19/30

L6997S

6.9 Soft start capacitor

Considering the soft start equations (Eq. 11) at page 10, it can be found:

The equations are valid without load. When an active load is present the equations result more complex; further

some active loads have unexpected effect, as higher current than the expected one during the soft start, can

change the start up time.

In this case the capacitor value can be selected on the application; anyway the Eq11 gives an idea about the

6.10 Sink mode

Figure 16. Efficiency vs output current

7

15A DEMO BOARD DESCRIPTION

are also present two switches and four jumpers. The two switches have different goals: the one nearest to the

to turn on/off the PFM feature. The device can be turned on also with the power supply, but a correct start up

is not respected the device will not start up. The jumpers are used to set the integrator feature and to use the

remote sensing; for more information refers to the Jumpers table. Sometimes when using the integrator config-

uration a low frequency filter is required in order to reduce the noise interaction. The pole value should be at

least five times higher than the switching frequency. The low pass filter should be inserted in this way: the re-

sistor, in the place of the INT jumper position and the capacitor between the resistor and ground (refers to the

schematic).

0,0

10,0

20,0

30,0

40,0

50,0

60,0

70,0

80,0

90,0

100,0

0,01,0

2,0

3,0

4,05,0

Current [A]

Eff [%]