Datasheet

L6730 - L6730B Application details
Doc ID 11938 Rev 3 37/52
6.5 Two quadrant or one quadrant operation mode (L6730)
After the soft-start phase the L6730 can work in source only (one quadrant operation mode)
or in sink/source (two quadrant operation mode), depending on the setting of the
multifunction pin (see Chapter 5.10 on page 27). The choice of one or two quadrant
operation mode is related to the application. One quadrant operation mode permits to have
a higher efficiency at light load, because the converter works in discontinuous mode (see
Figure 31). Nevertheless in some cases, in order to maintain a constant switching
frequency, it’s preferable to work in two quadrants, even at light load. In this way the
reduction of the switching frequency due to the pulse skipping is avoided. To parallel two or
more modules is requested the one quadrant operation in order not to have current sinking
between different converters. Finally the two quadrant operation allows faster recovers after
negative load transient. For example, let’s consider that the load current falls down from I
OUT
to 0A with a slew rate sufficiently greater than L/V
OUT
(where L is the inductor value). Even
considering that the converter reacts instantaneously setting to 0% the duty-cycle, the
energy ½*L*I
OUT
2
stored in the inductor will be transferred to the output capacitors,
increasing the output voltage. If the converter can sink current this overvoltage can be faster
eliminated.
Figure 31. Efficiency in discontinuous-current-mode and continuous-current-mode
EFFICIENCY: DCM vs. CCM
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
OUTPUT CURRENT (A)
EFF. (%
EFFICIENCY DCM
EFFICIENCY CCM