L6714 datasheet(43/70 Pages) STMICROELECTRONICS

43 / 70 page

L6714

Soft start

43/70

15.1

Intel mode

Once L6714 receives all the correct supplies and enables, and Intel Mode has been

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

ramps up to VBOOT = 1.081V (1.100V - 19mV) in T2 according to the SSOSC settings and

waits for T3 = 75µsec(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 14).

SSOSC 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. SSOSC sets then the

Output Voltage dV/dt during Soft-Start according to the resistor RSSOSC connected vs.

SGND. 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 15):

where TSS is the time spent to reach the programmed voltage VSS and RSSOSC the resistor

connected between SSOSC and SGND in k

Ω.

Protections are active during Soft-Start, UVP is enabled after the reference reaches 0.6V

while OVP is always active with a fixed 1.24V threshold before VBOOT and with the threshold

coming from the VID (or the programmed VOVP) after VBOOT (See red-dashed line in

Figure 14).

Note:

If during T3 the programmed VID selects an output voltage lower than VBOOT, the output

voltage will ramp to the programmed voltage starting from VBOOT.

SSOSC kΩ

[]

2 µs

[] 4.9783 10

–

⋅⋅

SS µs

[]

1075

µs

[]

SSOSC kΩ

[]

5.3816

–

⋅

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

⋅

if V

BOOT

()

SSOSC kΩ

[]

5.3816

–

⋅

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

BOOT

–

()

[]

⋅

if V

BOOT

()

⎩

⎪

⎨

⎪

⎧

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