AAT2120IES-0.6-T1 - AnalogicTech

SwitchReg™

2120.2007.10.1.1 1

Typical Application

3.0μH

118kΩ

59kΩ

4.7µF C2

4.7µF

EN FB

VIN

PGND

GND

AAT2120

VIN VO = 1.8V 500m

AAT2120

500mA Low Noise Step-Down Converter

General Description

The AAT2120 SwitchReg is a 1.8MHz step-down

converter with an input voltage range of 2.7V to

5.5V and output as low as 0.6V. Its low supply

current, small size, and high switching frequency

make the AAT2120 the ideal choice for portable

applications.

The AAT2120 delivers up to 500mA of load current,

while maintaining a low 45µA no load quiescent cur-

rent. The 1.8MHz switching frequency minimizes

the size of external components, while keeping

switching losses low. The AAT2120 feedback and

control delivers excellent load regulation and tran-

sient response with a small output inductor and

capacitor.

The AAT2120 maintains high efficiency throughout

the load range. The AAT2120’s unique architecture

produces reduced ripple and spectral noise. Over-

temperature and short-circuit protection safeguard

the AAT2120 and system components from damage.

The AAT2120 is available in a Pb-free, 8-pin,

2x2mm STDFN package and is rated over the -40°C

to +85°C temperature range.

Features

•V

IN Range: 2.7V to 5.5V

•V

OUT Range: 0.6V to VIN

• Up to 500mA Output Current

• Up to 96% Efficiency

• Low Noise Light Load Mode

• 45µA Typical Quiescent Current

• 1.8MHz Switching Frequency

• Soft-Start Control

• Over-Temperature and Current Limit

Protection

• 100% Duty Cycle Low-Dropout Operation

• <1µA Shutdown Current

• Small External Components

• Ultra-Small STDFN22-8 Package

• Temperature Range: -40°C to +85°C

Applications

• Bluetooth®Headsets

• Cellular Phones

• Digital Cameras

• Handheld Instruments

• Micro Hard Disk Drive

• Portable Music Players

• USB Devices

Pin Descriptions

Pin Configuration

STDFN22-8

(Top View)

GND

VIN

N/C

PGND

Pin # Symbol Function

1 VP Input power pin; connected to the source of the P-channel MOSFET. Connect to the input

capacitor.

2 VIN Input bias voltage for the converter.

3 GND Non-power signal ground pin.

4 FB Feedback input pin. Connect this pin to an external resistive divider for adjustable output.

5 N/C No connect.

6 EN Enable pin. A logic high enables normal operation. A logic low shuts down the converter.

7 LX Switching node. Connect the inductor to this pin. It is connected internally to the drain of

both high- and low-side MOSFETs.

8 PGND Input power return pin; connected to the source of the N-channel MOSFET. Connect to the

output and input capacitor return.

EP Exposed paddle (bottom): connect to ground directly beneath the package.

22120.2007.10.1.1

AAT2120

500mA Low Noise Step-Down Converter

Absolute Maximum Ratings1

Thermal Information

Symbol Description Value Units

PDMaximum Power Dissipation (STDFN22-8) 2 W

θJA Thermal Resistance2(STDFN22-8) 50 °C/W

Symbol Description Value Units

VIN Input Voltage and Bias Power to GND 6.0 V

VLX LX to GND -0.3 to VIN + 0.3 V

VOUT FB to GND -0.3 to VIN + 0.3 V

VEN EN to GND -0.3 to 6.0 V

TJOperating Junction Temperature Range -40 to 150 °C

TLEAD Maximum Soldering Temperature (at leads, 10 sec) 300 °C

1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at condi-

tions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.

2. Mounted on an FR4 board.

2120.2007.10.1.1 3

AAT2120

500mA Low Noise Step-Down Converter

Electrical Characteristics1

VIN = 3.6V, TA= -40°C to +85°C, unless otherwise noted; typical values are TA= 25°C.

