asd3003 - goldengate-ic.com

ASD3003

1.5A, 30V, 450kHz Asynchronous Step-Down Regulator

Golden Gate Integrated Circuits, Inc. of 13 REV: 1.0 2012.08.02

www.goldengate-ic.com Copyright © 2012 Golden Gate Integrated Circuits, Inc.


General Description

The ASD3003 is a high efficiency, non-synchronous step down regulator delivering up to 1.5A of output current making it ideal for medium to heavy load applications. It is designed to operate with wide input voltage range of 4.5 to 30V while maintaining 1.1mA of typical supply current at no load condition. The output voltage is set via two external resistors to as low as 1.25V.

The regulator operates at fixed 450kHz of switching frequency ensuring low output ripple across the entire load. An independent Enable pin provides electrical On/Off of the regulator. When connected to logic low, the regulator shuts down and consumes very low current. The internal feedback loop compensation offers excellent transient response, minimizes bill of materials cost, and reduces the design complexity for easy design in solution.

The device provides under-voltage lockout to prevent startup until input voltage reaches 3.9V; an internally set slow startup circuit limits the inrush current. In addition, the device includes output short circuit and over temperature protection to safeguard the device under fault conditions.

The ASD3003 is offered in thermally enhanced SOIC-8 and DFN3X3-8 packages, and it is rated for -40 to +85 °C temperature range.

Features

VIN range: 4.5 – 30V

Adjustable VOUT as low as 1.25V

1.5A maximum output current

450kHz switching frequency

100% Duty cycle capability

1.1mA typical supply current

Excellent line and load regulation

Enable (EN) pin for electrical on/off

Internal compensation

Internal Soft-Start

Undervoltage lockout

Cycle by cycle & Hiccup Mode Current limit

protection

Thermal shutdown protection

-40°C to +85°C temperature range

Available in SOIC-8 EDP and DFN3X3-8 packages

RoHS & WEEE compliant

Applications

Communication

DVD, Blue Ray

LCD-TV and LCD monitor

Infotainment

Set-Top-Box

High current point of load

Typical Application

ASD3003

VOUT=5VVIN= 12V

VIN LX

GND

EN FB

CIN=

10µF

COUT=

22µF

R1=

30K

R2=

10K

L=10µH

D1

B340C

ASD3003




Pin Description

Symbol Description

LX Switching node - connect an inductor between this pin and the output capacitor.

PVIN Input supply Voltage for the converter power stage. Connect a 10µF capacitor from this node to ground.

N/C No connection.

FB

Feedback Voltage. A resistor network of two resistors is used to set-up the output voltage connected between Vout and GND. The center tap of the two resistors is connected to FB pin.

EN

Enable pin. It controls the electrical on/off of the device. When connected to logic low, the device shuts off and consumes low supply current. A logic high will resume normal operation

GND Ground connection.

AVIN

Analog supply for the internal circuitry. Connect a resistor and capacitor combination between this pin and ground. Refer to application section.

EP

Expose pad. This is the center bottom side of the package exposed for thermal performance improvement. Connect to the ground plane.

Pin Configuration

SOIC-8 EDP (Top View)

Lx

EN

PVIN

GND

FB

EP

2

3

4

1

5

6

7

8 N/C

N/C

AVIN

Pin Configuration

DFN3X3-8 (Top View)

TOP VIEW1

2

3

EN

8

7

6

AVin

GND

FB 4 5

Lx

NC

PVin

GND

ASD3003




Absolute Maximum Ratings (1)

Maximum Input Supply Voltage ......................................................................................................................... -0.6V to 33V

Enable Voltage ................................................................................................................................................... -0.6V to 33V

Switch node Voltage .......................................................................................................................................... -0.6V to 33V

Feedback Voltage (FB) .................................................................................................................................... .-0.6V to 20V

Recommended Operating Conditions

Input Voltage ......................................................................................................................................................... 4.5 to 30V

Ambient Operating Temperature................................................................................................................... -40°C to +85°C

Thermal Information (2)

SOIC-8 θJA ............................................................................................................................................................ 40˚C/W

DFN3x3- 8 θJA ....................................................................................................................................................... 40˚C/W

Storage Temperature Range ............................................................................................................................. -65 to 150˚C

Lead Temperature (soldering 10s) ............................................................................................................................... 260˚C

Junction Temperature ................................................................................................................................. -40°C to +125°C

Electrical Characteristics

UNLESS OTHERWISE NOTED:

