PFS7323-7329
The minimum rated peak power shown in Table 1 is not derated
below the brown-in threshold when the device is operated in
the ‘Efficiency’ mode.
Soft-Start with Pin-to-Pin Short-Circuit Protection
The FEEDBACK pin which is connected to a resistor voltage
divider provides a means to overcome the inherently slow
feedback loop response. The controller has an integrated
non-linear amplifier function to limit the maximum overshoot
and undershoot during load transient events.
VCC+
To reduce switch and output diode current stress at start-up,
the HiperPFS slews the internal error-voltage from zero to its
steady-state value at start-up. Figure 7 illustrates the relative
relationship between the application of VCC and power limit
soft-start function through the internal error-voltage. The
error-voltage has a controlled slew rate of 0.25 V/ms at start-up,
corresponding to the tSOFT time duration for a full scale error
voltage of 5 V.
tSTART-DELAY
tSOFT
~5 V
The beginning of soft-start is gated by the VCC+, REFERENCE,
CONTROL and FEEDBACK pin voltage thresholds in the
sequence described below. Once the applied VCC is above the
VCC+ threshold, conditions for REFERENCE, COMPENSATION
t
PI-5336-110810
Figure 7.
Power Limit Soft-Start Function.
Soft-Start
Check
Sequence
Is
NO
IV > IUV+
?
Is
Is
NO
VCC > VCC+
?
IR Within
NO
Bounds for
Efficiency or
Full Mode?
YES
Apply
6 mA V Pin
Current Sink
YES
YES
YES
YES
Apply 0.5 µA on
on FB Pin to
Check Open
FB Pin
Apply PGT
Current Source
YES
NO
Is OTP OK?
Set Internal
Power Limit
Is
NO
NO
NO
VV < 1 V?
YES
YES
Is PG ‘OFF’
(PG High
NO
YES
Impedance)?
NO
Is
YES
Is
NO
IV > IUV+
VFB > FBOFF
VFB < FBOV
YES
?
Is
IR Within
Increase
FB Pin Current
to 20 µA
Bounds for
Efficiency or
Full Mode?
YES
YES
Detect Input
Voltage Peak
YES
NO
Source ~3 mA
to C Pin
Is VC > COFF
?
YES
Is the NLA
Charging or
Discharging?
NO
Feedback
short to C Pin
Is
VFB > FBOFF
VFB < FBON
VC > COFF
OTP OK?
Start
Converter
YES
YES
YES
YES
Is the NLA
Charging or
Discharging?
NO
NO
Decrease
FB Pin Current
to 0.5 µA
Is VC > 3 V?
Slow Power
Limit Over
Soft-Start
Duration
Remove
6 mA V Pin
Current Sink
YES
YES
YES
PI-6698-013013
Figure 8. Start-Up Sequence.
6
Rev. B 06/13
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