LTC3490
Single Cell 350mA
LED Driver
FEATURES
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DESCRIPTIO
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
V
IN
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
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 com-
ponent count.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIO S
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Portable Lighting
Rechargeable Flashlights
TYPICAL APPLICATIO
3.3µH
Single Cell Minimum Component LED Driver
100
90
80
V
IN
ON/OFF
1 NiMH OR
ALKALINE
CELL
SW
CAP
LTC3490
CTRL/SHDN LED
CELLS
1M
GND
LOBAT
350mA
4.7µF
HIGH
CURRENT
LED
Efficiency vs V
IN
at V
LED
= 3.5V
I
OUT
= 350mA
70
EFFICIENCY (%)
60
50
40
30
20
10
+
3490 TA01
0
1
1.5
2
V
IN
(V)
2.5
3
3490 TA02
U
3490fa
U
U
1
LTC3490
ABSOLUTE
AXI U
RATI GS
Supply Voltage (V
IN
) ................................... – 0.3V to 6V
Input Voltages (CTRL/SHDN, CELLS) ......... – 0.3V to 6V
Output Voltages (CAP, LED, SW) ................ – 0.3V to 6V
PACKAGE/ORDER I FOR ATIO
TOP VIEW
CELLS 1
V
IN
2
SW 3
GND 4
9
8
7
6
5
CTRL/SHDN
LOBAT
CAP
LED
DD PACKAGE
8-LEAD (3mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/ W (NOTE 4)
EXPOSED PAD (PIN 9) IS GND
MUST BE SOLDERED TO PCB (NOTE 5)
ORDER PART NUMBER
LTC3490EDD
Order Options
Tape and Reel: Add #TR
DD PART MARKING
LBRQ
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.
The
●
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 2.5V unless otherwise specified.
SYMBOL
V
IN
V
IN(START)
I
LED(MAX)
PARAMETER
Input Supply Range
Minimum Start-Up Voltage
LED Drive Current
(Note 3)
V
CTRL/SHDN
= V
IN
, DD Package
25°C to 85°C
– 40°C to <25°C
V
CTRL/SHDN
= V
IN
, S8 Package
25°C to 85°C
– 40°C to <25°C
I
LED(SHDN)
V
LED
V
LED(OVL)
I
IN(SHDN)
I
IN(ACTIVE)
f
SW
I
L(NMOS)
R
ON(NMOS)
LED Drive Current in Shutdown
Output Compliance Voltage
Output Voltage Overvoltage Limit
Input Current, Shutdown
Input Current, Active
Switching Frequency
Leakage Current, NMOS Switch
On-Resistance, NMOS Switch
Open LED
V
CTRL/SHDN
= 0V, Excluding Switch Leakage
Excluding Load Power
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
V
CTRL/SHDN
= 0V
●
●
2
U
U
W
W W
U
W
(Note 1)
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
IN
2
SW
3
GND
4
8
7
6
5
CTRL/SHDN
LOBAT
CAP
LED
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 150°C/ W (NOTE 4)
ORDER PART NUMBER
LTC3490ES8
S8 PART MARKING
3490
MIN
1
TYP
0.9
MAX
3.2
1
370
385
363
365
1
4
4.7
UNITS
V
V
mA
mA
mA
mA
µA
V
V
µA
mA
MHz
µA
Ω
3490fa
330
310
337
325
2.8
4.2
350
350
350
345
0.1
20
20
1.0
1.3
0.1
0.1
50
30
1.6
LTC3490
The
●
denotes specifications which apply over the full operating
temperature range, otherwise specifications are T
A
= 25°C. V
IN
= 2.5V unless otherwise specified.
