AAT1231ITP-1-T1 - Advanced Analog Technology, Inc.

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 1

SwitchReg™

General Description

The AAT1231/1231-1 are high frequency, high effi-

ciency constant current boost converters capable of

24V maximum output voltage. Both devices are

ideal power solutions for backlight applications with

up to six white LEDs in series or up to twelve white

LEDs in a parallel/series configuration. The input

voltage is 2.7V to 5.5V for single-cell lithium-

ion/polymer (Li-ion) based portable devices.

The LED current is digitally controlled across a 6x

operating range using AnalogicTech’s Simple Serial

Control™ (S2Cwire™) interface. Programmability

across 26 discrete current steps provides high reso-

lution, low noise, flicker-free, constant LED outputs.

In programming AAT1231 operation, LED brightness

increases based on the data received at the EN/SET

pin. In programming AAT1231-1 operation, LED

brightness decreases based on the data received at

the EN/SET pin. The SEL logic pin changes the feed-

back voltage between two programmable ranges.

The AAT1231 and the AAT1231-1 feature high current

limit and fast, stable transitions for stepped or pulsed

current applications. The high switching frequency (up

to 2MHz) provides fast response and allows the use

of ultra-small external components, including chip

inductors and capacitors. Fully integrated control cir-

cuitry simplifies design and reduces total solution size.

The AAT1231 and the AAT1231-1 offer a true load

disconnect feature which isolates the load from the

power source while in the OFF or disabled state. This

eliminates leakage current, making the devices ideal-

ly suited for battery-powered applications.

The AAT1231 and the AAT1231-1 are available in Pb-

free, thermally-enhanced 12-pin TSOPJW packages.

Features

• Input Voltage Range: 2.7V to 5.5V

• Maximum Continuous Output 24V @ 50mA

• Drives 6 LEDs in Series, 12 LEDs in Parallel/

Series Configuration

— Constant LED Current with 6% Accuracy

• Digital Control with S2Cwire Single Wire Interface

— 26 Discrete Steps

— No PWM Control Required

— No Additional Circuitry

• Up to 82% Efficiency

• Up to 2MHz Switching Frequency Allows

Small External Chip Inductor and Capacitors

• Hysteretic Control

— No External Compensation Components

— Excellent Load Transient Response

— High Efficiency at Light Loads

• Integrated Soft Start with No External Capacitor

• True Load Disconnect Guarantees <1.0µA

Shutdown Current

• Selectable Feedback Voltage Ranges for

High Resolution Control of Load Current

• Short-Circuit, Over-Voltage, and Over-

Temperature Protection

• 12-Pin TSOPJW Package

• -40°C to +85°C Temperature Range

Applications

• Digital Still Cameras (DSCs)

• Mobile Handsets

• MP3 Players

• PDAs and Notebook PCs

• White LED Drivers

Typical Application

LIN

2.2µF

226kΩ

12kΩ

BALLAST

)

30.1Ω

2.2µF

L = 2.2µH DS1

Capable of Driving

Six LEDs in Series

(see Applications Section)

OSRAM

LW M678

EN/SET

PGND

PVIN

AAT1231/

1231-1

SEL

Up to 24V/

50mA max

VIN

AGND

OVP

Li-Ion:

= 2.7V to 4.2V

Enable/Set

Select

Pin Descriptions

Pin Configuration

TSOPJW-12

(Top View)

PVIN

EN/SET

SEL

VIN

N/C

LIN

OVP

AGND

PGND

Pin # Symbol Function

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

input capacitor(s).

2 EN/SET IC enable pin and S2Cwire input control to set output current.

3 SEL FB voltage range select.

For the AAT1231, a logic LOW sets the FB voltage range from 0.1V to 0.4V; a logic

HIGH sets the FB voltage range from 0.3V to 0.6V.

For the AAT1231-1, a logic LOW sets the FB voltage range from 0.4V to 0.1V; a logic

HIGH sets the FB voltage range from 0.6V to 0.3V.

4 VIN Input voltage for the converter. Connect directly to the PVIN pin.

5 N/C No connection.

6, 7 SW Boost converter switching node. Connect the power inductor between this pin and LIN.

8 PGND Power ground for the boost converter.

9 AGND Ground pin.

10 FB Feedback pin. Connect a resistor to ground to set the maximum LED current.

11 OVP Feedback pin for over-voltage protection sense.

12 LIN Switched power input. Connect the power inductor between this pin and SW.

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

21231.2007.01.1.2

Part Number Descriptions

Absolute Maximum Ratings1

TA= 25°C unless otherwise noted.

Thermal Information

Symbol Description Value Units

θJA Thermal Resistance 160 °C/W

PDMaximum Power Dissipation 625 mW

Symbol Description Value Units

PVIN, VIN Input Voltage -0.3 to 6.0 V

SW Switching Node 28 V

LIN, EN/SET, Maximum Rating VIN + 0.3 V

SEL, FB

TJOperating Temperature Range -40 to 150 °C

TSStorage Temperature Range -65 to 150 °C

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

SEL Polarity S2C Feedback

Part Number HIGH LOW Voltage Programming

AAT1231ITP 0.3V ≤VFB ≤0.6V 0.1V ≤VFB ≤0.4V See Table 2

AAT1231ITP-1 0.6V ≥VFB ≥0.3V 0.4V ≥VFB ≥0.1V See Table 3

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 3

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.

