Applications Note:AN_SY8104
High Efficiency, 500kHz, 4A, 18V Input
Synchronous Step Down Regulator
General Description
Features
The SY8104 is a high efficiency 500 kHz synchronous
step-down DC-DC converter capable of delivering
4.0A current. The SY8104 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.
•
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
•
•
•
•
•
•
Ordering Information
SY8104 □(□□)□
Applications
Temperature Code
Package Code
Optional Spec Code
Ordering Number
SY8104ADC
Package type
TSOT23-6
•
•
•
•
low RDS(ON) for internal switches (top/bottom):
50mΩ/30mΩ
4.5-18V input voltage range
4.0A output current capability
500 kHz switching frequency
Instant PWM architecture to achieve fast transient
responses.
Internal softstart limits the inrush current
Output discharge function
Cycle-by-cycle peak current limitation
±1.5% 0.6V reference
Pb Free and Halogen Free
TSOT23-6 package
Note
--
•
•
•
•
•
Set Top Box
Portable TV
Access Point Router
DSL Modem
LCD TV
Typical Applications
Efficiency vs. Load Current
100
Efficiency (%)
90
80
VIN=12V,VOUT=5V
70
VIN=16V,VOUT=5V
60
0.001
0.01
0.1
1
10
Load Current (A)
Figure 1. Schematic Diagram
AN_SY8104 Rev. 0.9F
Figure 2. Efficiency vs. Load Current
Silergy Corp. Confidential- Prepared for Customer Use Only
1
AN_SY8104
Pinout (top view)
FB
BS
EN
LX
GND
IN
TSOT23-6
Top Mark: JRxyz, (Device code: JR, x=year code, y=week code, z= lot number code)
Pin Name
FB
Pin Number
1
EN
2
Pin Description
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.
GND
3
Ground pin
IN
LX
BS
4
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
Boot-Strap Pin. Supply high side gate driver. Decouple this pin to LX pin with
0.1uF ceramic cap.
Block Diagram
AN_SY8104 Rev. 0.9F
Silergy Corp. Confidential- Prepared for Customer Use Only
2
AN_SY8104
Absolute Maximum Ratings (Note 1)
Supply Input Voltage ------------------------------------------------------------------------------------------------------ 19V
Enable Voltage----------------------------------------------------------------------------------------------------- VIN + 0.3V
FB Voltage ------------------------------------------------------------------------------------------------------------------------ 4V
LX Voltage ------------------------------------------------------------------------------------------ -0.3V to 19V
BS-LX Voltage ------------------------------------------------------------------------------------------- -0.3V to 4V
Power Dissipation, PD @ TA = 25°C, TSOT23-6 --------------------------------------------------------------- 1.75W
Package Thermal Resistance (Note 2)
θ JA -------------------------------------------------------------------------------------------------------------------- 56°C/W
θ JC -------------------------------------------------------------------------------------------------------------------- 6.3°C/W
Junction Temperature Range ------------------------------------------------------------------------------------------ 150°C
Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------- 260°C
Storage Temperature Range --------------------------------------------------------------------------------- -65°C to 150°C
Dynamic LX voltage in 10ns duration ----------------------------------------------------------------- IN+3V to GND-5V
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_SY8104 Rev. 0.9F
Silergy Corp. Confidential- Prepared for Customer Use Only
3
AN_SY8104
Electrical Characteristics
(VIN = 12V, VOUT = 1.2V, L = 2.2uH, COUT = 47uF, TA = 25°C, IOUT = 1A unless otherwise specified)
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
UVLO Hysteresis
Min ON Time
Min OFF Time
Switching Frequency
Soft-start time
Output Discharge Current
Thermal Shutdown
Temperature
Thermal Shutdown
Hysteresis
Symbol
VIN
IQ
ISHDN
VREF
Test Conditions
IFB
RDS(ON)1
RDS(ON)2
ILIM,TOP
VFB=3.3V
Min
4.5
IOUT=0, VFB=VREF*105%
EN=0
0.591
100
5
0.6
-50
Max
18
10
0.609
50
50
30
8.5
ILIM,BOTTOM
4.0
VENH
VENL
VUVLO
VHYS
1.5
tss
IDIS
TSD
Typ
400
THYS
nA
mΩ
mΩ
A
A
0.4
4.5
VO=3.3V
Unit
V
µA
µA
V
0.3
80
160
500
800
70
150
1200
15
V
V
V
V
ns
ns
kHz
µs
mA
°C
°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 two-layer Silergy Evaluation Board..
Note 3: The device is not guaranteed to function outside its operating conditions
AN_SY8104 Rev. 0.9F
Silergy Corp. Confidential- Prepared for Customer Use Only
4
AN_SY8104
Efficiency (%)
Efficiency (%)
Efficiency (%)
Typical Performance Characteristics
AN_SY8104 Rev. 0.9F
Silergy Corp. Confidential- Prepared for Customer Use Only
5
AN_SY8104
EN Shutdown
Short Circuit Protection
(VIN=12V, VOUT=5V, ILOAD=4A)
(VIN=12V, VOUT=5V, 4A to Short)
EN
5V/div
VLX
10V/div
VOUT
2V/div
IL
Time (400µs/div)
VOUT
2V/div
IL
2A/div
2A/div
Time (1ms/div)
Short Circuit Protection
(VIN=12V, VOUT=5V, Open to Short)
VOUT
IL
2V/div
2A/div
Time (1ms/div)
AN_SY8104 Rev. 0.9F
Silergy Corp. Confidential- Prepared for Customer Use Only
6
AN_SY8104
recommended. And place the 100nF/0603 capacitor
close to IC to attenuate high frequency noise.
Operation
SY8104 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 high efficiency and fast transient
response. The high switching frequency allows using of
small profile inductor and capacitor and the highest
switch frequency simultaneously to minimize the
external inductor and capacitor size, and thus achieving
the minimum solution footprint.
Applications Information
Because of the high integration in the SY8104 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.
Feedback resistor dividers R1 and R2:
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:
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 47uF 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 × I OUT, MAX × 40%
where Fsw is the switching frequency and IOUT,MAX is
the maximum load current.
The SY8104 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.
VOUT
0.6V
R2 =
R1 .
VOUT − 0.6V
FB
GND
R2
Input capacitor CIN:
The ripple current through input capacitor is calculated
as:
I CIN _ RMS = I OUT ⋅ D(1 − D) .
To minimize the potential noise problem, place a
typical X5R or better grade ceramic capacitor really
close to the IN and GND pins. Care should be taken to
minimize the loop area formed by CIN, and IN/GND
pins. For most applications, a 10uF ceramic capacitor
in parallel with 100nF 0603 size ceramic capacitor are
AN_SY8104 Rev. 0.9F
ISAT, MIN > IOUT, MAX +
R1
3)
VOUT(1-VOUT/VIN,MAX)
2 ⋅ FSW ⋅ L
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