STOD13AS

Detailed description

Doc ID 022733 Rev 1

17/25

8

Detailed description

8.1

General description

The STOD13AS is a high efficiency dual DC-DC converter which integrates a step-up and

inverting power stage 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.

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 STOD13AS 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 STOD13AS avoids battery leakage thanks to the true-shutdown feature and it is self

protected from 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 STOD13AS operate in three different modes:

pulse skipping (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.

8.1.2

Pulse skipping operation

The STOD13AS works in pulse skipping mode when the load current is below some tens of

mA. The load current level at which this way of operation occurs depends on input voltage

only for the step-up converter and on input voltage and negative output voltage (VO2) for the

inverting converter.

8.1.3

Discontinuous conduction mode

When the load increases above a few mA, the STOD13AS 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.

8.1.4

Continuous conduction mode

At medium/high output loads, the STOD13AS enters full CCM at constant switching

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