Electrical Characteristics1

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

Symbol Description Conditions Min Typ Max Units

Power Supply

PVIN, VIN Input Voltage Range 2.7 5.5 V

VOUT(MAX) Maximum Output Voltage 24 V

IQOperating Current SEL = GND, FB = 0.1V 40 70 µA

ISHDN Shutdown Current EN/SET = GND 1.0 µA

IOUT

Maximum Continuous Output 2.7V < VIN < 5.5V, VOUT = 24V 50 mA

Current2

ΔVLINEREG(FB)/Line Regulation VIN = 2.7V to 5.5V, VFB = 0.6V 0.7 %/V

ΔVIN

RDS(ON) L Low Side Switch On Resistance 80 mΩ

RDS(ON) IN

Input Disconnect Switch 180 mΩ

On Resistance

TSS Soft-Start Time From Enable to Output Regulation; 300 µs

VFB = 300mV

VOVP

Over-Voltage Protection Threshold VOUT Rising 1.1 1.2 1.3 V

Over-Voltage Hysteresis VOUT Falling 100 mV

ILIMIT N-Channel Current Limit 2.5 A

TSD TJThermal Shutdown Threshold 140 °C

THYS TJThermal Shutdown Hysteresis 15 °C

SEL, EN/SET

VSEL(L) SEL Threshold Low 0.4 V

VSEL(H) SEL Threshold High 1.4 V

VEN/SET(L) Enable Threshold Low 0.4 V

VEN/SET(H) Enable Threshold High 1.4 V

TEN/SET (LO) EN/SET Low Time VEN/SET < 0.6V 0.3 75 µs

TEN/SET(HI) EN/SET High Time VEN/SET > 1.4V 75 µs

TOFF EN/SET Off Timeout VEN/SET < 0.6V 500 µs

TLAT EN/SET Latch Timeout VEN/SET > 1.4V 500 µs

IEN/SET EN/SET Input Leakage VEN/SET = 5V VIN = 5V -1 1 µA

AAT1231

VIN = 2.7V to 5.5V, SEL = GND, 0.09 0.1 0.11

FB FB Pin Regulation EN/SET = HIGH V

VIN = 2.7V to 5.5V, SEL = HIGH, 0.564 0.6 0.636

EN/SET = DATA16

AAT1231-1

VIN = 2.7V to 5.5V, SEL = GND, 0.09 0.1 0.11

FB FB Pin Regulation EN/SET = DATA16 V

VIN = 2.7V to 5.5V, SEL = HIGH, 0.564 0.6 0.636

EN/SET = HIGH

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

41231.2007.01.1.2

1. Specification over the -40°C to +85°C operating temperature range is assured by design, characterization, and correlation with statis-

tical process controls.

2. Maximum continuous output current increases with reduced output voltage, but may vary depending on operating efficiency and ther-

mal limitations.

Typical Characteristics

Feedback Voltage vs. Temperature

(RBALLAST = 30.1ΩΩ)

Temperature (°C)

Feedback Voltage (mV)

100

200

300

400

500

600

700

-40 -15 10 35 60 85

Shutdown Current vs. Input Voltage

(EN = GND)

Input Voltage (V)

Shutdown Current (µA)

0.0

0.2

0.4

0.6

0.8

1.0

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

-40°C

85°C

25°C

Efficiency vs. LED Current

(12 White LEDs; RBALLAST = 30.1Ω

)

LED Current (mA)

Efficiency (%)

2 4 6 8 10 12 14 16 18 20

VIN = 3.6V

VIN = 4.2V

VIN = 5V

Efficiency vs. LED Current

(6 White LEDs; R

BALLAST

= 30.1Ω

)

LED Current (mA)

Efficiency (%)

2 4 6 8 10 12 14 16 18 20

= 3.6V

= 4.2V

= 5V

Efficiency vs. LED Current

(5 White LEDs; RBALLAST = 30.1Ω

)

LED Current (mA)

Efficiency (%)

2 4 6 8 10 12 14 16 18 20

VIN = 3.6V

VIN = 4.2V

VIN = 5V

Efficiency vs. LED Current

(4 White LEDs; R

BALLAST

= 30.1Ω

)

LED Current (mA)

Efficiency (%)

2 4 6 8 10 12 14 16 18 20

= 3.6V V

= 4.2V

= 5V

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 5

Typical Characteristics

Output Ripple

(6 White LEDs; I

LED

= 20mA)

Time (200ns/div)

OUT

(DC

Offset 20.7V)

(20mV/div)

(V)

(A)

0.5

Output Ripple

(6 White LEDs; I

LED

= 13mA)

Time (400ns/div)

OUT

(DC

Offset 19.8V)

(50mV/div)

(V)

(A)

0.5

Shutdown

= 0.6V; I

LED

= 20mA)

Enable Voltage (V) (top)

Feedback Voltage (V) (middle)

Inductor Current (A) (bottom)

Time (50µs/div)

0.2

0.4

0.6

0.0

0.5

2.5V

Line Transient

(6 White LEDs; R

BALLAST

= 30.1Ω)

Input Voltage (top) (V)

Output Voltage (middle) (V)

Feedback Voltage (bottom) (V)

Time (50µs/div)

20.2

20.4

20.6

20.8

0.4

0.6

0.8

3.6V

4.2V

Accuracy ILED vs. Input Voltage

(VFB = 0.6V; RBALLAST = 30.1Ω

)

Input Voltage (V)

Accuracy ILED (%)

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.7 3.2 3.7 4.2 4.7 5.2 5.7

-40°C

25°C

85°C

Accuracy I

LED

vs. Temperature

= 0.6V; R

BALLAST

= 30.1Ω

)

Temperature (

Accuracy I

LED

(%)

-1.0

-0.8

-0.5

-0.3

0.0

0.3

0.5

0.8

1.0

-40 -15 10 35 60 85

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

61231.2007.01.1.2

Typical Characteristics

Transition of LED Current

(6 White LEDs; SEL = Low; I

LED

= 3.3mA to 13.3mA)

Output Voltage (top) (V)

Feedback Voltage (bottom) (V)

Time (20µs/div)

0.0

0.1

0.2

0.3

0.4

Transition of LED Current

(6 White LEDs; SEL = Low; I

LED

= 13.3mA to 6.6mA)

Output Voltage (top) (V)

Feedback Voltage (bottom) (V)

Time (20µs/div)

0.0

0.1

0.2

0.3

0.4

AAT1231-1 Soft Start

(6 White LEDs; V

= 0.6V)

Enable Voltage (top) (V)

Feedback Voltage (middle) (V)

Inductor Current (bottom) (A)

Time (50µs/div)

0.2

0.4

0.6

2.5V

AAT1231-1 Soft Start with S

Cwire

(6 White LEDs; V

= 0.3V)

Enable Voltage (top) (V)

Feedback Voltage (middle) (V)

Inductor Current (bottom) (A)

Time (100µs/div)

0.2

0.4

0.6

2.5V

AAT1231 Soft Start

(6 White LEDs; V

= 0.3V)

Enable Voltage (top) (V)

Feedback Voltage (middle) (V)

Inductor Current (bottom) (A)

Time (50µs/div)

0.2

2.5V

AAT1231 Soft Start with S

Cwire

(6 White LEDs; V

= 0.6V)

Time (100µs/div)

0.2

0.4

2.5V

Enable Voltage (top) (V)

Feedback Voltage (middle) (V)

Inductor Current (bottom) (A)

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 7

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

81231.2007.01.1.2

Typical Characteristics

Input Disconnect Switch Resistance

vs. Input Voltage

Input Voltage (V)

DS(ON)IN

(mΩΩ)

