typ) during which the device reads the VID lines. Output voltage

will then ramps up to the programmed value in T4 with the same slope as before (See

Figure 15).

SS/LTB/AMD defines the frequency of an internal additional soft-start-oscillator used to step

the reference from zero up to the programmed value; this oscillator is independent from the

main oscillator whose frequency is programmed through the OSC pin.

In particular, it allows to precisely programming the start-up time up to VBOOT (T2) since it is

a fixed voltage independent by the programmed VID. Total soft-start time dependence on

the programmed VID results (See Figure 17 and See Figure 19).

OUTEN

SS_END

Intel Mode

VOUT

T1 T2 T3 T4

TSS

OUTEN

PGOOD

AMD 6BIT Mode

VOUT

TSS

OVP

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