LT3494EDDB#TRM - Linear Technology

LT3494/LT3494A

3494fb

TYPICAL APPLICATION

FEATURES

APPLICATIONS

DESCRIPTION

Micropower Low Noise

Boost Converters with

Output Disconnect

The LT

3494/LT3494A are low noise boost converters

with integrated power switch, Schottky diode and output

disconnect circuitry. The parts use a novel* control tech-

nique resulting in low output voltage ripple as well as high

efﬁ ciency over a wide load current range. This technique

guarantees that the switching frequency stays above the

audio band for the entire load range. The parts feature a high

performance NPN power switch with a 350mA and 180mA

current limit for the LT3494A and LT3494 respectively. The

quiescent current is a low 65μA, which is further reduced

to less than 1μA in shutdown. The internal disconnect

circuitry allows the output voltage to be isolated from the

input during shutdown. An auxiliary reference input (CTRL

pin) overrides the internal 1.225V feedback reference with

any lower value allowing full control of the output voltage

during operation. The LT3494/LT3494A are available in a

tiny 8-lead 3mm × 2mm DFN package.

OLED Power Supply from One Li-Ion Cell

■ Low Quiescent Current

65μA in Active Mode

1μA in Shutdown Mode

■ Switching Frequency is Non-Audible Over Entire

Load Range

■ Integrated Power NPN:

350mA Current Limit (LT3494A)

180mA Current Limit (LT3494)

■ Integrated Schottky Diode

■ Integrated Output Disconnect

■ Integrated Output Dimming

■ Wide Input Range: 2.3V to 16V

■ Wide Output Range: Up to 40V

■ Tiny 8-Lead 3mm × 2mm DFN Package

■ OLED Power

■ Low Noise Power

■ MP3 Players

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

*Patent pending.

SW CAP

VCC

SHDN

CTRL

VOUT

GND

2.21M

3494 TA01a

LT3494

4.7μF

2.2μF

15μH

0.22μF

VIN

TO 4.2V

VOUT

16V

16mA

LOAD CURRENT (mA)

0.1

VOUT PEAK-TO-PEAK RIPPLE (mV)

1 10 100

3494 TA01b

LT3494

FIGURE 5 CIRCUIT

100MHz MEASUREMENT BW

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

POWER LOSS (mW)

1 10 100

3494 TA01c

160

200

240

280

120

VIN = 3.6V LOAD FROM

CAPACITOR

LOAD FROM

VOUT

Output Voltage Ripple

vs Load Current

Efﬁ ciency and Power Loss

vs Load Current

LT3494/LT3494A

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ELECTRICAL CHARACTERISTICS

PACKAGE/ORDER INFORMATIONABSOLUTE MAXIMUM RATINGS

VCC Voltage ...............................................................16V

SW Voltage ...............................................................40V

CAP Voltage ..............................................................40V

VOUT Voltage .............................................................40V

SHDN Voltage ...........................................................16V

CTRL Voltage ............................................................16V

FB Voltage ................................................................2.5V

Maximum Junction Temperature .......................... 125°C

Operating Temperature Range (Note 2) ... –40°C to 85°C

Storage Temperature Range ................... –65°C to 125°C

(Note 1)

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Operating Voltage 2.3 2.5 V

Maximum Operating Voltage 16 V

Feedback Voltage VCTRL = 3V (Note 3) ●1.205 1.225 1.245 V

FB Resistor ●179 182 184 kΩ

Quiescent Current Not Switching 65 75 μA

Quiescent Current in Shutdown V

⎯

N = 0V, VCC = 3V 0 1 μA

Minimum Switch Off Time After Start-Up Mode, VFB = 1V, VCTRL = 3V (Note 4)

During Start-Up Mode, VFB = 0.2V, VCTRL = 3V (Note 4)

100

450

Maximum Switch Off Time VFB = 1.5V ●15 20 30 μs

Switch Current Limit LT3494A (Note 5)

LT3494 (Note 5)

