PFS7323L datasheet(6/30 Pages) POWERINT

6 / 30 page

Rev. B 06/13

PFS7323-7329

www.powerint.com

Figure 8.

Start-Up Sequence.

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.

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 V

CC 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 t

SOFT time duration for a full scale error

voltage of 5 V.

The beginning of soft-start is gated by the V

CC+, 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

Soft-Start

Check

Sequence

VCC > VCC+?

Apply 0.5

µA on

on FB Pin to

Check Open

FB Pin

YES

Apply PGT

Current Source

YES

Is PG ‘OFF’

(PG High

Impedance)?

Feedback

short to C Pin

Start

Converter

Increase

FB Pin Current

to 20

µA

Is the NLA

Charging or

Discharging?

IR Within

Bounds for

Efﬁciency or

Full Mode?

YES

PI-6698-013013

YES

Source ~3 mA

to C Pin

Is VC > 3 V?

Is OTP OK?

YES

VFB > FBOFF

VFB < FBOV?

YES

Is VC > COFF?

YES

Is the NLA

Charging or

Discharging?

IV > IUV+?

YES

VV < 1 V?

YES

VFB > FBOFF

VFB < FBON

VC > COFF

OTP OK?

YES

IR Within

Bounds for

Efﬁciency or

Full Mode?

YES

Decrease

FB Pin Current

to 0.5

µA

Apply

6 mA V Pin

Current Sink

YES

Set Internal

Power Limit

Remove

6 mA V Pin

Current Sink

Slow Power

Limit Over

Soft-Start

Duration

IV > IUV+

YES

Detect Input

Voltage Peak

PI-5336-110810

tSTART-DELAY

tSOFT

VCC+

~5 V

Figure 7.

Power Limit Soft-Start Function.

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