Pin settings

HVLED001B

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DS12748 Rev 2

3

Pin settings

Figure 4. Pin connection

Table 2. Pin description

Symbol Pin

Description

HVSU

1

High voltage startup and input voltage detection.

The pin, able to withstand 800 V, is to be tied to the input voltage using a low value resistor (1 k



typ.). It embeds the internal start-up unit that charges the capacitor connected between the VCC pin

and GND pin during startup and low consumption.

During operational mode, the voltage at this pin is used to both measure the input voltage and

detect input over-voltages.

N.C.

2

Not connected pin.

TOFF

3

A blanking time, starting from first valley detection, can be set applying a voltage to this pin. This

variable blanking time is used to skip resonant valleys and, then, to fold back the operating

frequency. A null blanking time is obtained leaving the pin unconnected.

FB

4

Output of the error amplifier of primary side regulation loop regulation.

The pin is intended to be connected to the compensation network for primary side regulation.

An upper threshold VOFP detects an overload.

Burst mode is also related to the voltage applied to this pin.

OPTO

5

Input for optocoupler in secondary side control loop.

This pin is intended to be connected to the collector of the optocoupler.

The OPTO pin voltage is internally applied to an OR structure together with FB voltage to feed the

internal multiplier.

Low consumption mode is invoked pulling this pin lower than the VOPTO,dis threshold that features

as burst mode level when OPTO is in use.

ZCD

6

Multiple function pin able to detect the Zero Current instant, to sense the output voltage for the

primary side regulation and the input voltage for brownout detection. A negative-going edge triggers

the MOSFET's turn-on, while an internal starter unit is active to generate the triggering signal when

not externally available (e.g. startup).

CS

7

Input to the current sense comparator for the power regulation.

A second level overcurrent (OCP) threshold detects abnormal currents (e.g.: due to transformer's

saturation) and, on this occurrence, activates the second level overcurrent protection procedure.

GND

8

Reference pin.