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PDF IW2202 Data sheet ( Hoja de datos )
| Número de pieza | IW2202 | |
| Descripción | Digital SMPS Controller | |
| Fabricantes | iWatt Corporation | |
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iW2202
Digital SMPS Controller
Preliminary Data
1 Application
4 Description
Blue-Angel-compliant PFC-controlled switch-mode
power supplies up to 150 watts.
2 Features
§ PulseTrain™ regulation allows voltage, current
and PFC to be controlled independently
§ Primary-only feedback eliminates optoisolators
and simplifies design
§ No loop compensation components required
§ ±1% regulation over a 100:1 load variation
§ Built-in soft-start
§ Adaptive pulseTrain regulation keeps the bulk
capacitor voltage below 400V
§ Operates in critical discontinuous conduction
mode (CDCM)
§ Low start-up and supply current
§ Reduced EMI noise
§ SO-8 package
3 Benefits
§ Ideal for single-stage, single-switch power factor
correction (PFC)
§ Enables 97% power factor correction resulting in
EN6100-3-2 compliance
§ SmartSkip mode provides low standby dissipation
of the power supply enabling Blue Angel
Compliance
§ Efficiency greater than 85% across line and load
variation
§ Universal input (85-270V, 50-60 Hz)
§ Low parts count
§ Reduced design time due to the elimination of
loop compensation design
The iW2202 is a digital switching mode power supply
controller for PFC applications. Its is typically used
with the PFC-corrected BIFRED (Boost Integrated with
Flyback Rectifier/Energy storage DC/DC) topology,
shown in Figure 1. The BIFRED topology is a single-
stage, single-switch topology that combines a boost
converter with an isolated flyback converter, achieving
power-factor correction with a low parts count.
An iW2202-based power supply looks like a resistor to
the AC line. Unlike attempts to control the BIFRED
topology with analog controllers, the all-digital
iW2202 provides a near-unity power factor without
placing high voltage stresses on the bulk capacitor.
The iW2202 uses a proprietary new digital control
technology called pulseTrain™ to achieve efficiencies
in excess of 85% across a wide load range, and across
the universal input range of 85-270VAC, 50-60 Hz.
Internally, the iW2202 uses real-time waveform analysis
to determine crucial circuit parameters. The reflected
secondary voltage of the flyback transformer is sensed
at precisely calculated times to determine the
secondary voltage, the transformer reset time, and the
ideal zero-voltage switching point Measurements are
performed during the OFF time of every cycle, and the
results determine what is done on the next cycle. The
dynamic response time of the circuit is less than half a
cycle.
85-270 V,
50-60 Hz
AC
Input
Boost Inductor
Auxiliary
Winding
Switch
iW2202
Flyback
Winding
Output
+ Vout
Current
Sense
Boost
(Bulk)
Capacitor
GND
Figure 1. iW2202 system concept
Revision 1.1
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iW2202 Data Sheet
Preliminary Data
9 Block Diagram
ISENSE
VAUX
VSENSE
VIN
Waveform
Analyzer
Primary Current
Sense
Reflected Voltage
Waveform Detect
(Opt.) Secondary
Voltage Sense
PFC Line Voltage
Sense
Control Logic
Voltage
Reg.
Cycle Selection
• Power
• Sense
• Skip
Cycle Timing
• Rising Edge (ZVS)
• Falling Edge (Constant Ipeak)
V CC
Power-
On
Reset
Driver Output
Figure 3. Conceptual block diagram of the iW2202
GND
PGND
Cycle n
Cycle n+1
PulseTrain
State
Power Cycle
Sense Cycle
Switch
State
ON
OFF
ON
OFF
tn tn+1
VAUXThreshold
VAUX
High
Low
Cycle n+2
Cycle n+3
Power Cycle
Sense Cycle
ON
OFF
ON
OFF
tn+2 tn+3
High
Low
The voltage on the auxiliary winding, VAUX, is measured at a point near the end of the OFF period. This voltage is compared to
the VAUX threshold. If it is higher, the next cycle is a sense cycle. Otherwise, the next cycle is a power cycle.
Figure 4. Power pulses, sense pulses, and the reflected secondary voltage on the auxiliary winding
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iW2202 Data Sheet
the second cycle’s shorter ON time. This trend will
continue until, in a few cycles, the initial current is
zero and the transformer is operating in critically
discontinuous mode.
Vgate
Vdrain
Ipri
Preliminary Data
The nominal VCC voltage of the device is 12 volts. It
requires a start-up voltage that reaches 14
momentarily, initiating a start-up sequence
internally. The device protects itself from over-
voltage by shutting itself down if VCC exceeds 15
volts. Its under-voltage lockout circuit will cause it
to shut itself down if the voltage drops below 7.8
volts, and will remain shut down until the start-up
voltage is seen again. Both over- and under-voltage
shutdowns inhibit switching on the OUTPUT pin.
These mechanisms protect the device, while
protecting the rest of the circuit indirectly.
Additional protection can be achieved with external
sensors that shut down the iW2202 on a circuit
fault. The best way of shutting down the iW2202 is
to pull the Isense pin above 1.5V. This will inhibit
output pulses.
Figure 12. Example of current limiting during start-up
12 Designing iW2202 -Based Power Supplies
The schematic in Figure 2 shows a typical iW2202
system. Choosing component values is a
straightforward process, as shown in the example
below.
12.1 Description
For this example, we are designing an 70W, 19V
laptop computer power supply. It is a universal
input supply supporting input line voltages of 85-
265 VRMS, and operating in discontinuous flyback
mode. To keep component costs low, we wish to use
a switch with a maximum Vdrain of no more than
600V.
12.2 Primary Turns Ratio
The voltage across a flyback switch includes the
input voltage plus the reflected secondary voltage:
Vd = Vin + N*Vout.
The turns ratio between the primary and secondary,
N, is constrained by our desire to avoid stressing
the switch. We use the maximum safe value of Vd
and the highest input voltage for our worst-case
calculation:
Vd_max = Vline_max + N*Vsec
N = (Vd_max – Vline_max)/Vsec
12.2.1 Example
If we use a 600V switch and derate it by 100V as a
safety margin, we are left with 500V as our
maximum drain voltage, Vd_max.
N = (500V-380V)/19.7V = 6.09 ≈ 6.
12.3 Ipeak Selection
We next need to calculate the peak current value we
need to support worst-case operation. The constant
peak current circuitry will keep the output switch on
until this value is reached on every power cycle.
Iin is the average input current to the converter:
Iin = Po/(Vin*η)
Where η is the efficiency of the converter. Vsec is the
secondary voltage. It differs from the output voltage,
Revision 1.1
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