S-8352 Seiko Instruments, S-8352 Datasheet - Page 15

• Manufacturer Part Number: S-8352
• Description: (S-8351 / S-8352) SMALL PACKAGE PFM CONTROL STEP-UP SWITCHING REGULATOR
• Manufacturer: Seiko Instruments

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Rev.2.0
Operation
1. Step-up DC-DC Converter
Figure 15 Output Current (I
The S-8351/8352 Series is a DC-DC converter that uses a pulse frequency modulation method (PFM) and features
low current consumption. This series is an especially efficient DC-DC converter at an output current of 100
lower.
In conventional fixed-duty PFM DC-DC converters, although a low duty ratio allows a lower ripple voltage when the
current load is light, the efficiency is decreased when the output load current is large. Conversely, a high duty ratio
increases the output load current and efficiency, but increases the ripple voltage when the output load current is low.
In the A, B, and D types, the duty ratio is automatically switched 75% when the output load current is high to secure
the load drive capability and 50% when the output load current is low to control the load drive capability to decrease
pulse skipping. This suppresses a drop in the ripple frequency, enabling control of the increase in the ripple voltage.
The C type adopts a 75% fixed-duty PFM method. The ripple voltage increases more than that of the duty switching
type with the load is low, but the efficiency is better.
In the A, B, and D types, the duty ratio is not rapidly changed, but rather smoothly switched in the intermediate area
between 50% and 75%. Therefore, fluctuation of the ripple voltage caused by duty switching is minimized. Figures
15 to 16 show the ripple voltage characteristics versus the output current.
These figures show that the ripple voltage decreases as the output load current (I
The ripple voltage becomes particularly small when I
STEP-UP, SUPER-SMALL PACKAGE, PFM CONTROL SWITCHING REGULATOR / SWITCHING REGULATOR CONTROLLER
_00
100
S-8351A30MC
90
80
70
60
50
40
30
20
10
0
Characteristics
0
20
40
I
OUT
OUT
) vs. Ripple Voltage (V
[mA]
60
V
V
IN
IN
Ta = 25 ° C
= 1.5 V
= 2 V
80
Seiko Instruments Inc.
100
rp-p
OUT
)
is in the coil current discontinuous region of 20 mA or less.
Figure 16 Output Current (I
140
120
100
S-8351A50MC
80
60
40
20
Characteristics
0
0 20 40 60 80 100 120 140 160 180
OUT
I
OUT
OUT
) changes from large to small.
S-8351/8352 Series
) vs. Ripple Voltage (V
[mA]
V
V
Ta = 25 ° C
IN
IN
= 2 V
= 3 V
rp-p
µ
A or
)
15