140

160

180

200

220

240

260

280

300

2.5 3 3.5 4 4.5 5 5.5 6

120°C100°C

25°C

85°C

Low Side Switch On Resistance

vs. Input Voltage

Input Voltage (V)

DS(ON)L

(mΩ)

100

120

140

160

2.5 3 3.5 4 4.5 5 5.5 6

120°C

100°C

25°C85°C

EN/SET High Threshold vs. Input Voltage

Input Voltage (V)

(V)

0.6

0.5

0.4

0.7

0.8

0.9

1.0

1.1

1.2

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

25°C85°C

-40°C

EN/SET Low Threshold vs. Input Voltage

Input Voltage (V)

(V)

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

-40°C

25°C85°C

EN/SET Off Timeout vs. Input Voltage

Input Voltage (V)

EN/SET Off Timeout (µs)

100

150

200

250

300

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

25°C

85°C

-40°C

EN/SET Latch Timeout vs. Input Voltage

Input Voltage (V)

EN/SET Latch Timeout (µs)

100

150

200

250

300

350

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

85°C

-40°C

25°C

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 9

Functional Block Diagram

Control

Reference

Output

Select

SEL

EN/SET

PVIN LIN

AGND PGND

OVP

VIN

Functional Description

The AAT1231 and the AAT1231-1 consist of a

DC/DC boost controller, an integrated slew rate

controlled input disconnect MOSFET switch, and a

high voltage MOSFET power switch. A high voltage

rectifier, power inductor, output capacitor, and

sense resistors are required to implement a DC/DC

constant current boost converter. The input discon-

nect switch is activated when a valid input voltage

is present and the EN/SET pin is pulled high. The

slew rate control on the P-channel MOSFET

ensures minimal inrush current as the output volt-

age is charged to the input voltage, prior to the

switching of the N-channel power MOSFET.

Monotonic turn-on is guaranteed by the integrated

soft-start circuitry. Soft-start eliminates output volt-

age overshoot across the full input voltage range

and all loading conditions.

The maximum current through the LED string is set

by the ballast resistor and the feedback voltage of

the IC. The output current may be programmed by

adjusting the level of the feedback reference volt-

age which is programmed through the S2Cwire

interface. The SEL pin selects one of two feedback

voltage ranges. For the AAT1231 and with a LOW

logic level applied to the SEL pin, the FB pin volt-

age can be programmed from 0.1V to 0.4V. With a

logic HIGH applied to the SEL pin, the FB pin volt-

age can be programmed from 0.3V to 0.6V. In the

AAT1231-1, the SEL function is inverted in that the

FB pin voltage can be programmed from 0.4V to

0.1V with a logic LOW applied to the SEL pin and

0.6V to 0.3V with a logic HIGH applied to the SEL

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

10 1231.2007.01.1.2

pin. Regardless of which device is chosen, the

feedback voltage can be set to any one of 16 cur-

rent levels within each FB range, providing high-

resolution control of the LED current, using the sin-

gle-wire S2Cwire control.

For torch and flash applications where a short

duration, pulsed load is desired, applying a low-

to-high transition on the AAT1231's SEL pin pro-

duces a 1.5x to 3.0x LED current step. In the

AAT1231-1 on the other hand, the LED current

step for a low-to-high transition on the SEL pin

can be programmed from 3.0x to 1.5x. In both

products, the step size is determined by the pro-

grammed voltage at the FB pin where the internal

default setting is 3.0x in the AAT1231 and 1.5x in

the AAT1231-1.

Control Loop

The AAT1231/1231-1 provide the benefits of cur-

rent mode control with a simple hysteretic output

current loop providing exceptional stability and

fast response with minimal design effort. The

device maintains exceptional constant current

regulation, transient response, and cycle-by-cycle

current limit without additional compensation

components.

The AAT1231/1231-1 modulate the power MOS-

FET switching current to maintain the pro-

grammed FB voltage. This allows the FB voltage

loop to directly program the required inductor cur-

rent in order to maintain the desired LED current.

The switching cycle initiates when the N-channel

MOSFET is turned ON and current ramps up in

the inductor. The ON interval is terminated when

the inductor current reaches the programmed

peak current level. During the OFF interval, the

input current decays until the lower threshold, or

zero inductor current, is reached. The lower cur-

rent is equal to the peak current minus a preset

hysteresis threshold, which determines the induc-

tor ripple current. The peak current is adjusted by

the controller until the LED output current require-

ment is met.

The magnitude of the feedback error signal deter-

mines the average input current. Therefore, the

AAT1231/1231-1 controller implements a pro-

grammed current source connected to the output

capacitor, parallel with the LED string and ballast

resistor. There is no right-half plane zero, and

loop stability is achieved with no additional com-

pensation components.

An increase in the feedback voltage (VFB) results

in an increased error signal sensed across the

ballast resistor (R1). The controller responds by

increasing the peak inductor current, resulting in

higher average current in the inductor and LED

string(s). Alternatively, when the VFB is reduced,

the controller responds by decreasing the peak

inductor current, resulting in lower average cur-

rent in the inductor and LED string(s).

Under light load conditions, the inductor OFF inter-

val current goes below zero and the boost convert-

er enters discontinuous mode operation. Further

reduction in the load current results in a correspon-

ding reduction in the switching frequency. The

AAT1231/1231-1 provide pulsed frequency opera-

tion which reduces switching losses and maintains

high efficiency under light load conditions.

Operating frequency varies with changes in the

input voltage, output voltage, and inductor size.

Once the boost converter has reached continuous

mode, further increases in the LED current will not

significantly change the operating frequency. A

small 2.2µH (±20%) inductor is selected to main-

tain high frequency switching (up to 2MHz) and

high efficiency operation for outputs up to 24V.

Soft Start / Enable

The input disconnect switch is activated when a

valid input voltage is present and the EN/SET pin

is pulled high. The slew rate control on the P-

channel MOSFET ensures minimal inrush current

as the output voltage is charged to the input volt-

age, prior to switching of the N-channel power

MOSFET. Monotonic turn-on is guaranteed by the

built-in soft-start circuitry. Soft start eliminates

output current overshoot across the full input volt-

age range and all loading conditions.

After the soft start sequence has terminated, the

initial LED current is determined by the internal,

default FB voltage across the external ballast resis-

tor at the FB pin. Additionally, the AAT1231 and the

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 11

AAT1231-1 have been designed to offer the sys-

tem designer two choices for the default FB voltage

based on the state of the SEL pin. Changing the

LED current from its initial default setting is easy by

using the S2Cwire single wire serial interface; the

FB voltage can be increased (as in the AAT1231;

see Table 2) or decreased (as in the AAT1231-1;

see Table 3) relative to the default FB voltage.

