s-8521b51mc-aukt2g Seiko Instruments Inc., s-8521b51mc-aukt2g Datasheet - Page 13

• Manufacturer Part Number: s-8521b51mc-aukt2g
• Description: Step-down, Pwm Control Or Pwm / Pfm Switchable Switching Regulator Controller
• Manufacturer: Seiko Instruments Inc.

Rev.8.3
Operation
1. Switching control method
1. 1 PWM control (S-8520 Series)
1. 2 PWM / PFM switching control (S-8521 Series)
STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE SWITCHING REGULATOR CONTROLLOR
The S-8520 Series consists of DC-DC converters that employ a pulse-width modulation (PWM)
system. This series is characterized by its low current consumption. In conventional PFM system
DC-DC converters, pulses are skipped when they are operated with a low output load current, causing
variations in the ripple frequency of the output voltage and an increase in the ripple voltage. Both of
these effects constitute inherent drawbacks to those converters.
In the S-8520 series the pulse width varies in the range from 0 to 100% according to the load current,
yet ripple voltage produced by the switching can easily be removed by a filter since the switching
frequency is always constant. These converters thus provide a low-ripple voltage over wide range of
input voltage and load current. And it will be skippped to be low current consumption when the pulse
width is 0% or it is no load, input current voltage is high.
The 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%
when the output load current is high. On the other hand, when the output current is low, the S-8541
series operates under PFM control with the pulse width duty fixed at 25%, and pulses are skipped
according to the load current. The oscillator thus oscillates intermittently so that the resultant lower
current consumption prevents a reduction in the efficiency when the load current is low.
switching point from PWM control to PFM control depends on the external devices (coil, diode, etc.),
input voltage, and output voltage. This series is an especially efficient DC-DC converter at an output
current of around 100 µ A.
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Seiko Instruments Inc.
S-8520 / 8521 Series
The
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