S8520 Datasheet, PDF (16/44 Pages) Seiko Instruments Inc – STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER

STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE SWITCHING REGULATOR CONTROLLER
S-8520/8521 Series
Rev.9.0_01
 Selection of Products and External Parts
1. Method for selecting series products
The S-8520/8521 Series is classified into 12 types, according to the control systems (PWM control and PWM / PFM
switching control), the different oscillation frequencies, and set-up of an overload protection circuit. Please select
the type for your application according to the following features.
1. 1 Control systems
Two different control systems are available: PWM control system (S-8520 Series) and PWM / PFM switching
control system (S-8521 Series).
For applications for which the load current greatly differs between standby and operation, if the efficiency during
standby is important, applying the PWM/PFM switching system (S-8321 Series) realizes high efficiency during
standby.
For applications for which switching noise is critical, applying the PWM control system (S-8320 Series) whereby
switching frequency does not change due to load current allows the ripple voltage to be easily suppressed by
using a filter.
1. 2 Oscillation frequencies
Either oscillation frequency, 180 kHz (A and B types), 60 kHz (C and D types), or 300 kHz (E and F types), can
be selected.
The A, B, E and F types have high oscillation frequency, how ripple voltage and excellent transient response
characteristics. A small inductance can be used for these types because the peak current is low when inducing
the same load current. Use of small output capacitors is effective for downsizing devices.
The C and D types, whereby lower oscillation frequency realizes smaller self-consumption current, are highly
efficient under light loads. In particular, the D type, when combined with a PWM/PFM switching control system,
drastically improves the operation efficiency when the output load current is approximately 100 mA.
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