Application Note: SY8113I
High Efficiency, 3.0A, 18V Input
Synchronous Step Down Regulator
General Description
Features
The SY8113I is a high efficiency, 500kHz
synchronous step-down DC/DC regulator capable of
delivering up to 3A load current. It can operate over a
wide input voltage range from 4.2V to 18V and
integrate main switch and synchronous switch with
very low RDS(ON) to minimize the conduction loss.
The SY8113I adopts the instant PWM architecture to
achieve fast transient responses for high step down
applications and high efficiency at light loads. In
addition, it operates at pseudo-constant frequency of
500kHz to minimize the size of the inductor and the
capacitor.
Ordering Information
SY8113 □(□□)□
Temperature Code
Package Code
Optional Spec Code
Ordering Number
SY8113IADC
Package type
TSOT23-6
• Low RDS(ON) for Internal Switches (Top/Bottom):
80mΩ/40mΩ
• 4.2-18V Input Voltage Range
• 3A Output Current Capability
• 500kHz Switching Frequency Minimize the
External Components
• Stable with 10µF COUT and 2.2µH Inductor
• Instant PWM Architecture to Achieve Fast
Transient Responses
• Internal Soft-start Limits the Inrush Current
• Cycle-by-cycle Peak/Valley Current Limitation
• Hic-cup Mode Output Short Circuit Protection
• Thermal Shutdown with Auto Recovery
• Output Auto Discharge Function
• RoHS Compliant and Halogen Free
• Compact Package: TSOT23-6
Applications
•
•
•
•
•
•
Note
----
Set Top Box
Portable TV
DSL Modem
LCD TV
IP CAM
Networking
Typical Application
CBS 100nF
L 4.7uH
BS
VIN :4.2~18V
IN
Efficiency vs. Load Current
VOUT: 3.3V
LX
100
SY8113I
EN
FB
GND
RH
100k
CFF
100pF
COUT
10uF
RL
22.1k
Figure1. Schematic Diagram
95
90
Efficiency (%)
CIN
10uF
85
80
75
70
Inductor and COUT Selection Table
VOUT
[V]
1.2
3.3
5
L
[µH]
1.5
2.2
2.2
4.7
3.3
6.8
COUT [µF]
4.7
10
22
√
☆
√
√
√
☆
√
√
√
☆
VIN=5V, VOUT=3.3V
VIN=12V, VOUT=3.3V
VIN=18V, VOUT=3.3V
65
60
0.01
0.1
1
10
Load Current (A)
Figure2. Efficiency vs. Output Current
Note: ‘☆’ means recommended for most applications.
AN_SY8113I Rev0.9B
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SY8113I
Pinout (top view)
BS
1
6
LX
GND 2
5
IN
4
EN
FB
3
TSOT23-6
Pin Name
Top mark: dKxyz (Device code: dK, x=year code, y=week code, z= lot number code)
Pin Number
Pin Description
BS
1
GND
2
FB
3
EN
4
Boot-strap pin. Supply high side gate driver. Connect a 0.1µF ceramic capacitor
between BS and LX pins.
Power ground pin.
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+RH/RL).
Enable control. Pull high to turn on. Do not leave this pin floating.
IN
5
Input pin. Decouple this pin to GND pin with at least a 10µF ceramic capacitor.
LX
6
Inductor pin. Connect this pin to the switching node of inductor.