225

115

350

180

450

250

Switch VCESAT LT3494A, ISW = 200mA

LT3494, ISW = 100mA

180

110

Switch Leakage Current VSW = 5V, V

⎯

N = 0 0.01 1 μA

Schottky Forward Voltage IDIODE = 100mA 900 1100 mV

Schottky Reverse Leakage 0.05 1 μA

PMOS Disconnect VCAP – VOUT IOUT = 10mA, VCAP = 5V 250 mV

SHDN Input Voltage High 1.5 V

SHDN Input Voltage Low 0.3 V

SHDN Pin Bias Current VSHDN = 3V

VSHDN = 0V

0.1

μA

TOP VIEW

DDB PACKAGE

8-LEAD (3mm × 2mm) PLASTIC DFN

1SW

GND

VCC

CTRL

CAP

VOUT

SHDN

TJMAX = 125°C, θJA = 76°C/W

EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB

ORDER PART NUMBER DDB PART MARKING

LT3494EDDB

LT3494AEDDB

LCCD

LCRW

Order Options Tape and Reel: Add #TR

Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF

Lead Free Part Marking: http://www.linear.com/leadfree/

Consult LTC Marketing for parts speciﬁ ed with wider operating temperature ranges.

The ● denotes the speciﬁ cations which apply over the full operating

temperature range, otherwise speciﬁ cations are at TA = 25°C. VCC = 3V, VSHDN = VCC, unless otherwise noted. (Note 2)

LT3494/LT3494A

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Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 2: The LT3494/LT3494A are guaranteed to meet performance

speciﬁ cations from 0°C to 85°C. Speciﬁ cations over the –40°C to 85°C

operating temperature range are assured by design, characterization and

correlation with statistical process controls.

PARAMETER CONDITIONS MIN TYP MAX UNITS

CTRL Pin Bias Current VCTRL = 0.5V, Current Flows Out of Pin ●20 100 nA

CTRL to FB Offset VCTRL = 0.5V 8 15 mV

Maximum Shunt Current VFB = 1.3V, VCAP = 5V 230 μA

Note 3: Internal reference voltage is determined by ﬁ nding VFB voltage

level which causes quiescent current to increase 20μA above “Not

Switching” level.

Note 4: If CTRL is overriding the internal reference, Start-Up mode occurs

when VFB is less then half the voltage on CTRL. If CTRL is not overriding

the internal reference, Start-Up mode occurs when VFB is less then half the

voltage of the internal reference.

Note 5: Current limit guaranteed by design and/or correlation to static test.

ELECTRICAL CHARACTERISTICS

The ● denotes the speciﬁ cations which apply over the full operating

temperature range, otherwise speciﬁ cations are at TA = 25°C. VCC = 3V, VSHDN = VCC, unless otherwise noted. (Note 2)

TYPICAL PERFORMANCE CHARACTERISTICS

Switching Frequency

vs Load Currrent Load Regulation VOUT vs CTRL Voltage

LOAD CURRENT (mA)

0.1

800

SWITCHING FREQUENCY (kHz)

1000

1200

1400

1 10 100

3494 G01

600

400

200

LT3494

FIGURE 5 CIRCUIT

VCC = 3.6V

VOUT = 16V

LOAD CURRENT (mA)

VOUT VOLTAGE CHANGE (%)

1.0

3494 G02

–1.0

–2.0 10 20 30

515 25 35

2.0

–0.5

0.5

–1.5

1.5

LT3494

FIGURE 5 CIRCUIT

VCC = 3.6V

VOUT = 16V

CTRL VOLTAGE (V)

0.1

VOUT VOLTAGE (V)

0.3 0.5 0.7 0.9

3494 G03

1.1 1.3 1.5

LT3494

FIGURE 5 CIRCUIT

VCC = 3.6V

VOUT = 16V

LOAD CURRENT = 1mA

TA = 25°C unless otherwise noted.

LT3494/LT3494A

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Output Voltage vs Temperature Minimum Switching Frequency Quiescent Current–Not Switching

SHDN Current vs SHDN Voltage Peak Inductor Current (LT3494)

TEMPERATURE (°C)

–40

OUTPUT VOLTAGE CHANGE (%)

1.0

120

3494 G04

–1.0

–2.0 040 80

–20 20 60 100

2.0

–0.5

0.5

–1.5

1.5

LT3494

FIGURE 5 CIRCUIT

TEMPERATURE (°C)

–40

SWITCHING FREQUENCY (kHz)

49.0

50.0

120

3494 G05

48.0

47.0 040 80

–20 20 60 100

51.0

48.5

49.5

47.5

50.5

VCC = 3.6V

NO LOAD

VCC (V)

IVCC (μA)

100

578

3494 G06

46910

SHDN PIN VOLTAGE (V)

SHDN PIN CURRENT (μA)

