As1013

AS1013 300KHz, 23V/2A Step-down Converter GENERAL DESCRIPTION

FEATURES          

The AS1013 is a voltage mode, step-down DC-DC converter that is designed to meet 2A output current and utilizes PWM control scheme that switches with 300KHz fixed frequency. This device includes a voltage reference source, error amplifier, oscillation circuit, P-channel MOSFET etc.

Input Voltage Range: 3.6V to 23V Feedback Voltage: 0.8V ± 2% Low Quiescent Current: 3mA(Typ.) Fixed Operating Frequency: 300KHz(Typ.) Output Current: 2A External ON/OFF Control Low Shutdown Current: 1uA Current Limit & Thermal Shutdown Internal Built-in P-MOSFET Package: SOP-8L

The input voltage range of AS1013 is from 3.6V to 23V, and provides adjustable output voltage range from 0.8V to VIN for customers in application.

The AS1013 provides an enable function that can be controlled by external logic signal and excellent regulation during line or load transient due to the internal compensation. Other features of thermal protection, current limit and short circuit protection are also included. Due to the low Drain-Source resistance of internal power MOSFET, the AS1013 provides a high efficiency step-down application. It can also operate with a maximum duty cycle of 100% for use in low drop-out conditions.

APPLICATIONS    

LCD TV/Monitor Storage Device Communication Device Wireless Application

TYPICAL APPLICATION CIRCUIT

100

Efficiency vs Load Current

95

Vin

4

DC12V Cin 330uF ROCSET 3K

2

SW

IN

5, 6

AS1013 EN OCSET 3

FB GND 7, 8

1

L1 33uH R1 6.8K

R2 1.3K

Vout 5V/2A Cout 330uF

Efficiency (%)

D1 SK34

VOUT=5.0V

90 85 VOUT=3.3V

80 75 70 65

VIN=12V L=15uH

60 55 50 0

0.5

1

1.5

2

Load Current (A)

AS1013 rev2.4 05/05/2015

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1

AS1013 300KHz, 23V/2A Step-down Converter PIN CONFIGURATION TOP VIEW (SOP-8L) FB

1

8

GND

EN

2

7

GND

OCSET

3

6

SW

IN

4

5

SW

PIN

SYMBOL

FUNCTION

1

FB

Feedback Input. Connect this pin to

2

EN

3

OCSET

4

IN

5, 6

SW

Switching Output. Connect a LC filter from this pin to the output load and rectifier diode to the ground.

7, 8

GND

Ground.

a resistor divider to set the output voltage.

Enable Control. Float this pin or drive it to low level to turn off this device, drive it to high level to turn on this device. If this feature is not needed, connect this pin to IN pin directly.

Add an external resistor from this pin to IN pin to set peak current.

Power Supply Input. A suitably large capacitor must be connected from this pin to ground to bypass noise on the input of the IC.

BLOCK DIAGRAM IN

4 0.8V VOLTAGE REFERENCE

300K OSC

THERMAL SHUTDOWN

0.8V

FB

EN

1

2

AS1013 rev2.4 05/05/2015

+ ERROR AMP -

ENABLE CONTROL

+

OUTPUT DRIVER CONTROL

PWM CMP

5

SW

6

SW

INTERNAL SOFT START

3

7

8

OCSET

GND

GND

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2

AS1013 300KHz, 23V/2A Step-down Converter ORDER INFORMATION

AS1013KBT Packing: T=T/R Package: B = SOP-8L Operating Temperature: K = -40°C ~ +125°C Part Number

ABSOLUTE MAXIMUM RATINGS1)

(TA=25°C)

Parameter

Symbol

Supply Voltage Switch Output Voltage Output Source Current Feedback Voltage Enable Voltage Power Dissipation

Rating

VIN VSW IOUT VFB VEN PD ƟJA ƟJC TJ TST

Package Thermal Resistance2) Junction Temperature Storage temperature Range

-0.3 to 25 -0.3 to VIN +0.3 2 -0.3 to VIN -0.3 to VIN +0.3 650 60 20 150 -55~+125

Unit

V V A V V mW °C/W °C/W °C °C

RECOMMENDED OPERATING CONDITIONS3) Parameter

Supply Voltage Operating Temperature

Symbol VIN TA

Min 3.6 -40

Max

Unit

23 +125

V °C

NOTEs: 1) Exceeding these ratings may damage the device.

