SC4620812 [SILAN]
1.25MHz, 600mA, HIGH EFFICIENCY SYNCHRONOUS STEP-DOWN DC-DC CONVERTER; 1.25MHz的， 600毫安，高效率同步降压型DC -DC转换器
| 型号： | SC4620812 |
| 厂家： | 
SILAN MICROELECTRONICS JOINT-STOCK |
| 描述： | 1.25MHz, 600mA, HIGH EFFICIENCY SYNCHRONOUS STEP-DOWN DC-DC CONVERTER |
| 文件： | 总10页 (文件大小：509K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SC46208
1.25MHz, 600mA, HIGH EFFICIENCY SYNCHRONOUS STEP-DOWN DC-DC
CONVERTER
DESCRIPTION
SC46208 is a synchronous step-down DC-DC converter with high
efficiency. It adopts small flat package. The device features 2.5~5.5V
input voltage, 600mA output current, peak current mode PWM and
integrated compensation net, which is ideal for powering portable
equipment that runs from a single cell Li+ battery without external
components.
The device integrates an internal switch which eliminates the
Schottky diode, 1.25MHz high frequency allows the periphery to adopt
SMT inductor and capacitor, thus reduce the size of total solution. It
can also run at 100% duty cycle for low dropout operation, that is
lower than 1μA shutdown current and 20μA quiescent current in
power saving mode. It extends battery life in portable system through
increasing the efficiency under light loads.
SC46208 is available in an adjustable version and fixed version.
APPLICATION
* Cellular Telephones
FEATURES
* PDAs
* High efficiency up to 95%
* Wireless Equipment
* Automatic Power Saving Mode at light loads, only 20μA quiescent
* MP3 player
current.
* Digital Camera
* Wide input voltage range: +2. 5V~+5.5V
* Portable Instruments
* Output voltage range: 0.6V~VIN
* High output current 600mA
* Low dropout operation: 100%
* Shutdown current<1μA
* 1.25MHz fixed frequency
* No Schottky diode required
* Thermal shutdown protection
* 4KV HBM ESD protection
* Small 5-pin SOT-23package
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
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Page 1 of 11
SC46208
ORDERING INFORMATION
Device no
SC46208
Seal name
6208
Package
SOT-23-5
SOT-23-5
SOT-23-5
SOT-23-5
SOT-23-5
SOT-23-5
SOT-23-5
Remark
Note: “××” indicates the output
SC4620810
SC4620812
20810
20812
20815
20818
20825
20833
voltage: Default: adjustable
10 :1.0V
12 :1.2V
15 :1.5V
18 :1.8V
25 :2.5V
33 :3.3V
SC46208XX
SC4620815
SC4620818
SC4620825
SC4620833
BLOCK DIAGRAM
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SC46208
ABSOLUTE MAXIMUM RATING
Characteristics
Input Supply Voltage VIN
Enable Voltage EN
Symbol
Rating
Unit
V
-0.3 ~ +6
V
IN
EN
SW
-0.3 ~ V
V
IN
V
-0.3 ~ V +0.3
V
IN
SW Voltage
V
-0.3 ~ +6
-40 ~ + 85
-65 ~ +125
4.0
V
Output Feedback Voltage
Operating Temperature
Storage Temperature
ESD Characteristic(HBM)
V
FB
°C
°C
KV
T
T
amb
STG
ESD
ELECTRICAL CHARACTERISTICS(unless otherwise noted, Tamb =25°C, VIN=3.6V, L=2.2μH, COUT=10μF,
load current ILOAD=0)
Characteristics
Input Voltage Range
Symbol
Test conditions
Min.
2.5
Typ.
Max. Unit.
V
IN
5.5
0.615
30
V
V
Feedback Voltage
V
FB
Only for adjustable version
0.585
0.6
20
Quiescent Current (Switch Off)
Quiescent Current (Shutdown
Mode)
I
FB=0.62V,or V
=103%
OUT
μA
switch off
I
EN=0V
0.1
1
μA
μA
SHDN
FB=0.5V ,
Quiescent Current (PWM Mode)
Iq
200
300
Or V
=90%
OUT
Output Voltage Regulation
△V
0.5
0.1
%
mV/mA
nA
Ω
OUT
LOAD
FB
Output Voltage Load Regulation △V
0mA≤ IL ≤600mA
Only for adjustable version
Feedback Current
PMOS On Resistor
NMOS On Resistor
PMOS Limit Current
I
-50
50
0.5
0.4
1.75
1.5
R
R
I
I
=100mA
=-100mA
0.45
0.35
1.5
PMOS
NMOS
LIMIT
SW
SW
Ω
I
2.5V≤V ≤5.5V
1.25
1.