Current Limit and Over-Temperature

Protection

The switching of the N-channel MOSFET termi-

nates when a current limit of 2.5A (typical) is

exceeded. This minimizes power dissipation and

component stresses under overload and short-cir-

cuit conditions. Switching resumes when the cur-

rent decays below the current limit.

Thermal protection disables the AAT1231/1231-1

when internal dissipation becomes excessive.

Thermal protection disables both MOSFETs. The

junction over-temperature threshold is 140°C with

15°C of temperature hysteresis. The output voltage

automatically recovers when the over-temperature

fault condition is removed.

Over-Voltage Protection

Over-voltage protection prevents damage to the

AAT1231/1231-1 during open-circuit or high output

voltage conditions. An over-voltage event is

defined as a condition where the voltage on the

OVP pin exceeds the Over-Voltage Threshold Limit

(VOVP = 1.2V typical). When the voltage on the

OVP pin has reached the threshold limit, the con-

verter stops switching and the output voltage

decays. Switching resumes when the voltage on

the OVP pin drops below the lower hysteresis limit,

maintaining an average output voltage between the

upper and lower OVP thresholds multiplied by the

resistor divider scaling factor.

Under-Voltage Lockout

Internal bias of all circuits is controlled via the VIN

input. Under-voltage lockout (UVLO) guarantees

sufficient VIN bias and proper operation of all inter-

nal circuitry prior to soft start.

Application Information

Over-Voltage Protection

OVP Protection with Open Circuit Failure

The OVP protection circuit consists of a resistor

network tied from the output voltage to the OVP pin

(see Figure 1). To protect the device from open cir-

cuit failure, the resistor divider can be selected

such that the over-voltage threshold occurs prior to

the output reaching 24V (VOUT(MAX)). The value of

R3 should be selected from 10kΩto 20kΩto mini-

mize losses without degrading noise immunity.

Figure 1: Over-Voltage Protection Circuit.

Figure 2: Over-Voltage Protection

Open Circuit Response (No LED).

Over Voltage Protection Pin (top) (V)

Inductor Current (bottom (A)

Output Voltage (middle) (V)

Time (5ms/div)

222

1.168V

1.224V

OUT

VOUT

AAT1231/1231-1

OVP

GND

= R

· - 1

OUT(MAX)

OVP

⎛⎞

⎝⎠

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

12 1231.2007.01.1.2

Assume R3 = 12kΩand VOUT(MAX) = 24V. Selecting

1% resistor for high accuracy, this results in R2 =

226kΩ(rounded to the nearest standard value).

The minimum OVP threshold can be calculated:

To avoid OVP detection and subsequent reduction

in the programmed output current (see following

section), the maximum operating voltage should

not exceed the minimum OVP set point.

In some cases, this may disallow configurations

with high LED forward voltage (VFLED) and/or

greater than five series white LEDs. VFLED unit-to-

unit tolerance can be as high as +15% of nominal

for white LED devices.

OVP Constant Voltage Operation

Under closed loop constant current conditions, the

output voltage is determined by the operating cur-

rent, LED forward voltage characteristics (VFLED),

quantity of series connected LEDs (N), and the

feedback pin voltage (VFB).

When the rising OVP threshold is exceeded,

switching is stopped and the output voltage

decays. Switching automatically restarts when the

output drops below the lower OVP hysteresis volt-

age (100mV typical) and, as a result, the output

voltage increases. The cycle repeats, maintaining

an average DC output voltage proportional to the

average of the rising and falling OVP levels (multi-

plied by the resistor divider scaling factor). High

operating frequency and small output voltage ripple

ensure DC current and negligible flicker in the LED

string(s).

The waveform in Figure 3 shows the output voltage

and LED current at cold temperature with a six

series white LED string and VOVP = 19.4V. As

shown, the output voltage rises as a result of the

increased VFLED which triggers the OVP constant

voltage operation. Self heating of the LEDs trig-

gers a smooth transition back to constant current

control.

Figure 3: Over-Voltage Protection

Constant Voltage Operation

(6 White LEDs; ILED = 13mA;

R2= 182kΩΩ; R3= 12kΩΩ).

While OVP is active, the maximum LED current

programming error (ΔILED) is proportional to voltage

error across an individual LED (ΔVFLED).

To minimize the ΔILED error, the minimum OVP volt-

age (VOUT(OVP_MIN)) may be increased, yielding a

corresponding increase in the maximum OVP volt-

age (VOUT(OVP_MAX)). Measurements should confirm

that the maximum switching node voltage

(VSW(MAX)) is less than 28V under worst-case oper-

ating conditions.

(N · V

FLED(MAX)

- V

OUT(OVP_MIN)

- V

)

ΔV

FLED

OVP Constant Voltage Operation

LED

(10mA/div)

OUT

(5V/div)

ΔI

LED

Cold Temperature Applied Self-Recovery

Time (1s/div)

OUT

= V

+ N · V

FLED

OUT(MAX)

< V

OUT(OVP_MIN)

⎛⎞

· + 1

⎝⎠

OUT(OVP_MIN)

= V

OVP(MIN)

= 21.8V

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 13

VF= Schottky Diode DS1 forward voltage at turn-

OFF

VRING = Voltage ring occurring at turn-OFF

LED Selection and Current Setting

The AAT1231/1231-1 are well suited for driving

white LEDs with constant current. Applications

include main and sub-LCD display backlighting,

and color LEDs.

The LED current is controlled by the FB voltage

and the ballast resistor. For maximum accuracy, a

1% tolerance resistor is recommended.

The ballast resistor (RBALLAST) value can be cal-

culated as follows:

where:

VFB(MAX) = 0.4V when SEL = Low

VFB(MAX) = 0.6V when SEL = High

i.e., for a maximum LED current of 20mA (SEL =

High):

Table 1: Maximum LED Current and RBALLAST

Resistor Values (1% Resistor Tolerance).

Typical white LEDs are driven at maximum con-

tinuous currents of 15mA to 20mA. For maximum

output, two parallel strings of six series LEDs are

used. A total output current of 30mA or 40mA is

required (15mA to 20mA in each string). The

maximum quantity of series connected LEDs is

determined by the minimum OVP voltage of the

boost converter (VOUT(OVP_MIN)), minus the maxi-

mum feedback voltage (VFB(MAX)) divided by the

maximum LED forward voltage (VFLED(MAX)).

