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iWatt |
iW1678
Low-Power Off-line Digital Green-Mode PWM Controller
1.0 Features
2.0 Description
●● Primary-side feedback eliminates opto-isolators and
simplifies design
●● 64-kHz PWM switching frequency
●● No-load power consumption < 100 mW at 230 Vac with
tight dynamic load transient response
●● Able to meet < 30 mW no-load power consumption with
large value pre-load resistor
●● Adaptive multi-mode PWM/PFM control improves
efficiency
●● Quasi-resonant operation for highest overall efficiency
●● EZ-EMI ® design to easily meet global EMI standards
●● Direct drive of low-cost BJT switch
●● Dynamic base current control
●● Very tight constant voltage and constant current
regulation with primary-side-only feedback
The iW1678 is a high performance AC/DC power supply
controller which uses digital control technology to build peak
current mode PWM flyback power supplies. The iW1678’s
64-kHz PWM switching frequency allows the design of ultra-
compact AC/DC adapters and chargers. 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 iW1678 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.
●● No external compensation components required
●● Complies with EPA 2.0 energy-efficiency specifications
with ample margin
●● Low start-up current (8 μA typical)
●● Built-in soft start
iWatt’s innovative proprietary technology ensures that power
supplies built with iW1678 can achieve both highest average
efficiency and less than 100 mW no-load power consumption
in a compact form factor.
3.0 Applications
●● Built-in short circuit protection and output overvoltage ●● Low power compact AC/DC adapter/chargers for cell
protection
phones, PDAs, digital still cameras
●● Built-in current sense resistor short circuit protection
●● Linear AC/DC replacement
●● No audible noise over entire operating range
L
+
N
+ VOUT
GND
Rev. 1.1
U1
iW1678
1 VCC
OUTPUT 5
2 GND
3 VSENSE
ISENSE 4
Figure 3.1: iW1678 Typical Application Circuit
iW1678
3/12/12
Page 1
iW1678
Low-Power Off-line Digital Green-Mode PWM Controller
4.0 Pinout Description
iW1678
1 VCC
2 GND
OUTPUT 5
3 VSENSE
ISENSE 4
Figure 4.1: 5 Lead SOT-23 Package
Pin #
1
2
3
4
5
Name
VCC
GND
VSENSE
ISENSE
OUTPUT
Type Pin Description
Power Input Power supply for control logic.
Ground Ground.
Analog Input Auxiliary voltage sense (used for primary regulation).
Analog Input Primary current sense. Used for cycle-by-cycle peak current control and limit.
Output Base drive for BJT.
5.0 Absolute Maximum Ratings
Absolute maximum ratings are the parameter values or ranges which can cause permanent damage if exceeded. For
maximum safe operating conditions, refer to Electrical Characteristics in Section 6.0.
Parameter
DC supply voltage range (pin 1, ICC = 20mA max)
Continuous DC supply current at VCC pin (VCC = 15 V)
Output (pin 5)
VSENSE input (pin 3, IVsense ≤ 10 mA)
ISENSE input (pin 4)
Maximum junction temperature
Storage temperature
Lead temperature during IR reflow for ≤ 15 seconds
Thermal Resistance Junction-to-Ambient
ESD rating per JEDEC JESD22-A114
Latch-Up test per JEDEC 78
Symbol
VCC
ICC
TJ MAX
TSTG
TLEAD
θJA
Value
-0.3 to 18
20
-0.3 to 4.0
-0.7 to 4.0
-0.3 to 4.0
125
–65 to 150
260
190
2,000
±100
Units
V
mA
V
V
V
°C
°C
°C
°C/W
V
mA
Rev. 1.1
iW1678
3/12/12
Page 2
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