2468

3494 G07

10 12 14 16

Peak Inductor Current (LT3494A)

TEMPERATURE (°C)

–40

100

PEAK INDUCTOR CURRENT (mA)

150

200

250

300

04080 120

3494 G08

350

400

–20 20 60 100

FIGURE 5 CIRCUIT

VCC = 3.6V

VOUT = 16V

LT3494 Switching Waveforms at

No Load

VOUT

10mV/DIV

COUPLED

VOLTAGE

10V/DIV

VCC = 3.6V

VOUT = 16V

INDUCTOR

CURRENT

50mA/DIV

5μs/DIV 3494 G10

FIGURE 5 CIRCUIT

VOUT

10mV/DIV

COUPLED

VOLTAGE

10V/DIV

INDUCTOR

CURRENT

100mA/DIV

2μs/DIV 3494 G11

FIGURE 5 CIRCUIT

VCC = 3.6V

VOUT = 16V

VOUT

10mV/DIV

COUPLED

VOLTAGE

10V/DIV

INDUCTOR

CURRENT

100mA/DIV

500ns/DIV 3494 G12

FIGURE 5 CIRCUIT

VCC = 3.6V

VOUT = 16V

LT3494 Switching Waveforms at

1mA Load

LT3494 Switching Waveforms at

25mA Load

TEMPERATURE (°C)

–40

400

PEAK INDUCTOR CURRENT (mA)

450

500

550

600

04080 120

3494 G09

650

700

–20 20 60 100

FIGURE 6 CIRCUIT

VCC = 3.6V

VOUT = 16V

TYPICAL PERFORMANCE CHARACTERISTICS

TA = 25°C unless otherwise noted.

LT3494/LT3494A

3494fb

LT3494A Switching Waveforms at

No Load

LT3494A Switching Waveforms at

5mA Load

LT3494A Switching Waveforms at

30mA Load

LT3494 Start-Up Waveforms LT3494 Transient Response LT3494A Transient Response

CAP

VOLTAGE

5V/DIV

VOUT

VOLTAGE

5V/DIV

INDUCTOR

CURRENT

100mA/DIV

200μs/DIV 3494 G16

FIGURE 5 CIRCUIT

VCC = 3.6V

VOUT = 16V

VOUT

VOLTAGE

50mV/DIV

AC COUPLED

INDUCTOR

CURRENT

100mA/DIV

100μs/DIV 3494 G17

FIGURE 5 CIRCUIT

10mA→15mA→10mA LOAD PULSE

VCC = 3.6V

VOUT = 16V

VOUT

10mV/DIV

COUPLED

VOLTAGE

10V/DIV

INDUCTOR

CURRENT

50mA/DIV

s/DIV 3494 G13

FIGURE 6 CIRCUIT

VCC = 3.6V

VOUT = 16V

VOUT

10mV/DIV

COUPLED

VOLTAGE

10V/DIV

INDUCTOR

CURRENT

100mA/DIV

s/DIVVCC = 3.6V

VOUT = 16V

3494 G14

FIGURE 6 CIRCUIT VOUT

10mV/DIV

COUPLED

VOLTAGE

10V/DIV

INDUCTOR

CURRENT

200mA/DIV

500ns/DIVVCC = 3.6V

VOUT = 16V

3494 G15

FIGURE 6 CIRCUIT

VOUT

50mV/DIV

COUPLED

INDUCTOR

CURRENT

200mA/DIV

100μs/DIVVCC = 3.6V

VOUT = 16V

3494 G18

FIGURE 6 CIRCUIT

15mA→30mA→15mA LOAD PULSE

TYPICAL PERFORMANCE CHARACTERISTICS

TA = 25°C unless otherwise noted.

LT3494/LT3494A

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BLOCK DIAGRAM

PIN FUNCTIONS

SW (Pin 1): Switch Pin. This is the collector of the internal

NPN power switch. Minimize the metal trace area connected

to this pin to minimize EMI.

GND (Pin 2): Ground. Tie directly to local ground plane.

VCC (Pin 3): Input Supply Pin. Must be locally

bypassed.

CTRL (Pin 4): Dimming Pin. If not used, tie CTRL to 1.5V

or higher. If in use, drive CTRL below 1.225V to override

the internal reference. See Applications Information for

more information.

SHDN (Pin 5): Shutdown Pin. Tie to 1.5V or more to

enable device. Ground to shut down.