VFLED(MAX) can be estimated from the manufactur-

ers’ datasheet at the maximum LED operating

current.

Figure 4 shows the schematic of using six LEDs in

series. Assume VFLED @ 20mA = 3.5V (typical)

from LW M673 (OSRAM) datasheet.

Therefore, under typical operating conditions, six

LEDs can be used in series.

21.82V

- 0.6V

3.5V

N =

≈ 6.1

⎛⎞

· + 1

⎝⎠

OUT(OVP_MIN)

= 1.1V = 21.82V

226kΩ

12kΩ

OUT(OVP_MIN)

- V

FB(MAX)

)

FLED(MAX)

N =

⎛⎞

· + 1

⎝⎠

OUT(OVP_MIN)

= V

OVP(MIN)

Maximum ILED RBALLAST (ΩΩ)

Current (mA) SEL = High SEL = Low

50 12.1 8.06

40 15.0 10.0

35 16.9 11.3

30 20.0 13.3

25 24.3 16.2

20 30.1 20.0

15 40.2 26.7

10 60.4 40.2

5 121.0 80.6

LED(MAX)

0.6

0.020

BALLAST

= = = 30Ω ≈ 30.1Ω

FB(MAX)

LED(MAX)

BALLAST

⎛⎞

· + 1

+ V

RING

⎝⎠

SW(MAX)

= V

OVP(MAX)

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

14 1231.2007.01.1.2

LED Brightness Control

The AAT1231 and the AAT1231-1 use S2Cwire pro-

gramming to control LED brightness and does not

require PWM (pulse width modulation) or addition-

al control circuitry. This feature greatly reduces the

burden on a microcontroller or system IC to man-

age LED or display brightness, allowing the user to

"set it and forget it." With its high-speed serial inter-

face (1MHz data rate), the output current of the

AAT1231 and the AAT1231-1 can be changed suc-

cessively to brighten or dim the LEDs in smooth

transitions (i.e., to fade out) or in abrupt steps, giv-

ing the user complete programmability and real-

time control of LED brightness. Figure 5: Programming AAT1231 LED Current

with RBALLAST = 30.1ΩΩ.

147101316

LED Current (mA)

Cwire Data Register

SEL = HIGH

SEL = LOW

(Default)

Figure 4: AAT1231/1231-1 White LED Boost Converter Schematic.

= 2.7V to 5.5V

2.2µF C2

2.2µF

2.2µH

226K

12K

30.1Ω

OUT

= 24V/20m

Enable

JP1 R4 10K

Select

JP2

DS1

N/C

VIN

PGND

SEL

GND

OVP

LIN

TSOP12JW

U1 AAT1231/1231-1 TSOPJW-12

L1 2.2µH SD3814-2R2

C1 2.2µF 10V 0603

C2 2.2µF 25V 0805

D1-D6 LW M673 White LED

DS1 30V 0.2A BAT42W SOD-123

R1 30.1 0603

R2 226K 0603

R3 12K 0603

R4 10K 0603

U1 AAT1231/1231-1

LED

Figure 6: Programming AAT1231-1 LED

Current with RBALLAST = 30.1ΩΩ.

Alternatively, toggling the SEL logic pin from low to

high implements stepped or pulsed LED currents by

increasing the FB pin voltage. Figures 7 and 8 illus-

trate the SELECT pin scaling factor, defined as the

LED current with SEL=HIGH divided by the LED

current with SEL=LOW. For the AAT1231, scaling

factors from 1.5x to 3.0x are possible, depending on

the S2Cwire data register (default = 3.0x). In the

AAT1231-1, the possible scaling factors are 3.0x to

1.5x with the internal default setting of 1.5x.

Figure 7: AAT1231 SEL Pin Scaling Factor:

ILED (SEL = High) Divided by ILED (SEL = Low).

Figure 8: AAT1231-1 SEL Pin Scaling Factor:

ILED (SEL = High) Divided by ILED (SEL = Low).

S2Cwire Serial Interface

AnalogicTech's S2Cwire single wire serial interface

is a proprietary high-speed single-wire interface

available only from AnalogicTech. The S2Cwire

interface records rising edges of the EN/SET input

and decodes them into 16 individual states. Each

state corresponds to a reference feedback voltage

setting on the FB pin, as shown in Table 2.

S2Cwire Serial Interface Timing

The S2Cwire single wire serial interface data can be

clocked-in at speeds up to 1MHz. After data has

been submitted, EN/SET is held high to latch the

data for a period TLAT. The FB pin voltage is subse-

quently changed to the level as defined by the state

of the SEL logic pin. When EN/SET is set low for a

time greater than TOFF, the AAT1231/1231-1 is dis-

abled. When either the AAT1231 or the AAT1231-1

is disabled, the register is reset to its default value.

In the AAT1231, the default register value sets the

FB pin voltage to 0.6V if the EN/SET pin is subse-

quently pulled HIGH. In the AAT1231-1, the FB pin

voltage is set to 0.3V under the same condition.

Cwire Data Register

Select Pin Scaling Factor

(Low to High)

(Default)

1. 0

1. 5

2. 0

2. 5

3. 0

3. 5

14 7101316

1.0

1.5

2.0

2.5

3.0

3.5

14 7101316

Cwire Data Register

Select Pin Scaling Factor

(High to Low)

(Default)

Cwire Data Register

LED Current (mA)

147101316

SEL=LOW

SEL=HIGH

(Default)

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 15

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

16 1231.2007.01.1.2

Figure 9: AAT1231/1231-1 S2Cwire Timing Diagram to Program the Output Voltage.

Table 2: AAT1231 S2Cwire Reference Feedback Voltage Control Settings with RBALLAST = 30.1ΩΩ

(Assume Nominal Values).

