Rev.2.1
_01
STEP-DOWN, BUILT-IN FET, SYNCHRONOUS
RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
S-8550/8551 Series
The S-8550/8551 Series is a CMOS synchronous rectification step-down
switching regulator which mainly consists of a reference voltage circuit, an
oscillator, an error amplifier, a phase compensation circuit, a PWM controller, an
under voltage lockout circuit (UVLO), a current limit circuit, and a power MOS
FET. The oscillation frequency is high at 1.2 MHz, so a high efficiency, large
output current, step-down switching regulator can be achieved by using small
external parts.
The built-in synchronous rectification circuit makes achieving high efficiency
easier compared with conventional step-down switching regulators. A ceramic
capacitor can be used as an output capacitor. High-density mounting is
supported by adopting a small SOT-23-5 package.
The S-8550 and S-8551 Series are offered according to different pin configuration.
Features
•
Oscillation frequency :
1.2 MHz
•
Input voltage range :
2.0 to 5.5 V
•
Output voltage range :
Arbitrarily settable by external output voltage setting resistor
•
Output current :
600 mA
•
Reference voltage :
0.6 V
±2.0%
•
Efficiency :
92%
•
Soft-start function :
1 ms typ.
•
Shutdown function :
Shutdown current consumption : 1.0
µA
max.
•
Built-in current limit circuit
•
Pch power MOS FET on-resistance :
0.4
Ω
typ.
•
Nch power MOS FET on-resistance :
0.3
Ω
typ.
•
Constant continuous mode operation (no light load mode)
•
Small package :
SOT-23-5
•
Lead-free products
Applications
•
Mobile devices, such as mobile phones, Bluetooth devices, wireless devices, digital audio players, digital still
cameras, portable DVD players, and portable CD players
Package
Package Name
SOT-23-5
Drawing Code
Package
MP005-A
Tape
MP005-A
Reel
MP005-A
Seiko Instruments Inc.
1
STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
S-8550/8551 Series
Block Diagram
VIN
Current limit
circuit
FB
Error amplifier
−
+
Reference
voltage
+
−
PWM comparator
Triangular wave
generation
circuit
V
IN
C
IN
ON/OFF
circuit
UVLO
circuit
*1
Rev.2.1
_01
IC internal
power supply
PWM control
circuit
*1
CONT
L
C
FB
R
FB1
R
FB2
V
OUT
C
OUT
ON/OFF
VSS
*1.
Parasitic diode
Figure 1
2
Seiko Instruments Inc.
STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
Rev.2.1
_01
S-8550/8551 Series
Product Name Structure
Product name
S-855
x
A
A
- M5T1
G
Package name (abbreviation) and packing specification
*1
M5T1 : SOT-23-5
, tape
Oscillation frequency
A : 1.2 MHz
Pin configuration setting
0 : Pin configuration 1
1 : Pin configuration 2
*2
*1.
*2.
Refer to the taping specifications at the end of this book.
Refer to
Table 1
and
Table 2
of “
Pin Configurations”.
Seiko Instruments Inc.
3
STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
S-8550/8551 Series
Rev.2.1
_01
Pin Configurations
Table 1
SOT-23-5
Top view
5
4
S-8550 Series (Pin Configuration 1)
Description
IC power supply pin
GND pin
Shutdown pin
“H” : Power on (normal operation)
“L” : Power off (standby)
Output voltage feedback pin
External inductor connection pin
VIN
VSS
Pin No.
1
2
3
4
5
Symbol
ON/OFF
FB
CONT
1
2
3
Figure 2
Table 2
Pin No.
1
2
3
4
5
S-8551 Series (Pin Configuration 2)
Description
Shutdown pin
“H” : Power on (normal operation)
“L” : Power off (standby)
VSS
GND pin
External inductor connection pin
IC power supply pin
Output voltage feedback pin
Symbol
ON/OFF
CONT
VIN
FB
4
Seiko Instruments Inc.
STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
Rev.2.1
_01
S-8550/8551 Series
Absolute Maximum Ratings
Table 3
Parameter
VIN pin voltage
FB pin voltage
CONT pin voltage
ON/OFF pin voltage
CONT pin current
Power dissipation
Operating temperature
Storage temperature
[Mounted board]
(1) Board size: 114.3 mm × 76.2 mm × t1.6 mm
(2) Board name: JEDEC STANDARD51-7
Caution
1. The absolute maximum ratings are rated values exceeding which the product could suffer
physical damage.
These values must therefore not be exceeded under any conditions.
(Refer to Figure 3.)
2. Since this IC has a built-in power MOS FET, make sure that dissipation of the power MOS FET
does not exceed the allowable power dissipation of the package.
Generally, dissipation of a switching regulator can be calculated by the following equation.
Dissipation = (100 (%)
−
efficiency (%)) / efficiency (%)
×
output voltage
×
load current
The greater part of dissipation depends on the built-in power MOS FET, however, dissipation
of the inductor is also included.
In addition, since power dissipation of the package also changes according to a mounting
board or a mounting state, fully check them using an actually mounted mode.
700
Power dissipation (P
D
) [mW]
600
500
400
300
200
100
0
0
50
100
150
Ambient temperature (Ta) [°C]
Absolute Maximum Ratings
(Unless otherwise specified: Ta
=
25°C, V
SS
=
0 V)
Absolute Maximum Rating
V
SS
−
0.3 to V
SS
+ 6.0
V
SS
−
0.3 to V
IN
+ 0.3
V
SS
−
0.3 to V
IN
+ 0.3
V
SS
−
0.3 to V
IN
+ 0.3
1300
600
*1
−40
to +85
−40
to +125
Unit
V
V
V
V
mA
mW
°C
°C
Symbol
V
IN
V
FB
V
CONT
V
ON/OFF
I
CONT
P
D
T
opr
T
stg
*1.
When mounted on printed circuit board
Figure 3
Power Dissipation of Package (Mounted on Board)
Seiko Instruments Inc.
5
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