Application Note: AN_SY8089/SY8089A
High Efficiency 5.5V, 2A continuous, 3A peak, 1MHz
Synchronous Step Down Regulator
General DescriptionFeatures

The SY8089 and SY8089A are high-efficiency, highfrequency synchronous step-down DC-DC regulator IC
capable of delivering up to 2A output current. The
SY8089 and SY8089A operate over a wide input
voltage range from 2.7V 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):110mΩ/80mΩ• 2.7-5.5V input voltage range• 2A continuous, 3A peak load current capability• 1MHz switching frequency minimizes the externalcomponents• Internal softstart limits the inrush current• Reliable short circuit protection:
SY8089: Latch off protection
SY8089A: Hic-cup mode protection• Reliable over-voltage protection:
SY8089: Latch off protection
SY8089A: No latch off protection• 100% dropout operation• RoHS Compliant and Halogen Free
• Compact package: SOT23-5

Low output voltage ripple and small external inductorand capacitor sizes are achieved with greater than
1MHz switching frequency.
SY8089 integrates short circuit and over-voltage latch
off protection.

Ordering Information
SY8089 □(□□)□
Temperature CodePackage CodeOptional Spec CodeTemperature Range: -40°C to 85°C
Ordering Number
Package type
SY8089AAC
SOT23-5
SY8089AAAC
SOT23-5

Applications
•••
•
•

Note

LCD TVSet Top Box
Net PC
Mini-Notebook PC
Access Point Router

Typical Applications
4IN

LX

3 L1:2.2µH

CIN
22µF

R1200kFB

1ON/ OFFVOUT: 1.8V

5EN

R2100k

GND

C122pFCOUT
22µFх2Efficiency (%)

VIN: 2.7-5.5V

2

Figure 1.Schematic diagram

AN_SY8089/A Rev. 0.9A

Figure 2. Efficiency vs Load Current

Silergy Corp. Confidential- Prepared for Customer Use Only 1

SY8089/8089A
Pinout (top view)

SOT23-5①
Part Number
Package type
Top Mark
SY8089AAC
SOT23-5
JXxyz
SY8089AAAC
SOT23-5
KVxyz
Note① ： x=year code, y=week code, z= lot number code

Pin NameENGND
LXINFBPin Number12345

Pin Description
Enable control. Pull high to turn on. Do not float.
Ground pin.
Inductor pin. Connect this pin to the switching node of inductor.
Input pin. Decouple this pin to GND pin with at least 10µF ceramic cap.
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).

Absolute Maximum Ratings (Note 1)
Supply Input Voltage ----------------------------------------------------------------------------------------------- -0.3V to 6.0V
Enable, FB Voltage------------------------------------------------------------------------------------------ -0.3V to VIN + 0.6V
Power Dissipation, PD @ TA = 25°C,
SOT23-5 -------------------------------------------------------------------------------------------------------------- 0.6W
Package Thermal Resistance (Note 2)
θ JA --------------------------------------------------------------------------------------------------------------- 170°C/W
θ JC ----------------------------------------------------------------------------------------------------------------130°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

Recommended Operating Conditions (Note 3)
Supply Input Voltage ------------------------------------------------------------------------------------------------ 2.7V to 5.5V
Junction Temperature Range ------------------------------------------------------------------------------------ -40°C to 125°C
Ambient Temperature Range ------------------------------------------------------------------------------------- -40°C to 85°C

AN_SY8089/A Rev. 0.9A

Silergy Corp. Confidential- Prepared for Customer Use Only 2

SY8089/8089A
Block Diagram(SY8089)(SY8089A)

AN_SY8089/A Rev. 0.9A

Silergy Corp. Confidential- Prepared for Customer Use Only 3

SY8089/8089A
Electrical Characteristics(VIN = 5V, VOUT = 2.5V, L = 2.2µH, COUT = 22µF, TA = 25°C, unless otherwise specified)Parameter
Input Voltage Range
Quiescent Current