Rising Clock SEL = Low SEL = High

Edges/Data Reference LED Current (mA); Reference LED Current (mA);

1 0.1 (default) 3.32 0.3 (default) 9.97

2 0.12 3.99 0.32 10.63

3 0.14 4.65 0.34 11.30

4 0.16 5.32 0.36 11.96

5 0.18 5.98 0.38 12.62

6 0.20 6.64 0.40 13.29

7 0.22 7.31 0.42 13.95

8 0.24 7.97 0.44 14.62

9 0.26 8.64 0.46 15.28

10 0.28 9.30 0.48 15.95

11 0.30 9.97 0.50 16.61

12 0.32 10.63 0.52 17.28

13 0.34 11.30 0.54 17.94

14 0.36 11.96 0.56 18.60

15 0.38 12.62 0.58 19.27

16 0.40 13.29 0.60 19.93

EN/SET

2n-1 n ≤ 16

Data Reg 0n-1

LAT

OFF

S2Cwire Feedback Voltage

Programming

The FB pin voltage is set to the default level at ini-

tial powerup. The AAT1231 and the AAT1231-1 are

programmed through the S2Cwire interface. Table 2

illustrates FB pin voltage programming for the

AAT1231 and Table 3 illustrates FB pin voltage pro-

gramming for the AAT1231-1. The rising clock

edges applied at the EN/SET pin determine the FB

pin voltage. If a logic LOW is applied at the SEL pin,

the default feedback voltage range for the AAT1231

is 0.1V to 0.4V; for a logic HIGH condition at the

SEL pin, the default feedback voltage range is 0.3V

to 0.6V. Conversely, if a logic LOW is applied at the

SEL pin of the AAT1231-1, the default feedback

voltage range becomes 0.4V to 0.1V and 0.6V to

0.3V for a logic HIGH condition at the SEL pin.

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 17

Table 3: AAT1231-1 S2Cwire Reference Feedback Voltage Control Settings With RBALLAST = 30.1ΩΩ

(Assumes Nominal Values).

Rising Clock SEL = Low SEL = High

Edges/Data Reference LED Current (mA); Reference LED Current (mA);

1 0.4 (default) 13.29 0.6 (default) 19.93

2 0.38 12.62 0.58 19.27

3 0.36 11.96 0.56 18.60

4 0.34 11.30 0.54 17.94

5 0.32 10.63 0.52 17.28

6 0.30 9.97 0.50 16.61

7 0.28 9.30 0.48 15.95

8 0.26 8.64 0.46 15.28

9 0.24 7.97 0.44 14.62

10 0.22 7.31 0.42 13.95

11 0.20 6.64 0.40 13.29

12 0.18 5.98 0.38 12.62

13 0.16 5.32 0.36 11.96

14 0.14 4.65 0.34 11.30

15 0.12 3.99 0.32 10.63

16 0.10 3.32 0.30 9.97

Selecting the Schottky Diode

To ensure minimum forward voltage drop and no

recovery, high voltage Schottky diodes are consid-

ered the best choice for the AAT1231/1231-1 boost

converters. The output diode is sized to maintain

acceptable efficiency and reasonable operating

junction temperature under full load operating con-

ditions. Forward voltage (VF) and package thermal

resistance (θJA) are the dominant factors to consid-

er in selecting a diode. The diode non-repetitive

peak forward surge current rating (IFSM) should be

considered for high pulsed load applications, such

as camera flash. IFSM rating drops with increasing

conduction period. Manufacturers’ datasheets

should be consulted to verify reliability under peak

loading conditions. The diode's published current

rating may not reflect actual operating conditions

and should be used only as a comparative meas-

ure between similarly rated devices.

20V rated Schottky diodes are recommended for out-

puts less than 15V, while 30V rated Schottky diodes

are recommended for outputs greater than 15V.

The switching period is divided between ON and

OFF time intervals.

During the ON time, the N-channel power MOSFET

is conducting and storing energy in the boost induc-

tor. During the OFF time, the N-channel power

MOSFET is not conducting. Stored energy is trans-

ferred from the input battery and boost inductor to

the output load through the output diode.

= T

+ T

OFF

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

18 1231.2007.01.1.2

Duty cycle is defined as the ON time divided by the

total switching interval.

The maximum duty cycle can be estimated from

the relationship for a continuous mode boost con-

verter. Maximum duty cycle (DMAX) is the duty cycle

at minimum input voltage (VIN(MIN)).

The average diode current during the OFF time can

be estimated.

The following curves show the VFcharacteristics

for different Schottky diodes (100°C case). The VF

of the Schottky diode can be estimated from the

average current during the off time.

The average diode current is equal to the output

current.

The average output current multiplied by the for-

ward diode voltage determines the loss of the out-

put diode.

For continuous LED currents, the diode junction

temperature can be estimated.

J(DIODE)

= T

AMB

+ θ

· P

LOSS(DIODE)

= I

AVG(TOT)

= I

OUT

AVG(TOT)

= I

OUT

Forward Voltage (V)

Forward Current (mA)

100

1000

10000

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70

B340LA

MBR0530T

ZHCS350

BAT42W

OUT

1 - D

MAX

AVG(OFF)

OUT

- V

IN(MIN)

OUT

MAX

+ T

OFF

D =

= T

⋅ F

Table 4: Typical Surface Mount Schottky Rectifiers for Various Output Levels.

Rated Non-Repetitive Thermal

Part Forward Peak Surge Rated Resistance

Manufacturer Number Current (A) Current (A) Voltage (V) (θθJA, °C/W) Case

Diodes, Inc. B340LA 3 70.0 40 25 SMA

Diodes, Inc. BAT42W 0.2 4.0 30 500 SOD-123

ON Semi MBR0530T 0.5 5.5 30 206 SOD-123

Zetex ZHCS350 0.35 4.2 40 330 SOD-523

Central Semi CMDSH2-3 0.2 1.0 30 500 SOD-323

Output diode junction temperature should be main-

tained below 110ºC, but may vary depending on

application and/or system guidelines. The diode

θJA can be minimized with additional PCB area on

the cathode. PCB heat-sinking the anode may

degrade EMI performance. The reverse leakage

current of the rectifier must be considered to main-

tain low quiescent (input) current and high efficien-

cy under light load. The rectifier reverse current

increases dramatically at elevated temperatures.

Selecting the Boost Inductor

The AAT1231 and the AAT1231-1 controllers utilize

hysteretic control and the switching frequency

varies with output load and input voltage. The

value of the inductor determines the maximum

switching frequency of the boost converter.

Increased output inductance decreases the switch-

ing frequency, resulting in higher peak currents and

increased output voltage ripple. To maintain 2MHz

maximum switching frequency and stable opera-

tion, an output inductor sized from 1.5µH to 2.7µH

is recommended.

A better estimate of DMAX is possible once VFis

known.

Where VFis the Schottky diode forward voltage. If

not known, it can be estimated at 0.5V.

Manufacturer’s specifications list both the inductor

DC current rating, which is a thermal limitation, and

peak inductor current rating, which is determined

by the saturation characteristics. Measurements at

full load and high ambient temperature should be

completed to ensure that the inductor does not sat-

urate or exhibit excessive temperature rise.

