AAT3194 - AnalogicTech - Datasheet.Live

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

Typical Application

1µF

BATTERY

OUT

1µF

EN/SET

1µF

D4 D3 D2 D1

OUT

C1+

C1-

C2+

C2-

EN/SET

GND

AAT3194

3194.2006.09.1.0 1

ChargePump™

General Description

The AAT3194 is a low noise, constant frequency

charge pump DC/DC converters that use fractional

(1.5X) conversion to increase efficiency in white

LED applications. The devices can be used to pro-

duce current levels up to 20mA for each output

from a 2.7V to 5.5V input. A low external parts

count (two 1µF flying capacitors and two small

bypass capacitors at IN and OUT) makes these

devices ideally suited for small, battery-powered

applications.

AnalogicTech’s Simple Serial Control™ (S2Cwire™)

interface is used to enable, disable, and set the

LED drive current for 32-level logarithmic scale LED

brightness control. The AAT3194 has a thermal

management system for protection in the event of a

short-circuit condition on any of the output pins.

Built-in soft-start circuitry prevents excessive inrush

current during start-up. A high switching frequency

enables the use of small external capacitors. A low-

current shutdown feature disconnects the load from

VIN and reduces quiescent current to less than 1µA.

The AAT3194 is available in a Pb-free 12-pin

TSOPJW package.

Features

•V

IN Range: 2.7V to 5.5V

• 20mA Full-Scale Current

• Simple Serial Control (S2Cwire) Interface

— 32-Position Logarithmic Scale with Digital

Control

• Low Noise Constant Frequency Operation

• 33% Less Input Current Than Doubler

Charge Pump

• High Accuracy Brightness Matching

• Small Application Circuit

• Regulated Output Current

• Automatic Soft Start

• No Inductors

• 600kHz Switching Frequency

•I

Q<1µA in Shutdown

• Temperature Range: -40°C to 85°C

• 12-Pin TSOPJW Package

Applications

• Programmable Current Source

• White LED Backlighting

Pin Descriptions

Pin Configuration

TSOPJW-12

(Top View)

C2+

OUT

C1-

C1+

C2-

GND

EN/SET

Pin # Symbol Function

1 C2+ Flying capacitor 2 positive terminal. Connect a 1µF ceramic capacitor between C2+

and C2-.

2 OUT Charge pump output. Requires 1µF bypass capacitor to ground.

3 C1- Flying capacitor 1 negative terminal.

4 C1+ Flying capacitor 1 positive terminal. Connect a 1µF ceramic capacitor between C1+

and C1-.

5 D4 Current source output 4.

6 D3 Current source output 3.

7 D2 Current source output 2.

8 D1 Current source output 1. Required reference current source. Do not leave pin floating.

9 EN/SET Control pin using S2Cwire serial interface.

10 IN Input power supply. Requires 1µF or larger ceramic capacitor to ground.

11 GND Ground.

12 C2- Flying capacitor 2 negative terminal.

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

23194.2006.09.1.0

Absolute Maximum Ratings

TA= 25°C, unless otherwise noted.

Thermal Information1

Symbol Description Value Units

θJA Thermal Resistance 160 °C/W

PDMaximum Power Dissipation2625 mW

Symbol Description Value Units

VIN Input Voltage -0.3 to 6 V

VOUT Charge Pump Output -0.3 to 6 V

VEN/SET EN/SET to GND Voltage -0.3 to 6 V

VEN/SET(MAX) Maximum EN/SET to Input Voltage 0.3 V

IOUT Maximum DC Output Current (sum of IOUT and D currents) 120 mA

TJOperating Junction Temperature Range -40 to 150 °C

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

3194.2006.09.1.0 3

1. Mounted on an FR4 board.

2. Derate 6.25mW/°C above 25°C

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

43194.2006.09.1.0

Electrical Characteristics

VIN = 3.5V, TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= 25°C.

Symbol Description Conditions Min Typ Max Units

Input Power Supply

VIN Operation Range 2.7 V

ICC Operating Current Active, No Load Current 3 mA

ISHDN Shutdown Current EN = 0V 1 µA

IDX Output Current 3.0V ≤VIN ≤5.5V, TA= 25°C, All Outputs Max Current 16 20 24 mA

ΔID/ΔVIN

Output Current Line 3.0V ≤VIN ≤5.5V -3 3 %/V

Regulation

Current Matching

I(D-Match) Between Any VD1:Dn = 3.6V, VIN = 3.3V 0.3 %

Two Outputs

ηEfficiency VIN = 3.5V, IOUT(total) = 40mA 93 %

Charge Pump

tSS Soft-Start Time 400 µs

FCLK Clock Frequency 300 kHz

EN/SET

VEN(L) Enable Threshold Low VIN = 2.7V to 5.5V 0.5 V

VEN(H) Enable Threshold High VIN = 2.7V to 5.5V 1.4 V

tLO EN/SET Low Time 0.3 75 µs

tHI

Minimum EN/SET 50 ns

High Time

tOFF EN/SET Off Timeout 500 µs

Input EN/SET Input Leakage VIN = 5.5V -1 1 µA

Current

Typical Characteristics

VIN = 3.5V, CIN = COUT = C1= C2= 1µF; TA= 25°C, unless otherwise noted.

