Application Note: SY8113
High Efficiency, 500kHz, 3A, 18V Input
Synchronous Step Down Regulator
General Description
Features
The SY8113 is a high efficiency 500 kHz synchronous
step-down DC-DC converter capable of delivering 3A
current. The SY8113 operates over a wide input
voltage range from 4.5V to 18V and integrates main
switch and synchronous switch with very low RDS(ON)
to minimize the conduction loss.
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Low output voltage ripple and small external inductor
and capacitor sizes are achieved with 500 kHz
switching frequency. It adopts the instant PWM
architecture to achieve fast transient responses for high
step down applications
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Typical Applications
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Note
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Set Top Box
Portable TV
Access Point Router
DSL Modem
LCD TV
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Temperature Code
Package Code
Optional Spec Code
Temperature Range: -40°C to 85°C
Package type
TSOT23-6
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SY8113 □(□□)□
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Applications
Ordering Information
Ordering Number
SY8113ADC
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low RDS(ON) for internal switches (top/bottom):
80mΩ/40mΩ
4.5-18V input voltage range
3A output current capability
500 kHz switching frequency
Instant PWM architecture to achieve fast transient
responses.
Internal softstart limits the inrush current
±1.5% 0.6V reference
TSOT23-6 package
Figure 1. Schematic Diagram
AN_SY8113 Rev.0.9
Figure 2. Efficiency Figure
Silergy Corp. Confidential-prepared for Internal Use Only
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AN_SY8113
Pinout (top view)
BS
LX
GND
IN
FB
EN
TSOT23-6(FC)
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Top Mark: MLxyz, (Device code: ML, x=year code, y=week code, z= lot number code)
Pin Number
1
Pin Description
Boot-Strap Pin. Supply high side gate driver. Decouple this pin to LX pin with
0.1uF ceramic cap.
Ground pin
GND
2
FB
3
EN
4
Output Feedback Pin. Connect this pin to the center point of the output resistor
divider (as shown in Figure 1) to program the output voltage:
Vout=0.6*(1+R1/R2)
Enable control. Pull high to turn on. Do not float.
IN
LX
5
6
Input pin. Decouple this pin to GND pin with at least 1uF ceramic cap
Inductor pin. Connect this pin to the switching node of inductor
Absolute Maximum Ratings
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Pin Name
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(Note 1)
Supply Input Voltage ------------------------------------------------------------------------------------------------ 19V
Enable Voltage-------------------------------------------------------------------------------------------------------- VIN + 0.3V
FB Voltage ----------------------------------------------------------------------------------------------------------- 4V
Power Dissipation, PD @ TA = 25°C, TSOT23-6（FC）----------------------------------------------------- 1W
Package Thermal Resistance (Note 2)
θ JA -------------------------------------------------------------------------------------------------------------- 100°C /W
θ JC -------------------------------------------------------------------------------------------------------------- 11.2°C /W
Junction Temperature Range --------------------------------------------------------------------------------------- 125°C
Lead Temperature (Soldering, 10 sec.) ---------------------------------------------------------------------------- 260°C
Storage Temperature Range ------------------------------------------------------------------------------------- -65°C to 150°C
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Recommended Operating Conditions (Note 3)
Supply Input Voltage ---------------------------------------------------------------------------------------------- 4.5V to 18V
Junction Temperature Range ----------------------------------------------------------------------------------- -40°C to 125°C
Ambient Temperature Range ----------------------------------------------------------------------------------- -40°C to 85°C
AN_SY8113 Rev.0.9
Silergy Corp. Confidential-prepared for Internal Use Only
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AN_SY8113
Electrical Characteristics
(VIN = 12V, VOUT = 1.2V, L = 2.2uH, COUT = 47uF, TA = 25°C, IOUT = 1A unless otherwise specified)
Symbol
VIN
IQ
ISHDN
VREF
Test Conditions
Min
4.5
Typ
IOUT=0, VFB=VREF*105%
EN=0
100
5
0.6
0.591
IFB
RDS(ON)1
RDS(ON)2
ILIM
VFB=3.3V
-50
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80
40
10
0.609
Unit
V
µA
µA
V
50
90
50
4.25
nA
mΩ
mΩ
A
1.5
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VIN = 12V ,VOUT=1.2V, IOUT = 1A
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VENH
VENL
VUVLO
VHYS
TON
Max
18
tSS
TSD
THYS
150
50
140
0.4
4.5
0.3
200
80
170
500
800
150
250
120
220
15
V
V
V
V
ns
ns
ns
kHz
uS
°C
°C
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Parameter
Input Voltage Range
Quiescent Current
Shutdown Current
Feedback Reference
Voltage
FB Input Current
Top FET RON
Bottom FET RON
Bottom FET Valley
Current Limit
EN Rising Threshold
EN Falling Threshold
Input UVLO Threshold
UVLO Hysteresis
On Time
Min ON Time
Min OFF Time
Switching Frequency
Soft-start Time
Thermal Shutdown
Temperature
Thermal Shutdown
Hysteresis
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Note 1: Stresses beyond the “Absolute Maximum Ratings” may cause permanent damage to the device. These are
stress ratings only. Functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specification is not implied. Exposure to absolute maximum rating conditions for
extended periods may affect device reliability.