2) Measure on approximately 1’’square of 1 oz copper.

3) The device is not guaranteed to function outside of its operating conditions.

AS1013 rev2.4 05/05/2015

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3

AS1013 300KHz, 23V/2A Step-down Converter ELECTRICAL CHARACTERISTICS (TA=25°C) VIN = 12V, TA = 25°C Unless otherwise noted.

Parameter

Feedback Voltage

Symbol

Oscillation Frequency

fOSC

ILOAD=0.1A VIN=12V, VOUT=5V, ILOAD=5A VIN=5V, VOUT=3.3V, ILOAD=5A VIN=3.6V~23V, ILOAD=0.2~5A

Frequency of SCP

fSCP

VIN=3.6V~23V

Efficiency

Duty Cycle Over Current Protection PFET RDS(ON)

VFB

Conditions

ɳ

D IOCP RDS(ON)-P

Min

Max

Unit

0.8 90 88 300

0.816 360

30

50

70

VFB=0V force driver on

-

100

-

VFB=1.5V force driver off

-

0

-

VIN=5V, VFB=0V

-

160

180

VIN=12V, VFB=0V

-

100

120

-

3

10

mA

VEN=0V

-

1

10-

uA

Regulator OFF

-

Regulator ON

2.0

Regulator OFF

-

1

-

Regulator ON

-

20

-

VIN=3.6V~23V, VFB=1.5V force

0.784 240

Typ.

V

% KHz KHz % mΩ

Quiescent Current

IQ

Shutdown Current

ISD

EN Threshold Voltage

VEN

EN Bias Current

IEN

FB Bias Current

IFB

ILOAD=0.2A

-

0.1

0.5

uA

IOCSET

ILOAD=0.2A

75

90

105

uA

OCSET Bias Current

driver off

1.3

0.8

V

-

uA

Line Regulation

VIN=3.6V~23V, ILOAD=0.2A

-

2

-

%

Load Regulation

ILOAD=0.2~5A

-

0.1

-

%

Over Temperature Shutdown Over Temperature Shutdown Hysteresis

AS1013 rev2.4 05/05/2015

TSD

150

°C

THYS

25

°C

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4

AS1013 300KHz, 23V/2A Step-down Converter TYPICAL PERFORMANCE CHARACTERISTICS

VIN = 12V, L=15uH, CIN =330uF, COUT =330uF, TA = 25°C Unless otherwise noted.

Efficiency vs Load Current

100 95

5.20 VOUT=5.0V

5.10 Output Voltage (V)

Efficiency (%)

90 85 VOUT=3.3V

80 75 70 65

VIN=12V L=15uH

60 50 0.5

1

5.00 4.90 4.80 VOUT=5.0V

4.70 4.60

55 0

Output Voltage vs Load Current

1.5

4.50

2

0

0.5

Load Current (A)

Oscillator Frequency (KHz)

Output Voltage (V)

5.10 5.00 4.90 4.80 IOUT=0.5A

4.60 4.50 9

12

15

18

21

24

Supply Voltage (V)

AS1013 rev2.4 05/05/2015

2

Oscillator Frequency vs Supply Voltage

300

4.70

1.5

Load Current (mA)

Output Voltage vs Supply Voltage

5.20

1

290 280 270 260 250

IOUT=0.5A

240 230 9

12

15

18

21

24

Supply Voltage (V)

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5

AS1013 300KHz, 23V/2A Step-down Converter MARKING INFORMATION 8

7

6

5

1013 1206K

Pin1 1

2

3

1013: Part Number

4

K: Internal Code 06: Week (0~52) 12: Year (11=2011,12=2012ďźŒ...)

APPLICATION INFORMATION

OUTPUT VOLTAGE PROGRAMMING This device develops a band-gap between the feedback pin and ground pin. Therefore, the output voltage can be formed by R1 and R2. Use 1% metal film resistors for the lowest temperature coefficient and the best stability. Select lower resistor value to minimize noise pickup in the sensitive feedback pin, or higher resistor value to improve efficiency.

