iW1707

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

iW1707

1.0 Features

● Primary-side feedback eliminates opto-isolators and

simplifies design

● Adaptively controlled soft start enables fast and smooth

start-up for a wide range of capacitive loads (from

330 μF to 6,000 μF)

● Active start-up scheme enables shortest possible

turn-on delay

● Direct drive of low-cost BJT switch

● Very tight constant voltage regulation

● Intrinsically low common mode noise

● Optimized 72 kHz maximum PWM switching frequency

achieves best size and efficiency

● Adaptive multi-mode PWM/PFM control improves

efficiency

● Quasi-resonant operation for highest overall efficiency

● Dynamic base current control

● No external compensation components required

● Complies with EPA 2.0 energy-efficiency specifications

with ample margin

● Built-in short circuit protection and output overvoltage

protection

● Built-in current sense resistor short circuit protection

● Constant current control enables output current limit and

overload protection

● No audible noise over entire operating range

Figure 3.1: iW1707 Typical Application Circuit

(Using Depletion Mode NFET as Active Start-up Device)

2.0 Description

The iW1707 is a high performance AC/DC power supply

controller which uses digital control technology to build peak

current mode PWM flyback power supplies. The device

directly drives a power BJT and operates in quasi-resonant

mode to provide high efficiency along with a number of key

built-in protection features while minimizing the external

component count, simplifying EMI design and lowering the

total bill of material cost. The iW1707 features a distinctive

soft-start scheme, which allows for fast and yet smooth

start-up with both small and large capacitive loads. The

iW1707 removes the need for secondary feedback circuitry

while achieving excellent line and load regulation. It also

eliminates the need for loop compensation components

while maintaining stability over all operating conditions.

Pulse-by-pulse waveform analysis allows for a loop

response that is much faster than traditional solutions,

resulting in improved dynamic load response. The built-in

power limit function enables optimized transformer design

in universal off-line applications and allows for a wide input

voltage range.

iWatt’s innovative proprietary technology ensures that

power supplies built with the iW1707 can achieve both

highest average efficiency and less than 100 mW no-load

consumption, and have fast yet smooth start-up with a wide

range of capacitive loads with output voltage up to 12 V, and

are ideal for network and home appliance power supplies

applications.

3.0 Applications

● Network power adapters for ADSL, wireless access

points, routers

● AC/DC power supplies in home appliances

L

+

GND

+

U1

iW1707

ASU

OUTPUT

GND

1

5

3

6

4

2

N