Operation description

L6926

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4.1

Modes of operation

Depending on the SYNC pin value the device can operate in low consumption or low noise

mode. If the SYNC pin is high (higher than 1.3V) the low consumption mode is selected

while the low noise mode is selected if the SYNC pin is low (lower than 0.5V).

4.1.1

Low consumption mode

In this mode of operation, at light load, the device operates discontinuously based on the

COMP pin voltage, in order to keep the efficiency very high also in these conditions. While

the device is not switching the load discharges the output capacitor and the output voltage

goes down. When the feedback voltage goes lower than the internal reference, the COMP

pin voltage increases and when an internal threshold is reached, the device starts to switch.

In these conditions the peak current limit is set approximately in the range of 200mA-

400mA, depending on the slope compensation (see related section).

Once the device starts to switch the output capacitor is recharged. The feedback pin

increases and, when it reaches a value slightly higher than the reference voltage, the output

of the error amplifier goes down until a clamp is activated. At this point, the device stops to

switch. In this phase, most of the internal circuitries are off, so reducing the device

consumption down to a typical value of 25

µA.

4.1.2

Low noise mode

If for noise reasons, the very low frequencies of the low consumption mode are undesirable,

the low noise mode can be selected. In low noise mode, the efficiency is a little bit lower

compared with the low consumption mode in very light load conditions but for medium-high

load currents the efficiency values are very similar.

Basically, the device switches with its internal free running frequency of 600KHz. Obviously,

in very light load conditions, the device could skip some cycles in order to keep the output

voltage in regulation.

4.1.3

Synchronization

The device can also be synchronized with an external signal from 500KHz up to 1.4MHz.

In this case the low noise mode is automatically selected. The device will eventually skip

some cycles in very light load conditions.

The internal synchronization circuit is inhibited in shortcircuit and overvoltage conditions in

order to keep the protections effective (see relative sections).