S8353 datasheet(16/49 Pages) SII

16 / 49 page

STEP-UP, PWM CONTROL or PWM / PFM SWITCHABLE BUILT-IN TRANSISTOR SWITCHING REGULATOR

S-8353/8354 Series

Rev.3.0_01



Operation

1. Switching Control Types

1. 1 PWM Control (S-8353 Series)

The S-8353 Series is a DC-DC converter using a pulse width modulation method (PWM) and features 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.

In the S-8353 Series, the switching frequency does not change, although the pulse width changes from 0% to

83% (78% for H and J type) corresponding to each load current. The ripple voltage generated from switching can

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

1. 2 PWM / PFM Switching Control (S-8354 Series)

The S-8354 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-8354 Series operates under PWM control with the pulse width duty changing from 15% to 83% (78% for H

and J type) in a high output load current area. On the other hand, the S-8354 Series operates under PFM control

with the pulse width duty fixed at 15% in a low output load current area, and pulses are skipped according to the

load current.

The oscillation circuit thus oscillates intermittently so that the resultant lower self current

consumption can prevent 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 efficient DC-DC converter at an output current around 100

μA.

2. Soft Start Function

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

is turned on or the

OFF

pin is set to “H” level.

S8353 Datasheet(PDF) 16 Page - Seiko Instruments Inc