Block Diagram
IN
Current Sense
Internal
Power
BS
Input
UVLO
4.15V
PWM
Control &
Protect
Logic
EN
1.2V
FB
LX
Current Sense
0.6V
Internal
SST
Thermal
Protection
GND
Figure3. Block Diagram
AN_SY8113I Rev0.9B
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SY8113I
Absolute Maximum Ratings (Note 1)
Supply Input Voltage ------------------------------------------------------------------------------------------------ -0.3V to 19V
LX, EN Voltage----------------------------------------------------------------------------------------------- -0.3V to VIN + 0.3V
FB, BS-LX Voltage---------------------------------------------------------------------------------------------------- -0.3V to 4V
Power Dissipation, PD @ TA = 25°C TSOT23-6, ----------------------------------------------------------------------- 1.5W
Package Thermal Resistance (Note 2)
θ JA ---------------------------------------------------------------------------------------------------------------- 66°C/W
θ JC --------------------------------------------------------------------------- ------------------------------------- 15°C/W
Junction Temperature Range ------------------------------------------------------------------------------------ -40°C to 150°C
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------------ 260°C
Storage Temperature Range -------------------------------------------------------------------------------------- -65°C to 150°C
Dynamic LX Voltage in 10ns Duration (Note3) ---------------------------------------------------------- IN+3V to GND-5V
Recommended Operating Conditions (Note 3)
Supply Input Voltage -------------------------------------------------------------------------------------------------- 4.2V to 18V
Junction Temperature Range ------------------------------------------------------------------------------------- -40°C to 125°C
Ambient Temperature Range -------------------------------------------------------------------------------------- -40°C to 85°C
AN_SY8113I Rev0.9B
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SY8113I
Electrical Characteristics
(VIN = 12V, VOUT = 3.3V, L = 4.7µH, COUT = 10µF, TA = 25°C, IOUT = 1A unless otherwise specified)
Parameter
Input Voltage Range
Input UVLO Threshold
Input UVLO Hysteresis
Quiescent Current
Shutdown Current
Feedback Reference Voltage
FB Input Current
Output Discharge Resistance
Top FET RON
Bottom FET RON
EN Rising Threshold
EN Falling Threshold
Min ON Time
Min OFF Time
Symbol
VIN
VUVLO
VHYS
IQ
ISHDN
VREF
IFB
RDIS
RDS(ON)1
RDS(ON)2
VEN,R
VEN,F
tON,MIN
tOFF,MIN
Test Conditions
Min
4.2
Turn On Delay
tON,DLY
Soft-start Time
Switching Frequency
tSS
FSW
Top FET Current Limit
ILIM,TOP
4.5
A
Bottom FET Current Limit
Output Under Voltage
Protection Threshold
Output UVP Delay
UVP Hiccup ON Time
UVP Hiccup OFF Time
Thermal Shutdown
Temperature
Thermal Shutdown
Hysteresis
ILIM,BOT
3
A
IOUT=0, VFB=VREF×105%
EN=0
VFB=3.3V
591
-50
1.08
0.9
from EN high to LX start
switching
VOUT from 0 to 100%
VOUT=3.3V, CCM
Typ
0.3
200
5
600
40
80
40
1.2
1.0
50
200
Max
18
4.15
280
10
609
50
120
60
1.32
1.1
300
0.5
1
500
Unit
V
V
V
µA
µA
mV
nA
Ω
mΩ
mΩ
V
V
ns
ns
µs
1.5
ms
kHz
VUVP
33%
VREF
tUVP,DLY
tUVP,ON
tUVP,OFF
100
2
6
µs
ms
ms
TSD
150
˚C
THYS
15
˚C
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.
Note 2: θ JA is measured in the natural convection at TA = 25°C on a 2OZ two-layer Silergy evaluation board.
Paddle of TSOT23-6 package is the case position for SY8113I θ JC measurement.
Note 3: The device is not guaranteed to function outside its operating conditions.
AN_SY8113I Rev0.9B
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SY8113I
Typical Performance Characteristics
Efficiency vs. Load Current
100
95
95
90
90
Efficiency (%)
Efficiency (%)
Efficiency vs. Load Current
100
85
80
75
85
80
75
70
70
VIN=5V, VOUT=1.2V
VIN=12V, VOUT=1.2V
VIN=18V, VOUT=1.2V
65
VIN=5V, VOUT=1.8V
VIN=12V, VOUT=1.8V
VIN=18V, VOUT=1.8V
65
60
60
0.01
0.1
10
1
0.01
1
10
Efficiency vs. Load Current
Efficiency vs. Load Current
100
100
95
95
90
90
Efficiency (%)
Efficiency (%)
0.1
Load Current (A)
Load Current (A)
85
80
75
70
85
80
75
70
VIN=5V, VOUT=3.3V
VIN=12V, VOUT=3.3V
VIN=18V, VOUT=3.3V
65
VIN=7.4V,VOUT=5V
VIN=12V,VOUT=5V
VIN=18V,VOUT=5V
65
60
60
0.01
0.1
1
10
0.01
0.1
1
Load Current (A)
Load Current (A)
Output Ripple
Output Ripple
(VIN=12V, VOUT=3.3V, ILOAD=0A)
(VIN=12V, VOUT=3.3V, ILOAD=3A)
∆VOUT
200mV/div
VLX
5V/div
IL
1A/div
∆VOUT
VLX
IL
Time (2μs/div)
AN_SY8113I Rev0.9A
© 2018 Silergy Corp.
