S-8520D50MC-BWJ-T2 Seiko Instruments, S-8520D50MC-BWJ-T2 Datasheet - Page 10

• Manufacturer Part Number: S-8520D50MC-BWJ-T2
• Description: DC/DC Switching Regulators 5.0V Step-Down PWM
• Manufacturer: Seiko Instruments

Specifications of S-8520D50MC-BWJ-T2

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

PWM Control & PWM/PFM Control Step-Down Switching Regulator-Controllers
S-8520/8521 Series
10
Waveforms at
EXT pin
5. 100 % % % % Duty Cycle
Selection of Series Products and Associated External Components
1. Method for selecting series products
The S-8520/21 Series operates with a maximum duty cycle of 100 %. When a B, D, F Series product not
provided with an overload protection circuit is used, the switching transistor can be kept ON to supply
current to the load continually, even in cases where the input voltage falls below the preset output
voltage value.
subtracting, from the input voltage, the voltage drop caused by the DC resistance of the inductance and
the on-resistance of the switching transistor.
If an A, C, E Series product provided with an overload protection circuit is used, this protection circuit will
function when the 100 % duty state has lasted longer than the preset overload detection time (T
causing the IC to enter intermittent operation mode. Under these conditions, the IC will not be able to
supply current to the load continually, unlike the case described in the preceding paragraph.
The S-8520/21 Series is classified into 12 types, according to the way the control systems (PWM and
soft-start in the IC, and the reference voltage will rise slowly from 0 V. The reference voltage and the
feedback voltage obtained by dividing the output voltage are compared to each other. So long as the
reference voltage is lower, the EXT pin will be held at "H" to keep the oscillation inactive. If the reference
voltage keeps rising and exceeds the feedback voltage, the oscillation will resume.
If the load is heavy when the oscillation is restarted, and the EXT pin holds the "L" level longer than the
specified overload detection time (T
enter intermittent operation mode, in which it repeats the actions described above. Once the overload
state is eliminated, the IC resumes normal operation.
PWM/PFM-Switched), 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.
Figure 6 Waveforms Appearing at EXT Pin As the Overload Protection Circuit Operates
Control systems:
Oscillation frequencies:
Two different control systems are available: PWM control system (S-8520 Series) and PWM/PFM-
switched 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-
switched 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.
Three oscillation frequencies--180 kHz (A & B Series) and 60 kHz (C & D Series), 300 kHz (E, F
Series)--are available.
Because of their high oscillation frequency and low-ripple voltage the A, B, E, F Series 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
The output voltage delivered under these circumstances is one that results from
Overload detection time
(T
Seiko Instruments Inc.
PRO
)
PRO
), the overload protection circuit will operate again, and the IC will
Protection circuit ON
(T
SS
× 0.3)
Rev.7.4
_10
PRO
),