Application Note: SY8120B1
High Efficiency Fast Response, 2A, 18V Input
Synchronous Step Down Regulator
General Description
SY8120B1 develops high efficiency synchronous step-
down DC-DC converter capable of delivering 2A load
current . SY8120B1 operates over a wide input voltage
range from 4.5V to 18V and integrates main switch and
synchronous switch with very low R
DS(ON)
to minimize
the conduction loss.
SY8120B1 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
500 kHz under heavy load conditions to minimize the
size of inductor and capacitor.
Features
•
Low R
DS(ON)
for internal switches
(top/bottom):130/120 m
Ω
•
4.5-18V input voltage range
•
2A load current capability
•
Instant PWM architecture to achieve fast transient
responses Internal softstart limits the inrush current
•
2% 0.6V reference
•
Cycle-by-cycle peak current limitation
•
RoHS Compliant and Halogen Free
•
Compact package: SOT23-6
Ordering Number
SY8120B1ABC
Package type
SOT23-6
Typical Applications
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Figure 1. Schematic Diagram
2
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Temperature Code
Package Code
Optional Spec Code
Temperature Range:
-
40°C to 85°C
Note
--
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SY8120
□
(
□□
)
□
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•
•
•
•
•
•
•
•
Ordering Information
Applications
d
Set Top Box
Portable TV
Access Point Router
DSL Modem
LCD TV
CCTV
IP CAM
Networking
AN_SY8120B1 Rev.0.9
Silergy Corp. Confidential-prepared for Internal Use Only
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Figure 2. Efficiency Figure
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AN_SY8120B1
Pinout
(
top view)
(SOT23-6)
Pin Name
BS
GND
FB
EN
IN
LX
Pin Number
1
2
3
4
5
6
Absolute Maximum Ratings
(Note 1)
Supply Input Voltage ----------------------------------------------------------------------------------------- 19V
LX, EN Voltage---------------------------------------------------------------------------------------- V
IN
+ 0.3V
FB, BS-LX Voltage---------------------------------------------------------------------------------------------- 4V
Power Dissipation, P
D
@ T
A
= 25°C SOT23-6, ----------------------------------------------------------- 0.6W
Package Thermal Resistance (Note 2)
θ
JA
------------------------------------------------------------------------------------------------- 170°C/W
θ
JC
------------------------------------------------------------------------------------------------- 75°C/W
Junction Temperature Range -------------------------------------------------------------------------------- 150°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_SY8120B1 Rev.0.9
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Pin Description
Boot-Strap Pin. Supply high side gate driver. Decouple this pin to LX pin with
0.1uF ceramic cap.
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+R1/R2)
Enable control. Pull high to turn on. Do not float.
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
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Top Mark:
WBxyz
,
(Device
code: WB,
x=year code, y=week code, z= lot number code)
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AN_SY8120B1
Block Diagram
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AN_SY8120B1 Rev.0.9
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AN_SY8120B1
Electrical Characteristics
(
V
IN
= 12V,
V
OUT
= 1.2V,
L
= 2.2uH,
C
OUT
= 10uF,
T
A
= 25°C,
I
OUT
= 1A unless otherwise specified)
Note 3:
The device is not guaranteed to function outside its operating conditions.
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AN_SY8120B1 Rev.0.9
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Note 2:
θ
JA is measured in the natural convection at T
A
= 25°C on a low effective single layer thermal conductivity
test board of JEDEC 51-3 thermal measurement standard. Pin 2 of SOT-23-6 packages is the case position for
θ
JC
measurement.
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Note 1:
Stresses beyond “Absolute Maximum Ratings” may cause permanent damage to the device. These are for
stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect
device reliability.
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Parameter
Input Voltage Range
Quiescent Current
Shutdown Current
Feedback Reference
Voltage
FB Input Current
Top FET RON
Bottom FET RON
TOP FET Peak Current
Limit
Bottom FET Valley
Current Limit
EN Rising Threshold
EN Falling Threshold
Input UVLO Threshold
Switching Frequency
Min ON Time
Min Off Time
Soft-start Time
Thermal Shutdown
Temperature
Thermal Shutdown
Hysteresis
Symbol
V
IN
I
Q
I
SHDN
V
REF
I
FB
R
DS(ON)1
R
DS(ON)2
I
LIM,TOP
I
LIM,BOTTOM
V
ENH
V
ENL
V
UVLO
F
SW
Test Conditions
I
OUT=0,
V
FB
=V
REF
×105%
EN=0
Min
4.5
Typ
400
5
0.6
Max
18
10
0.612
50
0.588
V
FB
=V
IN
-50
Unit
V
µA
µA
V
nA
Ω
Ω
A
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1.5
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0.12
3.6
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0.4
4.5
500
50
100
800
150
15
t
SS
T
SD
T
HYS
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V
V
V
kHz
ns
ns
us
C
C
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AN_SY8120B1
Typical Performance Characteristics
Efficiency (%)
Efficiency (%)
Efficiency (%)
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AN_SY8120B1 Rev.0.9
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