AP3108LS

Document number: DS42105 Rev. 3 - 2

8 of 16

www.diodes.com

February 2021

© Diodes Incorporated

AP3108LS

Performance Characteristics (continued)

VBR-OUT vs. Ambient Temperature

Green Mode Frequency vs. Ambient Temperature

Operation Description

PWM Operation Principle

Figure 1 describes how the AP3108LS and AP4320 work together to achieve constant voltage (CV), constant current (CC) and primary constant

OCP (COCP) control. At secondary side, the sensed output voltage or output current signals are compared with the corresponding reference VREF

_CV and VREF_CC in AP4320. The inner CV and CC amplifier combine with an external compensation network to generate an amplified error signal

and transfer to the primary side FB pin through the opto-

coupler. It’s noted that only one amplifier works at one moment between CV and CC

amplifier. The scaled FB voltage comparing with the SENSE voltage after slope compensation will turn off primary switch and determine the duty

cycle.

Usually, secondary CC and CV provide a good enough static state performance for output voltage and current regulation under all load and line

conditions. If any over current conditions occur, primary constant OCP control provides moderate over current limit, under output short condition,

this method can restrain the device stress and output current value in a reasonable range. In primary constant OCP control, the product of

V

CSM

sampled from SENSE Pin and

tONS

t

sampled from DEM Pin will compare with a primary OCP reference of VREF and get a primary switch duty cycle,

which will determine a real-time constant output current, detail information can be found in the following section.

Slope

Compensation

KFB_CS

Kcc

VREF

FB

SENSE

Driving

Block

PWM

CV

COCP

VBUS

ZCOMP_CV

K

VREF_CC

VREF_CV

ZCOMP_CC

Vo

VCSM Sample

tONS Sample

VCSM*tONS /t

DEM

GATE

AP4320

AP3108LS

Figure 1

-40

-20

0

20

40

60

80

100

80

85

90

95

100

Ambient Temperature (

oC)

-40

-20

0

20

40

60

80

100

15

16

17

18

19

20

21

22

23

24

25

Ambient Temperature (

oC)