Datasheet A7221AE6R Datasheet (AiT) [ru]

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A7221A

DESCRIPTION

FEATURES

to minimize the

ORDERING INFORMATION

Package Type

Part Number

A7221AE6R

A7221AE6VR

APPLICATION

TYPICAL APPLICATION

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

A7221A is simple, easy to use, 2A synchronous

step-down (Buck) convertor in SOT-26 package, with

high efficiency and fast transient response. A7221A

operates over a wide input voltage range from 4.5V to

16V and integrates main switch and synchronous

switch with very low R

DS(ON)

conduction loss. A7221A adopts the active constant

on time PWM architecture to achieve fast transient

responses for high step down applications and high

efficiency at light loads. In addition, it keeps in

constant frequency of 500kHz under heavy load

conditions to minimize the size of inductor and

capacitor. Fault conditions also include cycle-by-cycle

current limit, output under voltage protection, output

over current protection, output short-circuit protection

and thermal shutdown

 Integrated 130mΩ and 120mΩ FETs
 4.5~16V input voltage range
 2A load current capability
 Active constant on time PWM architecture with

500kHz switching frequency

 Internal soft-start limits the inrush current
 2% 0.6V reference
 Available in SOT-26 Package

 Set Top Box
 Portable TV
 Access Point Router
 DSL Modem
 LCD TV

The A7221A is available in SOT-26 package.

SOT-26 E6

V: Halogen free Package

Note

R: Tape & Reel

SPQ:3,000pcs/Reel

AiT provides all RoHS products

Suffix “ V “ means Halogen free Package

Figure 1. Typical Application Circuit

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A7221A

Pin #

Symbol

Function

PIN DESCRIPTION

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

Top View

Boot-Strap Pin. Supply high side gate driver. Decouple this pin to LX

1 BS

pin with 0.1uF ceramic cap.

2 GND Ground pin.

Output Feedback Pin. Connect this pin to the center point of the output

3 FB

resistor divider (as shown in Figure 1) to program the output voltage:

V

=0.6x(1+R1/R2).

OUT

4 EN Enable control. Pull high to turn on. Do not float.

5 IN Input pin. Decouple this pin to GND pin with at least 1uF ceramic cap.

6 LX Inductor pin. Connect this pin to the switching node of inductor.

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A7221A

Parameter

Symbol

Min.

Max.

Unit

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

ABSOLUTE MAXIMUM RATINGS

VIN, Supply Voltage -0.3V ~ 18V

VSW, Switch Voltage -1V ~ VIN + 0.3V

VEN, Enable -1V ~ VIN + 0.3V

VBS, Bootstrap Voltage -0.3V ~ +4V

VFB, Feedback Voltage -0.3V~ +4V

Thermal Resistance

θJA 100℃/W

θJC 55℃/W

Junction Temperature +150℃

Lead Temperature (Soldering, 10s) +260℃

NOTE1

Storage Temperature -65℃~+150℃

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.
NOTE1: Measured on approximately 1” square of 1oz copper.

RECOMMENDED OPERATING CONDITIONS

NOTE2

Input Voltage VIN 4.5 16 V

Operating Temperature -40 85 ℃

NOTE2: The device is not guaranteed to function outside of its operating conditions.

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A7221A

Parameter

Conditions

Min.

Typ.

Max.

Unit

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

ELECTRICAL CHARACTERISTICS

= 12V, V

V

IN

Shutdown Supply Current VEN=0V 10 20 μA

= 3.3V, L = 4.7uH, TA = 25°C, unless otherwise specified

OUT

Supply Current I

=0, VFB=V

OUT

×105% 350 μA

REF

Feedback Voltage 5V<VIN<16V 588 600 612 mV

FB Input Current -50 50 nA

High-Side Switch-On Resistance 130 mΩ

Low-Side Switch-On Resistance 120 mΩ

High-Side Switch Leakage VEN = 0V, VSW = 0V 0 10 μA

Upper Switch Current Limit 3.0 3.5 A

Lower Switch Current Limit 1.3 A

Oscillator Frequency 500 kHz

EN Rising Threshold 1.2 V

EN Falling Threshold 0.4 V

Input UVLO Threshold Rising VIN Rising 3.8 4.2 4.5 V

Input UVLO Threshold Hysteresis 15 mV

Min ON Time 50 ns

Soft-start Time tSS 0.2 ms

Max Duty Cycle 85 %

Thermal Shutdown 160 ℃

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A7221A

1. Efficiency vs. I

OUT

@V

OUT

=1.2V

2. Efficiency vs. I

OUT

@V

OUT

=5V

3. Soft-Start (V

IN

=12V, VO=3.3V, IO=2A)

4. Soft-Start (V

IN

=12V,VO=3.3V,IO=0A)

5. Short Circuit

6. Short Circuit Recovery

TYPICAL PERFORMANCE CHARACTERISTICS

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

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A7221A

7. Efficiency vs. I

OUT

@V

OUT

=3.3V

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

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A7221A

BLOCK DIAGRAM

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

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A7221A

R2R1R2+

R2

R1

L

S

OUT

x ΔIF

V

IN

OUT

V

V

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

DETAILED INFORMATION

Operation

Functional Description

The A7221A is a synchronous rectified, current-mode, step-down regulator. It regulates input voltages from

4.5V to 16V down to an output voltage as low as 0.6V, and supplies up to 2A of load current.

The A7221A uses current-mode control to regulate the output voltage. The output voltage is measured at FB

through a resistive voltage divider and amplified through the internal transconductance error amplifier. The

converter uses internal N-Channel MOSFET switches to step-down the input voltage to the regulated output

voltage.