10
100mV/div
5V/div
2A/div
Time (2μs/div)
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SY8113I
Load Transient
Load Transient
(VIN=12V, VOUT=3.3V, ILOAD=0-1.5A)
(VIN=12V, VOUT=3.3V, ILOAD=0.3-3A)
∆VOUT
IL
200mV/div
1A/div
Time (400μs/div)
∆VOUT
IL
200mV/div
2A/div
Time (400μs/div)
Startup from Enable
Shutdown from Enable
(VIN=12V, VOUT=3.3V, ILOAD=3A)
(VIN=12V, VOUT=3.3V, ILOAD=3A)
EN
5V/div
EN
5V/div
VOUT
2V/div
VOUT
2V/div
VLX
10V/div
VLX
10V/div
IL
5A/div
IL
5A/div
Time (400µs/div)
VIN
VOUT
Time (400µs/div)
Startup from VIN
Shutdown from VIN
(VIN=12V, VOUT=3.3V, ILOAD=3A)
(VIN=12V, VOUT=3.3V, ILOAD=3A)
VIN
10V/div
VOUT
2V/div
10V/div
2V/div
VLX
10V/div
VLX
10V/div
IL
5A/div
IL
5A/div
Time (2ms/div)
AN_SY8113I Rev0.9A
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Time (2ms/div)
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SY8113I
Short Circuit Protection
Short Circuit Protection
(VIN=12V, VOUT=3.3V, Open to Short)
(VIN=12V, VOUT=3.3V, 3A to Short)
VOUT
2V/div
IL
2A/div
Time (20ms/div)
AN_SY8113I Rev0.9A
© 2018 Silergy Corp.
VOUT
2V/div
IL
2A/div
Time (20ms/div)
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SY8113I
Operation
The SY8113I is a high efficiency, 500kHz synchronous
step-down DC/DC regulator capable of delivering up to
3A load current. It can operate over a wide input
voltage range from 4.2V to 18V and integrate main
switch and synchronous switch with very low RDS(ON)
to minimize the conduction loss. The SY8113I adopts
the instant PWM architecture to achieve fast transient
responses for high step down applications and high
efficiency at light loads.
The SY8113I provides protection functions such as
cycle-by-cycle current limit and thermal shutdown
protection. The SY8113I will sense the output voltage
conditions for the fault protection.
Applications Information
Because of the high integration in the SY8113I, the
application circuit based on this IC is rather simple.
Only the input capacitor CIN, the output capacitor COUT,
the inductor L and the feedback resistors (RH and RL)
need to be selected for the targeted applications
specifications.
Feedback Resistor Dividers RH and RL
Choose RH and RL to program the proper output voltage.
To minimize the power consumption under light loads,
it is desirable to choose large resistance values for both
RH and RL. A value of between 10kΩ and 1MΩ is
highly recommended for both resistors. If V OUT is 3.3V,
RH=100k is chosen, then using the following equation,
RL can be calculated to be 22.1k:
RL =
Place a typical X5R or a better grade ceramic capacitor
really close to the IN and GND pins to minimize the
potential noise problem. Care should be taken to
minimize the loop area formed by CIN, and IN/GND
pins. In this case, a 10μF low ESR ceramic capacitor is
recommended.
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 a better grade ceramic
capacitor with 16V rating and more than 22µF
capacitance.
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:
L=
VOUT (1 − VOUT/VIN,MAX )
FSW IOUT,MAX 40%
Where FSW is the switching frequency and IOUT,MAX is
the maximum load current.
The IC is quite tolerant of different ripple current
amplitudes. Consequently, the final choice of the
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.
0.6V
RH
VOUT − 0.6V
ISAT, MIN IOUT, MAX +
VOUT(1-VOUT/VIN,MAX)
2 FSW L
VOUT
3)
RH
FB
RL
GND
Input Capacitor CIN
The ripple current through the input capacitor is
calculated as:
I CIN _ RMS = I OUT D(1 − D)
AN_SY8113I Rev0.9A
© 2018 Silergy Corp.
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