AN2067 데이터 시트보기 (PDF) - STMicroelectronics

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AN2067

VIPower™: dimmable white LED power supply with the VIPer53-E

STMicroelectronics 

Block diagram

1

Block diagram

AN2067

Figure 1. VIPer53-E block diagram

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Overload protection

4.35 V typical threshold is present on the COMP pin. This overload threshold is 150 mV

below the clamping voltage of 4.5 V, which corresponds to the current limitation of the

device. In case of a COMP voltage exceeds the overload threshold, the pull- up resistor on

TOVL pin is released and the external capacitor connected on this pin begins to charge.

When a value of 4 V typical is reached, the device stops switching and remains in this state

until the VDD voltage reaches VDDoff, or resumes the normal operation if the COMP voltage

returns to a value below the overload threshold.

The drain current that the device delivers without triggering the overload threshold is called

“current capability”, specified as IDmax in the datasheet. This value sizes correctly the

converter versus its maximum output power. When an overload occurs on secondary side of

the converter, the output power is limited by the current limitation of the device. If this

overload lasts more than a constant time defined by a capacitor connected on the TOVL pin,

the device is reset, and a new sequence starts by turning on the start-up current source.

Capacitors on the VDD pin and on the TOVL pin are defined together in order to insure a

correct startup and a low restart duty cycle in overload or short-circuit operation. Below the

equations:

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DocID10973 Rev 2

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