S-8550/8551 Series
www.sii-ic.com
© Seiko Instruments Inc., 2007-2010
STEP-DOWN, BUILT-IN FET, SYNCHRONOUS
RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
Rev.4.0
_00
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 packages small SOT-23-5 and super-small and thin SNT-8A.
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 V 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)
•
Lead-free, Sn 100%, halogen-free
*1
*1.
Refer to “
Product Name Structure”
for details.
Applications
•
Mobile devices, such as mobile phones, Bluetooth devices, wireless devices, digital audio players, digital still
cameras, portable DVD players, and portable CD players
Packages
•
•
SOT-23-5
SNT-8A
Seiko Instruments Inc.
1
STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
S-8550/8551 Series
Block Diagram
1. SOT-23-5
VIN
Current limit
circuit
FB
Error amplifier
−
+
Reference
voltage
+
−
PWM comparator
Triangular wave
generation
circuit
V
IN
C
IN
ON/OFF
circuit
UVLO
circuit
L
*1
Rev.4.0
_00
IC internal
power supply
PWM control
circuit
*1
CONT
R
FB1
V
OUT
C
FB
C
OUT
R
FB2
ON/OFF
VSS
*1.
Parasitic diode
Figure 1
2. SNT-8A
VIN
Current limit
circuit
FB
Error amplifier
−
+
Reference
voltage
+
−
PWM comparator
Triangular wave
generation
circuit
V
IN
C
IN
ON/OFF
circuit
UVLO
circuit
L
*1
IC internal
power supply
PWM control
circuit
*1
CONT
R
FB1
V
OUT
C
FB
C
OUT
R
FB2
ON/OFF
VSS
PVSS
*1.
Parasitic diode
Figure 2
2
Seiko Instruments Inc.
STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
Rev.4.0
_00
Product Name Structure
1.
Product name
S-855
x
A A
−
xxxx
x
Environmental code
U : Lead-free (Sn 100%), halogen-free
G : Lead-free (for details, please contact our sales office)
Package name (abbreviation) and packing specification
*1
M5T1 : SOT-23-5, tape
I8T1 : SNT-8A, tape
Oscillation frequency
A : 1.2 MHz
Pin configuration setting
*2
0 : Pin configuration 1 (SOT-23-5), Pin configuration 3 (SNT-8A)
1 : Pin configuration 2 (SOT-23-5)
*1.
*2.
Refer to the tape specifications at the end of this book.
Refer to
Table 1
to
Table 3
of “
Pin Configurations”.
S-8550/8551 Series
2.
Packages
Drawing Code
Package
MP005-A-P-SD
PH008-A-P-SD
Tape
MP005-A-C-SD
PH008-A-C-SD
Reel
MP005-A-R-SD
PH008-A-R-SD
Land
⎯
PH008-A-L-SD
Package Name
SOT-23-5
SNT-8A
Seiko Instruments Inc.
3
STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
S-8550/8551 Series
Rev.4.0
_00
Pin Configurations
Table 1
SOT-23-5
Top view
5
4
S-8550 Series (SOT-23-5, Pin Configuration 1)
Symbol
VIN
VSS
ON/OFF
FB
CONT
GND pin
Shutdown pin
“H” : Power on (normal operation)
“L” : Power off (standby)
Output voltage feedback pin
External inductor connection pin
Description
IC power supply pin
Pin No.
1
2
3
4
5
1
2
3
Figure 3
Table 2
Pin No.
1
2
3
4
5
S-8551 Series (SOT-23-5, Pin Configuration 2)
Symbol
Shutdown pin
ON/OFF
VSS
CONT
VIN
FB
“H” : Power on (normal operation)
“L” : Power off (standby)
GND pin
External inductor connection pin
IC power supply pin
Output voltage feedback pin
Description
Table
3 S-8550
Series (SNT-8A, Pin Configuration 3)
SNT-8A
Top view
1
2
3
4
8
7
6
5
Pin No.
1
2
3
4
5
6
7
8
Symbol
FB
NC
*1
VSS
*2
ON/ OFF
Description
Output voltage feedback pin
No connection
Small signal GND Pin
Shutdown pin
“H”：Power on (normal operation)
“L”：Power off (standby)
IC power supply pin
Power GND pin
No connection
External inductor connection pin
Figure 4
VIN
PVSS
*2
NC
*1
CONT
*1.
The NC pin is electrically open.
The NC pin can be connected to VIN, VSS or PVSS.
*2.
Connect VSS and PVSS to GND.
4
Seiko Instruments Inc.
STEP-DOWN, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
Rev.4.0
_00
S-8550/8551 Series
Absolute Maximum Ratings
Table 4
Parameter
VIN pin voltage
FB pin voltage
CONT pin voltage
ON/OFF pin voltage
CONT pin current
Power
SOT-23-5
dissipation SNT-8A
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 5.)
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
(P
D
) [mW]
600
500
400
300
200
100
0
0
50
100
150
Ambient temperature (Ta) [°C]
SNT-8A
SOT-23-5
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
450
*1
−40
to +85
−40
to +125
Unit
V
V
V
V
mA
mW
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 5
Power dissipation
Power Dissipation of Package (Mounted on Board)
Seiko Instruments Inc.
5
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