Symbol
VINIQ

Shutdown Current
Feedback Reference Voltage
FB Input Current
PFET RON
NFET RONPFET Current Limit
EN rising thresholdEN falling threshold
Input UVLO threshold
UVLO hysteresis
Oscillator Frequency
Short Circuit Protection Latch OffThreshold
Min ON TimeMax Duty Cycle
Soft Start Time
Output Discharge Switch On
Resistance
Thermal Shutdown Temperature

ISHDN
VREF
IFB
RDS(ON),PRDS(ON),NILIM
VENH
VENL
VUVLO
VHYS
FOSC
VSCP

Test Conditions

Min
2.7

IOUT=0,VFB=VREF ⋅ 105%
EN=0
VFB=VIN

TypMax
5.5

Unit
V
µA

10.612
50µA
VnAmΩ
mΩ
AVVVVMHzV

55

0.588
-50

0.1
0.611080

3.5
1.5
0.4
2.50.2
10.25

IOUT=500mA

75TSSRDISCH

1.250

ns%msΩ

TSD

160°C100

Note 1: Stresses beyond the “Absolute Maximum Ratings” may cause permanent damage to the device. These arestress ratings only. Functional operation of the device at these or any other conditions beyond those indicated in theoperational sections of the specification is not implied. Exposure to absolute maximum rating conditions forextended periods may affect device reliability.
Note 2: Test condition: Device mounted on 2” x 2” FR-4 substrate PCB, 2oz copper, with minimum recommended
pad on top layer and thermal vias to bottom layer ground plane.
Note 3: The device is not guaranteed to function outside its operating conditions.

AN_SY8089/A Rev. 0.9A

Silergy Corp. Confidential- Prepared for Customer Use Only 4

SY8089/8089A

Efficiency (%)

Efficiency (%)

Efficiency (%)

Typical Performance Characteristics

AN_SY8089/A Rev. 0.9A

Silergy Corp. Confidential- Prepared for Customer Use Only 5

SY8089/8089A

AN_SY8089/A Rev. 0.9A

Silergy Corp. Confidential- Prepared for Customer Use Only 6

SY8089/8089A
VOUT

Operation Principle
SY8089 is a synchronous buck regulator IC that
integrates the PWM control, top and bottom switcheson the same die to minimize the switching transition
loss and conduction loss. With ultra low RDS(ON) powerswitches and proprietary PWM control, this regulator
IC can achieve the highest efficiency and the highest
switch frequency simultaneously to minimize theexternal inductor and capacitor size, and thus achieving
the minimum solution footprint.
Short Circuit Protection（SY8089）After the soft start is over, if the output
voltage falls below 40% of the regulation level, IC willturn off both power switches, entering short circuit
protection. It will remain in this state until the IN or EN
voltage is recycled.
(SY8089A) The frequency is folded back to about 30%of the nominal frequency and the current limit is foldedback to 3.0A to prevent the inductor current fromrunaway and to reduce the power dissipation of the IC
under short circuit conditions.
Over-voltage Protection
If the output voltage exceeds 120% of the regulationlevel for more than 20µs, IC will turn off both powerswitches and turn on the discharge switch, entering
over-voltage protection. It will remain in this state until
IN or EN voltage is recycled.

Applications Information
Because of the high integration in the SY8089 IC, theapplication 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 underlight loads, it is desirable to choose large resistancevalues for both R1 and R2. A value of between 10k and
1M is highly recommended for both resistors. If Voutis 1.8V, R1=100k is chosen, then R2 can be calculated
to be 50k.:

0.6V
R2 =R 1 (Ω) .
VOUT -0.6V

AN_SY8089/A Rev. 0.9A

R1FB
GND

R2Input capacitor CIN:
This ripple current through input capacitor is calculatedas:

