VIPer0P

General description

DocID028423 Rev 2

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The FB is provided with an internal pull-up to prevent a wrong IC behavior when the pin is

accidentally left floating.

4.9

Secondary feedback

When a secondary feedback is required, the internal E/A has to be disabled shorting FB to

, (65 kΩ, typ.) and the voltage across COMP

is set by the current sunk.

This allows the output voltage value to be set through an external error amplifier (TL431 or

similar) placed on the secondary side, whose error signal is used to set the DRAIN peak

current setpoint corresponding to the output power demand. If isolation is required, the

error signal must be transferred through an optocoupler, with the phototransistor collector

connected across COMP and SGND.

4.10

Pulse frequency modulation

some PWM cycles are skipped. This mode of operation is referred to as “pulse frequency

modulation” (PFM), the number of the skipped cycles depends on the balance between the

output power demand and the power transferred from the input. The result is an equivalent

switching frequency which can go down to some hundreds Hz, thus reducing all the

frequency-related losses.

This kind of operation, together with the extremely low IC quiescent current, allows very low

input power consumption in no load and light load, while the low DRAIN peak current value,

reached.

4.11

Zero-power mode

The zero-power mode (ZPM) is a special idle state of VIPer0P, characterized by the

following features:



there is no switching activity, then neither voltage nor power, available at the output





all IC circuits, except the ones needed to exit ZPM, are turned off, reducing the

controller consumption to very low values

(20 μs, typ.).

The ZPM can be managed manually or by a microcontroller (MCU) or in mixed mode. In

case of mixed ZPM management (see Figure 29: "ZPM managed in mixed mode") the

MCU supervising the operation of the appliance shuts down the SMPS by pulling low OFF

through one of its GPIOs, cutting also its own supply voltage. The restart is commanded by

a pushbutton or a tactile switch pressed by the user that directly operates pin ON. For

safety reasons, this switch should operate at low voltage (SELV level). The MCU wakes up

after the SMPS is again up and running. This arrangement provides the minimum

consumption from the power line.