Short-circuit protection

AN1882

14/30

Doc ID 10209 Rev 4

Figure 11.

Valley current limit protection

4.1

Synchronization

The device can be synchronized with an external signal from 500 kHz up to 1.4 MHz through

the internal PLL. When the device is locked, the external signal and the high side turn on

rising edges are aligned. In this case the low noise mode is automatically selected. The

device will eventually skip some cycles in very light load conditions depending also on the

input/output conditions. The internal synchronization circuit is inhibited in short-circuit and

over-voltage conditions in order to keep the involved protections effective. The

synchronization signal amplitude can range typically from 1 V to VCC and the duty factor

can range typically from 20% to 80%. Sometimes, if the synchronization signal duty cycle is

some practical solutions are:

1.

Change the synchronization signal duty factor

2.

Decrease the synchronization signal amplitude

3.

Add 20 pF capacitor between the comp pin and ground.

The device switches at 600 kHz (typ.) if no synchronization signal is applied.

4.2

DROPOUT operation

When the input voltage is a Li-Ion battery, the voltage ranges from a minimum of 3 V or less

to 4.1 V - 4.2 V (depending on the anode material). In case the regulated output voltage is

from 2.5 V and 3.3 V, the device can work in linear mode or dropout operation. The minimum

input voltage necessary to ensure output regulation can be calculated as:

Equation 8

resistance.

V

INMIN

V

O

I

O

R

DS on

()HSMAX

R

L

+

()

⋅

+

=

--

-