A7121AE6VR [AITSEMI]

DC-DC CONVERTER BUCK;


型号：	A7121AE6VR
厂家：	AiT Semiconductor
描述：	DC-DC CONVERTER BUCK DC-DC转换器
文件：	总14页 (文件大小：528K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

DESCRIPTION

FEATURES

The A7121A is

synchronous buck regulator using

high efficiency monolithic

constant



High Efficiency: Up to 97%

1MHz Constant Switching Frequency

2.0A Output Current at V_IN=3V

Integrated Main Switch and Synchronous Rectifier

No Schottky Diode Required

2.7V to 6.0V Input Voltage Range

frequency, current mode architecture. Supply current

with no load is 60uA and drops to <1uA in shutdown.

The 2.7V to 6.0V input voltage range makes the

A7121A ideally suited for single Li-Ion, two to four AA

battery-powered applications. 100% duty cycle

provides low dropout operation, extending battery life

in portable systems. PWM pulse skipping mode

operation provides very low output ripple voltage for

noise sensitive applications. Switching frequency is

internally set at 1MHz, allowing the use of small

surface mount inductors and capacitors. The internal

synchronous switch increases efficiency and

eliminates the need for an external Schottky diode.

Low output voltages are easily supported with the

0.6V feedback reference voltage.



Output Voltage as Low as 0.6V

100% Duty Cycle in Dropout

Quiescent Current: 60μA(input < 4.2V)

Slope Compensated Current Mode Control for

Excellent Line and Load Transient Response

Robust protection features, OCP, SCP, TSD

Same BOM L-C passive components for V_IN=5V

to V_OUT= 3.3V, 2.5V, 1.8V, 1.2V, and 1.0V

Shutdown Current <1uA



Internal Soft start Circuitry

Available in SOT-25 and SOT-26 Packages

APPLICATION

The A7121A is available in SOT-25 and SOT-26

packages.



Set Top Box

Portable Instruments

ORDERING INFORMATION

Battery Powered Equipment

Wireless Access Point Router and DSL Modems

Personal and Notebook Computer

Microprocessors and DSP Core Supplies

Digital Still and Video Cameras

Package Type

Part Number

A7121AE5R

A7121AE5VR

A7121AE6R

A7121AE6VR

SOT-25

SPQ: 3,000pcs/Reel

SOT-26

SPQ: 3,000pcs/Reel

TYPICAL APPLICATION

V: Halogen free Package

R: Tape & Reel

Note

AiT provides all RoHS products

Figure 1. Typical Application Circuit

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 1 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

PIN DESCRIPTION

Top View

Symbol

Top View

Pin #

SOT-25

Function

SOT-26

Regulator Enable control input. Drive EN above

1.1V to turn on the part. Drive EN below 0.6V to turn it off. In

shutdown, all functions are disabled drawing <1μA supply current. Do

not leave EN floating.

GND

Ground

Power Switch Output. It is the Switch note connection to inductor.

This pin connects to the drains of the internal P-CH and N-CH

MOSFET switches.

Power supply input pin. Must be closely decoupled to GND with a

22μF or greater ceramic capacitor.

Power Good Indicator. This pin is an open drain logic output.

Connect PG to an external pull-up resistor and get a high level

output. PG is pulled to ground when the output voltage is less than

91.5% of the target output voltage.

Let PG float or connect to ground when don’t use PG function.

Feedback Input Pin. Connect FB to the center point of the external

resistor divider. The feedback threshold voltage is 0.6V.

VIN

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 2 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

ABSOLUTE MAXIMUM RATINGS

V_IN, Input Supply Voltage

EN, V_FBVoltages

-0.3V ~ +7V

-0.3V ~ V_IN+0.3V

±4 kV

SW Voltages

ESD Ratings Human Body Model

Package Thermal Resistance ^NOTE1

θ_JA, SOT-25, SOT-26

220°C/W

55°C/W

θ_JC, SOT-25, SOT-26

Operating Temperature Range

Junction Temperature ^NOTE2

Storage Temperature Range

Lead Temperature (Soldering, 10s)

-40°C ~ 85°C

Internal Limit

-65°C ~ 150°C

+260°C

Stress beyond above listed “Absolute Maximum Ratings” may lead permanent damage to the device. These are stress ratings only and

operations of the device at these or any other conditions beyond those indicated in the operational sections of the specifications are not

implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 3 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

ELECTRICAL CHARACTERISTICS^NOTE3

V_IN=V_EN= 3.6V, T_A= 25°C, unless otherwise noted.