Oscillator Frequency vs. Temperature

610

620

630

640

650

660

670

680

690

700

710

-40 -20 0 20 40 60 80 100

Temperature (

OSC

(kHz)

Shutdown Current vs. Temperature

0.001

0.010

0.100

1.000

-40 -20 0 20 40 60 80 100

Temperature (

Shutdown Current (

Efficiency vs. Load Current

020406080

Load Current (mA)

Efficiency (%)

Quiescent Current vs. Supply Voltage

0.6

0.7

0.8

0.9

1.0

1.1

1.2

3.0 3.5 4.0 4.5 5.0 5.5

Supply Voltage (V)

(mA)

Efficiency vs. Supply Voltage

100

3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4

Supply Voltage (V)

Efficiency (%)

80mA 60mA

40mA

30mA 20mA

Quiescent Current vs. Temperature

0.86

0.88

0.90

0.92

0.94

0.96

0.98

1.00

-40 -20 0 20 40 60 80 100

Temperature (

(mA)

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

3194.2006.09.1.0 5

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

63194.2006.09.1.0

Typical Characteristics

VIN = 3.5V, CIN = COUT = C1= C2= 1µF; TA= 25°C, unless otherwise noted.

0.750

0.775

0.800

0.825

0.850

0.875

0.900

0.925

0.950

0.975

1.000

2.5 3.0 3.5 4.0 4.5 5.0 5.5

(V)

and V

(V)

and V

vs. V

DIODE

vs. V

DIODE

100

3.0 3.2 3.4 3.6 3.8 4.0

DIODE

(V)

DIODE

(mA)

DIODE

Response

(-9dB to -10dB)

Time (10µs/div)

ENSET

(2V/div)

DIODE

-9dB

0dB

-10dB

-31dB

DIODE

vs. V

100

3.0 3.5 4.0 4.5

(V)

DIODE

(mA)

DIODE

Response

(-31dB to 0dB)

Time (10µs/div)

ENSET

(2V/div)

DIODE

-31dB

0dB

Normalized I

DIODE

vs. Temperature

0.95

0.96

0.97

0.98

0.99

1.00

1.01

1.02

-40 -20 0 20 40 60 80 100

Temperature (

DIODE

Typical Characteristics

VIN = 3.5V, CIN = COUT = C1= C2= 1µF; TA= 25°C, unless otherwise noted.

80mA Load Characteristics

Time (1µs/div)

20mV/div

OUT

DIODE

60mA Load Characteristics

Time (1µs/div)

20mV/div

OUT

DIODE

40mA Load Characteristics

Time (1µs/div)

10mV/div

OUT

DIODE

Turn-Off

Time (200µs/div)

ENSET

(2V/div)

OUT

(5V/div)

DIODE

(5V/div)

(50mA/div)

Turn-On

Time (100µs/div)

ENSET

(2V/div)

OUT

(5V/div)

DIODE

(2V/div)

(50mA/div)

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

3194.2006.09.1.0 7

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

83194.2006.09.1.0

Functional Block Diagram

Voltage

Reference

Soft Start

600kHz

Oscillator

1.5X

Charge

Pump

Cwire

Interface

32x8 bit

ROM

Current

Mode

DAC

C1+

C1-

C2+

C2-

OUT

GND

EN/SET

Functional Description

The AAT3194 is a high efficiency 1.5X fractional

charge pumps intended for white LED backlight

applications. The fractional charge pump consists

of a linear regulator followed by a 1.5X charge

pump. The AAT3194 requires only four external

components: two 1µF ceramic capacitors for the

charge pump flying capacitors (C1 and C2), one

1µF ceramic capacitor for CIN, and one 0.33µF to

1µF ceramic capacitor for COUT. The charge pump

output is converted into four constant current out-

puts (D1 to D4) to drive four individual LEDs with a

maximum of 20mA each. The current source out-

put magnitude is controlled by the EN/SET serial

data S2Cwire interface. The interface records rising

edges of the EN/SET pin and decodes them into 32

individual current level settings each 1dB apart (see

Table 1, Current Level Settings). Code 32 is full

scale, and Code 1 is full scale attenuated by 31dB.