The output inductor (L) is selected to avoid satura-

tion at minimum input voltage, maximum output load

conditions. Peak current may be estimated using

the following equation, assuming continuous con-

duction mode. Worst-case peak current occurs at

minimum input voltage (maximum duty cycle) and

maximum load. Switching frequency (FS) can be

estimated from the curves and assumes a 2.2µH

inductor.

At light load and low output voltage, the controller

reduces the operating frequency to maintain maxi-

mum operating efficiency. As a result, further

reduction in output load does not reduce the peak

current. Minimum peak current can be estimated

from 0.5A to 0.75A.

At high load and high output voltages, the switch-

ing frequency is somewhat diminished, resulting in

higher IPEAK. Bench measurements are recom-

mended to confirm actual IPEAK and ensure that the

inductor does not saturate at maximum LED cur-

rent and minimum input voltage.

The RMS current flowing through the boost induc-

tor is equal to the DC plus AC ripple components.

Under worst-case RMS conditions, the current

waveform is critically continuous. The resulting

RMS calculation yields worst-case inductor loss.

The RMS current value should be compared

against the manufacturer's temperature rise, or

thermal derating, guidelines.

OUT

(1 - D

MAX

)

MAX

IN(MIN)

PEAK

= +

Output Current (mA)

Switching Frequency (MHz)

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

40 50 60 70 80 90 100

= 3.6V

OUT

= 10V

= 3.6V

OUT

= 12V

= 2.7V

OUT

= 12V

= 2.7V

OUT

= 10V

= 3.0V

OUT

= 10V

= 3.0V

OUT

= 12V

Output Current (mA)

Switching Frequency (MHz)

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

40 50 60 70 80 90 100

= 2.7V

OUT

= 15V

= 2.7V

OUT

= 18V

= 3.0V

OUT

= 15V

= 3.0V

OUT

= 18V

= 3.6V

OUT

= 15V

= 3.6V

OUT

= 18V

OUT

+ V

- V

IN(MIN)

)

OUT

+ V

)

MAX

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 19

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

20 1231.2007.01.1.2

Table 5: Recommended Inductors for Various Output Levels (Select IPEAK < ISAT).

Maximum

Part Inductance DC ISAT DCR Size (mm)

Manufacturer Number (µH) Current (mA) (mΩΩ) LxWxH Type

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

www.sumida.com

Cooper Electronics SD3814-2R2 2.2 1900 77 4.0x4.0x1.4 Shielded

www.cooperet.com SD3110-2R2 2.2 910 161 3.1x3.1x1.0 Shielded

Murata LQH2MCN2R2M02L 2.2 455 440 2.0x1.6x0.7 Shielded

www.murata.com

NR3010T-2R2M 2.2 1100 95 3.0x3.0x1.0 Shielded

Taiyo Yuden CBC2016T2R2M 2.2 750 200 2.0x1.6x1.6 Chip

www.t-yuden.com Non-Shielded

CBC2518T2R2M 2.2 510 90 2.5x1.8x1.8 Shielded

For a given inductor type, smaller inductor size leads

to an increase in DCR winding resistance and, in

most cases, increased thermal impedance. Winding

resistance degrades boost converter efficiency and

increases the inductor’s operating temperature.

To ensure high reliability, the inductor case temper-

ature should not exceed 100ºC. In some cases,

PCB heatsinking applied to the LIN node (non-

switching) can improve the inductor's thermal

capability. PCB heatsinking may degrade EMI per-

formance when applied to the SW node (switching)

of the AAT1231/1231-1.

Shielded inductors provide decreased EMI and may

be required in noise sensitive applications.

Unshielded chip inductors provide significant space

savings at a reduced cost compared to shielded

(wound and gapped) inductors. In general, chip-

type inductors have increased winding resistance

(DCR) when compared to shielded, wound varieties.

Inductor Efficiency Considerations

The efficiency for different inductors is shown in

Figure 7 for six white LEDs in series. Smaller

inductors yield increased DCR and reduced oper-

ating efficiency.

Figure 10: AAT1231/1231-1 Efficiency for

Different Inductor Types (VIN = 3.6V;

Six White LEDs in Series).

25811141720

LED Current (mA)

Efficiency (%)

Cooper SD3814-2R2 (77mΩ)Cooper SD3110-2R2 (161mΩ)

Murata LQH2MCN2R2M02L (440mΩ)

LOSS(INDUCTOR)

= I

RMS2

· DCR

PEAK

RMS

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 21

Selecting the Boost Capacitors

The high output ripple inherent in the boost con-

verter necessitates low impedance output filtering.

Multi-layer ceramic (MLC) capacitors provide small

size and adequate capacitance, low parasitic

equivalent series resistance (ESR) and equivalent

series inductance (ESL), and are well suited for

use with the AAT1231/1231-1 boost regulator. MLC

capacitors of type X7R or X5R are recommended

to ensure good capacitance stability over the full

operating temperature range.

The output capacitor is sized to maintain the output

load without significant voltage droop (ΔVOUT) dur-

ing the power switch ON interval, when the output

diode is not conducting. A ceramic output capacitor

from 2.2µF to 4.7µF is recommended (see Table 5).

Typically, 25V rated capacitors are required for the

24V maximum boost output. Ceramic capacitors

sized as small as 0805 are available which meet

these requirements.

MLC capacitors exhibit significant capacitance

reduction with applied voltage. Output ripple meas-

urements should confirm that output voltage droop

and operating stability are acceptable. Voltage derat-

ing can minimize this factor, but results may vary with

package size and among specific manufacturers.

Output capacitor size can be estimated at a switch-

ing frequency (FS) of 500kHz (worst case).

To maintain stable operation at full load, the output

capacitor should be sized to maintain ΔVOUT

between 100mV and 200mV.

The boost converter input current flows during both

ON and OFF switching intervals. The input ripple

current is less than the output ripple and, as a

result, less input capacitance is required.

PCB Layout Guidelines

Boost converter performance can be adversely

affected by poor layout. Possible impact includes

high input and output voltage ripple, poor EMI per-

formance, and reduced operating efficiency. Every

attempt should be made to optimize the layout in

order to minimize parasitic PCB effects (stray resist-

ance, capacitance, and inductance) and EMI cou-

pling from the high frequency SW node. A suggest-

ed PCB layout for the AAT1231/1231-1 boost con-

verter is shown in Figures 10 and 11. The following

PCB layout guidelines should be considered:

1. Minimize the distance from Capacitor C1 and

C2 negative terminal to the PGND pins. This is

especially true with output capacitor C2, which

conducts high ripple current from the output

diode back to the PGND pins.

2. Minimize the distance between L1 to DS1 and

switching pin SW; minimize the size of the PCB

area connected to the SW pin.

