S-8521E18MC-BLD-T2 Seiko Instruments, S-8521E18MC-BLD-T2 Datasheet - Page 8

• 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

PWM Control & PWM/PFM Control Step-Down Switching Regulator-Controllers
S-8520/8521 Series
8
Measurement Circuits:
Operation:
1. Step-Down DC-DC Converter
1.1 PWM Control (S-8520 Series)
1.2 PWM/PFM-Switched Control (S-8521 Series)
1
3
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 converters of the S-8520 Series, the pulse width varies in a range from 0 % to 100 %, according to the
load current, and yet ripple voltage produced by the switching can easily be removed through a filter
because the switching frequency remains constant. Therefore, these converters provide a low-ripple
power over broad ranges of input voltage and load current.
modulation system (PWM) over to the pulse-frequency modulation system (PFM), and vice versa,
according to the load current. This series of converters features low current consumption.
the pulse-width duty varies from 25 % to 100 %. This function helps keep the ripple power low.
having their pulse-width duty fixed at 25 % are skipped depending on the quantity of the load current, and
are output to a switching transistor. This causes the oscillation circuit to produce intermittent oscillation.
As a result, current consumption is reduced and efficiency losses are prevented under low loads.
Especially for output load currents in the region of 100 µA, these DC/DC converters can operate at
extremely high efficiency.
The S-8521 Series consists of DC/DC converters capable of automatically switching the pulse-wide
In a region of high output load currents, the S-8521 Series converters function with PWM control, where
For certain low output load currents, the converters are switched over to PFM control, whereby pulses
+
−
A
VIN
ON/OFF
ON/OFF
VIN
0.68 kΩ
EXT
VSS
EXT
open
VSS
VOUT
VOUT
2200 pF
Seiko Instruments Inc.
open
+
−
Figure 3
2
V
+
-
A
VIN
ON/OFF
EXT
VSS
VOUT
Rev.7.4
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