FB (Pin 6): Feedback Pin. Reference voltage is 1.225V.

There is an internal 182k resistor from the FB pin to GND.

To achieve the desired output voltage, choose R1 accord-

ing to the following formula:

RVk

OUT MAX

1 182 1 225 1=⎛

⎝

⎜⎞

⎠

⎟

•.–

() Ω

VOUT (Pin 7): Drain of Output Disconnect PMOS. Place a

bypass capacitor from this pin to GND. See Applications

Information.

CAP (Pin 8): This is the cathode of the internal Schottky

diode. Place a bypass capacitor from this pin to GND.

Exposed Pad (Pin 9): Ground. This pin must be soldered

to PCB.

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LT3494/LT3494A

3494fb

OPERATION

The LT3494/LT3494A use a novel control scheme to pro-

vide high efﬁ ciency over a wide range of output current.

In addition, this technique keeps the switching frequency

above the audio band over all load conditions.

The operation of the part can be better understood by

refering to the Block Diagram. The part senses the output

voltage by monitoring the voltage on the FB pin. The user

sets the desired output voltage by choosing the value of

the external top feedback resistor. The parts incorporate

a precision 182k bottom feedback resistor. Assuming that

output voltage adjustment is not used (CTRL pin is tied to

1.5V or greater), the internal reference (VREF = 1.225V) sets

the voltage at which FB will servo to during regulation.

The Switch Control block senses the output of the ampli-

ﬁ er and adjusts the switching frequency as well as other

parameters to achieve regulation. During the start-up of

the circuit, special precautions are taken to insure that the

inductor current remains under control.

Because the switching frequency is never allowed to fall

below approximately 50kHz, a minimum load must be

present to prevent the output voltage from drifting too high.

This minimum load is automatically generated within the

part via the Shunt Control block. The level of this current

is adaptable, removing itself when not needed to improve

efﬁ ciency at higher load levels.

The LT3494/LT3494A also have an integrated Schottky

diode and PMOS output disconnect switch. The PMOS

switch is turned on when the part is enabled via the SHDN

pin. When the parts are in shutdown, the PMOS switch

turns off, allowing the VOUT node to go to ground. This

type of disconnect function is often required in power

supplies.

The only difference between the LT3494A and LT3494

is the level of the current limit. The LT3494A has a typi-

cal peak current limit of 350mA while the LT3494 has a

180mA limit.

APPLICATIONS INFORMATION

Choosing an Inductor

Several recommended inductors that work well with the

LT3494/LT3494A are listed in Table 1, although there are

many other manufacturers and devices that can be used.

Consult each manufacturer for more detailed information

and for their entire selection of related parts. Many dif-

ferent sizes and shapes are available. Use the equations

and recommendations in the next few sections to ﬁ nd the

correct inductance value for your design.

Inductor Selection—Boost Regulator

The formula below calculates the appropriate inductor

value to be used for a boost regulator using the LT3494/

LT3494A (or at least provides a good starting point).

This value provides a good trade off in inductor size and

system performance. Pick a standard inductor close to

this value. A larger value can be used to slightly increase

the available output current, but limit it to around twice

the value calculated below, as too large of an inductance

will decrease the output voltage ripple without providing

much additional output current. A smaller value can be

used (especially for systems with output voltages greater

than 12V) to give a smaller physical size. Inductance can

be calculated as:

L = (VOUT – VIN(MIN) + 0.5V) • 0.66 (μH)

where VOUT is the desired output voltage and VIN(MIN) is

the minimum input voltage. Generally, a 10μH or 15μH

inductor is a good choice.

Table 1. Recommended Inductors

PART FOR USE WITH

VALUE

(μH)

MAX DCR

(Ω)

MAX DC I

(mA)

