PN8368SSC-R1D datasheet(6/12 Pages) CHIPOWN

6 / 12 page

PN8368

Chipown

www.chipown.com

Rev.1710

Oct.-2017

6 / 12

Functional Description

The PN8368 is a high performance CC/CV

primary-side

controller.

PN8368

operates

primary-side sensing and regulation, so opto-coupler

and TL431 could be eliminated. Proprietary built-in

CV and CC control can achieve high precision

CC/CV control meeting most charger and adaptor

application requirements. Internal HV Start-up

circuit and the chip’s low consumption help the

system to meet strict standby power standard.

1. HV Start up Control

At start up, the internal high-voltage start-up

circuit provides the internal bias and charges the

external VDD capacitor, so that PN8368 starts up

quickly. When VDD reaches VDDon, the device starts

switching and the internal high-voltage current source

stops charging the capacitor. The device keeps in

normal operation provided as long as VDD keeps

above VDDoff. After startup, the bias is supplied from

the auxiliary transformer winding, the current of HV

start-up circuit is designed to be very low so that the

power consumption is very low.

2. CC Operation Mode

In CC operation mode, the PN8368 captures the

auxiliary flyback signal at FB pin through a resistor

dividing-network. The pulse width of the auxiliary

flyback signal determines the PN8368 oscillator

frequency. The higher the output voltage is, the

shorter the pulse width is, and the higher the chip

oscillator frequency is, thus the constant output

current can be achieved.

The current waveform of DCM mode is shown

in Figure 1. During MOSFET turn-on time, the

current in the primary winding (Ipri) ramps up. When

MOSFET turns off, the energy stored in the primary

winding is transferred to the secondary side, so the

peak current in the secondary winding is

pri

sec_

（

1）

The output current is

demag

sense

demag

sec_

（

2）

Because Vipk is constant and Tp is equal to tow

times Tdemag, the output current Io is constant.

Figure 1 The current waveform of DCM mode

3. CV Operation Mode

In CV mode，PN8368 uses a pulse to sample VFB

and it is hold until the next sampling. The sampled

voltage is compared with VREF_CV and the error is

amplified. The error amplified output reflects the load

condition and controls the switching off time to

regulate the output voltage, thus constant output

voltage can be achieved.

The relationship between the output voltage

and VREF_CV is

AUX

REF

)

(

（

3）

means Secondary winding,

AUX

means Auxiliary winding

The PN8368 operates in PFM_QR mode during

full load mode, since the peak current (Ipeak) of

MOSFET is constant, the chip frequency decreases

while the output current decreases. When the

switching frequency approaches to 25kHz, the

PN8368 enters PWM_QR mode, the chip frequency

decreases slowly while the output current decreases,

the Ipeak decreases while the output current

decreases. Therefore the PN8368 can avoid audible

noise, while achieving high efficiency at 25% load

conditions. When Vcs decreases to 170mV, the

PN8368 enters Standby mode. In this mode, Ipeak

PN8368SSC-R1D 数据表(PDF) 6 Page - Wuxi Chipown Micro-electronics limited

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