Symbol Description Conditions Min Typ Max Units

VIN Input Voltage 2.7 5.5 V

VIN Rising 2.3 V

VUVLO UVLO Threshold Hysteresis 70 mV

VIN Falling 1.4 V

VOUT Output Voltage Tolerance2IOUT = 0 to 500mA, -3.0 3.0 %

VIN = 2.7V to 5.5V

VOUT Output Voltage Range 0.6 VIN V

IQQuiescent Current No Load 45 85 µA

ISHDN Shutdown Current EN = GND 1.0 µA

ILIM P-Channel Current Limit 700 mA

RDS(ON)H High-Side Switch On Resistance 0.59 Ω

RDS(ON)L Low-Side Switch On Resistance 0.42 Ω

ΔVLinereg/ΔVIN Line Regulation VIN = 2.7V to 5.5V 0.2 %/V

VFB Feedback Threshold Voltage Accuracy VIN = 3.6V 0.591 0.600 0.609 V

IFB FB Leakage Current VOUT = 1.0V 0.2 µA

FOSC Oscillator Frequency 1.8 MHz

TSStartup Time From Enable to Output 100 µs

Regulation

TSD Over-Temperature Shutdown Threshold 105 °C

THYS Over-Temperature Shutdown Hysteresis 15 °C

VEN(L) Enable Threshold Low 0.6 V

VEN(H) Enable Threshold High 1.4 V

IEN Input Low Current VIN = VEN = 5.5V -1.0 1.0 µA

1. The AAT2120 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured

by design, characterization, and correlation with statistical process controls.

2. Output voltage tolerance is independent of feedback resistor network accuracy.

42120.2007.10.1.1

AAT2120

500mA Low Noise Step-Down Converter

Typical Characteristics

Load Regulation

(VOUT = 1.2V; L = 1.5µH)

Output Current (mA)

Load Regulation (%)

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

0.1 1 10 100

VIN = 3.6V

VIN = 4.2V

VIN = 2.7V

VIN = 5.0V

Efficiency vs. Load

(VOUT = 1.2V; L = 1.5µH)

Output Current (mA)

Efficiency (%)

100

0.1 1 10 100 100

VIN = 2.7V

VIN = 3.6V

VIN = 4.2V

VIN = 5.0V

Load Regulation

(VOUT = 1.8V; L = 3.3µH)

Output Current (mA)

Load Regulation (%)

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

0.1 1 10 100 1000

VIN = 4.2V

VIN = 2.7V

VIN = 3.6V

Efficiency vs. Load

(VOUT = 1.8V; L = 3.3µH)

Output Current (mA)

Efficiency (%)

100

0.1 1 10 100 1000

VIN = 2.7V VIN = 3.6V

VIN = 4.2V

Load Regulation

(VOUT = 3.0V; L = 4.7µH)

Output Current (mA)

Load Regulation (%)

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

0.1 1 10 100 1000

VIN = 3.6V VIN = 5.0V

VIN = 4.2V

Efficiency vs. Load

(VOUT = 3.0V; L = 4.7µH)

Output Current (mA)

Efficiency (%)

100

0.1 1 10 100 1000

VIN = 3.6V

VIN = 4.2V

VIN = 5.0V

2120.2007.10.1.1 5

AAT2120

500mA Low Noise Step-Down Converter

Typical Characteristics

No Load Quiescent Current vs. Input Voltage

Input Voltage (V)

Supply Current (µA)

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

85°C

25°C

-40°C

Switching Frequency Variation vs. Temperature

(VIN = 3.6V; VOUT = 1.8V)

Temperature (°C)

Variation (%)

-10

-8

-6

-4

-2

-40 -20 0 20 40 60 80 100

Frequency Variation vs. Input Voltage

Input Voltage (V)

Frequency Variation (%)

-4

-3

-2

-1

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

VOUT = 3.0V

VOUT = 1.8V

Output Voltage Error vs. Temperature

(VIN = 3.6V; VOUT = 1.8V; IOUT = 500mA)

Temperature (°C)