SIZE

(mm × mm × mm) VENDOR

LQH32CN100K53

LQH32CN150K53

LT3494/LT3494A

LT3494

0.3

0.58

450

300

3.5 × 2.7 × 1.7

Murata

www.murata.com

CDRH3D11-100

CDHED13/S-150

LT3494

LT3494/LT3494A

0.24

0.55

280

550

4.0 × 4.0 × 1.2

4.0 × 4.2 × 1.4

Sumida

www.sumida.com

LT3494/LT3494A

3494fb

APPLICATIONS INFORMATION

Capacitor Selection

The small size and low ESR of ceramic capacitors makes

them suitable for most LT3494/LT3494A applications. X5R

and X7R types are recommended because they retain their

capacitance over wider voltage and temperature ranges

than other types such as Y5V or Z5U. A 4.7μF input capaci-

tor and a 2.2μF to 10μF output capacitor are sufﬁ cient for

most LT3494/LT3494A applications. Always use a capacitor

with a sufﬁ cient voltage rating. Many capacitors rated at

2.2μF to 10μF, particularly 0805 or 0603 case sizes, have

greatly reduced capacitance when bias voltages are ap-

plied. Be sure to check actual capacitance at the desired

output voltage. Generally a 1206 size capacitor will be

adequate. A 0.22μF or 0.47μF capacitor placed on the

CAP node is recommended to ﬁ lter the inductor current

while the larger 2.2μF to 10μF placed on the VOUT node

will give excellent transient response and stability. Table 2

shows a list of several capacitor manufacturers. Consult

the manufacturers for more detailed information and for

their entire selection of related parts.

Table 2. Recommended Ceramic Capacitor Manufacturers

MANUFACTURER PHONE URL

Taiyo Yuden 408-573-4150 www.t-yuden.com

AVX 843-448-9411 www.avxcorp.com

Murata 814-237-1431 www.murata.com

Kemet 408-986-0424 www.kemet.com

Setting Output Voltage and

the Auxiliary Reference Input

The LT3494/LT3494A are equipped with both an internal

1.225V reference and an auxiliary reference input. This al-

lows the user to select between using the built-in reference

and supplying an external reference voltage. The voltage

at the CTRL pin can be adjusted while the chip is operat-

ing to alter the output voltage of the LT3494/LT3494A for

purposes such as display dimming or contrast adjustment.

To use the internal 1.225V reference, the CTRL pin must be

held higher than 1.5V. When the CTRL pin is held between

0V and 1.5V, the LT3494 will regulate the output such that

the FB pin voltage is nearly equal to the CTRL pin voltage.

At CTRL voltages close to 1.225V, a soft transition occurs

between the CTRL pin and the internal reference. Figure 1

shows this behavior.

To set the maximum output voltage, select the values of

R1 according to the following equation:

RVk

OUT MAX

1 182 1 225 1=⎛

⎝

⎜⎞

⎠

⎟

•.–

() Ω

When CTRL is used to override the internal reference,

the output voltage can be lowered from the maximum

value down to nearly the input voltage level. If the voltage

source driving the CTRL pin is located at a distance to the

LT3494/LT3494A, a small 0.1μF capacitor may be needed

to bypass the pin locally.

Choosing a Feedback Node

The single feedback resistor may be connected to the VOUT

pin or to the CAP pin (see Figure 2). Regulating the VOUT

pin eliminates the output offset resulting from the voltage

drop across the output disconnect PMOS. Regulating the

CAP pin does not compensate for the voltage drop across

the output disconnect, resulting in an output voltage VOUT

that is slightly lower than the voltage set by the resistor

divider. Under most conditions, it is advised that the

feedback resistor be tied to the VOUT pin.

Figure 1. CTRL to FB Transfer Curve

SW CAP

VCC

SHDN

CTRL

VOUT

GND

LT3494

VOUT

SW CAP

VCC

SHDN

CTRL

VOUT

GND

3494 F02

LT3494

Figure 2. Feedback Connection Using the CAP Pin or the VOUT Pin

CTRL VOLTAGE (V)

FB VOLTAGE (V)

0.250

0.500

0.750

1.000

1.500

.25 0.5 .75 1.0

3494 F01

1.25 1.5

1.250

LT3494/LT3494A

3494fb

APPLICATIONS INFORMATION

Connecting the Load to the CAP Node

The efﬁ ciency of the converter can be improved by con-

necting the load to the CAP pin instead of the VOUT pin.

The power loss in the PMOS disconnect circuit is then

made negligible. By connecting the feedback resistor to

the VOUT pin, no quiescent current will be consumed in the

feedback resistor string during shutdown since the PMOS

transistor will be open (see Figure 3). The disadvantage

of this method is that the CAP node cannot go to ground

during shutdown, but will be limited to around a diode

drop below VCC. Loads connected to the part should only

sink current. Never force external power supplies onto

the CAP or VOUT pins. The larger value output capacitor

(2.2μF to 10μF) should be placed on the node to which

the load is connected.

