l6706 STMicroelectronics, l6706 Datasheet - Page 31

• Manufacturer Part Number: l6706
• Description: Vr11.1 Single Phase Controller With Integrated Driver
• Manufacturer: STMicroelectronics

L6706
14
Note:
Soft-start
L6706 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 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 signal is set free.
Protections are active during soft-start: Under voltage is enabled when the reference voltage
reaches 0.6 V while over voltage is always enabled.
Figure 13. Soft-start
Once L6706 receives all the correct supplies and enables, it initiates the soft-start phase
with a T
V - 19 mV) in T
which the device reads the VID lines. Output voltage will then ramps up to the programmed
value in T
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.
The current flowing from SSOSC pin before the end of soft-start is used to program the
desiderated soft-start time (T
After that the soft-start is finished the current flowing from SSOSC pin is used to program
the maximum LTB switching frequency (F
In the
F
In particular, it allows to precisely programming the startup time up to V
a fixed voltage independent by the programmed VID. Total soft-start time dependence on
the programmed VID results (see
If during T
voltage will ramp to the programmed voltage starting from V
LIMIT
) in independent way.
Figure 14
D1
D4
D3
= 1.5 ms (typ) delay. After that, the reference ramps up to V
with the same slope as before
the programmed VID selects an output voltage lower than V
D2
is shown the SSOSC connection in order to select both parameter (T
according to the SSOSC settings and waits for T
SS_END
OUTEN
SS
V
Doc ID 15698 Rev 1
OUT
).
Figure
T
OVP
D1
T
15).
LIMIT
D2
T
(See Figure
SS
T
D3
).
T
D4
T
D5
13).
t
t
t
BOOT
.
D3
= 200
BOOT
BOOT
BOOT
= 1.081 V (1.100
μ
sec (typ) during
(T
, the output
D2
) since it is
Soft-start
SS
31/47
and