ICE2QR2280G-1_15 Datasheet, PDF (6/14 Pages) Infineon Technologies AG – 20 W 5 V SMPS Evaluation Board with Quasi- Resonant CoolSET™ ICE2QR2280G-1

20 W 5 V SMPS Evaluation Board with
Quasi-Resonant CoolSET™ ICE2QR2280G-1
Protection features
6.5
Burst mode operation
At light load condition, the SMPS enters into Active Burst Mode. At this stage, the controller is always active
but the VCC must be kept above the switch off threshold. During active burst mode, the efficiency increase
significantly and at the same time it supports low ripple on Vout and fast response on load jump.
For determination of entering Active Burst Mode operation, three conditions apply:
1. the feedback voltage is lower than the threshold of VFBEB(1.25 V). Accordingly, the peak current sense
voltage across the shunt resistor is 0.18;
2. the up/down counter is 7;
3. and a certain blanking time (tBEB).
Once all of these conditions are fulfilled, the Active Burst Mode flip-flop is set and the controller enters
Active Burst Mode operation. This multi-condition determination for entering Active Burst Mode operation
prevents mistriggering of entering Active Burst Mode operation, so that the controller enters Active Burst
Mode operation only when the output power is really low during the preset blanking time.
During active burst mode, the maximum current sense voltage is reduced from 1 V to 0.34 V so as to reduce
the conduction loss and the audible noise. At the burst mode, the FB voltage is changing like a sawtooth
between 3.0 and 3.6 V.
The feedback voltage immediately increases if there is a high load jump. This is observed by one
comparator. As the current limit is 34% during Active Burst Mode a certain load is needed so that feedback
voltage can exceed VFBLB (4.5 V). After leaving active busrt mode, maximum current can now be provided to
stabilize VO. In addition, the up/down counter will be set to 1 immediately after leaving Active Burst Mode.
This is helpful to decrease the output voltage undershoot.
7
Protection features
7.1
VCC over voltage and under voltage protection
During normal operation, the VCC voltage is continuously monitored. When the VCC voltage falls below the
under voltage lock out level (VCC,off) or the VCC voltage increases up to VCC,OVP, the IC will enter into autorestart
mode.
7.2
Foldback point protection
For a quasi-resonant flyback converter, the maximum possible output power is increased when a constant
current limit value is used for all the mains input voltage range. This is usually not desired as this will
increase additional cost on transformer and output diode in case of output over power conditions.
The internal fold back protection is implemented to adjust the VCS voltage limit according to the bus voltage.
Here, the input line voltage is sensed using the current flowing out of ZC pin, during the MOSFET on-time. As
the result, the maximum current limit will be lower at high input voltage and the maximum output power
can be well limited versus the input voltage.
7.3
Open loop/over load protection
In case of open control loop, feedback voltage is pulled up with internally block. After a fixed blanking time
30 ms, the IC enters into auto restart mode. In case of secondary short-circuit or overload, regulation voltage
VFB will also be pulled up, same protection is applied and IC will auto restart.
Application Note
6
Revision 1.1, 2015-04-02