iW1696

Low-Power Off-line Digital Green-Mode PWM Controller

iW1696

8.0 Functional Block Diagram

1

5

2

4

GND

Output

Start-up

Digital

Logic

Control

Signal

Conditioning

DAC

1.1 V

BJT

Base

Drive

Enable

3

OCP

= 1.538 V

Figure 8.1: iW1696 Functional Block Diagram

9.0 Theory of Operation

The iW1696 is a digital controller which uses a new,

proprietary primary-side control technology to eliminate the

opto-isolated feedback and secondary regulation circuits

required in traditional designs. This results in a low-cost

solution for low power AC/DC adapters. The core PWM

processor uses fixed-frequency Discontinuous Conduction

Mode (DCM) operation at higher power levels and switches

to variable frequency operation at light loads to maximize

efficiency. Furthermore, iWatt’s digital control technology

enables fast dynamic response, tight output regulation, and

full featured circuit protection with primary-side control.

Referring to the block diagram in Figure 8.1, the digital logic

control block generates the switching on-time and off-time

information based on the output voltage and current feedback

signal and provides commands to dynamically control the

external BJT base current. The system loop is automatically

compensated internally by a digital error amplifier. Adequate

system phase margin and gain margin are guaranteed by

design and no external analog components are required for

loop compensation. The iW1696 uses an advanced digital

control algorithm to reduce system design time and increase

reliability.

Furthermore, accurate secondary constant-current operation

is achieved without the need for any secondary-side sense

and control circuits.

The iW1696 uses adaptive multi-mode PWM/PFM control

to dynamically change the BJT switching frequency for

efficiency, EMI, and power consumption optimization. In

addition, it achieves unique BJT quasi-resonant switching to

further improve efficiency and reduce EMI. Built-in protection

features include overvoltage protection (OVP), output short

circuit protection (SCP), over current protection (OCP),

single pin fault protection and I

iWatt’s digital control scheme is specifically designed to

address the challenges and trade-offs of power conversion

design. This innovative technology is ideal for balancing new

regulatory requirements for green mode operation with more

practical design considerations such as lowest possible cost,

smallest size and high performance output control.