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
* PDAs
* Wireless Equipment
* MP3 player
* Digital Camera
* Portable Instruments
FEATURES
* High efficiency up to 95%
* Automatic Power Saving Mode at light loads, only 20μA quiescent
current.
* Wide input voltage range: +2. 5V~+5.5V
* Output voltage range: 0.6V~V
IN
* 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
Http://www.silan.com.cn
REV:1.1
2008.09.10
Page 1 of 11
SC46208
ORDERING INFORMATION
Device no
SC46208
SC4620810
SC4620812
SC46208XX
SC4620815
SC4620818
SC4620825
SC4620833
Seal name
6208
20810
20812
20815
20818
20825
20833
Package
SOT-23-5
SOT-23-5
SOT-23-5
SOT-23-5
SOT-23-5
SOT-23-5
SOT-23-5
voltage:
Default: adjustable
10 :1.0V
12 :1.2V
15 :1.5V
18 :1.8V
25 :2.5V
33 :3.3V
Remark
Note: “××” indicates the output
BLOCK DIAGRAM
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
REV:1.1
2008.09.10
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SC46208
ABSOLUTE MAXIMUM RATING
Characteristics
Input Supply Voltage V
IN
Enable Voltage EN
SW Voltage
Output Feedback Voltage
Operating Temperature
Storage Temperature
ESD Characteristic(HBM)
Symbol
V
IN
V
EN
V
SW
V
FB
T
amb
T
STG
ESD
Rating
-0.3 ~ +6
-0.3 ~ V
IN
-0.3 ~ V
IN
+0.3
-0.3 ~ +6
-40 ~ + 85
-65 ~ +125
4.0
Unit
V
V
V
V
°C
°C
KV
ELECTRICAL CHARACTERISTICS
(unless otherwise noted, T
amb
=25°C, V
IN
=3.6V, L=2.2μH, C
OUT
=10μF,
load current I
LOAD
=0)
Characteristics
Input Voltage Range
Feedback Voltage
Quiescent Current (Switch Off)
Quiescent Current (Shutdown
Mode)
Quiescent Current (PWM Mode)
Output Voltage Regulation
Output Voltage Load Regulation
Feedback Current
PMOS On Resistor
NMOS On Resistor
PMOS Limit Current
Switch Frequency
Max. Duty
Switch Leakage Current SW
EN Input High Level
EN Input Low Level
EN Leakage Current
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
Temperature
Symbol
V
IN
V
FB
Only for adjustable version
I
switch off
FB=0.62V,or V
OUT
=103%
I
SHDN
Iq
△
V
OUT
△
V
LOAD
0mA≤ IL
≤600mA
I
FB
R
PMOS
R
NMOS
I
LIMIT
F
S
D
MAX
I
LSW
V
H
V
L
I
LEN
T
j(sd)
T
hys
t
--
--
Only for adjustable version
I
SW
=100mA
I
SW
=-100mA
2.5V≤V
IN
≤5.5V
FB=0.6V,or V
OUT
=100％
FB=0 V,or V
OUT
=0
FB=0.5V
EN=0V,SW=0V or 5V,V
IN
=5V
--
--
--
--
--
±0.01
150
20
1.5
0.3
±1
--
--
100
±0.01
±1
1.25
1.
-50
0.45
0.35
1.5
1.25
600
EN=0V
FB=0.5V ,
Or V
OUT
=90%
Test conditions
Min.
2.5
0.585
0.6
20
0.1
200
0.5
0.1
50
0.5
0.4
1.75
1.5
Typ.
Max.
5.5
0.615
30
1
300
Unit.
V
V
μA
μA
μA
%
mV/mA
nA
Ω
Ω
A
MHz
KHz
%
μA
V
V
μA
°C
°C
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
REV:1.1
2008.09.10
Page 3 of 11
SC46208
PIN CONFIGURATION
FB/V
OUT
5
V
IN
4
SC46208
1
EN
2
GND
3
SW
PIN DESCRIPTION
Pin no.
1
2
3
4
5
Pin name
EN
GND
SW
V
IN
FB/V
OUT
I/O
I
--
I/O
--
I
Descriptions
Enable input port, this pin should not float.
Ground.
Power switch which connect to inductor and output voltage.
Supply input pin.
Output voltage feedback pin. In the adjustable version, this pin used for
connecting external resistive divider.
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
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
REV:1.1
2008.09.10
Page 4 of 11
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 C
IN
and
C
OUT
:
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 V
OUT
:
I
ripple
=
1 V
IN
−
V
OUT
V
OUT
×
×
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
I
ripple
approximately 40% of the
maximum load current
I
LOAD(max)
, so the rating current
I
sat
satisfied with following formula:
1
I
sat
>
I
LOAD(max)
+
I
ripple
=
(1
+
20%)I
LOAD(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.
HANGZHOU SILAN MICROELECTRONICS CO.,LTD
Http://www.silan.com.cn
REV:1.1
2008.09.10
Page 5 of 11
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