VIN=12V; VOUT=5V; CIN=10µF; COUT=22µF; CFF=22pF; -40˚C≤TA=TJ≤85˚C; TJ(MAX.)= 125C; TYPICAL VALUES ARE TA= 25C

Parameter Symbol Conditions Min. Typ. Max. Units

Under Voltage Lockout UVLO 3.9 V

Feedback Voltage VFB Adjustable VOUT only 1.231 1.25 1.269 V

Feedback bias current IFB_Bias Adjustable VOUT only 10 100 nA

Maximum Output Current IOUT_Max 1.5 A

Load Regulation IOUT= 10mA – 1.5A -1.5 +1.5 %

Line Regulation VIN=4.5 – 30; IOUT=10mA -0.5 +0.5 %

Supply Current ISUP No load 1.1 5.0 mA

Shutdown Current ISHDN VEN= 0V 1.0 800 µA

Saturation Voltage VSAT IOUT= 1A 1.2 V

Oscillator Frequency FOSC. 380 450 520 KHz

Current Limit2 ILIM 1.9 A

Soft start time2 TSS IOUT= 100mA 500 µs

Maximum duty cycle2 DMAX 100 %

Minimum duty cycle2 DMIN 0 %

Enable Threshold Low VEN(L) 1.9 2.2 V

Enable Threshold High VEN(H) 2.7 2.5 V

Input Enable Low Current IEN(L) VEN = V; VEN = 20V 0.25 1.0 µA

Input Enable High Current IEN(H) VEN = 19V; VEN = 20V 1.0 200 µA

Thermal Shutdown TSD 125 C

Thermal Shutdown Hysteresis TSD_HYS 15 C

ASD3003




Notes:

1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device.

2. Measured on approximately 1” square of 1oz copper

3. The ASD3003 is guaranteed to meet performance specifications over the -40°C to +125°C operating temperature range and is assured by design,

characterization, and correlation with statistical process control.

4. Load regulation is measured using pulse techniques with duty cycle <5%.

ASD3003




Typical Characteristics

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.00 0.50 1.00 1.50

Eff

icie

ncy

(%)

Output Current (A)

Load Current vs Efficiency VIN=12V; VOUT=5V

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

4 14 24 34Ou

tpu

t V

olt

ag

e C

han

ge (

%)

Input Voltage (V)

Line Regulation VOUT=5V

1.00

1.05

1.10

1.15

1.20

1.25

1.30

1.35

1.40

5.0 15.0 25.0 35.0

I SU

P

( m

A )

Output Current (A)

Supply current vs Input Voltage

-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.0

10.0E-3 100.0E-3 1.0E+0 10.0E+0Ou

tpu

t V

olt

ag

e C

han

ge (

%)

Output Current (A)

Load Regulation VIN=12V; VOUT=5V

0.0

0.5

1.0

1.5

2.0

2.5

0.0 5.0 10.0 15.0 20.0

I EN

( µ

A )

VEN (V)

Enable Input Current vs Enable Voltage

0

50

100

150

200

250

4 8 12 16 20 24 28 32Sh

utd

ow

n C

urr

en

t (µ

A)

Input Voltage (V)

Shutdown Current vs Input Voltage

ASD3003




Typical Characteristics

Transient Response VIN=12V; VOUT=5V; Load Step= 0.27A; CIN=10µF;

COUT=22µF;CFF=22pF

Enable Startup VIN=12V; VOUT=5V; Load Step= 0.27A; CIN=10µF;

COUT=22µF;CFF=22pF

0.0

1.0

2.0

3.0

4.0

5.0

6.0

1.0 2.0 3.0 4.0

Ou

tpu

t V

olt

ag

e (

V )

Enable Voltage (V)

Enable Voltage vs Output Voltage

Low to High

High to Low

ASD3003




Functional Block Diagram

+

-

Error

AmpVREF

1.25V

FB

PWM

Logic

Over Temperature

Protection

AVIN

Internal

Regulator

+

-

PWM

Comp

450KHz

Oscillator

+-

Under Voltage

Lockout

Soft Start

GND

+

-

Error

AmpVREF

EN

LX

Shutdown

Comparator

PVIN

RSENSE

∑

Current

Limit

Application Hints

Input Capacitor (CIN

)

The ASD3003 has two separate input supplies powering the regulator. The PVIN is used to power the high side switch of the output power stage, and AVIN is used for the rest of the circuit. Since PVIN provides the entire load current each time the switch turns on, it contains all the switching noise. A bulk 10µF capacitor from PVIN to ground is recommended.

