LINEAR TECHNOLOGY LTC3490 Technical data

FEATURES

■

350mA Constant Current Output

■

2.8V to 4V Output Compliance

■

1- or 2-Cell NiMH or Alkaline Input

■

Synchronous Rectification: Up to 90% Efficiency

■

Fixed Frequency Operation: 1.3MHz

■

Low Quiescent Current: <1mA

■

Very Low Shutdown Current: <50µA

■

Open LED Output Limited to 4.7V

■

VIN Range: 1V to 3.2V

■

Dimming Control

■

Undervoltage Lockout to Protect Batteries

■

Low Profile (0.75mm) 3mm × 3mm Thermally
Enhanced 8-Lead DD and S8 Packages

U

APPLICATIO S

■

Portable Lighting

■

Rechargeable Flashlights

LTC3490

Single Cell 350mA

LED Driver

U

DESCRIPTIO

The LTC®3490 provides a constant current drive for 1W
LED applications. It is a high efficiency boost converter
that operates from 1 or 2 NiMH or alkaline cells and
generates 350mA of constant current with up to 4V of
compliance. It contains a 100mΩ NFET switch and a
130mΩ PFET synchronous rectifier. The fixed switching
frequency is internally set to 1.3MHz.

The LTC3490 limits the output voltage to 4.7V if the output
load is disconnected. It also features an analog dimming
capability that reduces the drive current proportional to
the CTRL/SHDN pin voltage. A low-battery logic output
signals when the battery has dropped below 1V/cell. An
undervoltage lockout circuit shuts down the LTC3490
when the battery voltage drops below 0.85V/cell. The
feedback loop is internally compensated to minimize com­ponent count.

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

All other trademarks are the property of their respective owners.

TYPICAL APPLICATIO

Single Cell Minimum Component LED Driver

3.3µH

V

IN

1 NiMH OR

ALKALINE

CELL

ON/OFF

+

1M

LTC3490

CTRL/SHDN

CELLS

GND

LOBAT

SW

CAP

LED

U

350mA

4.7µF

HIGH
CURRENT
LED

3490 TA01

Efficiency vs V

100

I

= 350mA

OUT

90

80

70

60

50

40

EFFICIENCY (%)

30

20

10

0

1

1.5

IN

2

VIN (V)

at V

LED

= 3.5V

2.5

3

3490 TA02

3490fa

1

LTC3490

WWWU

ABSOLUTE AXI U RATI GS

(Note 1)

Supply Voltage (VIN) ................................... –0.3V to 6V

Input Voltages (CTRL/SHDN, CELLS) ......... – 0.3V to 6V

Output Voltages (CAP, LED, SW)................ – 0.3V to 6V

/

PACKAGE

O

RDER I FOR ATIO

1CELLS

V

2

IN

SW

3

GND

4

8-LEAD (3mm × 3mm) PLASTIC DFN

T

= 125°C, θJA = 43°C/ W (NOTE 4)

JMAX

EXPOSED PAD (PIN 9) IS GND

MUST BE SOLDERED TO PCB (NOTE 5)

ORDER PART NUMBER

LTC3490EDD

TOP VIEW

9

DD PACKAGE

WU

8

CTRL/SHDN

LOBAT

7

CAP

6

LED

5

DD PART MARKING

LBRQ

U

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

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

Lead Temperature (Soldering, 10 sec, S8) .......... 300°C

TOP VIEW

CELLS

1

V

2

IN

SW

3

GND

4

S8 PACKAGE

8-LEAD PLASTIC SO

T

= 125°C, θJA = 150°C/ W (NOTE 4)

JMAX

CTRL/SHDN

8

LOBAT

7

CAP

6

LED

5

ORDER PART NUMBER S8 PART MARKING

LTC3490ES8

3490

Order Options

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 specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

Tape and Reel: Add #TR

The ● denotes specifications which apply over the full operating

temperature range, otherwise specifications are TA = 25°C. VIN = 2.5V unless otherwise specified.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

IN

V

IN(START)

I

LED(MAX)

I

LED(SHDN)

V

LED

V

LED(OVL)

I

IN(SHDN)

I

IN(ACTIVE)

f

SW

I

L(NMOS)

R

ON(NMOS)

Input Supply Range 1 3.2 V
Minimum Start-Up Voltage (Note 3) 0.9 1 V
LED Drive Current V

LED Drive Current in Shutdown V
Output Compliance Voltage
Output Voltage Overvoltage Limit Open LED
Input Current, Shutdown V
Input Current, Active Excluding Load Power 20 30 mA
Switching Frequency
Leakage Current, NMOS Switch 0.1 µA
On-Resistance, NMOS Switch 0.1 Ω