The output voltage is given by the following formula:

đ?‘‰đ?‘‰đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚ = đ?‘‰đ?‘‰đ??šđ??šđ??šđ??š Ă— ďż˝1 + Where VFB=0.8V SW

đ?‘…đ?‘…1 ďż˝ đ?‘…đ?‘…2

GND 7,8

R2

_

SHORT CIRCUIT PROTECTION This device includes short circuit protection. When the output is shorted to ground, the protection circuit will be triggered and force the oscillation frequency down to approximately 50KHz. The oscillation frequency will return to the normal value once the output voltage or the feedback voltage rises above 0V.

AS1013 rev2.4 05/05/2015

IN

ROCSET GND 7,8

Where : IPK: Peak Current IOCSET: OCSET Pin Bias Current RDS(ON): Internal MOSFET ON-Resistance

1 +

4

đ??źđ??źđ?‘ƒđ?‘ƒđ?‘ƒđ?‘ƒ = (đ??źđ??źđ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚ Ă— đ?‘…đ?‘…đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚ )/đ?‘…đ?‘…đ??ˇđ??ˇđ??ˇđ??ˇ(đ?‘‚đ?‘‚đ?‘‚đ?‘‚) )

VOUT

5,6

VFB

VIN

OCSET 3

R1 FB

PEAK CURRENT SETTING This device reserves OCSET pin to set the switching peak current.

In general, the peak current must be 1.5 times of the continuous output current. It can be calculated as below:

DELAY START-UP The following circuit uses the EN pin to provide a time delay between the input voltage is applied and the output voltage comes up. As the instant of the input voltage rises, the charging of capacitor CDELAY pulls the EN pin low, keeping the device off.

Once the capacitor voltage rises above the EN pin threshold voltage, the device will start to operate.

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6

AS1013 300KHz, 23V/2A Step-down Converter

VIN

4

RDELAY + CDELAY

2

The tr, tf and QGate are the rising, falling time, and gate charge of the internal power switch. The typical value of (tr+tf) is approximately 50ns, and the QGate is approximately 15nC. The VGS is approximately equal VIN.

IN

EN

VEN -

GND 7,8

For example, setting at VIN=12V, RDELAY=100K, CDELAY=0.1uF. The start-up delay time can be calculated as below: T VC =VIN × �1-e- t � >VEN

The value of junction to case thermal resistance θJC is also popular to users. This thermal parameter is convenient for users to estimate the internal junction operated temperature of packages while IC operating. The operated junction temperature can be calculated by the following formula:

Where: VC is Capacitor Voltge VEN =1.3V(Typ.); EN pin threshold voltage T=Delay time t = RDELAY X CDELAY This feature is useful in situations where the input power source is limited in the amount of current it can deliver. It allows the input voltage to rise to a higher voltage before the device starts operating.

THERMALL CONSIDERATIONS Thermal protection limits total power dissipation in this device.

When the junction temperature reaches approximately 150ÂşC, the thermal sensor signals the shutdown logic turning off this device.

The thermal sensor will turn this device on again after the devices’ junction temperature cools by 25ºC. For continuous operation, do not exceed the maximum operation junction temperature 125ºC. the power dissipation across this device can be calculated by the following formula:

1 đ?‘ƒđ?‘ƒđ??ˇđ??ˇ = (đ??źđ??źđ??żđ??żđ??żđ??żđ??żđ??żđ??żđ??ż ) Ă— đ?‘…đ?‘…đ??ˇđ??ˇđ??ˇđ??ˇ(đ?‘‚đ?‘‚đ?‘‚đ?‘‚) Ă— đ??ˇđ??ˇ + Ă— đ?‘‰đ?‘‰đ??źđ??źđ??źđ??ź Ă— đ??źđ??źđ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚ 2 Ă— ďż˝đ?‘Ąđ?‘Ąđ?‘&#x;đ?‘&#x; + đ?‘Ąđ?‘Ąđ?‘“đ?‘“ ďż˝ Ă— đ?‘“đ?‘“đ?‘†đ?‘† +đ?‘„đ?‘„đ??şđ??şđ??şđ??şđ??şđ??şđ??şđ??ş Ă— đ?‘‰đ?‘‰đ??şđ??şđ??şđ??ş Ă— đ?‘“đ?‘“đ?‘†đ?‘† + đ??źđ??źđ?‘„đ?‘„ Ă— đ?‘‰đ?‘‰đ??źđ??źđ??źđ??ź

