AP3981C

Document number: DS41619 Rev. 2 - 2

1 of 16

www.diodes.com

June 2019

© Diodes Incorporated

AP3981C

PRIMARY SIDE REGULATED POWER SWITCHER

Description

The AP3981C is a high performance power switchers integrated with

a primary side regulation controller and an N-channel power

MOSFET. It can be used for battery charger and adaptor applications,

accurate Constant Voltage (CV) and Constant Current (CC) can be

achieved without an opto-coupler and secondary control circuitry.

The AP3981C operates in Pulse Frequency Modulation (PFM) mode

and peak current Amplitude Modulation (AM) mode to form a fine tune

frequency curve within the whole power range. Therefore, the

AP3981C can achieve high average efficiency and improve audible

noise.

The AP3981C provides comprehensive protections without additional

circuitry. It contains VCC over voltage protection, output over voltage

protection, output under voltage protection, output short circuit

protection, cycle-by-cycle current limit, open loop protection, and

internal over temperature protection, etc.

The AP3981C is available in SO-8 package.

Features



Primary Side Control for Eliminating Opto-Coupler



Built-In 650V Power MOSFET



75mW No-Load Input Power



Flyback Topology in DCM Operation



External Adjustable Line Compensation for CC



Fixed Internal Cable Compensation



Multiple Segment AM/PFM Control Mode to Improve Audio

Noise and Efficiency



Frequency Jitter to Improve System EMI



Capacitive Load Start-Up Capability



Valley-On for the Higher Efficiency and Better EMI Behavior



Multiple Protections:



Secondary-Side Over Voltage Protection (SOVP)



Secondary-Side Under Voltage Protection (SUVP)



Output Short Circuit Protection (SCP)



Transformer Saturation Protection (TSP) via Primary Peak

Current Limitation



Internal Over Temperature Protection (OTP)



SO-8 Package



Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)



Halogen and Antimony Free.

“Green” Device (Note 3)

Pin Assignments

(Top View)

SO-8

Applications



Routers



Set-Top Box (STB) Power Supply



Network Adaptors

Notes:

1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS), 2011/65/EU (RoHS 2) & 2015/863/EU (RoHS 3) compliant.

2. See https://www.diodes.com/quality/lead-

free/ for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green" and

Lead-free.

3. Halogen- and Antimony-fre

e "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and

<1000ppm antimony compounds.

1

2

3

4

8

6

5

7

FB

VCC

SOURCE

GND

Drain

Drain

Drain

Drain