Output Error (%)

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

-40 -20 0 20 40 60 80 100

Line Regulation

(VOUT = 1.8V)

Input Voltage (V)

Accuracy (%)

-0.30

-0.20

-0.10

0.00

0.10

0.20

0.30

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

IOUT = 10mA

IOUT = 500mA

IOUT = 250mA

IOUT = 150mA

IOUT = 50mA

IOUT = 0mA

Soft Start

(VIN = 3.6V; VOUT = 1.8V; 500mA)

Time (100µs/div)

Enable and Output Voltage

(top) (V)

Inductor Current (bottom) (A)

-4

-3

-2

-1

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

ILX

62120.2007.10.1.1

AAT2120

500mA Low Noise Step-Down Converter

Typical Characteristics

Line Response

(VOUT = 1.8V @ 500mA)

Time (25µs/div)

Output Voltage (top) (V)

Input Voltage (bottom) (V)

1.50

1.55

1.60

1.65

1.70

1.75

1.80

1.85

1.90

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

VIN

Load Transient Response

(350mA to 500mA; VIN = 3.6V; VOUT = 1.8V;

COUT = 4.7µF; CFF = 100pF)

Time (25µs/div)

Output Voltage (top) (V)

Load and Inductor Current

(bottom) (100mA/div)

1.0

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2.0

ILX

Load Transient Response

(1mA to 500mA; VIN = 3.6V; VOUT = 1.8V;

COUT = 4.7µF; CFF = 100pF)

Time (20µs/div)

Output Voltage (top) (V)

Load and Inductor Current

(bottom) (400mA/div)

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

ILX

N-Channel RDS(ON) vs. Input Voltage

Input Voltage (V)

RDS(ON) (mΩΩ)

300

350

400

450

500

550

600

650

700

750

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

100°C

85°C

120°C

25°C

P-Channel RDS(ON) vs. Input Voltage

Input Voltage (V)

RDS(ON) (mΩΩ)

300

400

500

600

700

800

900

1000

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

100°C

85°C

120°C

25°C

2120.2007.10.1.1 7

AAT2120

500mA Low Noise Step-Down Converter

Typical Characteristics

Output Ripple

(VIN = 3.6V; VOUT = 1.8V; IOUT = 500mA)

Time (200ns/div)

Output Voltage (AC Coupled)

(top) (mV)

Inductor Current

(bottom) (A)

-120

-100

-80

-60

-40

-20

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

ILX

Output Ripple

(VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA)

Time (2µs/div)

Output Voltage (AC Coupled)

(top) (mV)

Inductor Current

(bottom) (A)

-120

-100

-80

-60

-40

-20

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

ILX

82120.2007.10.1.1

AAT2120

500mA Low Noise Step-Down Converter

Functional Description

The AAT2120 is a high performance 500mA,

1.8MHz monolithic step-down converter designed

to operate with an input voltage range of 2.7V to

5.5V. The converter operates at 1.8MHz, which

minimizes the size of external components. Typical

values are 3.3µH for the output inductor and 4.7µF

for the ceramic output capacitor.

The device is designed to operate with an output

voltage as low as 0.6V. Power devices are sized for

500mA current capability while maintaining over

90% efficiency at full load. Low current efficiency is

maintained at greater than 80% down to 1mA of

load current.

At dropout, the converter duty cycle increases to

100% and the output voltage tracks the input volt-

age minus the RDS(ON) drop of the P-channel high-

side MOSFET.

A high-DC gain error amplifier with internal com-

pensation controls the output. It provides excellent

transient response and load/line regulation. Soft

start eliminates any output voltage overshoot when

the enable or the input voltage is applied.

