STOD03B

Detailed description

Doc ID 022613 Rev 1

15/22

8

Detailed description

8.1

General description

The STOD03B is a high efficiency dual DC-DC converter which integrates a step-up with an

LDO and inverting power stages suitable for supplying AMOLED panels. Thanks to the high

level of integration it needs only 6 external components to operate and it achieves very high

efficiency using a synchronous rectification technique for each of the two DC-DC converters.

This topology of a boost followed by an LDO regulator offers an efficient ripple reduction

solution for loads up to 200 mA. The controller uses an average current mode technique in

order to obtain good stability and precise voltage regulation in all possible conditions of input

voltage, output voltage, and output current. In addition, the peak inductor current is

monitored in order to avoid saturation of the coils. The STOD03B implements a power

saving technique in order to maintain high efficiency at very light load and it switches to

PWM operation as the load increases, in order to guarantee the best dynamic performance

and low noise operation. The STOD03B avoids battery leakage thanks to the true-shutdown

feature and it is self protected by overtemperature. Undervoltage lockout and soft-start

guarantee proper operation during startup.

8.1.1

Multiple operation modes

Both the step-up and the inverting stage of the STOD03B operate in three different modes:

pulse skipping mode (PSM), discontinuous conduction mode (DCM), and continuous

conduction mode (CCM). It switches automatically between the three modes according to

input voltage, output current, and output voltage conditions.

Pulse skipping operation:

The STOD03B works in pulse skipping mode when the load current is below a few mA.

The load current level at which this way of operating occurs depends on input voltage only

inverting converter.

Discontinuous conduction mode:

When the load increases above some tens of mA, the STOD03B enters DCM operation.

In order to obtain this type of operation the controller must avoid the inductor current going

negative. The discontinuous mode detector (DMD) blocks sense the voltage across the

synchronous rectifiers (P1B for the step-up and N2 for the inverting) and turn off the

switches when the voltage crosses a defined threshold which, in turn, represents a certain

current in the inductor. This current can vary according to the slope of the inductor current

which depends on input voltage, inductance value, and output voltage.

Continuous conduction mode:

At medium/high output loads, the STOD03B enters full CCM at constant switching

frequency mode for each of the two DC-DC converters.