ST619LB

Operating principle

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3

Operating principle

The ST619LB is able to provide a regulated 5 V output from a 2 V to 3.6 V (two battery cells)

input. Internal charge pump and external capacitors generate the 5 V output, eliminating the

need for inductors. The output voltage is regulated to 5 V, ±4 % by a pulse skipping

controller that turns on the charge pump when the output voltage begins to drop. To

maintain the greatest efficiency the internal charge pump of the device operates as a

from 2.0 V to 2.5 V.

In triple mode (see block diagram), when the S1 switches close, the S2 switches open and

connected in series between IN and OUT when the S1 switches open and S2 switches

close. In the doubler mode only C2 is used. During one oscillator cycle, energy is transferred

from the input to the charge pump capacitors, and then from the charge pump capacitors to

the output capacitors and load. The number of cycles within a given time frame increases as

the load increases or as the input supply voltage decreases. In the limiting case, the charge

pumps operate continuously, and the oscillator frequency is nominally 500 kHz.

3.1

Shut down mode

The ST619LB enters low power shut down mode when SHDN is a logic high. In shut down

ground for normal operation. SHDN is a CMOS compatible input.