NCP1611BDR2G【PDF 7/29 页】IC PFC CTLR HE ENHANCED 8-SOIC

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Sheet目录45

3页 4页 5页 6页 [7页]8页 9页 10页 11页

NCP1611

http://onsemi.com

DETAILED PIN DESCRIPTION

Pin Number

Name

Function

CONTROL

The error amplifier output is available on this pin. The network connected between this pin and

ground adjusts the regulation loop bandwidth that is typically set below 20 Hz to achieve high

Power Factor ratios.

Pin1 is grounded when the circuit is off so that when it starts operation, the power increases

slowly to provide a softstart function.

SENSE

A portion of the instantaneous input voltage is to be applied to pin 2 in order to detect

brownout conditions. If V

pin2

is lower than 0.9 V for more than 50 ms, the circuit stops pulsing

until the pin voltage rises again and exceeds 1.0 V.

This pin also detects the line range. By default, the circuit operates the lowline gain mode. If

pin2

exceeds 2.2 V, the circuit detects a highline condition and reduces the loop gain by 3.

Conversely, if the pin voltage remains lower than 1.7 V for more than 25 ms, the lowline gain

is set.

Connecting the pin 2 to ground disables the part once the 50 ms blanking time has elapsed.

CONTROL

This pin sources a current representative to the line current. Connect a resistor between pin3

and ground to generate a voltage representative of the line current. When this voltage exceeds

the internal 2.5 V reference (V

REF

), the circuit operates in critical conduction mode. If the pin

voltage is below 2.5 V, a deadtime is generated that approximately equates

[66 ms x (1 (V

pin3

REF

))]. By this means, the circuit forces a longer deadtime when the

current is small and a shorter one as the current increases.

The circuit skips cycles whenever V

pin3

is below 0.65 V to prevent the PFC stage from

operating near the line zero crossing where the power transfer is particularly inefficient. This

does result in a slightly increased distortion of the current. If superior power factor is required,

offset pin 3 by more than 0.75 V offset to inhibit the skip function.

CS / ZCD

This pin monitors the MOSFET current to limit its maximum current.

This pin is also connected to an internal comparator for Zero Current Detection (ZCD). This

comparator is designed to monitor a signal from an auxiliary winding and to detect the core

reset when this voltage drops to zero. The auxiliary winding voltage is to be applied through a

diode to avoid altering the current sense information for the ontime (see application

schematic).

Ground

Connect this pin to the PFC stage ground.

Drive

The highcurrent capability of the totem pole gate drive (0.5/+0.8 A) makes it suitable to

effectively drive high gate charge power MOSFETs.

This pin is the positive supply of the IC. The circuit starts to operate when V

exceeds 10.5 V

(A version, 17.0 V for the B version) and turns off when V

goes below 9.0 V (typical values).

After startup, the operating range is 9.5 V up to 35 V. The A version is preferred in

applications where the circuit is fed by an external power source (from an auxiliary power

supply or from a downstream converter). Its maximum startup level (11.25 V) is set low

enough so that the circuit can be powered from a 12 V rail. The B version is optimized for

applications where the PFC stage is selfpowered.

Feedback

This pin receives a portion of the PFC output voltage for the regulation and the Dynamic

Response Enhancer (DRE) that drastically speedsup the loop response when the output

voltage drops below 95.5% of the desired output level.

pin8

is also the input signal for the (nonlatching) OverVoltage (OVP) and UnderVoltage

(UVP) comparators. The UVP comparator prevents operation as long as V

pin8

is lower than

12% of the reference voltage (V

REF

). A soft OVP comparator gradually reduces the dutyratio

when V

pin8

exceeds 105% of V

REF

. If despite of this, the output voltage still increases, the

driver is immediately disabled if the output voltage exceeds 107% of the desired level (fast

OVP).

A 250 nA sink current is builtin to trigger the UVP protection and disable the part if the

feedback pin is accidentally open.

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