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PDF IW1692 Data sheet ( Hoja de datos )
| Número de pieza | IW1692 | |
| Descripción | Low Power Off-Line Digital PWM Controller | |
| Fabricantes | iWatt | |
| Logotipo |  |
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iW1692
Low-Power Off-line Digital PWM Controller
1.0 Features
• Primary-side feedback eliminates opto-isolators and
simplifies design
• Multi-mode operation for highest overall efficiency
• Built-in cable drop compensation
• Very tight output voltage regulation
• No external loop compensation components required
• Complies with CEC/EPA/IEC no load power consumption
and average efficiency regulations
• Built-in output constant-current control with primary-side
feedback
• Low start-up current (10 µA typical)
• Built-in soft start
• Built-in short circuit protection
• AC line under/overvoltage and output overvoltage
protection
• 40 kHz PWM switching frequency
• PFM operation at light load
• Built-in ISENSE pin short protection
• Space-saving SOT-23 package
2.0 Description
The iW1692 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
provides high efficiency along with a number of key built-in
protection features while minimizing the external component
count and bill of material cost. The iW1692 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.
The low start-up power and PFM operation at light load
ensure that the iW1692 is ideal for applications targeting the
newest regulatory standards for standby power.
3.0 Applications
• Low power AC/DC adapter/chargers for cell phones,
PDAs, digital still cameras
• Standby supplies for televisions, DVDs, set-top boxes
and other consumer electronics
L
N
+
+ + VOUT
RTN
+
4 VCC
OUTPUT 3
5 ISENSE
GND 2
6 VIN
VSENSE 1
U1
iW1692
Figure 2.0.1 iW1692 Typical Application Circuit
Rev. 2.0
iW1692
February 13, 2012
Page 1
1 page  
iW1692
Low-Power Off-line Digital PWM Controller
8.0 Functional Block Diagram
VIN
6
VINSW
VSENSE
1
GND
2
VCC
4
ADC
VIN_A
0.2 V ~ 2.0 V
VINSW
Start-up
Signal
Conditioning
VVMS
VFB
Digital
Logic
Control
VOCP
DAC
Gate
Driver
– 1.0 V
+
VIPK
IPEAK
0.2 V ~ 0.9 V
+
––
OUTPUT
3
ISENSE
5
Figure 8.0.1 iW1692 Functional Block Diagram
9.0 Theory of Operation
The iW1692 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 heavy load 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 8.0.1, the digital
logic control generates the switching on-time and off-time
information based on the line voltage and the output voltage
feedback signal. The system loop is internally compensated
inside the digital logic control, and no external analog
components are required for loop compensation. The iW1692
uses an advanced digital control algorithm to reduce system
design time and improve reliability.
Furthermore, accurate secondary constant-current operation
is achieved without the need for any secondary-side sense
and control circuits.
The iW1692 uses PWM mode control at higher output
power levels and switches to PFM mode at light load to
minimize power dissipation. Additional built-in protection
features include overvoltage protection (OVP), output
short circuit protection (SCP), AC low line brown out, over
current protection, single pin fault protection and ISENSE fault
detection.
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.
Rev. 2.0
iW1692
February 13, 2012
Page 5
5 Page 
iW1692
Low-Power Off-line Digital PWM Controller
I PRI _ PK
= VIsense _ CC
RIsense
(10.12)
I PRI _ PK
<
0.9V
RIsense
(10.17)
Substituting this into equation 10.11 gives:
=VIsense(CC )
2 × IOUT × RIsense × TPERIOD
NTR × hX
TRESET
(10.13)
Thus, LM is limited by:
( )LM _ MIN =
VIN ⋅TON MAX
0.9V RIsense
(10.18)
During constant current mode, where output current is at
its maximum, the first term in Equation 10.13 is constant.
Therefore, we can call this KC. Substituting this back into
equation 10.13 we get:
There is also a lower limit on ISENSE signal of 0.2 V. This gives
a second maximum value on LM; compare this with the value
obtained from equation 10.16 and pick the smaller of the two
values.
VIse=nse _ CC
TPERIOD
TRESET
×
KC
(10.14)
For iW1692 KC is 0.264 V, therefore RIsense depends on the
maximum output current by:
=RIsense
Ntr × KC
2 × IOUT
× hx
(10.15)
( )LM _ MAX
=
2×
PXFMR _ MAX × RI2sense
0.2V 2 × 40kHz
(10.19)
We can obtain the amount of power that needs to come out
of the transformer as:
PXF=MR _ MAX
5=.5V ×1A
87%
6.332W
Using this equation and Ntr from section 10.4 assume ηX is
87%:
Substituting this into equation 10.16 we get:
RIsense
=13× 0.264V
2 ×1A
× 87%
=1.5W
=L'M _ MAX
(750V ⋅ms)2 × 40kHz
=
2× 6.322W
1.78mH
We recommend using ±1% tolerance resistors for RIsense.
10.7 Magenitizing Inductance
A feature of the iW1692 is the lack of dependence on the
magnetizing inductance for the CC curve.
Although the constant current limit does not depend on the
magnetizing inductance, there are still restrictions on the
magnetizing inductance. The maximum LM is limited by the
amount of power that needs to come out of the transformer
in order for the power supply to regulate. This is given by:
( )L'M _ MAX
=
VIN ⋅TON
2
max
×
40kHz
2 × PXFMR _ MAX
PXFMR _ MAX
= VOUT × IOUT
hX
(10.16)
The minimum LM is limited by the maximum allowable
primary peak current (IPRI_PK). 0.9 V on the ISENSE pin should
correspond to the maximum allowable primary peak current.
Therefore, the maximum primary peak current is:
To get the minimum value of the primary inductance, use the
value for RISENSE from section 10.6.
I PRI _ PK
<
0.9V
1.5W
=.6 A
Substituting this primary peak current into equation 10.18:
=LM _ MIN
7=50V ⋅m sec
0.9V 1.5W
1.25mH
Choose a primary inductance somewhere between 1.78 mH
and 1.42 mH; we chose 1.5 mH.
10.8 Primary Winding
In order to keep the transformer from saturation, the maximum
flux density must not be exceeded. Therefore the minimum
primary winding on the transformer must meet:
( )NPRI ≥
VIN ⋅TON MAX
BMAX × Ae
(10.19)
Where: BMAX is maximum flux density and Ae is the cross-
sectional area of the core.
Rev. 2.0
iW1692
February 13, 2012
Page 11
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet IW1692.PDF ] | |
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