iW1707

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

iW1707

8.0 Functional Block Diagram

1

6

5

4

GND

Output

Start-up

Digital

Logic

Control

Signal

Conditioning

DAC

1.15 V

BJT

Base

Drive

ENABLE

2

OCP

= 1.533 V

VCC

VFB

VSENSE(NOM)

VSENSE

ISENSE

VIPK

IPK

ENABLE

0.23 V ~ 1.00 V

Figure 8.1: iW1707 Functional Block Diagram

9.0 Theory of Operation

The iW1707 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 iW1707

operates in peak current mode control. 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 I

analog input configured to sense the primary current in a

voltage form. In order to achieve the peak current mode

control and cycle-by-cycle current limit, the V

threshold for the I

range of 0.23 V (typical) and 1.00 V (typical) under different

line and load conditions. 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 iW1707 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 iW1707 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

single-point fault protection features include overvoltage

protection (OVP), output short circuit protection (SCP),

over current protection (OCP), and I

In particular, it ensures that power supplies built with the

iW1707 are best suited for power adapter applications such

as ADSL modems that have large input capacitance.

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.