The modulo 32 interface wraps states back to state

1 after the 32nd clock. With each EN/SET pulse,

the output current increases by 1dB. To decrease

the output current by 1dB, 31 EN/SET clock pulses

are required. The counter can be clocked at

speeds up to 1MHz, so intermediate states are not

visible. The first rising edge of EN/SET enables the

IC and initially sets the output LED current to -31dB,

the lowest setting equal to 525µA. Once the final

clock cycle is input for the desired brightness level,

the EN/SET pin is held high to maintain the device

output current at the programmed level. The device

is disabled 500µs after the EN/SET pin transitions

to a logic low state.

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

3194.2006.09.1.0 9

Applications Information

Current Level Settings

LED current level is set via the serial interface

according to a logarithmic scale where each code

is 1dB greater than the previous code. In this man-

ner, the LED brightness appears linear with each

increasing code.

Table 1: Current Level Settings.

Code 20mA max Code 20mA max

1 0.549 17 3.529

2 0.627 18 4.000

3 0.706 19 4.471

4 0.784 20 5.020

5 0.863 21 5.647

6 1.020 22 6.353

7 1.098 23 7.059

8 1.255 24 7.922

9 1.412 25 8.941

10 1.569 26 10.039

11 1.804 27 11.216

12 1.961 28 12.627

13 2.275 29 14.118

14 2.510 30 15.843

15 2.824 31 17.804

16 3.137 32 20.000

Normalized Current Level Settings

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1 2 3 4 5 6 7 8 9 1011121314151617181920212223242526272829303132

Code

Normalized Current to Full Scale

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

10 3194.2006.09.1.0

EN/SET Serial Interface

The current source output magnitude is controlled

by the EN/SET pin using AnalogicTech’s Simple

Serial Control (S2Cwire) interface. The interface

records rising edges of the EN/SET pin and

decodes them into 32 individual current level set-

tings each 1dB apart. Code 32 is full scale, and

Code 1 is full scale attenuated by 31dB. The mod-

ulo 32 interface wraps states back to state 1 after

the 32nd clock, so 1dB of attenuation is achieved by

clocking the EN/SET pin 31 times (see graph titled,

“IDIODE Response -9dB to -10dB”). The counter can

be clocked at speeds up to 1MHz, so intermediate

states are not visible. The first rising edge of

EN/SET enables the IC and initially sets the output

LED current to -31dB, the lowest setting equal to

525µA. Once the final clock cycle is input for the

desired brightness level, the EN/SET pin is held

high to maintain the device output current at the

programmed level. The device is disabled 500µs

after the EN/SET pin transitions to a logic low state.

The EN/SET timing is designed to accommodate a

wide range of data rates. After the first rising edge

of EN/SET, the charge pump is enabled and reach-

es full capacity after the soft-start time (TSS).

During the soft-start time, multiple clock pulses

may be entered on the EN/SET pin to set the final

output current level with a single burst of clocks.

Alternatively, the EN/SET clock pulses may be

entered one at a time to gradually increase the

LED brightness over any desired time period. A

constant current is sourced as long as EN/SET

remains in a logic high state. The current source

outputs are switched off after EN/SET has

remained in a low state for at least the tOFF timeout

period (see Figure 1).

LED Selection

The AAT3194 is designed to drive white LEDs with

forward voltages to 4.2V. Since the D1:D4 output

current sources are matched with negligible voltage

dependence, the LED brightness will be matched

regardless of their forward voltage matching.

Charge Pump Efficiency

The AAT3194 uses a fractional charge pump. The

efficiency (η) can be simply defined as a linear volt-

age regulator with an effective output voltage that is

equal to one and one half times the input voltage.

Efficiency (η) for an ideal 1.5X charge pump can

typically be expressed as the output power divided

by the input power:

In addition, with an ideal 1.5X charge pump, the

output current may be expressed as 2/3 of the

input current. The expression to define the ideal

efficiency (η) can be rewritten as:

-or-

For a charge pump with an output of 5 volts and a

nominal input of 3.5 volts, the theoretical efficiency

is 95%. Due to internal switching losses and IC

quiescent current consumption, the actual efficien-

cy can be measured at 93%. These figures are in

close agreement for output load conditions from

1mA to 100mA. Efficiency will decrease as load

η(%) = 100 V

OUT

1.5V

⎛⎞

⎝⎠

η = P

OUT

= V

OUT

· I

OUT

= V

OUT

· 1.5I

OUT

1.5V

η = P

Figure 1: EN/SET Timing Diagram.

EN/SET

Code 123

OFFOFF

OFF

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

3194.2006.09.1.0 11

current drops below 0.05mA or when the level of

the power supply of IN approaches OUT. Refer to

the Typical Characteristics section of this datasheet

for measured plots of efficiency versus input volt-

age and output load current for the given charge

pump output voltage options.

