S-8521E18MC-BLD-T2 Seiko Instruments, S-8521E18MC-BLD-T2 Datasheet - Page 11

• Manufacturer Part Number: S-8521E18MC-BLD-T2
• Description: DC/DC Switching Regulators 1.8V Step-Dn PWM/PFM
• Manufacturer: Seiko Instruments

Specifications of S-8521E18MC-BLD-T2

• Output Voltage: 1.8 V
• Mounting Style: SMD/SMT
• Package / Case: SOT-23-5
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Rev.7.4
2. Inductor
The inductance value greatly affects the maximum output current I
As the L-value is reduced gradually, the peak current I
current I
begin decreasing because the current drive capacity of the switching transistor becomes insufficient.
Conversely, as the L-value is augmented, the loss due to I
the efficiency is maximized at a certain L-value. If the L-value is made even larger, the loss due to the
series resistance of the coil will increase to the detriment of the efficiency.
If the L-value is increased in an S-8520/21 Series product, the output voltage may turn unstable in some
cases, depending on the conditions of the input voltage, output voltage, and the load current. Perform
thorough evaluations under the conditions of actual service and decide on an optimum L-value.
In many applications, selecting a value of A/B/C/D Series 47µH, E, F Series 22 µH will allow a S-8520/21
Series product to yield its best characteristics in a well balanced manner.
When choosing an inductor, pay attention to its allowable current, since a current applied in excess of
the allowable value will cause the inductor to produce magnetic saturation, leading to a marked decline in
efficiency.
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Overload protection circuit:
PWM Control & PWM/PFM Control Step-Down Switching Regulator-Controllers
make the A & B Series ideal products for downsizing the associated equipment.
On the other hand, the C & D Series, having a lower oscillation frequency, are characterized by a
small self-consumption of current and excellent efficiency under light loads. In particular, the D
Series, which employs a PWM/PFM-switched control system, enables the operation efficiency to be
improved drastically when the output load current is approximately 100 µA. (See Reference Data.)
Products can be chosen either with an overload protection circuit (A, C, E Series) or without one (B,
D, F Series).
Products with an overload protection circuit (A, C, E Series) enter intermittent operation mode when
the overload protection circuit operates to accommodate overloads or load short-circuiting. This
protects the switching elements and inductors. Nonetheless, in an application where the load needs
to be fed continually with a current by taking advantage of the 100 % duty cycle state, even if the input
voltage falls below the output voltage value, a B, D, F Series product will have to be used. Choose
whichever product best handles the conditions of your application.
The symbol " " denotes an indispensable condition, while the symbol " " indicates that the corresponding
series has superiority in that aspect. The symbol " " indicates particularly high superiority.
An
circuit is required
The input voltage range
exceeds 10 V
The efficiency under light
loads(load current ≤1 mA)
is an important factor
To be operated with a
medium load current (200
mA class)
To be operated with a high
load current (1 A class)
It is important to have a
low-ripple voltage
Importance is attached to
the downsizing of external
components
The table below provides a rough guide for selecting a product type depending on the requirements
of the application. Choose the product that gives you the largest number of circles (O).
In making the selection, please keep in mind that the upper limit of the operating voltage range is
either 10 V (A, C, E Series) or 16 V (B, D, F Series), depending on whether the product comes with
an overload protection circuit built in.
overload
OUT
when the L-value has fallen to a certain point. If the L-value is made even smaller, I
protection
A
Seiko Instruments Inc.
B
S-8520
C
D
E
F
pk
increases, to finally reach the maximum output
pk
A
in the switching transistor will decrease until
OUT
B
and the efficiency η.
C
S-8521
D
S-8520/8521 Series
E
F
OUT
will
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