iW1688
Low-Power Off-line Digital PWM Controller
8.0 Functional Block Diagram
V
IN
5
V
SW
V
CC
CC
4
V
SW
Start-up
Control
IN
A/D
t
ON
25k�
Calcuator
GND
2
V
CC
CC/CV
Control
Output
Pulse
Reference
OUTPUT
3
Control
V
V
FB
Digital
Error
Amp
SENSE
1
–
CMP
t
+
OFF
1.55V
1.8V
0.2V
Real Time
Waveform
Analyzer
Calcuator
–
CMP
+
–
CMP
+
Figure 8.0.1 iW1688 Functional Block Diagram
9.0 Theory of Operation
The iW1688 is a digital controller which uses a new, digital control algorithm to reduce system design time and
proprietary primary-side control technology to eliminate the improve reliability.
opto-isolated feedback and secondary regulation circuits
Furthermore, accurate secondary constant-current operation
required in traditional designs. This results in a low-cost
is achieved without the need for any secondary-side sense
solution for low power AC/DC adapters. The core PWM
and control circuits. This eliminates the need for opto-
processor uses fixed-frequency Discontinuous Conduction
couplers. The iW1688 sets the internal primary current
Mode (DCM) operation at higher power levels and switches
limit at 130% (typical) of the specified maximum load with
foldback current limiting.
to variable frequency operation at light loads to maximize
efficiency. Furthermore, iWatt’s digital control technology
enables fast dynamic response, tight output regulation, and
The iW1688 uses PWM mode control at higher output power
full featured circuit protection with primary-side control.
levels and switches to PFM mode at light load to minimize
power dissipation to meet the Blue Angel specification.
Referring to the block diagram in Figure 8.0.1, the digital
Additional built-in protection features include overvoltage
error amplifier and tON/tOFF calculator blocks generate the
protection (OVP), output short circuit protection (SCP) and
switching on-time and off-time information based on the line
voltage and the output voltage feedback signal. The system
soft-start.
loop is automatically compensated internally by the digital
iWatt’s digital control scheme is specifically designed to
error amplifier. Adequate system phase margin and gain
address the challenges and trade-offs of power conversion
margin are guaranteed by design and no external analog
design. This innovative technology is ideal for balancing new
components are required for loop compensation. Traditional
regulatory requirements for green mode operation with more
complex loop analysis is not required during the design
practical design considerations such as lowest possible cost,
phase. Primary side control eliminates the secondary control
smallest size and high performance output control.
reference and opto-isolator. The iW1688 uses an advanced
MK-4AA003-E
03/16/06
PAGE 5
PRELIMINARY
ETC [ ETC ]
