IL44608 Datasheet, PDF (11/13 Pages) IK Semicon Co., Ltd – External Components Reliable and Flexible SMPS Controller

IL44608N
Figure 9. Output Switching Speed
Figure 10. Frequency Stability
The data in Figure 9 corresponds to the waveform in Figure 10. The Figure 10 shows V_CC, I_CC, Isense (pin 2) and V_out
(pin 5). Vout (pin 5) in fact shows the envelope of the output switching pulses. This mode corresponds to an overload con-
dition.
The secondary reconfiguration is activated by the mP through the switch. The dV/dt appearing on the high voltage
winding (pins 14 of the transformer) at every TMOS switch off, produces a current spike through the series RC network R7,
C17. According to the switch position this spike is either absorbed by the ground (switch closed) or flows into the thyristor
gate (switch open) thus firing the MCR22–6. The closed position of the switch corresponds to the Pulsed Mode activation.
In this secondary side SMPS status the high voltage winding (12–14) is connected through D12 and DZ1 to the 8.0 V low
voltage secondary rail. The voltages
The Figure 11 shows the SMPS behavior while working in the reconfigured mode. The top curve represents the V_CC vol-
tage (pin 6 of the IL44608). The middle curve represents the 8.0 V rail. The regulation is taking place at 11.68 V. On the
bottom curve the pin 2 voltage is shown. This voltage represents the current sense signal. The pin 2 applied to the secondary
windings 12–14, 10–11 and 6–7 (Vaux) are thus divided by ratio N12–14 / N9–8 (number of turns of the winding 12–14
over number of turns of the winding 9–8). In this reconfigured status all the secondary voltages are lowered except the 8.0
V one. The regulation during every pulsed or burst is performed by the zener diode DZ3 which value has to be chosen high-
er than the normal mode regulation level. This working mode creates a voltage ripple on the 8.0 V rail which generally must
be post regulated for the microProcessor supply. voltage is the result of the 200 mA current source activated during the
start–up phase and also during the working phase which flows through the R4 resistor. The used high resolution mode of the
oscilloscope does not allow to show the effective ton current flowing in the sensing resistor R11.
Figure 11. SMPS Pulsed Mode
2011, February, Rev. 01