Power Efficiency and Device Evaluation

The charge pump efficiency discussion in the previ-

ous section only accounts for efficiency of the

charge pump section itself. Due to the unique cir-

cuit architecture and design of the AAT3194, it is

very difficult to measure efficiency in terms of a per-

cent value comparing input power over output

power. Since the device outputs are pure constant

current sources, it is difficult to measure the output

voltage for a given output (D1 to D4) to derive an

output power measurement. For any given appli-

cation, white LED forward voltage levels can differ,

yet the output drive current will be maintained as a

constant. This makes quantifying output power a

difficult task when taken in the context of comparing

to other white LED driver circuit topologies. A bet-

ter way to quantify total device efficiency is to

observe the total input power to the device for a

given LED current drive level. The best white LED

driver for a given application should be based on

trade-offs of size, external components count, relia-

bility, operating range, and total energy usage...not

just "% efficiency."

Capacitor Selection

Careful selection of the four external capacitors

CIN, C1, C2, and COUT is important because they will

affect turn-on time, output ripple, and transient per-

formance. Optimum performance will be obtained

when low equivalent series resistance (ESR)

ceramic capacitors are used. In general, low ESR

may be defined as less than 100mΩ. A value of

1µF for all four capacitors is a good starting point

when choosing capacitors. If the LED current

sources are only programmed for minimal current

levels, then the capacitor size may be decreased.

Capacitor Characteristics

Ceramic composition capacitors are highly recom-

mended over all other types of capacitors for use

with the AAT3194. Ceramic capacitors offer many

advantages over their tantalum and aluminum elec-

trolytic counterparts. A ceramic capacitor typically

has very low ESR, is lowest cost, has a smaller

PCB footprint, and is non-polarized. Low ESR

ceramic capacitors help maximize charge pump

transient response. Since ceramic capacitors are

non-polarized, they are not prone to incorrect con-

nection damage.

Equivalent Series Resistance: ESR is an impor-

tant characteristic to consider when selecting a

capacitor. ESR is a resistance internal to a capac-

itor that is caused by the leads, internal connec-

tions, size or area, material composition, and ambi-

ent temperature. Capacitor ESR is typically meas-

ured in milliohms for ceramic capacitors and can

range to more than several ohms for tantalum or

aluminum electrolytic capacitors.

Ceramic Capacitor Materials: Ceramic capacitors

less than 0.1µF are typically made from NPO or

C0G materials. NPO and C0G materials generally

have tight tolerance and are very stable over tem-

perature. Larger capacitor values are usually com-

posed of X7R, X5R, Z5U, or Y5V dielectric materi-

als. Large ceramic capacitors (i.e., greater than

2.2µF) are often available in low-cost Y5V and Z5U

dielectrics, but capacitors greater than 1µF are not

typically required for AAT3194 applications.

Capacitor area is another contributor to ESR.

Capacitors that are physically large will have a lower

ESR when compared to an equivalent material

smaller capacitor. These larger devices can improve

circuit transient response when compared to an

equal value capacitor in a smaller package size.

AAT3194 Input Power vs. LED Current

100

200

300

400

500

600

700

0 20 40 60 80 100

Output (LED) Current (mA)

Input Power (mW)

= 3.6V

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

12 3194.2006.09.1.0

Application Circuits

Typical AAT3194 Application Circuit:

1μF

BATTERY

OUT

1μF

EN/SET

1μF

D4 D3 D2 D1

OUT

C1+

C1-

C2+

C2-

EN/SET

GND

AAT3194

ON/1

> 50ns 50ns minimum to enable300ns < T

< 75μs

23456 n

(n < =32) OFF

Enable / Disable / LED Brightness Level Set Data Input

Test Current/Channel Disable

Each channel of the output is equipped with a test

current function. The AAT3194 uses a small (~2µA)

current source injected into each output pin to

detect the presence of an LED. Unused channels

that are tied to ground or LED load fail short will be

automatically diasbled instead of wasting the pro-

grammed output current.

Thermal Protection

The AAT3194 has a thermal protection circuit that

will shut down the charge pump and current out-

puts if the die temperature rises above the thermal

limit.

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

3194.2006.09.1.0 13

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 UUXYY AAT3194ITP-20-T1

1. XYY = assembly and date code.

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

AAT3194

High Efficiency 1.5X Fractional Charge

Pump For White LED Applications

14 3194.2006.09.1.0

Advanced Analogic Technologies, Inc.

830 E. Arques Avenue, Sunnyvale, CA 94085

Phone (408) 737-4600

Fax (408) 737-4611

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