Application Information

Setting the Output Voltage

The output voltage is set using a resistive voltage divider from the output voltage to FB (see Typical

Application circuit on page 1). The voltage divider divides the output voltage down by the ratio:

V

Where V

is the feedback voltage and V

FB

= V

FB

is the output voltage.

OUT

OUT

x

Thus the output voltage is:

V

= 0.6 x (1+

OUT

)

Inductor

The inductor is required to supply constant current to the output load while being driven by the switched input

voltage. A larger value inductor will result in less ripple current that will result in lower output ripple voltage.

However, the larger value inductor will have a larger physical size, higher series resistance, and/or lower

saturation current. A good rule for determining the inductance to use is to allow the peak-to-peak ripple

current in the inductor to be approximately 30% of the maximum switch current limit. Also, make sure that the

peak inductor current is below the maximum switch current limit. The inductance value can be calculated by:

L =

x (1-

)

Where V

is the output voltage, VIN is the input voltage, fS is the switching frequency, and ΔIL is the

OUT

peak-to-peak inductor ripple current.

Choose an inductor that will not saturate under the maximum inductor peak current. The peak inductor current

can be calculated by:

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A7221A

Lx F x 2

V

S

OUT

IN

OUT

V

V

Vendor

P/N

L(μH)

DCR(mΩ)

I

sat

(A)

IN

OUT

IN

OUT

V

V

)x

V

V

(1−

S

LOAD

F x C1

I

IN

OUT

V

V

IN

OUT

V

V

Lx F

V

S

OUT

IN

OUT

V

V

C2x F x 6.28

1

S

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

here I

is the load current.

LOAD

ILP = I

LOAD

+

x (1-

)

The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI

requirements.

AiT-Components PIA6045-100MA 10 48 3.2

AiT-Components PIA5040-4R7N 4.7 30 3.5

Table 1. Recommended Inductors

Input Capacitor

The input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the

AC current to the step-down converter while maintaining the DC input voltage. Use low ESR capacitors for the

best performance. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also

suffice. Choose X5R or X7R dielectrics when using ceramic capacitors. Since the input capacitor absorbs the

input switching current it requires an adequate ripple current rating. The RMS current in the input capacitor

can be estimated by:

I

The worst-case condition occurs at V

C1

= 2V

IN

= I

LOAD

, where I

OUT

CIN

= I

/2. For simplification, choose the input

LOAD

capacitor whose RMS current rating greater than half of the maximum load current. The input capacitor can

be electrolytic, tantalum or ceramic. When using electrolytic or tantalum capacitors, a small, high quality 0.1uF

ceramic capacitor should be placed as close to the IC as possible. When using ceramic capacitors, make sure

that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at input.

The input voltage ripple for low ESR capacitors can be estimated by:

ΔV

IN =

x

x (1-

)

Where C1 s the value of the input capacitor.

Output Capacitor

The output capacitor is required to maintain the DC output voltage. Ceramic, tantalum, or low ESR electrolytic

capacitors are recommended. Low ESR capacitors are preferred to keep the output voltage ripple low. The

output voltage ripple can be estimated by:

ΔV

OUT =

x (1-

) x (R

ESR

+

)

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A7221A

C2 x Lx F x 6.28

V

OUT

2

S

IN

OUT

V

V

Lx F

V

S

OUT

IN

OUT

V

V

V

OUT

R1(kΩ)

R2(kΩ)

L1(uH)

C1(uF)

C2(uF)

Where C2 is the output capacitance value and R

is the equivalent series resistance (ESR) value of the

ESR

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

output capacitor. In the case of ceramic capacitors, the impedance at the switching frequency is dominated by

the capacitance. The output voltage ripple is mainly caused by the capacitance. For simplification, the output

voltage ripple can be estimated by:

ΔV

OUT

=

x (1-

)

In the case of tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching

frequency. For simplification, the output ripple can be approximated to:

ΔV

OUT

=

x (1-

) x R

ESR

The characteristics of the output capacitor also affect the stability of the regulation system. The A7221A can

be optimized for a wide range of capacitance and ESR values. For A7221A normal operation, the input and

output can be an electrolytic capacitor in parallel.

5.0V 91 12 4.7 22 22

3.3V 53.6 12 4.7 22 22

2.5V 39 12 4.7 22 22

1.8V 24 12 4.7 22 22

1.5V 18 12 4.7 22 22

1.2V 12 12 4.7 22 22

1.0V 8.2 12 4.7 22 22

Table 2 Recommended Component Values for typical Output Voltage

Layout Guidance

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

A7221A.

1. The power traces, including the GND trace, the SW trace and the V

trace should be kept short, direct

IN

and wide.

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

connected between the (+) plate of C2 and ground.

3. Connect the (+) plate of C1 to the IN pin of A7221A as closely as possible. This capacitor provides the

AC current to internal power MOSFET.

4. Keep the switching node, SW, away from the sensitive V

5. Keep the (-) plates of C1 and C2 as close as possible.

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node.

FB

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A7221A

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

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A7221A

Symbol

Millimeters

Inches

Min

Max

Min

Max

PACKAGE INFORMATION

Dimension in SOT-26 Package (Unit: mm)

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

A 1.050 1.250 0.041 0.049

A1 0.000 0.100 0.000 0.004

A2 1.050 1.150 0.041 0.045

b 0.300 0.500 0.012 0.020

c 0.100 0.200 0.004 0.008

D 2.820 3.020 0.111 0.119

E 1.500 1.700 0.059 0.067

E1 2.650 2.950 0.104 0.116

e 0.950(BSC) 0.037(BSC)

e1 1.800 2.000 0.071 0.079

L 0.300 0.600 0.012 0.024

θ 0° 8° 0° 8°

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A7221A

DC-DC CONVERTER BUC K (STEP-DOWN)

2A, 16V SYNCHRONOUS

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 servere 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.

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