LED System Driver ICs

ICLS6x Series

Functional Description

Data Sheet

23

Version 1.0, 2011-05-19

The other fault detection function which can result in the Auto Restart mode during startup and has the 8.0 µs

blanking time is for overtemperature detection. This block checks for a junction temperature of higher than 140 °C

for malfunctioning operation.

Once Auto Restart mode is entered, the internal bias is switched off in order to reduce the current consumption of

the IC as much as possible. In this mode, the average current consumption is only 300 µA as the only working

blocks are the reference block and the Undervoltage Lockout (UVLO), which controls the startup cell by switching

As there is no longer a self supply provided by the auxiliary winding, VCC starts to drop. The UVLO switches on

the integrated startup cell when VCC falls below 10.3 V. It continues to charge VCC up to 18 V, at which point it

is switched off again and the IC enters the startup phase.

Once all fault conditions have been removed, the IC automatically powers up as usual with a switching cycle at

the GATE output after the soft start period has elapsed – hence the name Auto Restart mode.

3.6.2.2

Auto Restart Mode during RUN Mode

In the case of overload or open loop, the FB voltage exceeds 4.5 V, which is observed by C4. At this time, the

activated as both inputs of the gate G5 are high.

Figure 17

Auto Restart mode during RUN mode

This charging of the soft start capacitor from 3.2 V ~ 3.6 V to 4.0 V defines a blanking window, which prevents the

system from entering Auto Restart mode during RUN mode unintentionally during large load jumps. In this event,

FB will rise close to 5.0 V for a short duration before the loop regulates FB to less than 4.5 V.

In the case of VCC undervoltage – i.e., VCC falls below 10.3 V, the IC is turned off with the startup cell charging

VCC as described earlier in this section. Once VCC is charged to above 18 V, the IC starts a new startup cycle.

3.6.2.3

Floating Load Protection (FLP)

The circuit starts up as usual, but a missing load leads to a rise in the output and auxiliary voltages.

Reaching the VCC threshold of 24.5 V (voltage divider RD2/R4 and Q2) leads to a reduction in the feedback

voltage and hence to reduced output current pulses in order to keep the output voltage below the maximum rating

of the components. If the feedback level falls below 1.35 V, the Soft Start voltage begins to rise up to a threshold

of 4 V (depends on the C4 value) and the IC is switched into the FLP mode.

C3

4.0V

C4

4.5V

&

G5

Control Unit

SoftS

Internal

Bias

Auto

Restart

Mode

FB