A
IN
FB=0.6V,or V =100％
OUT
1.25
600
MHz
KHz
%
Switch Frequency
F
S
FB=0 V,or V
FB=0.5V
=0
OUT
Max. Duty
D
MAX
100
1.5
Switch Leakage Current SW
EN Input High Level
EN Input Low Level
I
EN=0V,SW=0V or 5V,V =5V
±0.01
±1
μA
V
LSW
IN
V
--
--
H
V
0.3
±1
--
V
L
EN Leakage Current
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
Temperature
I
--
--
±0.01
150
μA
°C
LEN
T
--
--
j(sd)
T
t
--
20
--
°C
hys
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Page 3 of 11
SC46208
PIN CONFIGURATION
FB/VOUT
5
VIN
4
SC46208
1
2
3
EN
GND
SW
PIN DESCRIPTION
Pin no.
Pin name
EN
I/O
I
Descriptions
1
2
3
4
Enable input port, this pin should not float.
Ground.
GND
SW
--
I/O
--
Power switch which connect to inductor and output voltage.
Supply input pin.
VIN
Output voltage feedback pin. In the adjustable version, this pin used for
connecting external resistive divider.
5
FB/VOUT
I
FUNCTION DESCRIPTIONS
SC46208 is a 1.25MHz constant frequency, current mode PWM step-down converter. The device integrates
PMOS switch and a NMOS synchronous rectifier. It also includes a voltage reference, error amplifier, oscillator,
PWM comparator, current comparator, slope compensation, current sense, logic driver, etc...
In normal PWM mode, in one cycle, when the oscillator sets RS trigger, internal PMOS conduct, while PWM
comparator resets the RS trigger, PMOS is cut off, the peak current of inductor is controlled by error amplifier
output. When PMOS is off, the synchronous NMOS will be turned on and stay on until the inductor current
reverses (controlled by current comparator ICOMP) or the next clock cycle begins.
SC46208 detects the load current automatically, when the load current decreases to a threshold(relate to the
input/output voltage and inductance), the system starts power saving mode. In this mode, the dissipation
current is only 20μA, thus to improve the conversion efficiency under light loads. Pay attention to the ripple of
output voltage, you can add a phase-lead capacitor (pF grade) between the VOUT and FB to reduce the ripple
in power saving mode.
Dropout Operation
When the input voltage decreases toward the value of output voltage, the duty increases, and the input voltage
decrease more, PMOS switch on in one cycle and the duty reaches 100%. The output voltage then is the input
voltage minus the voltage drop across the PMOS switch and the inductor.
Short Circuit Protection
When the output is short to ground, the frequency of internal oscillator decreases to 600KHz in order to remain
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SC46208
enough attenuation time for inductor, thus prevent it from running away. When the output voltage increases, the
frequency increases to 1.25MHz gradually.
Over Voltage Detection
When the over-voltage detect circuit detects the output voltage is more than 6% of the set value, it will shutdown
the PMOS switch to prevent the output voltage from over-shoot until the voltage drops to set value.
Current Limit and Thermal Shutdown
Current limit is implemented through internal comparator, it limits the PMOS current in the 1.5A in one cycle,
thus to protect the SC46208 in over load condition.
When the die temperature is over 150°C due to the long time over load operation, SC46208 is shutdown
automatically until the temperature lower to normal state, the hysteresis temperature during this period is about
20°C.
APPLICATION NOTES
Refering to typical application circuit of fig 1, the components selection begins with inductor L, then CIN and
COUT:
Inductor Selection
The SC46208 can utilize small surface mount and chip inductors due to its fast 1.25MHz switching frequency.
