DocID022607 Rev 2

11/22

STOD1317B

Detailed description

6

Detailed description

The STOD1317B is a high efficiency DC-DC converter which integrates a step-up and LDO

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.

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 STOD1317B 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 performances and low noise operation.

In order to guarantee very low ripple on the output voltage, the step-up output is filtered by

provide the right voltage to the output, while the boost control loop is internally set to provide

the minimum possible drop.

The STOD1317B avoids battery leakage thanks to the true-shutdown feature and it is self

soft-start guarantee proper operation during startup.

6.1

BOOST multiple mode of operation

The boost DC-DC operates in three different modes: pulse skipping (PS), 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.

6.1.1

Pulse skipping operation

The STOD1317B 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 the input and

output voltage.

6.1.2

Discontinuous conduction mode

When the load increases above some tens of mA, the STOD1317B 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) block senses the voltage across the

synchronous rectifier and turns off the switch 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.

6.1.3

Continuous conduction mode

At medium/high output loads the STOD1317B enters full CCM at constant switching

frequency mode.