s-8521b51mc-aukt2g Seiko Instruments Inc., s-8521b51mc-aukt2g Datasheet - Page 16

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

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STEP-DOWN, PWM CONTROL or PWM / PFM SWITCHABLE SWITCHING REGULATOR CONTROLLOR
S-8520 / 8521 Series
Selection of Series Products and Associated External Components
1. Method for selecting series products
The S-8520 / 8521 Series is classified into 12 types, according to the way the control systems (PWM
control and PWM / PFM Switching control), the different oscillation frequencies, and the inclusion or
exclusion of an overload protection circuit are combined one with another. Please select the type that
best suits your needs by taking advantage of the features of each type described below.
1. 1 Control systems
1. 2 Oscillation frequencies
Two different control systems are available: PWM control system (S-8520 Series) and PWM / PFM
switching control system (S-8521 Series).
If particular importance is attached to the operation efficiency while the load is on standby -- for
example, in an application where the load current heavily varies from that in standby state as the load
starts operating -- a high efficiency will be obtained in standby mode by selecting the PWM / PFM
switching control system (S-8521 Series).
Moreover, for applications where switching noise poses a serious problem, the PWM control system
(S-8520 Series), in which the switching frequency does not vary with the load current, is preferable
because it can eliminate ripple voltages easily using a filter.
The oscillation frequencies are selectable in 180 kHz (A and B types), 60 kHz (C, D types), and 300
kHz (E, F types).
Because of their high oscillation frequency and low ripple voltage the A, B, E and F types offer
excellent transient response characteristics. The products in these series allow the use of small-
sized inductors since the peak current remains smaller in the same load current than with products of
the other series. In addition, they can also be used with small output capacitors. These outstanding
features make the A, B, E and F types ideal products for downsizing the associated equipment.
On the other hand, the C and D types, having a lower oscillation frequency, are characterized by a
small self-consumption of current and excellent efficiency under light loads. In particular, the D type,
which employs a PWM / PFM switching control system, enables the operation efficiency to be
improved drastically when the output load current is approximately 100 µ A (Refer to “ Reference
Data ”).
Seiko Instruments Inc.
Rev.8.3
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