Parameter

Input Voltage Range

Input DC Supply Current

Active Mode

Conditions

Min.

2.7

Typ.

Max.

6.0

Unit

V_FB=0.5V or V_OUT=90%

V_FB=0V, V_IN=4.2V

T_A= +25°C

300

μA

Shutdown Mode

0.1

0.5880 0.6000 0.6120

0.5865 0.6000 0.6135

0.5820 0.6000 0.6180

±30

Regulated Feedback Voltage

V_FBInput Bias Current

0°C ≤ T_A≤ 85°C

-40°C ≤ T_A≤ 85°C

V_FB= 0.65V

%/V

%/A

Reference Voltage Line Regulation V_IN= 2.7V to 5.5V, I_OUT=300mA

0.5

0.60

Output Voltage Line Regulation

Output Voltage Load Regulation

V_IN= 2.7V to 5.5V I_OUT=300mA

I_OUT=300 to 2000mA

0.25

V_IN=3V, V_FB=0.5V or

Peak Inductor Current

4.5

V_OUT=90%, Duty Cycle <35%

Oscillator Frequency

V_FB=0.6V or V_OUT=100%

I_LX= 300mA

0.8

1.0

110

1.2

±1

MHz

mΩ

R_DS(ON)of P-CH MOSFET

R_DS(ON)of N-CH MOSFET

I_LX= -300mA

V_EN= 0V, V_LX= 0V or 5V,

LX Leakage

Soft start

UVLO

±0.01

μA

V_IN= 5V

V_INRising

V_INFalling

2.3

2.5

2.2

2.7

2.4

0.6

EN Threshold Low

-40°C ≤ T_A≤ 85°C

EN Threshold High

EN Leakage Current

Thermal Shutdown ^{NOTE 4}

1.1

±0.01

155

±1

μA

℃

Measured FB, With Respect to

V_REF

91.5

NOTE 1: Thermal Resistance is specified with approximately 1 square of 1 oz copper.

NOTE 2: T_Jis calculated from the ambient temperature T_Aand power dissipation P_Daccording to the following formula:

A7121A: T_J= T_A+ (P_D)x(220°C/W)

NOTE 3: Specifications over the temperature range are guaranteed by design and characterization.

NOTE 4: Guaranteed by design and characterization only.

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 4 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

TYPICAL OPERATING CHARACTERISTICS

Test Figure 1 above unless otherwise specified

Efficiency vs. I_OUT@V_OUT=1.2V

Efficiency vs. I_OUT@V_OUT=3.3V

Ripple

V_IN=3.6V,V_O=1.8V,I_O=0

V_IN=3.6V,V_O=1.8V,I_O=2.0A

Load Transient

V_IN=5V,V_O=1.2V,I_O=0.5-1.5A

V_IN=5V,V_O=1.2V,I_O=0.5-2A

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 5 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

Soft-start

7. V_IN=3.6V,V_O=1.8V,I_O=0

V_IN=3.6V,V_O=1.8V,I_O=2A

Efficiency vs. I_OUT@V_OUT=1.8V

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 6 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

BLOCK DIAGRAM

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 7 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

DETAILED INFORMATION

Operation

A7121A is a monolithic switching mode Step-Down DC-DC converter. It utilizes internal MOSFETs to achieve

high efficiency and can generate very low output voltage by using internal reference at 0.6V. It operates at a

fixed switching frequency, and uses the slope compensated current mode architecture. This Step-Down

DC-DC Converter supplies 2.0A output current at V_OUT= 1.8V with input voltage range from 2.7V to 6.0V.

Current Mode PWM Control

Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for

excellent load and line responses and protection of the internal main switch (P-Ch MOSFET) and

synchronous rectifier (N-CH MOSFET). During normal operation, the internal P-Ch MOSFET is turned on for

a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when

the peak inductor current is above the error voltage. The current comparator, I_COMP, limits the peak inductor

current. When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until

either the inductor current starts to reverse, as indicated by the current reversal comparator, I_ZERO, or the

beginning of the next clock cycle.

