PN8368SSC-R1D datasheet(7/12 Pages) CHIPOWN

7 / 12 page

PN8368

Chipown

www.chipown.com

Rev.1710

Oct.-2017

7 / 12

keeps around constant, the chip oscillator frequency

decreases while the output current decreases. Figure 2

illustrates the relations of the switching frequency,

Ipeak and Loading for PN8368.

Figure 2 The Switching Frequency, Vipeak VS. LOAD

4. Current Sensing and Leading Edge

Blanking

Cycle-by-Cycle current limiting is offered in

PN8368. The switch current is detected by a sense

resistor at CS pin. The CC set-point and maximum

output power can be externally adjusted by external

current sense resistor at CS pin. An internal leading

edge blanking circuit chops off the sensed voltage

spike at initial power MOSFET on-state so that the

external RC filtering on sense input is no longer

needed.

5. Programmable Cable Drop

Compensation

In PN8368, an offset voltage is generated at FB

pin by an internal current flowing into the divider

resister, as shown in Figure 3. The Cable Drop

Compensation block compensates the voltage drop

across the cable. As the load current decreases from

full load to no load, the voltage drop across the cable

decreases. It can be programmed by adjusting the

external resistor R2 or R1 at FB pin. The maximum

compensation is

cable

)

(

（

4）

Because of the influence of the chip’s sampling

position and devices of the system, the actual

maximum compensation is less than theoretical value.

Figure 3 Icable

6. Reference Negative Temperature

Compensation

As shown in Figure 3, the voltage of FB pin is

()

AUX

)

(

（

5）

Where

has a negative temperature coefficient,

K is a constant.

In PN8368, the voltage reference uses the

negative temperature compensation technology. At

room temperature, the voltage reference is 2.5V. The

voltage reference (VREF_CV) decreases while the

temperature of chip increases. The reference negative

temperature compensation block compensates the

Δ , thus the output voltage keeps constant at full

range of temperature. The reference negative

temperature compensation improves output precision.

7. Quasi-Resonant Switching

The PN8368 incorporates a unique proprietary

quasi-resonant switching scheme that achieves

valley-mode turn on for every switching cycle in CV

mode. This unique feature greatly reduces the

switching loss. The actual switching frequency can

vary slightly cycle by cycle, providing the additional

benefit of reducing EMI.

Figure 4 QR Mode

PN8368SSC-R1D 数据表(PDF) 7 Page - Wuxi Chipown Micro-electronics limited

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