SYMBOL
I
L(PMOS)
R
ON(PMOS)
V
IH
V
IL
I
IN
K
CTRL
R
ON(LOBAT)
V
IN(LOBAT1)
V
IN(LOBAT2)
V
IN(UVLO2)
V
IN(UVLO1)
PARAMETER
Leakage Current, PMOS Switch
On-Resistance, PMOS Switch
Input High (CELLS)
Input High (SHDN)
Input Low (CELLS)
Input Low (SHDN)
Input Current (CTRL/SHDN, CELLS)
Control Gain, I
LED
/V
CTRL
On-Resistance, LOBAT Output
Input Voltage, Low Battery, 1 Cell
Input Voltage, Low Battery, 2 Cells
Scales Linearity with V
IN
, V
IN
= 1V
V
IN
< V
IN(LOBAT)
V
CELLS
= 0V
V
CELLS
= V
IN
●
●
●
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
TYP
0.1
0.13
MAX
UNITS
µA
Ω
V
V
V
IN
– 0.4
V
IN
• 0.9
0.4
V
IN
• 0.2
0.01
500
300
0.8
1.8
1.4
0.7
1.12
2.24
1.8
0.9
V
V
µA
mA/V
Ω
V
V
V
V
Input Voltage, Undervoltage Lockout, V
CELLS
= V
IN
2 Cells
Input Voltage, Undervoltage Lockout, V
CELLS
= 0 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 3:
The LTC3490 input voltage may drop below the minimum start-up
voltage once the LED voltage has risen above 2.3V.
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.
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
vs Temperature
1.400
400
350
1.360
300
FREQUENCY (MHz)
I
LED
(mA)
I
LED
(mA)
250
MAXIMUM
200
150
MINIMUM
100
1.320
1.280
1.240
50
1.200
–50
50
0
TEMPERATURE (°C)
U W
3490 G01
I
LED
vs V
CTRL
375
I
LED
vs V
IN
V
LED
= 3.5V
350
325
300
275
100
0
250
0
0.2
0.6
V
CTRL
/V
IN
(V)
0.4
0.8
1
3490 G02
1
1.5
2
V
IN
(V)
2.5
3
3490 G03
3490fa
3
LTC3490
TYPICAL PERFOR A CE CHARACTERISTICS
I
LED
vs V
LED
360
358
356
V
IN
= 2.4V
100
90
80
I
LED
(mA)
352
350
348
346
344
342
340
2.8
3
3.2
3.4
3.6
V
LED
(V)
3.8
4
3490 G04
EFFICIENCY (%)
354
PI FU CTIO S
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
V
IN
) will set the thresholds for 2 cells.
V
IN
(Pin 2):
Supply Voltage.
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 indi-
cating a low-battery condition.
CTRL/SHDN (Pin 8):
Analog Control Voltage and Shut-
down. When V
IN
• 0.2 < V
CTRL
< V
IN
• 0.9, the LED drive
current varies according to the formula:
⎛
V
⎞
I
LED
=
500 •
⎜
CTRL
– 0.2
⎟
mA
⎝
V
IN
⎠
4
U W
Efficiency vs I
LED
V
IN
= 2.4V
70
60
50
40
30
20
10
0
0
100
V
IN
= 1.2V
200
I
LED
(mA)
300
400
3490 G05
U
U
U
When V
CTRL
> V
IN
• 0.9, the LED drive current is clamped
at 350mA. When V
CTRL
< V
IN
• 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
LTC3490
FU CTIO AL DIAGRA
2
GATE
CONTROL
AND
DRIVERS
LIMIT
SENSE
AMP
19.2Ω
0.1Ω
PWM
LOGIC
OSCILLATOR
START-UP
DIMMING
AMP
8
1
CELLS
+
CTRL/
SHDN
I
REF
BATTERY
MONITOR
GND
4
SHUTDOWN
–
+
+
V
IN
W
3
SW
–
–
U
U
P BODY
CONTROL
CAP
6
+
–
LED
250k
5
OVERVOLTAGE
DETECT
40k
V
REF
/2
LOBAT
7
3490 FD
3490fa
5
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