Functional Block Diagram

Err

Amp

Logic

PGND

GND

Voltage

Reference

INPUT

VIN

2120.2007.10.1.1 9

AAT2120

500mA Low Noise Step-Down Converter

AAT2120

500mA Low Noise Step-Down Converter

10 2120.2007.10.1.1

Control Loop

The AAT2120 is a 500mA current mode step-down

converter. The current through the P-channel

MOSFET (high side) is sensed for current loop

control, as well as short-circuit and overload pro-

tection. A fixed slope compensation signal is added

to the sensed current to maintain stability for duty

cycles greater than 50%. The peak current mode

loop appears as a voltage-programmed current

source in parallel with the output capacitor.

The output of the voltage error amplifier programs

the current mode loop for the necessary peak switch

current to force a constant output voltage for all load

and line conditions. Internal loop compensation ter-

minates the transconductance voltage error amplifier

output. The error amplifier reference is fixed at 0.6V.

Soft Start / Enable

Soft start increases the inductor current limit point in

discrete steps when the input voltage or enable

input is applied. It limits the current surge seen at

the input and eliminates output voltage overshoot.

When pulled low, the enable input forces the

AAT2120 into a low-power, non-switching state. The

total input current during shutdown is less than 1µA.

Current Limit and

Over-Temperature Protection

For overload conditions, the peak input current is lim-

ited. As load impedance decreases and the output

voltage falls closer to zero, more power is dissipated

internally, raising the device temperature. Thermal

protection completely disables switching when inter-

nal dissipation becomes excessive, protecting the

device from damage. The junction over-temperature

threshold is 105°C with 15°C of hysteresis.

Under-Voltage Lockout

Internal bias of all circuits is controlled via the VIN

power. Under-voltage lockout (UVLO) guarantees

sufficient VIN bias and proper operation of all inter-

nal circuits prior to activation.

Applications Information

Inductor Selection

The step-down converter uses peak current mode

control with slope compensation to maintain stability

for duty cycles greater than 50%. The output induc-

tor value must be selected so the inductor current

down slope meets the internal slope compensation

requirements. The internal slope compensation for

the adjustable and low-voltage fixed versions of the

AAT2120 is 0.45A/µsec. This equates to a slope

compensation that is 75% of the inductor current

down slope for a 1.8V output and 3.0µH inductor.

This is the internal slope compensation for the

AAT2120. When externally programming to 3.0V,

the calculated inductance is 5.0µH.

In this case, a standard 4.7µH value is selected.

For most designs, the AAT2120 operates with an

inductor value of 1µH to 4.7µH. Table 1 displays

inductor values for the AAT2120 with different output

voltage options.

Manufacturer's specifications list both the inductor

DC current rating, which is a thermal limitation, and

the peak current rating, which is determined by the

saturation characteristics. The inductor should not

show any appreciable saturation under normal load

conditions. Some inductors may meet the peak and

average current ratings yet result in excessive loss-

es due to a high DCR. Always consider the losses

associated with the DCR and its effect on the total

converter efficiency when selecting an inductor.

0.75 ⋅ V

L = =

≈

1.67

⋅ V

= 1.67 ⋅ 3.0V = 5.0µH

0.75

⋅

0.45A

µsec

0.75 ⋅ V

m = = = 0.45

0.75 ⋅ 1.8V

3.0µH

µsec

AAT2120

500mA Low Noise Step-Down Converter

2120.2007.10.1.1 11

Table 1: Inductor Values.

The 3.0µH CDRH2D09 series inductor selected

from Sumida has a 150mΩ DCR and a 470mA DC

current rating. At full load, the inductor DC loss is

9.375mW which gives a 2.08% loss in efficiency for

a 250mA, 1.8V output.

Input Capacitor

Select a 4.7µF to 10µF X7R or X5R ceramic capac-

itor for the input. To estimate the required input

capacitor size, determine the acceptable input rip-

ple level (VPP) and solve for CIN. The calculated

value varies with input voltage and is a maximum

when VIN is double the output voltage.

Always examine the ceramic capacitor DC voltage

coefficient characteristics when selecting the prop-

er value. For example, the capacitance of a 10µF,

6.3V, X5R ceramic capacitor with 5.0V DC applied

is actually about 6µF.

