ICE3BR1765JZ Datasheet, PDF (11/31 Pages) Infineon Technologies AG – Off-Line SMPS Current Mode Controller with integrated 650V

ICE3BR1765JZ
Functional Description
3.4
Startup Phase
S oft S tart co un te r
When the V_VCC exceeds the on-threshold voltage, the
IC starts the Soft Start mode (see Figure 10).
The function is realized by an internal Soft Start
resistor, an current sink and a counter. And the
amplitude of the current sink is controlled by the
counter (see Figure 11).
S oftS
S oft S tart
S o ft S ta rt
S oft-S tart
C om para to r
C7
&
G7
G a te D river
5V
SoftS
R _{S oftS}
0 .6 7 V
PWM OP
x3 .3
Soft Start ^{32I 8I 4I 2I}
I
Counter
CS
Figure 9 Soft Start
In the Startup Phase, the IC provides a Soft Start
period to control the primary current by means of a duty
cycle limitation. The Soft Start function is a built-in
function and it is controlled by an internal counter.
.
Figure 11 Soft Start Circuit
After the IC is switched on, the V_SFOFTS voltage is
controlled such that the voltage is increased step-
wisely (32 steps) with the increase of the counts. The
Soft Start counter would send a signal to the current
sink control in every 600us such that the current sink
decrease gradually and the duty ratio of the gate drive
increases gradually. The Soft Start will be finished in
20ms (T_Soft-Start) after the IC is switched on. At the end
of the Soft Start period, the current sink is switched off.
V_SoftS
V_SOFTS32
T_Soft-Start
V_SoftS
V_SoftS2
V_SoftS1
Gate
t
Driver
Figure 10 Soft Start Phase
Version 2.0
t
Figure 12 Gate drive signal under Soft-Start Phase
11
12 Nov 2009