STOD13CM

Detailed description

024087 Rev 1

15/25

7

Detailed description

7.1

Overview

The STOD13CM is a high efficiency dual DC-DC converter which integrates a step-up and

inverting power stage suitable to supply AMOLED panels. Thanks to a high level of

integration, it requires only 6 external components to operate and it achieves very high

efficiency using synchronous rectification technique for both the two DC-DC converters.

The controller uses an average current mode technique 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 STOD13CM implements a power saving technique 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 STOD13CM avoids battery leakage thanks to the true-shutdown feature and its

overtemperature self-protection. Undervoltage lockout and soft-start guarantee proper

operation during startup.

7.2

Multiple modes of operation

Both the step-up and the inverting stages of the STOD13CM operate in three different

modes: Pulse Skipping (PSM), Discontinuous Conduction Mode (DCM) and Continuous

Conduction Mode (CCM). It switches automatically among the three modes based on input

voltage, output current and output voltage conditions.

Pulse skipping operation

The STOD13CM works in pulse skipping mode when the load current is below a few mA.

The load current level at which this mode 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.

Discontinuous conduction mode

When the load increases above a few tens of milliamperes, the STOD13CM enters DCM

operation. In order to obtain this mode 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, represent 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 STOD13CM enters full CCM at constant switching

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