S-8520A20MC-AVFT2X Datasheet, PDF (13/44 Pages) Seiko Instruments Inc – SWITCHING REGULATOR CONTROLLER

STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
Rev.9.0_01
S-8520/8521 Series
 Operation
1. Switching control method
1. 1 PWM control (S-8520 Series)
The S-8520 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 100% 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. And the ripple voltage will be skipped to be low current
consumption when the pulse width is 0% or it is no load, input current voltage is high.
1. 2 PWM / PFM switching control (S-8521 Series)
S-8521 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-8521 Series operates under PWM control with the pulse width duty changing from 25 to 100% in a high
output load current area.
The S-8521 Series operates under PFM control with the pulse width duty fixed at 25%, 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.
The S-8521 Series is an especially highly efficient DC-DC converter at an output current around 100 μA.
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