The AVIN pin powers the internal LDO and the entire analog circuitry of the regulator. It is important to minimize the switching frequency ripple from PVIN to this pin. A combination of 100Ω resistor and 1µF capacitor from this pin to ground is recommended. Refer to the figure below:

VIN

PVIN

CIN=

10µF

AVIN

R=

100

CIN=

1µF

Figure 1: Filtering power supply

For reliable operation, select bulk capacitors with voltage and current ratings above the maximum input voltage and largest RMS current required by the circuit. Their voltage rating should be at least 1.25 times greater than the maximum input voltage, while a voltage rating of 1.5 times is a conservative guideline. Placement of the capacitor is critical for good high frequency noise rejection. See layout guidelines section for details. Switching frequency ripple is also filtered by ceramic bypass input capacitor.

Output Capacitor (COUT

)

The output capacitor is not only used to filter out the inductor current, but also, enhances the load transient response. The inductor current filtering requirement is a function of the switching frequency and the magnitude of the ripple current. The load transient requirement is a function of the slew rate (di/dt) and the magnitude of load current step. These requirements are generally met with a mix of capacitors and careful layout.

Since ASD3003 is internally compensated, a 22µF ceramic capacitor in conjunction with a 10µH inductor is sufficient for stability and filtering the ripple current. Use only bulk, low-ESR capacitors intended for switching-regulator applications. The bulk capacitor’s ESR will determine the output ripple voltage and the initial voltage drop after a high slew-rate transient.

ASD3003




The transient response is determined by the speed of the control loop and the ability of the output capacitor to provide the initial current of a load transient. However, in most applications, increasing the capacitance over 66µF provides diminishing improvement because the bandwidth of the control loop decreases as the output capacitance increases. If an improved transient performance is required, adding a feed forward capacitance, CFF, will significantly help. Refer to the below circuit:

VOUT=5V

LX

FB

COUT=

44µF

R1=

30K

L=10µH

R2=

10K

CFF=

22PF

Figure 2: Feed forward capacitance When selecting a ceramic capacitor, only X5R and X7R dielectric types should be used. Other types such as Z5U and Y5F have such severe loss of capacitance due to effects of temperature variation and applied voltage, they may provide as little as 20% of rated capacitance in many typical applications.

Always consult the capacitor manufacturer’s data curves before selecting a capacitor. High-quality ceramic capacitors can be obtained from Taiyo-Yuden, AVX, and Murata.

Inductor Selection

The inductor selection is critical to the performance of the ASD3003. The inductor affects stability, transient response and efficiency. A good compromise between physical size, transient response and efficiency is achieved when we set the inductor ripple current ratio between 0.2 and 0.4.

Setting the ripple current to 40% of the full load, we can use the below equation to solve for the inductor:

( )

( )

Once the appropriate value is determined, the component is selected based on the DC current and the peak (saturation) current. Select an inductor that has a DC current rating greater than the full load current of the application. The DC current rating is also reflected in the DC resistance (DCR) specification of the inductor. The inductor DCR should limit the inductor loss to less than 2% of the step down converter output power.

Output Voltage Setting

The adjustable output voltage allows the user to program the output voltage by using an external resistor divider. ASD3003 uses a 1.25V reference voltage at the positive terminal of the error amplifier. To set the voltage, a programming resistor from the feedback pin (FB) to ground must be selected. A 10kΩ resistor is a good selection for a programming resistor R2 (see figure 2). A higher value may result in an excessively sensitive feedback node while a lower value will draw more current and degrade the light load efficiency. The equation for selecting the voltage specific resistor is:

FBO VR

RV *

2

11

The table below provides the resistor values for some common voltages.

R2 R1 VOUT

10kΩ 30kΩ 5.0V

10kΩ 16.6kΩ 3.3V

10kΩ 10kΩ 2.5V

10kΩ 4.4kΩ 1.8V

Table 1: Feedback Resistor Values

Rectifier Selection

The catch diode conducts during the switch off-time. A Schottky diode is recommended for its fast switching times and low forward voltage drop. The catch diode should be chosen so that its current rating is greater than:

ID = IOUT x (1-D) The reverse breakdown rating of the diode must be at least the maximum input voltage plus appropriate margin. To improve efficiency, choose a Schottky diode with a low forward voltage drop.

Soft-start

The ASD3003 has a fixed internal soft-start of 500µs (typ). During soft-start, the error amplifier’s reference voltage ramps from 0.0 V to its nominal value of 1.0 V in

ASD3003




approximately 500µs. This forces the regulator output to ramp in a controlled fashion, which helps reduce inrush current.

