S8355 datasheet(23/72 Pages) SII

23 / 72 page

STEP-UP, SUPER-SMALL PACKAGE, 600 kHz, PWM CONTROL or PWM/PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER

Rev.8.1_01

S-8355/56/57/58 Series



Operation

1. Switching Control Types

1.1 PWM Control (S-8355/57 Series)

The S-8355/57 Series is a DC-DC converter using a pulse width modulation method (PWM) and features a low

current consumption.

In conventional PFM DC-DC converters, pulses are skipped when the output load current is low, causing a

fluctuation in the ripple frequency of the output voltage, resulting in an increase in the ripple voltage.

The switching frequency does not change, although the pulse width changes from 0 to 83% (78% for F, G, H, J, L,

M, N, P and Q types) corresponding to each load current. The ripple voltage generated from switching can thus

be removed easily through a filter because the switching frequency is constant.

1.2 PWM/PFM Switching Control (S-8356/58 Series)

S-8356/58 Series is a DC-DC converter that automatically switches between a pulse width modulation method

(PWM) and a pulse frequency modulation method (PFM), depending on the load current, and features low current

consumption.

The S-8356/58 Series operates under PWM control with the pulse width duty changing from 15 to 83% (78% for F,

G, H, J, L, M, N, P and Q types) in a high output load current area.

The S-8356/58 Series operates under PFM control with the pulse width duty fixed at 15%, and pulses are skipped

according to the load current. The oscillation circuit thus oscillates intermittently so that the resultant lower self

current consumption prevents a reduction in the efficiency at a low load current. The switching point from PWM

control to PFM control depends on the external devices (coil, diode, etc.), input voltage and output voltage. This

series are an especially highly efficient DC-DC converter at an output current around 100

μA.

2. Soft Start Function

For this IC, the built-in soft start circuit controls the rush current and overshoot of the output voltage when

powering on or when the

OFF

pin is switched to the “H” level.

S8355 Datasheet(PDF) 23 Page - Seiko Instruments Inc