CTRL/SHDN

25°C to 85°C 330 350 370 mA
–40°C to <25°C 310 350 385 mA

V

CTRL/SHDN

25°C to 85°C 337 350 363 mA
–40°C to <25°C 325 345 365 mA

CTRL/SHDN

CTRL/SHDN

= VIN, DD Package

= VIN, S8 Package

= 0V 0.1 1 µA

●

2.8 4 V

●

4.2 4.7 V

= 0V, Excluding Switch Leakage 20 50 µA

●

1.0 1.3 1.6 MHz

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2

LTC3490

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are T

A

The ● denotes specifications which apply over the full operating

= 25°C. VIN = 2.5V unless otherwise specified.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

L(PMOS)

R

ON(PMOS)

V

IH

Leakage Current, PMOS Switch 0.1 µA
On-Resistance, PMOS Switch 0.13 Ω
Input High (CELLS) VIN – 0.4 V
Input High (SHDN) VIN • 0.9 V

V

IL

Input Low (CELLS) 0.4 V
Input Low (SHDN) VIN • 0.2 V

I

IN

K

CTRL

R

ON(LOBAT)

V

IN(LOBAT1)

V

IN(LOBAT2)

V

IN(UVLO2)

Input Current (CTRL/SHDN, CELLS) 0.01 µA
Control Gain, I

LED/VCTRL

On-Resistance, LOBAT Output VIN < V
Input Voltage, Low Battery, 1 Cell V
Input Voltage, Low Battery, 2 Cells V
Input Voltage, Undervoltage Lockout, V

Scales Linearity with VIN, VIN = 1V 500 mA/V

CELLS

CELLS

CELLS

IN(LOBAT)

= 0V
= V

IN

= V

IN

●

●

0.8 1.12 V

●

1.8 2.24 V

●

1.4 1.8 V

300 Ω

2 Cells

V

IN(UVLO1)

Input Voltage, Undervoltage Lockout, V

CELLS

= 0 V

●

0.7 0.9 V

1 Cell

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 LTC3490 is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C range are
assured by design, characterization and correlation with statistical process
controls.

Note 4: This device includes overtemperature protection intended to
protect the device during momentary overload conditions. The maximum
junction temperature may be exceeded when overtemperature protection
is active. Continuous operation above the specified maximum operating
junction temperature may result in device degradation or failure.

Note 5: The Exposed Pad of the DFN package must be soldered to a
PCB pad for optimum thermal conductivity. This pad must be connected
to ground.

Note 3: The LTC3490 input voltage may drop below the minimum start-up
voltage once the LED voltage has risen above 2.3V.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

Oscillator Frequency

vs V

400

350

300

250

(mA)

200

LED

I

150

100

I

LED

50

0

0

CTRL

MAXIMUM

MINIMUM

0.2 0.4 0.8
V

CTRL/VIN

0.6
(V)

vs Temperature

1.400

1.360

1.320

1.280

FREQUENCY (MHz)

1.240

1.200
–50

0

TEMPERATURE (°C)

50

100

3490 G01

3490 G02

I

vs V

LED

375

350

325

(mA)

LED

I

300

275

250

1

1

IN

V

= 3.5V

LED

1.5

2

VIN (V)

2.5

3

3490 G03

3490fa

3

LTC3490

I

LED

(mA)

0

0

EFFICIENCY (%)

10

30

40

50

100

70

100

200

3490 G05

20

80

90

60

300

400

VIN = 2.4V

VIN = 1.2V

UW

TYPICAL PERFOR A CE CHARACTERISTICS

I

360

358

356

354

352

(mA)

350

LED

I

348

346

344

342

340

LED

VIN = 2.4V

2.8

vs V

3 3.2

LED

3.4 3.6 3.8

V

(V)

LED

4

3490 G04

Efficiency vs I

LED

PI FU CTIO S

U

UU

CELLS (Pin 1): A logic input to set the low-battery and
undervoltage shutdown thresholds. A logic low (tied to
GND) will set the thresholds for 1 cell. A logic high (tied to
VIN) will set the thresholds for 2 cells.

(Pin 2): Supply Voltage.

V

IN

SW (Pin 3): Switch Input. Connect this pin to an external

inductor from V

IN

.

GND (Pin 4): Circuit Ground.

LED (Pin 5): Output Drive Current to LED.

CAP (Pin 6): Filter Capacitor. A 4.7µF low ESR capacitor

should be tied to this pin.

LOBAT (Pin 7): Low active, open-drain logic output indi­cating a low-battery condition.

4

CTRL/SHDN (Pin 8): Analog Control Voltage and Shut­down. When V

• 0.2 < V

IN

< VIN • 0.9, the LED drive

CTRL

current varies according to the formula:

⎛

I

LED

When V

500 0 2•–.

=

CTRL

V

⎜
⎝

> VIN • 0.9, the LED drive current is clamped

at 350mA. When V

CTRL

V

IN

CTRL

⎞

mA

⎟
⎠

< VIN • 0.2, then the part is in low

power shutdown.

Exposed Pad (Pin 9, DD Package): Ground. This pin must
be soldered to the PCB to provide both electrical contact
to ground and good thermal contact to the PCB.

3490fa