Where: D: Duty Cycle Fs: Switching Frequency VGS: MOSFET Gate Voltage IQ: Quiescent Current AS1013 rev2.4 05/05/2015

đ?‘ƒđ?‘ƒđ??ˇđ??ˇ(đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ ) = (đ?‘‡đ?‘‡đ??˝đ??˝ + đ?‘‡đ?‘‡đ??´đ??´ )/đ?œƒđ?œƒđ??˝đ??˝đ??˝đ??˝

Where TJ –TA is the temperature difference between the die junction and surrounding environment, θJA is the thermal resistance from the junction to the surrounding environment.

T > 1.147ms

2

The maximum power dissipation of this device depends on the thermal resistance of the IC package and PCB layout, the temperature difference between the die junction and ambient air, and the rate of airflow. The maximum power dissipation can be calculated by the following formula:

đ?‘‡đ?‘‡đ??˝đ??˝ = đ?‘‡đ?‘‡đ??śđ??ś + đ?‘ƒđ?‘ƒđ??ˇđ??ˇ Ă— đ?œƒđ?œƒđ??˝đ??˝đ??˝đ??˝

Tc is the package case temperature measured by thermal sensor.

Therefore it’s easy to estimate the junction temperature by any condition.

There are many factors affect the thermal resistance. Some of these factors include trace width, copper thickness, total PCB copper area, and etc.

For the best thermal performance, wide copper traces and generous amounts of PCB copper should be used in the board layout. It further improve thermal characteristics are needed, double sided and multi-layer PCB with large copper areas and airflow will be recommended.

LAYOUT CONSIDERATIONS PC Board layout is very important, especially for switching regulators of high frequencies and large peak currents. A good layout minimizes EMI on the feedback path and provides best efficiency. The following layout guides should be used to ensure proper operation of the device.

1. The power charge path that consists of the IN trace, the SW trace, external inductor and the GND trace should be kept wide and as short as possible.

2. The power discharge path that consists of the SW trace, external inductor, external diode and the GND trace should be kept wide and as short as possible.

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7

AS1013 300KHz, 23V/2A Step-down Converter 3.

4.

5.

The feedback path of Voltage divider should be close to the FB pin and keep noisy traces away; also keep them separate using grounded copper.

The (+) plates of input capacitors should be close to the regulator.

Keep the (-) plates of input and output capacitors as close as possible.

(4) Calculate the minimum value of inductor use maximum input voltage. That is the worst case condition because it gives the maximum ∆IL-

đ??żđ??ż

≼

[đ?‘‰đ?‘‰đ??źđ??źđ??źđ??ź(đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ ) − đ??źđ??źđ??żđ??żđ??żđ??żđ??żđ??żđ??żđ??ż Ă— ďż˝đ?‘…đ?‘…đ??ˇđ??ˇđ??ˇđ??ˇ(đ?‘‚đ?‘‚đ?‘‚đ?‘‚) + đ?‘…đ?‘…đ??żđ??ż ďż˝ − đ?‘‰đ?‘‰đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚ ] Ă— đ??ˇđ??ˇđ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ ∆đ??źđ??źđ??żđ??ż Ă— đ?‘“đ?‘“đ?‘†đ?‘†

This formula can be simplified to

COMPONENT SELECTION

[đ?‘‰đ?‘‰đ??źđ??źđ??źđ??ź(đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ ) − đ?‘‰đ?‘‰đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚ ] Ă— đ??ˇđ??ˇđ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ ∆đ??źđ??źđ??żđ??ż Ă— đ?‘“đ?‘“đ?‘†đ?‘†

1. INDUCTOR SELECTION The conduction mode of power stage depends on input voltage, output voltage, output current, and the value of the inductor.

Select an inductor to maintain this device operating in continuous conduction mode(CCM). The minimum value of inductor can be determined by the following procedure.

đ??żđ??ż ≼

(1). Calculate the minimum duty ratio:

(5) Calculate the inductor peak current and choose a suitable inductor to prevent saturation.