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Note 2: θ JA is measured in the natural convection at TA = 25°C on a low effective 4-layer thermal conductivity test
board of JEDEC 51-3 thermal measurement standard. Pin2 of TSOT23-6 packages is the case position for θ JC
measurement.
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Note 3: The device is not guaranteed to function outside its operating conditions
AN_SY8113 Rev.0.9
Silergy Corp. Confidential-prepared for Internal Use Only
3
AN_SY8113
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Block Diagram
AN_SY8113 Rev.0.9
Silergy Corp. Confidential-prepared for Internal Use Only
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AN_SY8113
Typical Performance Characteristics
Efficiency vs. Load Current
100
95
90
85
80
75
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VIN=6V,VOUT=5V
VIN=12V,VOUT=5V
VIN=16V,VOUT=5V
0.01
0.10
1.00
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Load Current (A)
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Efficiency vs. Load Current
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90
85
80
VIN=5V,VOUT=1.2V
VIN=12V,VOUT=1.2V
VIN=16V,VOUT=1.2V
70
65
0.10
1.00
10.00
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0.01
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75
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Load Current (A)
AN_SY8113 Rev.0.9
Silergy Corp. Confidential-prepared for Internal Use Only
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AN_SY8113
Short Circuit Protection
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Short Circuit Protection
(VIN=12V, VOUT=3.3V, Open to Short)
2V/div
1A/div
VOUT
2V/div
IL
1A/div
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VOUT
(VIN=12V, VOUT=3.3V, 3A to Short)
Time (2ms/div)
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Time (2ms/div)
AN_SY8113 Rev.0.9
Silergy Corp. Confidential-prepared for Internal Use Only
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AN_SY8113
SY8113 provides protection functions such as cycle by
cycle current limiting and thermal shutdown protection.
SY8113 will sense the output voltage conditions for the
fault protection.
Feedback resistor dividers R1 and R2:
0.6VFB
GND
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VOUT (1 − VOUT /VIN, MAX )
FSW × I OUT, MAX × 40%
where Fsw is the switching frequency and IOUT,MAX is
the maximum load current.
The SY8113 regulator IC is quite tolerant of different
ripple current amplitude. Consequently, the final choice
of inductance can be slightly off the calculation value
without significantly impacting the performance.
2) The saturation current rating of the inductor must
be selected to be greater than the peak inductor
current under full load conditions.
ISAT, MIN > IOUT, MAX +
VOUT
VOUT(1-VOUT/VIN,MAX)
2 ⋅ FSW ⋅ L
R1
3)
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Choose R1 and R2 to program the proper output voltage.
To minimize the power consumption under light loads,
it is desirable to choose large resistance values for both
R1 and R2. A value of between 10kΩ and 1MΩ is
highly recommended for both resistors. If Vout is 3.3V,
R1=100k is chosen, then using following equation, R2
can be calculated to be 22.1k:
0.6V
R1 .
VOUT − 0.6V
L=
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Because of the high integration in the SY8113 IC, the
application circuit based on this regulator IC is rather
simple. Only input capacitor CIN, output capacitor COUT,
output inductor L and feedback resistors (R1 and R2)
need to be selected for the targeted applications
specifications.
R2 =
Output inductor L:
There are several considerations in choosing this
inductor.
1) Choose the inductance to provide the desired
ripple current. It is suggested to choose the ripple
current to be about 40% of the maximum output
current. The inductance is calculated as:
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Applications Information
Output capacitor COUT:
The output capacitor is selected to handle the output
ripple noise requirements. Both steady state ripple and
transient requirements must be taken into consideration
when selecting this capacitor. For the best performance,
it is recommended to use X5R or better grade ceramic
capacitor greater than 22uF capacitance.
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SY8113 is a synchronous buck regulator IC that integrates
the PWM control, top and bottom switches on the same die to
minimize the switching transition loss and conduction loss.
With ultra low Rds(on) power switches and proprietary PWM
control, this regulator IC can achieve the highest efficiency
and the highest switch frequency simultaneously to minimize
the external inductor and capacitor size, and thus achieving
the minimum solution footprint.
minimize the loop area formed by CIN, and IN/GND
pins. In this case, a 10uF low ESR ceramic capacitor is
recommended.
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Operation
Input capacitor CIN:
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The ripple current through input capacitor is calculated
as：
I CIN _ RMS = I OUT ⋅ D(1 − D) .
The DCR of the inductor and the core loss at the
switching frequency must be low enough to
achieve the desired efficiency requirement. It is
desirable to choose an inductor with DCR