Figure 3. Improved Efﬁ ciency

Maximum Output Load Current

The maximum output current of a particular LT3494/

LT3494A circuit is a function of several circuit variables.

The following method can be helpful in predicting the

maximum load current for a given circuit:

Step 1: Calculate the peak inductor current:

II V

Lamps

PK LIMIT IN

••

–

400 10 9

where ILIMIT is 0.180A and 0.350A for the LT3494 and

LT3494A respectively. L is the inductance value in Henrys

and VIN is the input voltage to the boost circuit.

Step 2: Calculate the inductor ripple current:

IVV

Lamps

RIPPLE OUT IN

()

1 150 10 9

–••

–

where VOUT is the desired output voltage.

If the inductor ripple current is greater than the peak cur-

rent, then the circuit will only operate in discontinuous

conduction mode. The inductor value should be increased

so that IRIPPLE < IPK. An application circuit can be designed

to operate only in discontinuous mode, but the output

current capability will be reduced.

Step 3: Calculate the average input current:

Iamps

IN AVG PK RIPPLE

() –=2

Step 4: Calculate the nominal output current:

IIV

Vamps

OUT NOM

IN AVG IN

OUT

()

••.

=075

Step 5: Derate output current:

OUT = IOUT(NOM) • 0.7 amps

For low output voltages the output current capability will

be increased. When using output disconnect (load cur-

rent taken from VOUT), these higher currents will cause

the drop in the PMOS switch to be higher resulting in

reduced output current capability than those predicted

by the preceding equations.

Inrush Current

When VCC is stepped from ground to the operating volt-

age while the output capacitor is discharged, a higher

level of inrush current may ﬂ ow through the inductor

and integrated Schottky diode into the output capacitor.

Conditions that increase inrush current include a larger

more abrupt voltage step at VIN, a larger output capacitor

tied to the CAP pin and an inductor with a low saturation

current. While the internal diode is designed to handle

such events, the inrush current should not be allowed to

exceed 1A. For circuits that use output capacitor values

within the recommended range and have input voltages

of less than 5V, inrush current remains low, posing no

hazard to the device. In cases where there are large steps

at VCC (more than 5V) and/or a large capacitor is used

at the CAP pin, inrush current should be measured to

ensure safe operation. The LT3494A circuits experience

higher levels of current during start-up and steady-state

operation. An external diode placed from the SW pin to

SW CAP

VCC

SHDN

CTRL

VOUT

GND

3494 F03

LT3494

C1 ILOAD

LT3494/LT3494A

3494fb

TYPICAL APPLICATIONS

Figure 5. One Li-Ion Cell Input Boost Converter with the LT3494

APPLICATIONS INFORMATION

the CAP pin will improve efﬁ ciency and lower the stress

placed on the internal Schottky diode.

Board Layout Considerations

As with all switching regulators, careful attention must be

paid to the PCB board layout and component placement.

To maximize efﬁ ciency, switch rise and fall times are made

as short as possible. To prevent electromagnetic interfer-

ence (EMI) problems, proper layout of the high frequency

switching path is essential. The voltage signal of the SW pin

has sharp rising and falling edges. Minimize the length and

area of all traces connected to the SW pin and always use

a ground plane under the switching regulator to minimize

interplane coupling. In addition, the FB connection for

the feedback resistor R1 should be tied directly from the

Vout pin to the FB pin and be kept as short as possible,

ensuring a clean, noise-free connection. Recommended

component placement is shown in Figure 4.

GND

VCC

CTRL

CAP

VOUT

SHDN

GND

CTRL

VIAS TO GROUND PLANE REQUIRED

TO IMPROVE THERMAL PERFORMANCE

SHDN

3494 F04

Figure 4. Recommended Layout

SW CAP

VCC

SHDN

CTRL

VOUT

GND

TURN ON/OFF

VOUT DIMMING

3494 F05

LT3494

4.7μF

15μH

0.22μF

2.2μF

C1, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING

C3: MURATA GRM31MR71E225K

L1: MURATA LQH32CN150K53

VIN

3V TO 4.2V

VOUT

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

POWER LOSS (mW)

1 10 100

3494 TA01c

160

200

240

280

120

VIN = 3.6V LOAD FROM

CAPACITOR

LOAD FROM

VOUT

3.6V to 16V Efﬁ ciency

VOUT

R1 VALUE REQUIRED

(MΩ)

