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PDF S-8551 Data sheet ( Hoja de datos )

Número de pieza S-8551
Descripción (S-8550 / S-8551) PWM CONTROL SWITCHING REGULATORS
Fabricantes Seiko Instruments 
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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 typ.
Nch power MOS FET on-resistance :
0.3 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
Package
MP005-A
Drawing Code
Tape
MP005-A
Reel
MP005-A
Seiko Instruments Inc.
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S-8551 pdf
www.DSaTtaESPhe-DetO4UW.cNom, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
Rev.2.1_01
S-8550/8551 Series
„ Absolute Maximum Ratings
Table 3 Absolute Maximum Ratings
(Unless otherwise specified: Ta = 25°C, VSS = 0 V)
Parameter
Symbol
Absolute Maximum Rating
Unit
VIN pin voltage
VIN
FB pin voltage
VFB
CONT pin voltage
VCONT
ON/OFF pin voltage
VON/OFF
CONT pin current
ICONT
Power dissipation
PD
Operating temperature
Topr
Storage temperature
Tstg
*1. When mounted on printed circuit board
VSS 0.3 to VSS + 6.0
VSS 0.3 to VIN + 0.3
VSS 0.3 to VIN + 0.3
VSS 0.3 to VIN + 0.3
1300
600*1
40 to +85
40 to +125
V
V
V
V
mA
mW
°C
°C
[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.
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. (Refer to Figure 3.)
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
600
500
400
300
200
100
0
0 50 100 150
Ambient temperature (Ta) [°C]
Figure 3 Power Dissipation of Package (Mounted on Board)
Seiko Instruments Inc.
5

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S-8551 arduino
www.DSaTtaESPhe-DetO4UW.cNom, BUILT-IN FET, SYNCHRONOUS RECTIFICATION, PWM CONTROL SWITCHING REGULATORS
Rev.2.1_01
S-8550/8551 Series
2. Backflow current
The S-8550/8551 Series performs PWM synchronous rectification even if IL min. is less than 0 A, so a backflow
current is generated in VIN and the backflow current becomes maximum when no load is applied (see Figure 9).
Use the following equation to calculate the maximum backflow current value, which should be taken into
consideration when designing.
Duty (IOUT = 0) = VOUT / VIN
Example : VIN = 3.6 V, VOUT = 1.8 V …… Duty = 50%
IL = ∆V / L × ton = (VIN VOUT) × Duty / (L × fOSC)
Example : VIN = 3.6 V, VOUT = 1.8 V, fOSC = 1.2 MHz, L = 3.3 µH …… IL = 227 mA
IL max. = ∆IL / 2 = 113.5 mA, IL min. = −∆IL / 2 = −113.5 mA
The current value waveform of the inductor is a triangular wave, of which the maximum value is IL max. and the
minimum value is IL min. (negative value), and the negative value (the portion marked by diagonal lines in
Figure 9) backflows when no load is applied (see Figure 9).
If about 113.5 mA of IOUT flows in the above conditions, the minimum value (IL min.) of the triangular wave is
made 0 mA and no backflow current flows.
When an input capacitor (CIN) is connected, the backflow current is absorbed by CIN, thus reducing the backflow
current to flow in the power supply. Be sure to connect an input capacitor to reduce backflow current to the
power supply (see Figure 10).
The above presents the conditions required to prevent backflow current from flowing, which is only a guideline.
Perform sufficient confirmation using an actual application.
Inductor current with no load
IL
Inductor current when load is a
current of 113.5 mA
IL
227 mA
IL max.
113.5 mA
0 mA
IOUT
113.5 mA
IL max.
IL
Backflow
current
IL min.
113.5 mA
IOUT
0 mA
IL
IL min.
Backflow current = 0 mA
Figure 9 Example of Conditions to Prevent Backflow Current from Flowing
VIN
VIN CIN
Backflow current
CONT
VOUT
Inductor
current IL
Figure 10 Backflow Current
Seiko Instruments Inc.
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