S-8353A20MC-IQFT2X Datasheet, PDF (16/49 Pages) Seiko Instruments Inc – BUILT-IN TRANSISTOR SWITCHING REGULATOR

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 ON / OFF pin is set to “H” level.
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