s-8551 Seiko Instruments Inc., s-8551 Datasheet - Page 14

• Manufacturer Part Number: s-8551
• Description: Step-down, Built-in Fet, Synchronous Rectification, Pwm Control Switching Regulators
• Manufacturer: Seiko Instruments Inc.

*1. Parasitic diode
14
STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
S-8550/8551 Series
Standard Circuit
Precaution
Caution The above connection diagram and constant will not guarantee successful operation. Perform
V
•
•
•
•
•
•
IN
Mount external capacitors, diodes, and inductor as close as possible to the IC.
Characteristics ripple voltage and spike noise occur in IC containing switching regulators. Moreover rush current
flows at the time of a power supply injection. Because these largely depend on the inductor, the capacitor and
impedance of power supply used, fully check them using an actually mounted model.
The 1.0 µF capacitance connected between the VIN and VSS pins is a bypass capacitor. It stabilizes the power
supply in the IC when application is used with a heavy load, and thus effectively works for stable switching
regulator operation. Allocate the bypass capacitor as close to the IC as possible, prioritized over other parts.
Although the IC contains a static electricity protection circuit, static electricity or voltage that exceeds the limit of
the protection circuit should not be applied.
The power dissipation of the IC greatly varies depending on the size and material of the board to be connected.
Perform sufficient evaluation using an actual application before designing.
Seiko Instruments Inc. assumes no responsibility for the way in which this IC is used on products created using
this IC or for the specifications of that product, nor does Seiko Instruments Inc. assume any responsibility for any
infringement of patents or copyrights by products that include this IC either in Japan or in other countries.
4.7 µF
C
IN
thorough evaluation using an actual application to set the constants.
FB
Error amplifier
Reference
voltage
+
−
ON/OFF
circuit
ON/OFF
PWM comparator
+
−
Seiko Instruments Inc.
Current limit
UVLO circuit
circuit
Figure 11
Triangular wave
PWM control
generation
circuit
circuit
IC internal
power supply
VSS
VIN
Ground point
*1
*1
CONT
1.0 µF
68 pF
3.3 µH
L
C
FB
Rev.2.1
R
36 kΩ
R
18 kΩ
FB1
FB2
V
OUT
C
10 µF
_01
OUT