UPC1909GS datasheet(9/16 Pages) NEC

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Data Sheet G14309EJ1V0DS00

µµµµPC1909

TIMING CHART

tqc

Oscillation

waveform CT

Feedback input

OUT1

output waveform

OUT2

output waveform

Oscillation

waveform CT’

tqd

(1) Oscillation waveform (CT)

This waveform is determined by the external capacitor connected to the CT pin (pin 16) and the external resistor

connected to the RT pin (pin 15). It is usually a 1.5-V to 3.5-V triangle waveform (the rise and fall times are the

same).

(2) Output waveform (OUT1)

Whichever is the lower of the DTC1 pin (pin 13) and FB pin (pin 12) voltages is compared with the triangle wave

of the CT pin (pin 16). The OUT1 pin (pin 11) is high level while the triangle wave is low.

(3) Output waveform (OUT2)

Whichever is the higher of the DTC2 pin (pin 5) and FB pin (pin 12) voltages is compared with the level-shifted

triangle wave (CT’). The OUT2 pin (pin 6) is high level while the level-shifted triangle wave is high.

(4) Triangle wave level shift

The triangle wave that controls OUT2 is the original triangle wave of the CT pin (pin 16) shifted to a lower

potential via the level shift circuit (OLS). The amount of shift (Vd) can be adjusted using the resistor (RCT2)

connected between the CT2 pin (pin 2) and the VREF pin.

The relationship between the shift amount (Vd) and the resistance value (k

Ω) of the resistor RCT2 connected to

the CT2 pin (pin 2) is as follows.

Vd =

× 2 [V]

RCT2[k

Ω] + 10

4.3

(5) Dead-time (tqc, tqd) adjustment

The dead time between the fall of OUT1 and the rise of OUT2 (tqc) and the dead time between the fall of OUT2

and the rise of OUT1 (tqd) is determined by the oscillation frequency and the amount of level shift of the triangle

wave. Although usually tqc = tqd, if setting these independently, connect a suitable resistor between the CT pin

and the VREF pin, as well as between the CT pin and GND, and adjust the dead time by making the oscillation

waveform asymmetrical.

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