For most applications the SC46208 operates with inductors of 1μH to 4.7μH. The large inductance will decrease
the ripple current, but high inductance values will also increase the PCB size, and the low inductance value result
in high ripple currents. The ripple also relative with the VIN and VOUT:
V
IN − VOUT VOUT
1
Iripple
=
×
×
fs
L
V
IN
The rating current of inductor is equal to half of the max. load current adds half the max. ripple current ,to handle
the peak inductor current without saturating. Choose inductor ripple current Iripple approximately 40% of the
maximum load currentILOAD(max) , so the rating current Isat satisfied with following formula:
1
Isat > ILOAD(max)
+ Iripple = (1+ 20%)ILOAD(max)
2
The max. load current is 600mA, for most applications, the inductor of 720mA rating value is enough; for higher
efficiency, please choose an inductor with low DC series resistance (DCR). To reduce the noise, use a shielded
bobbin inductor.
Capacitor Selection
The low ESR capacitor is required to keep the output voltage ripple small. There, the multilayer ceramic
capacitor is recommended due to their low ESR and small size. In the most applications, 10-22μF output
capacitors are enough, higher capacitor can be used to reduce the output ripple and improve transient
response.
The low ESR input capacitor reduces the surge current drawn from the input and switching noise from the
device. Ceramic capacitor is the best selection for input capacitor, and the capacitor should be as near as
possible to chip. A 4.7μF ceramic capacitor is sufficient for most applications.
Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small
temperature coefficients.
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SC46208
Setting The Output Voltage
For voltage adjustable version, SC46208 adjusts the output voltage through two serial resistors, refer to fig.
R1
R2
below. We can calculate the output voltage through the following equation:
VOUT = (1+
)X0.6V
The selection of resistor R1, R2 should give attention to the quiescent power and external interfere. Higher
impedance reduces the quiescent current (I=0.6V/R2), and lower resistance gives better noise immunity, and is
less sensitive to interference, layout parasitics and FB node leakage current. A proper value of feed-forward
capacitor C1 can improve the noise immunity of the feedback loops, especially in an improper layout.
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SC46208
TYPICAL APPLICATION CIRCUIT
Fig. 1：Output voltage adjustable regulator, single battery to 2.5V converter
Fig.2：Output voltage fixed regulator
Note: The circuit and parameters are reference only, please set the parameters of the real application circuit
based on the real test.
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SC46208
TYPICAL ELECTRICAL CHARACTERISTICS CURVES (Tamb=25°C, unless otherwise specified)
Efficiency VS Input Voltage of SC46208
100
95
IOUT=100mA
IOUT=10mA
90
IOUT=1mA
85
IOUT=600mA
80
75
70
65
IOUT=0.1mA
60
VOUT=1.8V
55
50
2
3
4
5
6
Input Voltage(V)
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SC46208
TYPICAL ELECTRICAL CHARACTERISTICS CURVES (Tamb=25°C, unless otherwise specified)
Output Voltage VS Load Current
VIN＝3.6V
1.844
1.834
1.824
1.814
1.804
1.794
1.784
1.774
TA=25 C
0
100 200 300 400 500
700
900
800
600
Load Current(mA)
Output Ripple Voltage
SC46208 Load Step
VOUT
100mV/DIV
AC COUPLED
VOUT
(5mV/DIV)
SW
(5V/DIV)
IL
500mA/DIV
IL
(500mA/DIV)
ILOAD
500mA/DIV
20mS/DIV
Time(500ns/DIV)
VIN=3.6V
VOUT=1.8V
VIN=3.6V
VOUT=1.2V
ILOAD=600mA
ILOAD=50mA to 600mA
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
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SC46208
PACKAGE OUTLINE
SOT-23-5
Unit: mm
2.92±0.10
0～8°
0.35
0.2
0.950
0.15±0.05
1.90±0.10
MOS DEVICES OPERATE NOTES:
Electrostatic charges may exist in many things. Please take following preventive measures to prevent
effectively the MOS electric circuit as a result of the damage which is caused by discharge:
z
z
z
z
The operator must put on wrist strap which should be earthed to against electrostatic.
Equipment cases should be earthed.
All tools used during assembly, including soldering tools and solder baths, must be earthed.
MOS devices should be packed in antistatic/conductive containers for transportation.
Note：Silan reserves the right to make changes without notice in this specification for the improvement of the design and performance.
Silan will supply the best possible product for customers.
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
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2008.09.10
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Page 10 of 11
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