Idle Mode Operation

At very light loads, the A7121A automatically enters pulse skipping Mode. In the pulse skipping Mode, the

inductor current may reach zero or reverse on each pulse. The PWM control loop will automatically skip

pulses to maintain output regulation. The bottom MOSFET is turned off by the current reversal comparator,

_ZERO, and the switch voltage will ring. This is discontinuous mode operation, and is normal behavior for the

switching regulator.

Power Good Output (PG)

PGOOD is an open-drain type output and requires a pullup resistor. PGOOD is actively held low in soft-start,

standby, and shutdown. It is released when the output voltage rises above 91.5% of nominal regulation point.

The PGOOD signal goes low if the output is turned off or falls below 91.5% of nominal regulation point.

Dropout Operation

When the input voltage decreases toward the value of the output voltage, the A7121A allows the main switch

to remain on for more than one switching cycle and increases the duty cycle ^NOTE5until it reaches 100%. The

output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. At low

input supply voltage, the R_DS(ON)of the P-Channel MOSFET increases, and the efficiency of the converter

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 8 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

decreases. Caution must be exercised to ensure the heat dissipated not to exceed the maximum junction

temperature of the IC.

NOTE 5: The duty cycle D of a step-down converter is defined as:

V^OUT

VIN

D = t_ONx f _OSCx 100%≈

x 100%

Where t_ONis the main switch on time and f _OSCis the oscillator frequency (1MHz).

Maximum Load Current

The A7121A will operate with input supply voltage as low as 2.7V, however, the maximum load current

decreases at lower input due to large I-R drop on the main switch and synchronous rectifier. The slope

compensation signal reduces the peak inductor current as a function of the duty cycle to prevent

sub-harmonic oscillations at duty cycles greater than 50%. Conversely the current limit increases as the duty

cycle decreases.

Layout Guidance

When laying out the PCB board, the following suggestions should be taken to ensure proper operation of the

A7121A. These items are also illustrated graphically in Figure 2(illustrated by A7121A-A).

The power traces, including the GND trace, the LX trace and the V_INtrace should be kept short, direct

and wide.

The V_FBpin should be connected directly to the feedback resistor. The resistive divider R1/R2 must be

connected between the (+) plate of C3 and ground.

Connect the (+) plate of C1 to the V_INpin as closely as possible. This capacitor provides the AC current

to internal power MOSFET.

Keep the switching node, LX, away from the sensitive V_FBnode.

Keep the (-) plates of C1 and C3 as close as possible.

Figure 2. A7121A Suggested Layout

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 9 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

Application Information

Setting the Output Voltage

Figure 1 above shows the basic application circuit with A7121A. The external resistor sets the output voltage

according to the following equation:









_OUT= 0.6V X 1+





R1=150kΩ for all outputs; R2= 100kΩ for V_OUT=1.0V, R2=150kΩ for V_OUT=1.2V, R2=300kΩ for V_OUT=1.8V,

and R2=475kΩ for V_OUT=2.5V, R2=604kΩ for V_OUT=3.0V, and R2=680kΩ for V_OUT=3.3V. (Use 1% tolerance

resistor)

Inductor Selection

For most designs, the A7121A operates with inductors of 1μH to 4.7μH. Low inductance values are physically

smaller but require faster switching, which results in some efficiency loss. The inductor value can be derived

from the following equation:

OUT x (VIN − VOUT

)

L =

IN x ΔI x fOSC

WhereΔI_Lis inductor Ripple Current. Large value inductors lower ripple current and small value inductors

result in high ripple currents. Choose inductor ripple current approximately 35% of the maximum load current

2000mA, or ΔI_L=700mA.

For output voltages above 2.0V, when light-load efficiency is important, the minimum recommended inductor

is 2.2μH. For optimum voltage-positioning load transients, choose an inductor with DC series resistance in the

50mΩ to 150mΩ range. For higher efficiency at heavy loads (above 500mA), or minimal load regulation (but

some transient overshoot), the resistance should be kept below 100mΩ. The DC current rating of the inductor

should be at least equal to the maximum load current plus half the ripple current to prevent core saturation.