The maximum input capacitor RMS current is:

The input capacitor RMS ripple current varies with

the input and output voltage and will always be less

than or equal to half of the total DC load current.

for VIN = 2 · VO

The term appears in both the input

voltage ripple and input capacitor RMS current

equations and is a maximum when VOis twice VIN.

This is why the input voltage ripple and the input

capacitor RMS current ripple are a maximum at

50% duty cycle.

The input capacitor provides a low impedance loop

for the edges of pulsed current drawn by the

AAT2120. Low ESR/ESL X7R and X5R ceramic

capacitors are ideal for this function. To minimize

stray inductance, the capacitor should be placed as

closely as possible to the IC. This keeps the high

frequency content of the input current localized,

minimizing EMI and input voltage ripple.

The proper placement of the input capacitor (C1)

can be seen in the evaluation board layout in

Figure 2.

A laboratory test set-up typically consists of two

long wires running from the bench power supply to

the evaluation board input voltage pins. The induc-

tance of these wires, along with the low-ESR

ceramic input capacitor, can create a high Q net-

work that may affect converter performance. This

problem often becomes apparent in the form of

excessive ringing in the output voltage during load

transients. Errors in the loop phase and gain meas-

urements can also result.

Since the inductance of a short PCB trace feeding

the input voltage is significantly lower than the

power leads from the bench power supply, most

applications do not exhibit this problem.

⎛⎞

· 1 -

⎝⎠

VIN

RMS(MAX)

⎛⎞

· 1 - = D · (1 - D) = 0.52 =

⎝⎠

VIN

⎛⎞

IRMS = IO · · 1 -

⎝⎠

VIN

CIN(MIN) = 1

⎛⎞

- ESR · 4 · FS

⎝⎠

VPP

⎛⎞

· 1 - = for VIN = 2 · VO

⎝⎠

VIN

⎛⎞

· 1 -

⎝⎠

VIN

CIN =

VIN

⎛⎞

- ESR · FS

⎝⎠

VPP

Output Voltage (V) L1 (µH)

1.0 1.5

1.2 2.2

1.5 2.7

1.8 3.0

2.5 3.9

3.0 4.7

3.3 5.6

AAT2120

500mA Low Noise Step-Down Converter

12 2120.2007.10.1.1

In applications where the input power source lead

inductance cannot be reduced to a level that does

not affect the converter performance, a high ESR

tantalum or aluminum electrolytic should be placed

in parallel with the low ESR, ESL bypass ceramic.

This dampens the high Q network and stabilizes

the system.

Output Capacitor

The output capacitor limits the output ripple and

provides holdup during large load transitions. A

4.7µF to 10µF X5R or X7R ceramic capacitor typi-

cally provides sufficient bulk capacitance to stabi-

lize the output during large load transitions and has

the ESR and ESL characteristics necessary for low

output ripple. For enhanced transient response

and low temperature operation application, a 10µF

(X5R, X7R) ceramic capacitor is recommended to

stabilize extreme pulsed load conditions.

The output voltage droop due to a load transient is

dominated by the capacitance of the ceramic out-

put capacitor. During a step increase in load cur-

rent, the ceramic output capacitor alone supplies

the load current until the loop responds. Within two

or three switching cycles, the loop responds and

the inductor current increases to match the load

current demand. The relationship of the output volt-

age droop during the three switching cycles to the

output capacitance can be estimated by:

Once the average inductor current increases to the

DC load level, the output voltage recovers. The

above equation establishes a limit on the minimum

value for the output capacitor with respect to load

transients.

The internal voltage loop compensation also limits

the minimum output capacitor value to 4.7µF. This

is due to its effect on the loop crossover frequency

(bandwidth), phase margin, and gain margin.

Increased output capacitance will reduce the

crossover frequency with greater phase margin.

The maximum output capacitor RMS ripple current

is given by:

Dissipation due to the RMS current in the ceramic

output capacitor ESR is typically minimal, resulting in

less than a few degrees rise in hot-spot temperature.