Enable

The enable pin provides electrical on/off of the regulator. To assure the regulators will switch on; the EN must be greater than 2.6 volts. The device will shut down when the voltage on the EN pin falls below 2.0 volts. In shutdown, the regulator will consume low current. If the enable function is not needed in a specific application, it may be tied to Vin to keep the device in a continuously on state.

PCB Layout

The following guidelines should be followed to insure proper layout. 1. VIN Capacitor. A low ESR ceramic bypass capacitor

must be placed as close to the IC as possible.

2. Schottky Diode. During the off portion of the switching cycle the inductor current flows through the Schottky diode to the output cap and returns to the inductor through the output capacitor. The trace that connects the output diode to the output capacitor sees a current signal with a very high di/dt. To minimize the associated spiking and ringing, the inductance and resistance of this trace should be minimized by connecting the diode anode to the output capacitor return with a short wide trace.

3. Feedback Resistors. The feedback resistors should be placed as close as possible the IC. Minimize the length of the trace from the feedback pin to the resistors. This is a high impedance node susceptible to interference from external RF noise sources.

4. Inductor. Minimize the length of the SW node trace. This minimizes the radiated EMI associated with the SW node.

5. Ground. The most quiet ground or return potential available is the output capacitor return. The inductor current flows through the output capacitor during both the on time and off time, hence it never sees a high di/dt. The only di/dt seen by the output capacitor is the inductor ripple current which is much less than the di/dt of an edge to a square wave current pulse. This is the best place to make a solid connection to the IC ground and input capacitor. This node is used as the star ground shown in Figure 1. This method of grounding helps to reduce high di/dt traces, and the detrimental effect associated with them, in a step-down converter. The inductance of these traces should always be

minimized by using wide traces, ground planes, and proper component placement.

6. For good thermal performance vias are required to couple the exposed tab of the SO-8 package to the PCB ground plane. The via diameter should be 0.3mm to 0.33mm positioned on a 1.2mm grid.

PC Inductance

High di/dt

ION

IOFF

ION + IOFF

ION + IOFF

ION

IOFF

ION

IOFF

High di/dt trace reduction

“Star Ground”

Figure 3: Step Down Converter Layout

ASD3003




Application Schematic

VOUT=5VVIN= 12V

PVIN LX

GND

EN FB

CIN2=

10µF

COUT=

2 x 22µF

R1=

30K

R2=

10K

L=10µH

D1

B340C

R3=

100

CIN=

10µF

AVIN CFF=

22pFASD3003CIN

1=

220µF

Component Manufacturer Part Number Description

CIN1 Panasonic – ECG P5572-ND CAP ALUM 220UF 50V 20% RADIAL

CIN2 Taiyo Yuden UMK325BJ106KM-T 10µF, 50V, X5R, 1210 Ceramic

COUT Taiyo Yuden LMK212BJ226MG-T CAP CER 22µF 10V X5R 0805

CFF Murata Electronics GRM1885C1H220JA01D CAP CER 22PF 50V 5% C0G 0603

R1 Vishay/Dale CRCW060330K0FKEA RES 30.0K OHM 1/10W 1% 0603 SMD

R2 Vishay/Dale CRCW060310K0FKEA 10KΩ, 0.1W, 0603, 1%

R3 Panasonic – ECG ERJ-3GEYJ100V RES 100 OHM 1/10W 5% 0603 SMD

D1 Diodes Inc. B340LB-13-F 3A; 40V; Schottky Diode

L Murata Electronics LQH88PN100M38 10µH; Isat=3.6A; DCR= 29mΩ; Shielded

Table 2: Bill of Materials

ASD3003




Recommended Board Layout

Top Side

Bottom Side

ASD3003




Ordering Information

Outline Drawing and Landing Pattern – DFN3X3-8

Device Package Output Voltage Packing Method & Quantity

ASD3003M8 SO8EDP Adjustable 2500 Tape & Reel

ASD3003DF3308 DFN3x3-8 Adjustable 2500 Tape & Reel

ASD3003




Outline Drawing and Landing Pattern – SOIC-8

Disclaimer:

The information furnished in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Golden Gate Integrated Circuits (GGIC) for its use. GGIC reserves the right to change circuitry and specifications at any time without notification to the customer.

Golden Gate Integrated Circuits reserves the right to make changes to the information herein for the improvement of the design and

performance without further notice! Customers should obtain the latest relevant information before placing orders and should verify that such

information is complete and current.

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