3. Maintain a ground plane and connect to the IC

PGND pin(s) as well as the GND terminals of

C1 and C2.

4. Consider additional PCB area on DS1 cathode

to maximize heatsinking capability. This may

be necessary when using a diode with a high

VFand/or thermal resistance.

OUT

· D

MAX

· ΔV

OUT

Table 6: Recommended Ceramic Capacitors.

Manufacturer Part Number Value (µF) Voltage Rating Temp Co Case Size

Murata GRM188R60J225KE19 2.2 6.3 X5R 0603

Murata GRM188R61A225KE34 2.2 10 X5R 0603

Murata GRM219R61E225KA12 2.2 25 X5R 0805

Murata GRM21BR71E225KA73L 2.2 25 X7R 0805

Murata GRM21BR61E475KA12 4.7 25 X5R 0805

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

22 1231.2007.01.1.2

Figure 11: AAT1231/1231-1 Evaluation Figure 12: AAT1231/1231-1 Evaluation

Board Top Side Layout (with six LEDs Board Bottom Side Layout (with six LEDs

and microcontroller). and microcontroller).

AAT1231/1231-1

White LED

Driver

Cwire

Microcontroller

Figure 13: AAT1231/1231-1 Evaluation Board Schematic (with six LEDs and microcontroller).

2.2µF

2.2µH

226K

12K

30.1Ω

VOUT

2.2µF

Schottky

DS1

N/C

VIN

PGND

SEL

GND

OVP

LIN

AAT1231/1231-1

U1 D1

LED

VDD

GP5

GP4

GP3

GP2

GP1

GP0

VSS

PIC12F675

1µF

VCC

10K

Down

Select

330

RED

12 34 5

SW1

12 34 5

SW2

12 34 5

SW3

GREEN

(Select indicator)

Cwire

Microcontroller

AAT1231/1231-1

White LED

Driver

330

123

JP1

DC- DC+

VCC

J2 J3

U1 AnalogicTech AAT1231/1231-1 TSOPJW-12 package

U2 PIC12F675

C1 GRM188R60J225KE01

C2 GRM21BR71E225KA73

C3 GRM216R61A105KA01

R1 30.1Ω, 1%, 1/4W; 0603

R2 226kΩ, 1%, 1/4W; 0603

R3 12.1kΩ, 1%, 1/4W; 0603

R4 10kΩ, 5%, 1/4W; 0603

R5, R6, R7 1KΩ, 5%, 1/4W; 0805

R8, R9 330Ω, 5%, 1/4W; 0805

JP1 0Ω, 5%; 0805

DS1 BAT42W

L1 Cooper Electronics 2.2µH SD3814-2R2

D1-D6 White Hyper-Bright LED LW M673

D7 Red LED 1206

D8 Green LEC 1206

SW1 - SW3 SPST, 5mm

J1, J2, J3 Conn. Header, 2mm

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 23

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

24 1231.2007.01.1.2

Additional Applications

Figure 14: Four LEDs In Series Configuration.

Figure 15: Five LEDs In Series Configuration.

Efficiency vs. LED Current

(5 White LEDs; R

BALLAST

= 30.1Ω

)

LED Current (mA)

Efficiency (%)

2 4 6 8 10 12 14 16 18 20

= 3.6V

= 4.2V

= 5V

LIN

L = 2.2µH DS1

2.2µF

196kΩ

12kΩ

30.1Ω 20mA

ENSET

PGND

PVIN

AAT1231/

1231-1

SEL

Up to 24V/

50mA max

VIN

AGND

OVP

Li-Ion

= 2.7V

to 5.5V

Efficiency vs. LED Current

(4 White LEDs; R

BALLAST

= 30.1Ω

)

LED Current (mA)

Efficiency (%)

2 4 6 8 10 12 14 16 18 20

= 3.6V V

= 4.2V

= 5V

LIN

L = 2.2µH DS1

2.2µF

187kΩ

12kΩ

30.1Ω 20mA

ENSET

PGND

PVIN

AAT1231/

1231-1

SEL

Up to 24V/

50mA max

VIN

AGND

OVP

Li-Ion

= 2.7V

to 5.5V

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 25

Figure 16: Six LEDs In Series Configuration.

Figure 17: Twelve LEDs In Series/Parallel Configuration.

Efficiency vs. LED Current

(12 White LEDs; R

BALLAST

= 30.1Ω

)

LED Current (mA)

Efficiency (%)

2 4 6 8 10 12 14 16 18 20

= 3.6V

= 4.2V

= 5V

LIN

EN/SET

PGND

PVIN

2.2µF

226kΩ

12kΩ

30.1Ω

20mA

30.1Ω

20m

L = 2.2µH DS1

AAT1231/

1231-1

SEL

Up to 24V/

50mA max

VIN

AGND

OVP

Li-Ion

= 2.7V

to 5.5V

Efficiency vs. LED Current

(6 White LEDs; R

BALLAST

= 30.1Ω

)

LED Current (mA)

Efficiency (%)

2 4 6 8 10 12 14 16 18 20

= 3.6V

= 4.2V

= 5V

LIN

EN/SET

PGND

PVIN

2.2µF

226kΩ

12kΩ

30.1Ω

20mA

L = 2.2µH DS1

AAT1231/

1231-1

SEL

Up to 24V/

50mA max

VIN

AGND

OVP

Li-Ion

= 2.7V

to 5.5V

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

26 1231.2007.01.1.2

Ordering Information

Package Information

TSOPJW-12

All dimensions in millimeters.

0.20 + 0.10

- 0.05

0.055 ± 0.045 0.45 ± 0.15

7° NOM

4° ± 4°

3.00 ± 0.10

2.40 ± 0.10

2.85 ± 0.20

0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC

0.15 ± 0.05

0.9625

0.0375

1.00 + 0.10

- 0.065

0.04 REF

0.010

2.75 ± 0.25

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.

Package Marking1Part Number (Tape and Reel)2

TSOPJW-12 SDXYY AAT1231ITP-T1

TSOPJW-12 TUXYY AAT1231ITP-1-T1

1. XYY = assembly and date code.

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

AAT1231/1231-1

Step-Up DC/DC Converters for

White LED Backlight Applications

1231.2007.01.1.2 27

Advanced Analogic Technologies, Inc.

830 E. Arques Avenue, Sunnyvale, CA 94085

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 without notice.

Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold sub-

ject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech

warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech’s standard warranty. Testing and other quality con-

trol 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 regis-

tered trademarks or trademarks of their respective holders.