ICE2HS01G Datasheet, PDF (12/29 Pages) Infineon Technologies AG – High Performance Resonant Mode Controller

High Performance Resonant Mode Controller
ICE2HS01G
Functional description
switching frequency during load and line regulation. The actual switching frequency of the converter can also be
checked from Figure 6 by using the equivalent resistance at FREQ pin.
3.3 Dead time
As shown in Figure 4, the dead time can be adjusted by changing the current flowing into TD pin. There is a 5V
reference voltage provided on Vref pin. By connecting a resistor R_TD from Vref pin to TD pin, the current can be
set. The dead time is longer if the resistance is larger and vice versa. A typical value of 300ns dead time can be
achieved by setting R_TD=180kΩ. The relationship between R_TD and dead time is shown in Figure 7. Furthermore,
a minimum dead time limitation, 135ns, is built inside the IC for protection.
1000
900
800
700
600
500
400
300
200
100
0
0
R_TD(kΩ)
100
150
180
220
270
300
330
360
390
TD(ns)
180
255
300
360
435
480
525
570
615
50 100 150 200 250 300 350 400 450 500 550 600 650
Rtd(kΩ )
Figure 7
Dead time versus R_TD
3.4 Softstart
Soft start is implemented by sweeping the operating frequency from an initial high value until the control loop takes
over. This initial switching frequency should be high enough so that the resonant current at first pulse can be
limited within the desired value.
The internal block diagram for softstart funciton block is shown in Figure 8. Initially, capacitor C_OCP is fully
discharged by IC internal switch, so that R_OCP is effectively in parallel to R_FMIN and the resulting parallel resistance
determines the initial frequency.
During start up, C_SS is continuously charged until its voltage reaches the internal 2V reference voltage, and
accordingly the current through R_OCP drops to zero. Before this time, the LLC output voltage will have rise up to a
level close to the regulated value and the feedback loop takes over, so that it will be the current through
phototransistor to determine the operating frequency.
To ensure a smooth rise of output voltage during start up, different internal current will be used to charge up the
softstart capacitor C_SS. At the moment softstart block is enabled, all three current sources I_SS1 through I_SS3 will
turned on. Therefore, the charge current at this moment will be the sum of these three current plus the current
flows from FREQ pin, through R_OCP, to C_SS. When the voltage V_CSS is higher than V_SS1 (1.5V), current source I_SSa
(150µA) is turned off. When C_SS is charged to higher than V_SS2 (1.8V), the second current source I_SSb (50µA) is
Version 2.0
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11 May 2010