đ??ˇđ??ˇđ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ =

đ?‘‰đ?‘‰đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚ + đ??źđ??źđ??żđ??żđ??żđ??żđ??żđ??żđ??żđ??ż Ă— đ?‘…đ?‘…đ??żđ??ż + đ?‘‰đ?‘‰đ??šđ??š đ?‘‡đ?‘‡đ?‘‚đ?‘‚đ?‘‚đ?‘‚ = đ?‘‰đ?‘‰đ??źđ??źđ??źđ??ź(đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ ) − đ??źđ??źđ??żđ??żđ??żđ??żđ??żđ??ż Ă— đ?‘…đ?‘…đ??ˇđ??ˇđ??ˇđ??ˇ(đ?‘‚đ?‘‚đ?‘‚đ?‘‚) + đ?‘‰đ?‘‰đ??šđ??š đ?‘‡đ?‘‡đ?‘†đ?‘†

Where RL is the DC resistance of external inductor, VF is the forward voltage of external diode, and TS is the switching period.

This formula can be simplified to

đ??ˇđ??ˇđ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ = 0≤D≤1

��������

đ?‘‰đ?‘‰đ??źđ??źđ??źđ??ź(đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ )

=

������ ����

(2). Define a value of minimum current that is approximately 10%~30% of full load current to maintain continuous conduction mode, usually referred to as the critical current(ICRIT).

đ??źđ??źđ??śđ??śđ??śđ??śđ??śđ??śđ??śđ??ś = đ?›żđ?›ż Ă— đ??źđ??źđ??żđ??żđ??żđ??żđ??żđ??żđ??żđ??ż đ?›żđ?›ż = 0.1~0.3

(3) Calculate the inductor ripple current (∆IL). In steady state conditions, the inductor ripple current increase, (∆IL+) during the ON time and the current decrease, (∆IL-) during the OFF time muse be equal.

∆đ??źđ??źđ??żđ??ż = 2 Ă— đ??źđ??źđ??śđ??śđ??śđ??śđ??śđ??śđ??śđ??ś AS1013 rev2.4 05/05/2015

The higher value inductor results in lower output ripple current and ripple voltage. It also reduces the conduction loss. But higher value inductor requires larger physical size and cost.

đ??źđ??źđ??żđ??ż(đ?‘ƒđ?‘ƒđ?‘ƒđ?‘ƒđ?‘ƒđ?‘ƒđ?‘ƒđ?‘ƒ ) = đ??źđ??źđ??żđ??żđ??żđ??żđ??żđ??żđ??żđ??ż +

∆đ??źđ??źđ??żđ??ż 2

Coil inductors and surface mount inductors are all available. The surface mount inductors can reduce the board size but they are more expensive and its larger DC resistance results in more conduction loss. The power dissipation is due to the DC resistance can be calculated as below: 2 đ?‘ƒđ?‘ƒđ??ˇđ??ˇ_đ??źđ??źđ??źđ??źđ??źđ??źđ??źđ??źđ??źđ??źđ??źđ??źđ??źđ??źđ??źđ??ź = đ??źđ??źđ??żđ??żđ??żđ??żđ??żđ??żđ??żđ??ż Ă— đ?‘…đ?‘…đ??żđ??ż

2. OUTPUT RECTIFIER DIODE SELECTION The rectifier diode provides a current path for the inductor current when the internal power switch of the converter turns off. The best solution is schottky diode, and some parameters about the diode must be take care as below: (1) The forward current rating of diode must be higher than the continuous output current.

(2) The reverse voltage rating of diode must be higher than the maximum input voltage.

(3) The lower forward voltage of diode will reduce the conduction loss.

(4) The faster reverse recovery time of diode will reduce the switching loss, but it is very small compared to conduction loss.

(5) The power dissipation can be calculated by the forward voltage and output current for the time that the diode is conducting.

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8

AS1013 300KHz, 23V/2A Step-down Converter đ?‘ƒđ?‘ƒđ??ˇđ??ˇ_đ??ˇđ??ˇđ??ˇđ??ˇđ??ˇđ??ˇđ??ˇđ??ˇđ??ˇđ??ˇ = đ??źđ??źđ??żđ??żđ??żđ??żđ??żđ??żđ??żđ??ż Ă— đ?‘‰đ?‘‰đ??šđ??š Ă— (1 − đ??ˇđ??ˇ)

3. OUTPUT CAPACITOR SELECTION The functions of the output capacitor are to store energy and maintain the output voltage. The low ESR capacitors are preferred to reduce the output ripple voltage and conduction loss.

