ICE2AS01_06 INFINEON [Infineon Technologies AG], ICE2AS01_06 Datasheet - Page 8

• Manufacturer Part Number: ICE2AS01_06
• Description: Off-Line SMPS Current Mode Controller
• Manufacturer: INFINEON [Infineon Technologies AG]

The primary current is sensed by the series resistor
R
Switch. By means of Current Mode the regulation of the
secondary voltage is insensitive on line variations. Line
variation causes variation of the increasing current
slope which controls the duty cycle.
The external R
the maximum source current of the external Power
Switch.
Figure 6
To improve the Current Mode during light load
conditions the amplified current ramp of the PWM-OP
is superimposed on a voltage ramp, which is built by
the switch T
low pass filter composed of R
Figure 7). Every time the oscillator shuts down for max.
duty cycle limitation the switch T2 is closed by V
When the oscillator triggers the Gate Driver T2 is
opened so that the voltage ramp can start (see Figure
7).
In case of light load the amplified current ramp is to
small to ensure a stable regulation. In that case the
Voltage Ramp is a well defined signal for the
comparison with the FB-signal. The duty cycle is then
controlled by the slope of the Voltage Ramp.
By means of the C5 Comparator the Gate Driver is
switched-off until the voltage ramp exceeds 0.3V. It
allows the duty cycle to be reduced continuously till 0%
by decreasing V
Datasheet
Preliminary Data
Sense
Oscillator
FB
Voltage Ramp
Soft-Start Comparator
inserted in the source of the external Power
V
OSC
Improved Current Mode
2
T
, the voltage source V
2
Sense
C
FB
1
0.3V
below that threshold.
allows an individual adjustment of
10kΩ
R
20pF
1
PWM Comparator
C5
1
0.8V
and C
V
1
Gate Driver
PWM-Latch
1
and the 1st order
1
PWM OP
(see Figure 6,
x3.65
OSC
.
8
Figure 7
3.2.1
The input of the PWM-OP is applied over the internal
leading edge blanking to the external sense resistor
R
source current into a sense voltage. The sense voltage
is amplified with a gain of 3.65 by PWM OP. The output
of the PWM-OP is connected to the voltage source V1.
The voltage ramp with the superimposed amplified
current signal is fed into the positive inputs of the PWM-
Comparator, C5 and the Soft-Start-Comparator.
3.2.2
The PWM-Comparator compares the sensed current
signal of the external Power Switch with the feedback
signal V
optocoupler or external transistor in combination with
the internal pullup resistor R
information of the feedback circuitry. When the
amplified current signal of the external Power Switch
exceeds the signal V
off the Gate Driver.
Sense
0.8V
0.3V
Voltage Ramp
FB
V
Gate Driver
connected to pin ISense. R
FB
OSC
(see Figure 8). V
PWM-OP
PWM-Comparator
Light Load Conditions
Duty Cycle
max.
FB
Functional Description
the PWM-Comparator switches
FB
FB
ICE2AS01/S01G
ICE2BS01/S01G
is created by an external
and provides the load
Sense
30 Jun 2006
converts the
t
t
t