ICE2A165 Datasheet, PDF (8/23 Pages) Infineon Technologies AG – Off-Line SMPS Current Mode Controller with integrated 650V/800V CoolMOS™

CoolSET™-F2
ICE2A165/265/365
ICE2A180/280
Functional Description
The primary current is sensed by the external series
resistor R_Sense inserted in the source of the integrated
CoolMOS™. By means of Current Mode the regulation
of the secondary voltage is insensitive on line
variations. Line variation causes varition of the
increasing current slope which controls the duty cycle.
The external R_Sense allows an individual adjustment of
the maximum source current of the integrated
CoolMOS™.
V_OSC
max.
Duty Cycle
Soft-Start Com parator
Voltage Ram p
t
PW M Com parator
FB
0.8V
FB
PW M-Latch
0.3V
O scillator ^0.3V
C5
G ate Driver
t
V_OSC
Gate Driver
T₂
C₁
0.8V
10kΩ
R₁
V₁
20pF
x3.65
PWM OP
Voltage Ram p
Figure 6 Improved Current Mode
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 T₂, the voltage source V₁ and the 1st order
low pass filter composed of R₁ and C₁(see Figure 6,
Figure 7). Every time the oscillator shuts down for max.
duty cycle limitation the switch T2 is closed by V_OSC.
When the oscillator triggers the Gate Driver T2 is
opened so that the voltage ramp can start.
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 continously till 0%
by decreasing V_FB below that threshold.
t
Figure 7 Light Load Conditions
3.2.1 PWM-OP
The input of the PWM-OP is applied over the internal
leading edge blanking to the external sense resistor
R_Sense connected to pin ISense. R_Sense converts the
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 singal is fed into the positive inputs of the PWM-
Comparator, C5 and the Soft-Start-Comparator.
3.2.2 PWM-Comparator
The PWM-Comparator compares the sensed current
signal of the integrated CoolMOS^TM with the feedback
signal V_FB (see Figure 8). V_FB is created by an external
optocoupler or external transistor in combination with
the internal pullup resistor R_FB and provides the load
information of the feedback circuitry. When the
amplified current signal of the integrated CoolMOS™
exceeds the signal V_FB the PWM-Comparator switches
off the Gate Driver.
Datasheet
8
September 2001