Adjustable Output Resistor Selection

Resistors R1 and R2 of Figure 1 program the output

to regulate at a voltage higher than 0.6V. To limit the

bias current required for the external feedback resis-

tor string while maintaining good noise immunity, the

suggested value for R2 is 59kΩ. Decreased resistor

values are necessary to maintain noise immunity on

the FB pin, resulting in increased quiescent current.

Table 2 summarizes the resistor values for various

output voltages.

With enhanced transient response for extreme

pulsed load application, an external feed-forward

capacitor, (C3 in Figure 1), can be added.

Table 2: Adjustable Resistor Values For

Step-Down Converter.

R2 = 59kΩR2 = 221kΩ

VOUT (V) R1 (kΩ) R1 (kΩ)

0.8 19.6 75

0.9 29.4 113

1.0 39.2 150

1.1 49.9 187

1.2 59.0 221

1.3 68.1 261

1.4 78.7 301

1.5 88.7 332

1.8 118 442

1.85 124 464

2.0 137 523

2.5 187 715

3.3 267 1000

⎛⎞

⎝⎠

R1 = -1 · R2 = - 1 · 59kΩ = 267kΩ

VOUT

VREF

⎛⎞

⎝⎠

3.3V

0.6V

VOUT · (VIN(MAX) - VOUT)

RMS(MAX)

IL · FS · VIN(MAX)

=·

COUT =

3 · ΔILOAD

VDROOP · FS

AAT2120

500mA Low Noise Step-Down Converter

2120.2007.10.1.1 13

Thermal Calculations

There are three types of losses associated with

the AAT2120 step-down converter: switching loss-

es, conduction losses, and quiescent current loss-

es. Conduction losses are associated with the

RDS(ON) characteristics of the power output switch-

ing devices. Switching losses are dominated by

the gate charge of the power output switching

devices. At full load, assuming continuous conduc-

tion mode (CCM), a simplified form of the losses is

given by:

IQis the step-down converter quiescent current.

The term tsw is used to estimate the full load step-

down converter switching losses.

For the condition where the step-down converter is

in dropout at 100% duty cycle, the total device dis-

sipation reduces to:

Since RDS(ON), quiescent current, and switching

losses all vary with input voltage, the total losses

should be investigated over the complete input

voltage range.

Given the total losses, the maximum junction tem-

perature can be derived from the θJA for the

STDFN22-8 package which is 50°C/W.

TJ(MAX) = PTOTAL · ΘJA + TAMB

PTOTAL = IO

2 · RDS(ON)H + IQ · VIN

PTOTAL

2 · (RDS(ON)H · VO + RDS(ON)L · [VIN - VO])

VIN

+ (tsw · FS · IO + IQ) · VIN

Figure 1: AAT2120 Schematic.

Adj.

59kΩ

4.7μF

GND

N/C 5

EN 6

LX 7

PGND 8

VIN

AAT2120

VIN

GND

+VOUT

GND

(optional)

100pF

AAT2120

500mA Low Noise Step-Down Converter

14 2120.2007.10.1.1

Figure 2: AAT2120 Evaluation Board Figure 3: Exploded View of AAT2120

Top Side Layout. Evaluation Board Top Side Layout.

Figure 4: AAT2120 Evaluation Board

Bottom Side Layout.

Layout

The suggested PCB layout for the AAT2120 in an

STDFN22-8 package is shown in Figures 2, 3, and 4.

The following guidelines should be used to help

ensure a proper layout.

1. The input capacitor (C1) should connect as

closely as possible to VP (Pin 1), PGND (Pin 8),

and GND (Pin 3)

2. C2 and L1 should be connected as closely as pos-

sible. The connection of L1 to the LX pin (Pin 7)

should be as short as possible. Do not make the

node small by using narrow trace. The trace

should be kept wide, direct and short.