Table 1 lists some typical surface mount inductors that meet target applications for the A7121A.

Vendor

Sunlord

P/N

L(μH) DCR(mΩ)

_Rating(A)

2.95

5.5

_sat(A)

4.9

Size(L*W*H), (mm)

4.0 x 4.0 x 3.0

5.7 x 5.4 x 3.0

4.3 x 4.3 x 2.0

SWPA4030S2R2NT

2.2

Mag.Layers MMD-05CZ-2R2M-M2

Mag.Layers MND-04BZN2R2M-XG

23.5

3.5

Table 1 Recommended Inductor

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 10 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

Input Capacitor Selection

The input capacitor reduces the surge current drawn from the input and switching noise from the device. The

input capacitor impedance at the switching frequency shall be less than input source impedance to prevent

high frequency switching current passing to the input. A low ESR input capacitor sized for maximum RMS

current must be used. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of

their low ESR and small temperature coefficients. A 22μF ceramic capacitor for most applications is sufficient.

Output Capacitor Selection

The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability.

The output capacitor must have low impedance at the switching frequency. Ceramic capacitors with X5R or

X7R dielectrics are recommended due to their low ESR and high ripple current. The output ripple V_OUTis

determined by:

^OUTx (VIN − V^OUT

)













ΔV_OUT

≤

ESR +

IN x fOSC x L

6.28 x f^OSCx C3

V_OUTR1(kΩ) R2(kΩ) L1(μH) C2(pF)

C1(μF)

C3(μF)

3.3V

3.0V

2.5V

1.8V

1.2V

1.0V

150

680

604

475

300

150

100

2.2

Table 2 Recommended Component Values for Figure 1 A7121A Typical Application Circuit

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 11 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

PACKAGE INFORMATION

Dimension in SOT-25 (Unit: mm)

Millimeters

Inches

Symbol

Min

Max

Min

Max

1.050

0.000

1.050

0.300

0.100

2.820

1.500

2.650

1.250

0.100

1.150

0.500

0.200

3.020

1.700

2.950

0.041

0.000

0.041

0.012

0.004

0.111

0.059

0.104

0.049

0.004

0.045

0.020

0.008

0.119

0.067

0.116

0.950(BSC)

0.037(BSC)

1.800

0.300

0°

2.000

0.600

8°

0.071

0.012

0°

0.079

0.024

8°

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 12 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

Dimension in SOT-26 (Unit: mm)

Millimeters

Inches

Symbol

Min

Max

Min

Max

1.050

0.000

1.050

0.300

0.100

2.820

1.500

2.650

1.250

0.100

1.150

0.500

0.200

3.020

1.700

2.950

0.041

0.000

0.041

0.012

0.004

0.111

0.059

0.104

0.049

0.004

0.045

0.020

0.008

0.119

0.067

0.116

0.950(BSC)

0.037(BSC)

1.800

0.300

0°

2.000

0.600

8°

0.071

0.012

0°

0.079

0.024

8°

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 13 -

A7121A

DC-DC CONVERTER BUCK (STEP-DOWN)

1MHz, 2.0A, SYNCHRONOUS

AiT Semiconductor Inc.

www.ait-ic.com

IMPORTANT NOTICE

AiT Semiconductor Inc. (AiT) reserves the right to make changes to any its product, specifications, to

discontinue any integrated circuit product or service without notice, and advises its customers to obtain the

latest version of relevant information to verify, before placing orders, that the information being relied on is

current.

AiT Semiconductor Inc.'s integrated circuit products are not designed, intended, authorized, or warranted to

be suitable for use in life support applications, devices or systems or other critical applications. Use of AiT

products in such applications is understood to be fully at the risk of the customer. As used herein may involve

potential risks of death, personal injury, or server property, or environmental damage. In order to minimize

risks associated with the customer's applications, the customer should provide adequate design and

operating safeguards.

AiT Semiconductor Inc. assumes to no liability to customer product design or application support. AiT

warrants the performance of its products of the specifications applicable at the time of sale.

REV1.3

- JUL 2013 RELEASED, NOV 2016 UPDATED -

- 14 -

A7121AE6VR [AITSEMI]

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