Application Notes: AN_SY8088
High Efficiency 1.5MHz, 1A
Synchronous Step Down Regulator
General Description
Features
SY8088 is a high efficiency 1.5MHz synchronous step
down DC/DC regulator IC capable of delivering up to
1A output current. It can operate over a wide input
voltage range from 2.5V to 5.5V and integrate main
switch and synchronous switch with very low RDS (ON)
to minimize the conduction loss.
Low RDS(ON) for internal switches (top/bottom)
260m /170m
2.5~5.5V input voltage range
40 A typical quiescent current
High light load efficiency
Ordering Information
High switching frequency 1.5MHz minimizes the
external components
SY8088
Internal soft-start limits the inrush current
(
)
Temperature Code
Package Code
Optional Spec Code
Temperature Range: -40°C to 85°C
Ordering Number
SY8088AAC
Package Type
SOT23-5
Note
1A
100% dropout operation
RoHS Compliant and Halogen Free
Compact package: SOT23-5
Applications
ortable Navigation Device
Set Top Box
USB Dongle
Media Player
Smart phone
Typical Application
Figure1. Schematic Diagram
AN_SY8088 Rev. 0.1
Figure2. Efficiency
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1
AN_SY8088
Pinout (Top View)
(SOT23-5)
Top Mark: LD
Pin Name
EN
GND
LX
IN
Pin Number
1
2
3
4
FB
5
(device code: LD,
Pin Description
Enable control. Pull high to turn on. Do not float.
Ground pin.
Inductor pin. Connect this pin to the switching node of the inductor.
Input pin. Decouple this pin to the GND pin with at least 4.7uF ceramic
capacitor.
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).Add optional C1 (10pF~47pF) to speed up the transient
response.
Absolute Maximum Ratings (Note 1)
Supply Input Voltage -------------------------------------------------------------------------------------------------------- 6.0V
Enable, FB Voltage---------------------------------------------------------------------------------------------------- VIN + 0.6V
Power Dissipation, PD @ TA = 25°C, SOT23-5--------------------------------------------------------------------------- 0.6W
Package Thermal Resistance (Note 2)
JA -------------------------------------------------------------------------------------------------------------- 170°C/W
JC ---------------------------------------------------------------------------------------------------------- ----130°C/W
Junction Temperature Range ----------------------------------------------------------------------------------------------125°C
Lead Temperature (Soldering, 10 sec.) ---------------------------------------------------------------------------------- 260°C
Storage Temperature Range ----------------------------------------------------------------------------------- -65°C to 150°C
Recommended Operating Conditions (Note 3)
Supply Input Voltage ----------------------------------------------------------------------------------------------- 2.5V to 5.5V
Junction Temperature Range ----------------------------------------------------------------------------------- -40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------------ -40°C to 85°C
AN_SY8088 Rev. 0.1
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AN_SY8088
Electrical Characteristics
(V IN = 5V, VOUT = 2.5V, L = 2.2uH, COUT = 10uF, TA = 25°C, unless otherwise specified)
Parameter
Input Voltage Range
Quiescent Current
Shutdown Current
Feedback Reference Voltage
PFET RON
Symbol
VIN
IQ
ISHDN
VREF
RDS(ON),P
NFET RON
PFET Current Limit
EN rising threshold
EN falling threshold
Input UVLO threshold
UVLO hysteresis
Oscillator Frequency
Min ON Time
Max Duty Cycle
Soft Start Time
Thermal Shutdown Temperature
Thermal Shutdown Hysteresis
RDS(ON),N
ILIM
VENH
VENL
VUVLO
VHYS
FOSC
Test Conditions
Min
2.5
IOUT=0, VFB=VREF 105%
EN=0
0.588
Typ
40
0.1
0.6
260
1
0.612
170
1.3
1.5
0.4
2.5
0.1
1.5
80
100
TSS
TSD
THYS
Max
5.5
1
160
15
Unit
V
µA
µA
V
m
m
A
V
V
V
V
MHz
ns
%
ms
°C
°C
Note 1: Stresses beyond the “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 for
extended periods may remain possibility to affect device reliability.
Note 2: JA is measured in the natural convection at TA = 25°C on a low effective single layer thermal conductivity
test board of JEDEC 51-3 thermal measurement standard. Exposed Paddle of DFN package is the case position for
JC measurement.
Note 3: The device is not guaranteed to function outside its operating conditions.
AN_SY8088 Rev. 0.1
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AN_SY8088
Typical Performance Characteristics
AN_SY8088 Rev. 0.1
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4
AN_SY8088
AN_SY8088 Rev. 0.1
Silergy Corp. Confidential- Prepared for Customer Use Only
5
AN_SY8088
Operation
The SY8088 is a high-efficiency 1.5MHz synchronous
step-down DC-DC converters capable of delivering up
to 1A output current. It operates over a wide input
voltage range from 2.5V to 5.5V and integrates main
switch and synchronous switch with very low RDS(ON)
to minimize the conduction loss.
Applications Information
Because of the high integration in the SY8088 IC, the
application circuit based on this regulator IC is rather
simple. Only input capacitor C IN, 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 100k
and 1M is highly recommended for both resistors. If
R2=120k is chosen, then R1 can be calculated to be:
R1
(VOUT 0.6V) R2
0.6V
where Fsw is the switching frequency and Iout,max is
the maximum load current.
The SY8088 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 (1-VOUT/VIN,MAX)
ISAT, MIN IOUT, MAX
2 FSW L
3) 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
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