3. The feedback pin (Pin 4) should be separate

from any power trace and connect as closely as

possible to the load point. Sensing along a

high-current load trace will degrade DC load

regulation. Feedback resistors should be

placed as closely as possible to the FB pin (Pin

4) to minimize the length of the high imped-

ance feedback trace. If possible, they should

also be placed away from the LX (switching

node) and inductor to improve noise immunity.

4. The resistance of the trace from the load return

to PGND (Pin 8) and GND (Pin 3) should be

kept to a minimum. This will help to minimize

any error in DC regulation due to differences in

the potential of the internal signal ground and

the power ground.

5. A high density, small footprint layout can be

achieved using an inexpensive, miniature, non-

shielded, high DCR inductor.

AAT2120

500mA Low Noise Step-Down Converter

2120.2007.10.1.1 15

Step-Down Converter Design Example

Specifications

VO= 1.8V @ 250mA, Pulsed Load ΔILOAD = 200mA

VIN = 2.7V to 4.2V (3.6V nominal)

FS= 1.8MHz

TAMB = 85°C

1.8V Output Inductor

(use 3.0µH; see Table 1)

For Sumida inductor CDRH2D09-3R0, 3.0µH, DCR = 150mΩ.

1.8V Output Capacitor

VDROOP = 0.1V

1 1.8V · (4.2V - 1.8V)

3.0µH · 1.8MHz · 4.2V

RMS

IL1 · FS · VIN(MAX)

= ·

3 · ΔILOAD

VDROOP · FS

3 · 0.2A

0.1V · 1.8MHz

COUT = = = 3.3µF (use 3.3µF)

· = 66mArms

(VO) · (VIN(MAX) - VO)=

Pesr = esr · IRMS2 = 5mΩ · (66mA)2 = 21.8µW

1.8

1.8V

ΔI

⋅ 1 - = ⋅ 1 - = 190m

L1 ⋅ F

3.0µH ⋅ 1.8MHz

4.2V

PKL1

= I

+ ΔI

= 250mA + 95mA = 345mA

= I

⋅ DCR = 250mA

⋅ 150mΩ = 9.375mW

⎛

⎝⎞

⎠

⎛

⎝⎞

⎠

L1 = 1.67 ⋅ V

= 1.67 ⋅ 1.8V = 3µH

µsec

Input Capacitor

Input Ripple VPP = 25mV

AAT2120 Losses

TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 26.14mW = 86°C

PTOTAL

+ (tsw · FS · IO + IQ) · VIN

2 · (RDS(ON)H · VO + RDS(ON)L · [VIN -VO])

VIN

+ (5ns · 1.8MHz · 0.2A + 45µA) · 4.2V = 19.71mW

0.22 · (0.59Ω · 1.8V + 0.42Ω · [4.2V - 1.8V])

4.2V

RMS

P = esr · IRMS

2 = 5mΩ · (0.1A)2 = 0.05mW

= = 0.1Arms

CIN = = = 1.16µF (use 4.7µF

)

⎛⎞

- ESR · 4 · FS

⎝⎠

VPP

⎛⎞

- 5mΩ · 4 · 1.8MHz

⎝⎠

25mV

0.2A

AAT2120

500mA Low Noise Step-Down Converter

16 2120.2007.10.1.1

AAT2120

500mA Low Noise Step-Down Converter

2120.2007.10.1.1 17

Table 3: Evaluation Board Component Values.

Table 4: Suggested Inductors and Suppliers.

Inductance Max DC DCR Size (mm)