The output ripple voltage can be calculated as below:

∆đ?‘‰đ?‘‰đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚ = ∆đ??źđ??źđ??żđ??ż Ă— (đ??¸đ??¸đ??¸đ??¸đ??¸đ??¸_đ??śđ??śđ??śđ??śđ??śđ??śđ??śđ??ś +

1

8Ă—đ?‘“đ?‘“ đ?‘†đ?‘† Ă—đ??śđ??śđ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚

)

(1). When low ESR ceramic capacitor is used as output capacitor, the output ripple voltage due to the ESR can be ignored results in all the output ripple voltage is due to the capacitance. Choose suitable capacitors must define the expectative value of output ripple voltage first.

The minimum capacitance can be determined by the switching frequency, the output ripple current, and the expectative output ripple voltage. The above formula can be simplified to:

đ??śđ??śđ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚ (đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€) ≼

∆đ??źđ??źđ??żđ??ż 8 Ă— đ?‘“đ?‘“đ?‘†đ?‘† Ă— ∆đ?‘‰đ?‘‰đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚

Besides, the compensation components must be used to stabilize the control loop in some applications, such as using a 1nF ceramic capacitor across the high side resistor of the output voltage divider.

(2) the ESR of the aluminum electrolytic or tantalum output capacitor is an important parameter to determine the output ripple voltage. But the manufacturers usually do not specify ESR in the specifications. Assuming the capacitance is enough results in the output ripple voltage is due to the capacitance can be ignored, the ESR should be limited to achieve the expectative output ripple voltage. The maximum ESR can be calculated as below:

đ??¸đ??¸đ??¸đ??¸đ??¸đ??¸_đ??śđ??śđ??śđ??śđ??śđ??śđ??śđ??ś ≤

∆đ?‘‰đ?‘‰đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚ ∆đ??źđ??źđ??żđ??ż

50~80 Ă— 10−6 đ??¸đ??¸đ??¸đ??¸đ??¸đ??¸_đ??śđ??śđ??śđ??śđ??śđ??śđ??śđ??ś

AS1013 rev2.4 05/05/2015

đ??źđ??źđ?‘…đ?‘…đ?‘…đ?‘…đ?‘…đ?‘…_đ??śđ??śđ??śđ??śđ??śđ??śđ??śđ??ś =

∆đ??źđ??źđ??żđ??ż

√12

= ∆đ??źđ??źđ??żđ??ż Ă— 0.289

đ?‘ƒđ?‘ƒđ??ˇđ??ˇ_đ??śđ??śđ??śđ??śđ??śđ??śđ??śđ??ś = (đ??źđ??źđ?‘…đ?‘…đ?‘…đ?‘…đ?‘…đ?‘… đ??śđ??śđ??śđ??śđ??śđ??śđ??śđ??ś )2 Ă— đ??¸đ??¸đ??¸đ??¸đ??¸đ??¸_đ??śđ??śđ??śđ??śđ??śđ??śđ??śđ??ś

(4) Besides, the capacitors’ ESL maybe causes ringing in the low frequency region. Choose low ESL capacitors, limiting lead length of PCB and capacitor to replace with a larger one will reduce the ringing phenomenon.

4. INPUT CAPACITOR SELECTION The input capacitor is required to supply current to the regulator and maintain the DC input voltage. Low ESR capacitors are preferred those provide the better performance and the less ripple voltage.

(1). The input capacitors need and adequate RMS current rating.

It can be calculated by the following formula and should not be exceeded.

đ??źđ??źđ?‘…đ?‘…đ?‘…đ?‘…đ?‘…đ?‘…_đ??śđ??śđ??śđ??śđ??śđ??ś = đ??źđ??źđ??żđ??żđ??żđ??żđ??żđ??żđ??żđ??ż (đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ ) Ă— ďż˝đ??ˇđ??ˇ Ă— (1 − đ??ˇđ??ˇ) This formula has a maximum at VIN=2VOUT. That is the worst case and the above formula can be simplified to:

đ??źđ??źđ?‘…đ?‘…đ?‘…đ?‘…đ?‘…đ?‘…_đ??śđ??śđ??śđ??śđ??śđ??ś =

đ??źđ??źđ??żđ??żđ??żđ??żđ??żđ??żđ??żđ??ż (đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ ) 2

Therefore, choose a suitable capacitor at input whose ripple current rating must greater than half of the maximum load current.