MAXIMUM OUTPUT CURRENT AT

3V INPUT (mA)

25 3.57 8.6

24 3.40 9.3

23 3.24 10.0

22 3.09 10.6

21 2.94 11.3

20 2.80 12.1

19 2.67 12.9

18 2.49 13.6

17 2.37 14.8

16 2.21 16.0

15 2.05 17.2

LT3494/LT3494A

3494fb

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

PACKAGE DESCRIPTION

DDB Package

8-Lead Plastic DFN (3mm × 2mm)

(Reference LTC DWG # 05-08-1702 Rev B)

2.00 ±0.10

(2 SIDES)

NOTE:

1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE

0.40 ± 0.10

BOTTOM VIEW—EXPOSED PAD

0.56 ± 0.05

(2 SIDES)

0.75 ±0.05

R = 0.115

TYP

R = 0.05

TYP

2.15 ±0.05

(2 SIDES)

3.00 ±0.10

(2 SIDES)

PIN 1 BAR

TOP MARK

(SEE NOTE 6)

0.200 REF

0 – 0.05

(DDB8) DFN 0905 REV B

0.25 ± 0.05

0.50 BSC

PIN 1

R = 0.20 OR

0.25 × 45°

CHAMFER

0.25 ± 0.05

2.20 ±0.05

(2 SIDES)

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

0.61 ±0.05

(2 SIDES)

1.15 ±0.05

0.70 ±0.05

2.55 ±0.05

PACKAGE

OUTLINE

0.50 BSC

LT3494/LT3494A

3494fb

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

LT 0507 REV B • PRINTED IN USA

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TYPICAL APPLICATION

PART NUMBER DESCRIPTION COMMENTS

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LT1615/LT1615-1 300mA/80mA (ISW), High Efﬁ ciency Step-Up DC/DC Converters VIN: 1V to 15V, VOUT(MAX) = 34V, IQ = 20μA, ISD < 1μA,

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LT1930/LT1930A 1A (ISW), 1.2MHz/2.2MHz, High Efﬁ ciency Step-Up DC/DC

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ThinSOT Package

LT1945 (Dual) Dual Output, Boost/Inverter, 350mA (ISW), Constant Off-Time, High

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10-Lead MS Package

LT1946/LT1946A 1.5A (ISW), 1.2MHz/2.7MHz, High Efﬁ ciency Step-Up DC/DC

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8-Lead MS Package

LT3467/LT3467A 1.1A (ISW), 1.3MHz/2.1MHz, High Efﬁ ciency Step-Up DC/DC

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LT3463/LT3463A Dual Output, Boost/Inverter, 250mA (ISW), Constant Off-Time, High

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DFN Package

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VIN: 2.4V to 16V, VOUT(MAX) = ±40V, IQ = 2.5mA, ISD < 1μA,

DFN Package

Figure 6. One Li-Ion Cell Input Boost Converter with the LT3494A

SW CAP

VCC

SHDN

CTRL

VOUT

GND

3494 F06

LT3494A

4.7μF

C1, C2: X5R OR X7R WITH SUFFICIENT VOLTAGE RATING

C3: TAIYO YUDEN TMK316BJ106ML

D1: CENTRAL SEMICONDUCTOR CMDSH-3

L1: MURATA LQH32CN100K53

10μH

0.47μF

10μF

VIN

3V TO 4.2V

VOUT

LOAD CURRENT (mA)

0.1

EFFICIENCY (%)

POWER LOSS (mW)

1 10 100

3494 F06b

100

200

300

150

250

VIN = 3.6V

VOUT = 16V

LOAD FROM CAPACITOR

LOAD FROM VOUT

LOAD CURRENT (mA)

0.1

VOUT PEAK-TO-PEAK RIPPLE (mV)

1 10 100

3494 F06c

100MHz MEASUREMENT BW

Efﬁ ciency and Power Loss vs Load Current

Output Voltage Ripple vs Load Current

VOUT

R1 VALUE REQUIRED

(MΩ)

MAXIMUM OUTPUT CURRENT AT

3V INPUT (mA)

25 3.57 13.0

24 3.40 14.0

23 3.24 15.0

22 3.09 16.5

21 2.94 17.5

20 2.80 19.0

19 2.67 20.0

18 2.49 21.5

17 2.37 23.0

16 2.21 25.0

15 2.05 27.0