Manufacturer Part Number (µH) Current (mA) (mΩ) LxWxH Type

Sumida CDRH2D14-1R5 1.5 1800 50 3.0x3.0x1.55 Shielded

Sumida CDRH2D14-2R2 2.2 1500 75 3.0x3.0x1.55 Shielded

Sumida CDRH2D14-2R7 2.7 1350 85 3.0x3.0x1.55 Shielded

Sumida CDRH2D14-3R3 3.3 1200 100 3.0x3.0x1.55 Shielded

Sumida CDRH2D14-3R9 3.9 1100 110 3.0x3.0x1.55 Shielded

Sumida CDRH2D14-4R7 4.7 1000 135 3.0x3.0x1.55 Shielded

Sumida CDRH2D14-5R6 5.6 950 150 3.0x3.0x1.55 Shielded

Sumida CDRH2D11-1R5 1.5 900 54 3.2x3.2x1.2 Shielded

Sumida CDRH2D11-2R2 2.2 780 78 3.2x3.2x1.2 Shielded

Sumida CDRH2D11-3R3 3.3 600 98 3.2x3.2x1.2 Shielded

Sumida CDRH2D11-4R7 4.7 500 135 3.2x3.2x1.2 Shielded

Taiyo Yuden NR3010 1.5 1200 80 3.0x3.0x1.0 Shielded

Taiyo Yuden NR3010 2.2 1100 95 3.0x3.0x1.0 Shielded

Taiyo Yuden NR3010 3.3 870 140 3.0x3.0x1.0 Shielded

Taiyo Yuden NR3010 4.7 750 190 3.0x3.0x1.0 Shielded

FDK MIPWT3226D-1R5 1.5 1200 90 3.2x2.6x0.8 Chip shielded

FDK MIPWT3226D-2R2 2.2 1100 100 3.2x2.6x0.8 Chip shielded

FDK MIPWT3226D-3R0 3 1000 120 3.2x2.6x0.8 Chip shielded

FDK MIPWT3226D-4R2 4.2 900 140 3.2x2.6x0.8 Chip shielded

Output Voltage R2 = 59kΩR2 = 221kΩ1

VOUT (V) R1 (kΩ) R1 (kΩ) L1 (µH)

0.62— — 1.5

0.8 19.6 75 1.5

0.9 29.4 113 1.5

1.0 39.2 150 1.5

1.1 49.9 187 1.5

1.2 59.0 221 1.5

1.3 68.1 261 1.5

1.4 78.7 301 2.2

1.5 88.7 332 2.7

1.8 118 442 3.0/3.3

1.85 124 464 3.0/3.3

2.0 137 523 3.0/3.3

2.5 187 715 3.9/4.2

3.3 267 1000 5.6

1. For reduced quiescent current, R2 = 221kΩ.

2. R2 is opened, R1 is shorted.

AAT2120

500mA Low Noise Step-Down Converter

18 2120.2007.10.1.1

Table 5: Surface Mount Capacitors.

Value Voltage Temp. Case

Manufacturer Part Number (µF) Rating Co. Size

Murata GRM118R60J475KE19B 4.7 6.3 X5R 0603

Murata GRM188R60J106ME47D 10 6.3 X5R 0603

Ordering Information

All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means

semiconductor products that are in compliance with current RoHS standards, including

the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more

information, please visit our website at http://www.analogictech.com/pbfree.

Output Voltage Package Marking1Part Number (Tape and Reel)2

0.6V STDFN22-8 YDXYY AAT2120IES-0.6-T1

1. XYY = assembly and date code.

2. Sample stock is generally held on all part numbers listed in BOLD.

2120.2007.10.1.1 19

AAT2120

500mA Low Noise Step-Down Converter

AAT2120

500mA Low Noise Step-Down Converter

20 2120.2007.10.1.1

Advanced Analogic Technologies, Inc.

3230 Scott Boulevard, Santa Clara, CA 95054

Phone (408) 737-4600

Fax (408) 737-4611

AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work

rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service with-

out notice. Except as provided in AnalogicTech’s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied war-

ranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent,

copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the

customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty.

Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated.

All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.

Package Information1

STDFN22-8

All dimensions in millimeters.

2.00

0.05

Index Area

(D/2 x E/2) 0.80

0.05

0.35

0.05

2.00

0.05

1.45

0.05

0.45

0.05

Top View

Side View

Bottom View

Detail "A"

0.23

0.05

Pin 1 Indicator

(optional)

0.05

0.55

0.05

0.15

0.025

Detail "A"

1. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the

lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required

to ensure a proper bottom solder connection.