Choose the output capacitance by the average value of the RC product as below:

đ??śđ??śđ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚đ?‘‚ ≈

(3) The ESR and ripple current results in power dissipation in the capacitor. It will increase the internal temperature. Usually, the capacitors’ manufactures specify ripple current ratings and should not be exceeded to prevent excessive temperature shorten the life time. Choose a smaller inductor causes higher ripple current which maybe result in the capacitor overstress. The RMS ripple current flowing through the output capacitor and power dissipation can be calculated as below:

(2) The input ripple voltage mainly depends on the input capacitors’ ESR and its capacitance. Assuming the input current of the regulator is constant, the required input capacitance for a given input ripple voltage can be calculated as below:

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AS1013 300KHz, 23V/2A Step-down Converter

đ??śđ??śđ??źđ??źđ??źđ??ź =

đ??źđ??źđ??żđ??żđ??żđ??żđ??żđ??żđ??żđ??ż (đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ ) Ă— đ??ˇđ??ˇ Ă— (1 − đ??ˇđ??ˇ) đ?‘“đ?‘“đ?‘†đ?‘† Ă— (∆đ?‘‰đ?‘‰đ??źđ??źđ??źđ??ź − đ??źđ??źđ??żđ??żđ??żđ??żđ??żđ??żđ??żđ??ż (đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€đ?‘€ ) Ă— đ??¸đ??¸đ??¸đ??¸đ??¸đ??¸_đ??śđ??śđ??śđ??śđ??śđ??ś

If using aluminum electrolytic or tantalum input capacitors, parallel connecting a 0.1uF ceramic capacitor as close to the IN pin of regulator as possible. If using ceramic capacitor, make sure the capacitance is enough to prevent the excessive input ripple current.

AS1013 rev2.4 05/05/2015

(3) The power dissipation of input capacitor causes a small conduction loss can be calculated as below:

đ?‘ƒđ?‘ƒđ??ˇđ??ˇ_đ??śđ??śđ??śđ??śđ??śđ??ś = (đ??źđ??źđ?‘…đ?‘…đ?‘…đ?‘…đ?‘…đ?‘… đ??śđ??śđ??śđ??śđ??śđ??ś )2 Ă— đ??¸đ??¸đ??¸đ??¸đ??¸đ??¸_đ??śđ??śđ??śđ??śđ??śđ??ś

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10

AS1013 300KHz, 23V/2A Step-down Converter PACKAGE INFORMATION

SOP-8L

0.189(4.80) 0.197(5.00)

0.024(0.61)

8

0.050(1.27)

5 0.063(1.60)

0.150(3.80) 0.157(4.00)

PIN1 ID

0.228(5.80) 0.244(6.20)

0.213(5.40)

4

1

RECOMMEND LAND PATTERN

TOP VIEW

0.053(1.35) 0.069(1.75) 0.013(0.33) 0.020(0.51)

0.050(1.27) BSC

0.0075(0.19) 0.0098(0.25)

0.004(0.10) 0.010(0.25)

SEE DETAIL “A”

SIDE VIEW

FRONT VIEW

0.010(0.25) X 45º 0.020(0.50)

GAUGE PLANE 0.010(0.25) BSC

0º~8º

0.016(0.41) 0.050(1.27)

DETAIL “A”

NOTE: 1. CONTROL DIMENSION IS IN INCHES. DEMENSION IN BRACKET IS IN MILLIMETERS. 2. PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 3. PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. 4. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.004" INCHES MAX. 5. DRAWING CONFORMS TO JEDEC MS-012, VARIATION AA. 6. DRAWING IS NOT TO SCALE.

NOTICE: The information in this document is subject to change without notice. Please contact AniSem for current specifications. Users should warrant and guarantee that third party Intellectual Property rights are not infringed upon when integrating AniSem products into any application. AniSem will not assume any legal responsibility for any said applications.

AS1013 rev2.4 05/05/2015

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11