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PDF iW1691 Data sheet ( Hoja de datos )
| Número de pieza | iW1691 | |
| Descripción | Digital PWM Current-Mode Controller | |
| Fabricantes | iWatt | |
| Logotipo |  |
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iW1691
Digital PWM Current-Mode Controller for Quasi-Resonant Operation
1.0 Features
●● Primary-side feedback eliminates opto-isolators and
simplifies design
●● Quasi-resonant operation for highest overall efficiency
●● EZ-EMI ® design to easily meet global EMI standards
●● Up to 130 kHz switching frequency enables small
adapter size
●● Built-in cable drop compensation
●● Very tight output voltage regulation
●● No external compensation components required
●● Complies with CEC/EPA 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 and output overvoltage
protection
●● Optional AC line under/overvoltage protection
●● PFM operation at light load
●● Current sense resistor short protection
●● Overtemperature Protection
2.0 Description
The iW1691 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 operates in quasi-resonant mode at heavy load 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 iW1691 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
current limit function enables optimized transformer design
in universal off-line applications over a wide input voltage
range.
The ultra-low operating current at light load ensures that
the iW1691 is ideal for applications targeting the newest
regulatory standards for average efficiency and standby
power.
3.0 Applications
●● AC/DC adapter/chargers for cell phones, PDAs, digital
still cameras
●● AC/DC adapters for consumer electronics
L
N
+
+ VOUT
RTN
+
Optional
NTC
Thermistor
1 NC
VCC 8
2 VSENSE OUTPUT 7
3 VIN
ISENSE 6
4 SD
GND 5
U1
iW1691
Figure 3.1 : Typical Application Circuit
Rev. 2.0
iW1691
February 3, 2012
Page 1
1 page  
iW1691
Digital PWM Current-Mode Controller for Quasi-Resonant Operation
7.0 Typical Performance Characteristics
9.0
6.0
3.0
0.00.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
VCC (V)
Figure 7.1 : VCC vs. VCC Supply Start-up Current
0.3 %
-0.3 %
-0.9 %
-1.5 %
-50
-25 0 25 50 75 100
Ambient Temperature (°C)
125
Figure 7.3 : % Deviation of Switching Frequency to
Ideal Switching Frequency vs. Temperature
12.2
12.0
11.8
11.6
-50
-25 0
25 50 75 100
Ambient Temperature (°C)
125
Figure 7.2 : Start-Up Threshold vs. Temperature
2.01
2.00
1.99
1.98-50 -25 0 25 50 75 100
Ambient Temperature (°C)
Figure 7.4 : Internal Reference vs. Temperature
125
Rev. 2.0
iW1691
February 3, 2012
Page 5
5 Page 
iW1691
Digital PWM Current-Mode Controller for Quasi-Resonant Operation
10.0 Design Example
10.1 Design Procedure
This design example gives the procedure for a flyback
converter using iW1691. Refer to Figure 13.1 for the
application circuit. The design objectives for this adapter
are given in table 10.1. It meets UL, IEC, and CEC
requirements.
Determine the Design Specifications
(Vout, Iout_max, Vin_max, Vin_min, ƒline, Ripple specification)
Determine Part Number
Determine Rvin Resistors
Determine Turns Ratio
Determine Operating VinTon Limit
Parameter
Input Voltage
Frequency
No Load Input
Output Voltage
Output Current
Output Ripple
Power Out
CEC Efficiency
Symbol
VIN
fIN
PIN
VOUT(Cable)
IOUT
VRIPPLE
POUT
h
Range
85 - 264 VRMS
47 - 64 Hz
100 mW
5.0 V
1 A
< 100 mV
5 W
69%
Table 10.1 : iW1691 Design Specification Table
10.2 Determine Part Number
Based on design specifications, choose the most suitable
part for the design. For more information on the options see
section 11.0.
Determine Magnetizing Inductance
Determine Primary Turns
Determine Secondary Turns
Determine Bias Turns and Vcc Capacitance
Determine Vsense Resistors
No Can you wind this transformer ?
Yes
Determine Current Sensing Resistor
Determine Input Bulk Capacitance
Determine Output Capacitance
Determine Snubber Network
Determine Current Sensing Filter
Finish
Figure 10.1 : iW1691 Design Flow Chart
Cable Drop Compensation
Cable Drop Compensation is an optional feature for the
iW1691. This option helps maintain the output voltage at the
end of the cable that the power supply is designed for. During
CV (constant voltage) mode the output current changes as
the voltage remains constant. This is true for the output
voltage at the output of the power supply board; however, in
certain applications the device to be charged is not directly
connected to the power supply, but rather, is connected
via a cable. This cable is seen by the power supply as a
resistance. So, as the output current increases the output
voltage at the end of the cable begins to drop. With the
cable compensation option, the iW1691 can compensate for
the resistance of the cable by incrementally increasing the
output voltage seen on the power supply board to cancel out
the selected cable resistance.
To find the right cable compensation necessary for a given
cable, pick the cable drop compensation number that is
closest to the voltage drop of the cable under maximum
output current.
Use equation 10.1 for VOUT in the following calculations,
where VFD is the forward voltage of the output diode.
VOUT = VOUT (Cable) + VCableDrop + VFD
(10.1)
For this example there is no cable so VCableDrop is 0 V ,
assuming VFD is 0.5, VOUT is:
VOUT = 5.0V + 0V + 0.5V = 5.5V
Rev. 2.0
iW1691
February 3, 2012
Page 11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet iW1691.PDF ] | |
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