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Application Notes: AN_SY8204

High Efficiency Fast Response, 4A, 30V Input

Synchronous Step Down Regulator

General Description Features

SY8204 develops a high efficiency synchronous step-down DC-DC converter capable of delivering 4A

•

Low RDS(ON) for internal switches (top/bottom):

80/50 mΩ

output current. SY8204 operates over a wide input

voltage range from 4.5V to 30V and integrates main

•

4.5-30V input voltage range

switch and synchronous switch with very low R•

Instant PWM architecture to achieve fast transient

DS(ON)

to minimize the conduction loss.

responses

•

External softstart limits the inrush current

SY8204 adopts the proprietary instant PWM

•

Pseudo-constant frequency: 500kHz at heavy loads

architecture to achieve fast transient responses for high

•

4A continuous, 5A peak load current capability

step down applications and high efficiency at light

•

1.5% 0.6V reference

loads. In addition, it operates at pseudo-constant

•

Output over current limit

frequency of 500kHz under continous conduction mode

•

Output short circuit protection with current fold

to minimize the size of inductor and capacitor.

back

Ordering Information

•

Thermal shutdown and auto recovery

•

RoHS Compliant and Halogen Free

SY8204□(□□)□•

Compact package: SO8E

Temperature CodePackage Code

Applications

Optional Spec Code•

LCD-TV

-

Temperature Range:40°C to 85°C

•

SetTop Box

•

Notebook

•

High power AP router

•

LCD Monitor

•

DVR/NVR

•

NAS

Typical Applications

AN_SY8204 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 1

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AN_SY8204

Pinout (top view)

AN_SY8204 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 2

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AN_SY8204

Electrical Characteristics

(VIN = 12V, VOUT = 5V, COUT = 47uF, TA = 25°C, IOUT = 1A unless otherwise specified)

Sil

AN_SY8204 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 3

ergNote 2:

θJA 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. Paddle of SO8E packages is the case position for

θJC

measurement.

Note 3: The device is not guaranteed to function outside its operating conditions.

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Corp.

ConNote 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.

fidentialParameter

Input Voltage Range

Quiescent Current

Shutdown Current

Feedback Reference

Voltage

FB Input Current

Top FET RON

Bottom FET RON

Bottom FET Current

Limit

EN falling threshold

EN threshold hysteresis

Input UVLO threshold

UVLO hysteresis

Oscillator Frequency

Min ON Time

Min OFF Time

Internal LDO Output

Thermal Shutdown

Temperature

Thermal Shutdown

Hysteresis

Symbol

VIN

IQ

ISHDN

VREF

IFB

RDS(ON)1

RDS(ON)2

ILIM

VENL

VEN,HYS

VUVLO

VHYS

FOSC

VVCC

TSD

TSD,HYS

Test Conditions

IOUT=0,

VFB=VREF*105%

EN=0

VFB=VCC

IOUT=200mA

VIN=4V

Min

4.5

0.591

-50

5

1.1

3.2

Typ

200

5

0.6

80

50

Max

30

10

0.609

50

1.3

4

3.4

Unit

V

µA

µA

V

nA

mΩ

mΩ

A

V

V

V

V

MHz

ns

ns

V

°C

°C

-Prepared

for

ry1.2

0.1

0.2

0.5

80

120

3.3

160

20

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AN_SY8204

Function Block

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AN_SY8204

Typical Performance Characteristics

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AN_SY8204 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 5

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AN_SY8204

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Short Circuit Protection(VIN=12V, VOUT=1.8V, Open to Short)VOUT

2V/divepa-Prtialonfiden

IL

2A/divreVOUT

5V/divVOUT

2V/divIL

2A/divIL

2A/divTime (2ms/div)d

foShort Circuit Protection(VIN=12V, VOUT=1.8V, 4A to Short)Time (2ms/div)

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AN_SY8204 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 6

AN_SY8204

Operation

SY8204 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 highest efficiency and the highest

switch frequency simultaneously to minimize the

external inductor and capacitor size, and thus achieving

the minimum solution footprint.

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Because of the high integration in the SY8204 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 R1and 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:

on

R2=0.6VR1.

VOUT−0.6Vorp.0.6VFB

R2GND

Input capacitor CIN:

The ripple current through input capacitor is calculated

as：

I=I⋅D(1−D).

CIN_RMSSil

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

AN_SY8204 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 7

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foApplications Information

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rySY8204 provides protection functions such as cycle by

cycle current limiting and thermal shutdown protection.

SY8204 will sense the output voltage conditions for the

fault protection.

pins.

In this case, a 10uF 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 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:

V(1−VOUT/VIN,MAX)

L=OUTFSW×IOUT,MAX×40%

where Fsw is the switching frequency and IOUT,MAX is

the maximum load current.

The SY8204 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<10mΩ

to achieve a good overall efficiency.

Soft-start

Connect a capacitor from softstart programming pin to

ground to program the softstart time.

Tss=Css*0.6V/10uA

Enable Operation

Pulling the EN pin low (<1.2V) will shut down the

device. During shutdown mode, the SY8204

shutdown current drops to lower than 5uA, Driving the

EN pin high (>1.3V) will turn on the IC again.

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AN_SY8204

External Boostrap Cap

This capacitor provides the gate driver voltage for

internal high side MOSEFET. A 100nF low ESR

ceramic capacitor connected between BS pin and LX

pin is recommended.

VCC LDO

The 3.3V internal reference. This pin should be

bypassed to ground with a 1uf ceramic capacitor. This

pin may be used with an external DC load of 20mA or

less

.

AN_SY8204 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 8

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AN_SY8204

SO8E Package outline & PCB layout design

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Recommended Pad Layout

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Notes: All dimensions are in millimeters.

All dimensions don’t include mold flash & metal burr.

AN_SY8204 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 9

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