SSL4120T datasheet(18/47 Pages) NXP

18 / 47 page

SSL4120T

All information provided in this document is subject to legal disclaimers.

Objective data sheet

Rev. 1 — 21 June 2012

18 of 47

NXP Semiconductors

SSL4120T

Resonant power supply control IC with PFC

This is achieved by connecting a resistor Rss(PFC) and a capacitor Css(PFC) between

pin SNSCURPFC and the current sense resistor Rcur(PFC). At start-up, an internal current

source Ich(ss)(PFC) charges the capacitor to VSNSCURPFC =Ich(ss)(PFC)

× Rss(PFC). The

voltage is limited to the maximum PFC soft start clamp voltage, Vclamp(ss)PFC. The

additional voltage across the charged capacitor results in a reduced peak current. After

start-up, the internal current source is switched-off, capacitor Css(PFC) discharges across

Rss(PFC) and the peak current increases.

The start level and the time constant of the rising primary current can be adjusted

externally by changing the values of Rss(PFC) and Css(PFC).

Soft stop is achieved by switching on the internal current source Ich(ss)(PFC).This current

charges Css(PFC) and the increasing capacitor voltage reduces the peak current. The

charge current will flow as long as the voltage on pin SNSCURPFC is below the maximum

PFC soft start voltage (typ. 0.5 V). If VSNSCURPFC exceeds the maximum PFC soft start

voltage, the soft start current source will start limiting the charge current. To accurately

determine if the capacitor is charged, the voltage is only measured during the off-time of

the PFC power switch. The operation of the PFC is stopped when VSNSCURPFC >

Vstop(ss)(PFC).

7.7.7 PFC overcurrent regulation, OCR-PFC (pin SNSCURPFC)

The maximum peak current is limited cycle-by-cycle by sensing the voltage across an

external sense resistor (Rcur(PFC)) connected to the source of the external MOSFET. The

voltage is measured via the SNSCURPFC pin and is limited to Vocr(PFC).

A voltage peak will appear on VSNSCURPFC when the PFC MOSFET is switched on due to

the discharging of the drain capacitance. The leading edge blanking time, tleb(PFC),

ensures that the overcurrent sensing block will not react to this transitory peak.

7.7.8 PFC mains undervoltage protection/brownout protection, UVP-mains

(pin SNSMAINS)

The voltage on the SNSMAINS pin is sensed continuously to prevent the PFC trying to

operate at very low mains input voltages. PFC switching stops as soon as VSNSMAINS

drops below Vuvp(SNSMAINS). Mains undervoltage protection is also called brownout

protection.

VSNSMAINS is clamped to a minimum value of Vpu(SNSMAINS) for fast restart as soon as the

mains input voltage recovers after a mains-dropout. The PFC (re)starts once VSNSMAINS

exceeds the start level Vstart(SNSMAINS).

7.7.9 PFC boost overvoltage protection, OVP-boost (pin SNSBOOST)

An overvoltage protection circuit has been built in to prevent boost overvoltages during

load steps and mains transients.

Cur PFC

() pk

()

ocr PFC

()

ch ss

() PFC

()

ss PFC

()

–

cur PFC

()

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

ss PFC

()

ss PFC

()

SSL4120T датащи(PDF) 18 Page - NXP Semiconductors

SSL4120T датащи(HTML) 18 Page - NXP Semiconductors

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

датащи скачать

ссылки URL