ICIN_RMS =IOUT × D(1-D)
This formula has a maximum at VIN=2VOUT condition,
where ICIN_RMS=IOUT/2. This simple worst-casecondition is commonly used for DC/DC design.
With the maximum load current at 2.0A. A typical
X5R or better grade ceramic capacitor with 6.3V rating
and more than 1 pcs 22µ F capacitor can handle thisripple current well. To minimize the potential noiseproblem, ceramic capacitor should really be placed
close to the IN and GND pins. Care should be taken tominimize the loop area formed by CIN, and IN/GNDpins
Output capacitor COUT:
The output capacitor is selected to handle the output
ripple noise requirements. Both steady state ripple andtransient 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 with 6.3V rating and greater than 22µF
capacitance.
Output inductor L:
There are several considerations in choosing thisinductor.
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 isthe maximum load current.
The SY8089 regulator IC is quite tolerant of different
ripple current amplitude. Consequently, the final choice

Silergy Corp. Confidential- Prepared for Customer Use Only 7

SY8089/8089Aof 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(1-VOUT/VIN,MAX)2 ⋅ FSW ⋅ L3) The DCR of the inductor and the core loss at theswitching frequency must be low enough toachieve the desired efficiency requirement. It is
desirable to choose an inductor with DCR<50mΩ
to achieve a good overall efficiency.
Enable Operation
Pulling the EN pin low (<0.4V) will shut down thedevice. During shut down mode, the SY8089 shutdown
current drops to lower than 0.1uA. Driving the EN pinhigh (>1.5V) will turn on the IC again.
Load Transient Considerations:
The SY8089 regulator IC integrates the compensation
components to achieve good stability and fast transient
responses. In some applications, adding a 22pF ceramic
cap in parallel with R1 may further speed up the loadtransient responses and is thus recommended forapplications with large load transient step requirements.

AN_SY8089/A Rev. 0.9A

Layout Design:
The layout design of SY8089 regulator is relativelysimple. For the best efficiency and minimum noiseproblems, we should place the following components
close to the IC: CIN, L, R1 and R2.
1) It is desirable to maximize the PCB copper areaconnecting to GND pin to achieve the best thermal andnoise performance. If the board space allowed, aground plane is highly desirable.
2) CIN must be close to Pins IN and GND. The loop
area formed by CIN and GND must be minimized.
3) The PCB copper area associated with LX pin must
be minimized to avoid the potential noise problem.
4) The components R1, R2, and the trace connecting tothe FB pin must NOT be adjacent to the LX net on thePCB layout to avoid the noise problem.
5) If the system chip interfacing with the EN pin has ahigh impedance state at shutdown mode and the IN pin
is connected directly to a power source such as a LiIon
battery, it is desirable to add a pull down 1MΩ resistor
between the EN and GND pins to prevent the noisefrom falsely turning on the regulator at shutdown mode.

Silergy Corp. Confidential- Prepared for Customer Use Only 8

SY8089/8089A
SOT23-5 Package outline & PCB layout design
0.55

1.50 - 1.70

0.80

2.70 - 3.00

2.40

2.80 - 3.10

0.95 TYP

0.30 - 0.50

0.01 - 0.1

0.1 - 0.15

0.25 REF

Recommended Pad Layout

1.0 - 1.3

0.95 TYP

0.3 - 0.6

1.90 TYP

Notes: All dimensions are in millimeters.
All dimensions don’t include mold flash & metal burr.

AN_SY8089/A Rev. 0.9A

Silergy Corp. Confidential- Prepared for Customer Use Only 9

SY8089/8089A
Taping & Reel Specification
1. Taping orientation
SOT23-5
3.9/4.1

7.7/8.3

1.45/1.55

Feeding direction

2. Carrier Tape & Reel specification for packages
ReelWidth

ReelSizePackagetypes

Tapewidth(mm)Pocketpitch(mm)Reel size(Inch)

Reelwidth(mm)Trailerlength(mm)Leader length(mm)

Qty perreel

SOT23-5

847"

8.4

280

160

3000

3. Others: NA

AN_SY8089/A Rev. 0.9A

Silergy Corp. Confidential- Prepared for Customer Use Only 10