L6986H datasheet(21/68 Pages) STMICROELECTRONICS

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Figure 16. Low noise mode operation

4.8.2

Low consumption mode (LCM)

The low consumption mode maximizes the efficiency at light-load. The regulator prevents the switching activity

whenever the switch peak current request is lower than the ISKIP threshold. As a consequence the L6986H device

works in bursts and it minimizes the quiescent current request in the meantime between the switching operation.

In LCM operation, the pin SYNCH/ISKIP level dynamically defines the ISKIP current threshold (see

Table 5. Electrical characteristics) as shown in Table 11. ISKIP programmable current threshold.

Table 11. ISKIP programmable current threshold

SYNCH / ISKIP (pin 4)

ISKIP current threshold

Low

ISKIPH = 0.6 A typical

High

ISKIPL = 0.2 A typical

The ISKIP programmability helps to optimize the performance in terms of the output voltage ripple or efficiency at

the light-load, that are parameters which disagree each other by definition. A lower skip current level minimizes

the voltage ripple but increases the switching activity (time between bursts gets closer) since less energy per

burst is transferred to the output voltage at the given load. On the other side, a higher skip level reduces the

switching activity and improves the efficiency at the light-load but worsen the voltage ripple.

No difference in terms of the voltage ripple and conversion efficiency for the medium and high load current level,

that is when the device operates in the discontinuous or continuous mode (DCM vs. CCM).

The L6986H allows changing the skip current threshold level while the device is switching in order to adapt the

pulse skipping operation to the loading condition. The time needed to detect and implement this transition is

negligible with respect to the switching period.

When the L6986H is configured in the low consumption mode, the SYNCH/ISKIP pin operates as a logic gate

input pin with an internal pull-down (4.5 µA typ.) guaranteeing the ISKIPH operation when leaving the pin floating.

Table 12. SYNCH/ISKIP pin voltage thresholds and driving current reports the VSYNCH/ISKIP thresholds and the

minimum current needed to drive the pin.

L6986H

Light-load operation

DS12905 - Rev 2

page 21/68

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