LINEAR TECHNOLOGY LTC3215 Technical data

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FEATURES

■

High Efficiency Operation: 1x, 1.5x or 2x Boost
Modes with Automatic Mode Switching

■

Ultralow Dropout I

■

Output Current up to 700mA

■

Low Noise Constant Frequency Operation*

■

Wide VIN Range: 2.9V to 4.4V

■

Open/Shorted LED Protection

■

LED Disconnect in Shutdown

■

Low Shutdown Current: 2.5µA

■

4% LED Current Programming Accuracy

■

Automatic Soft-Start Limits Inrush Current

■

No Inductors

■

Tiny Application Circuit (All Components <1mm

Current Control

LED

Profile)

■

3mm × 3mm 10-Lead DFN Package

U

APPLICATIO S

■

LED Torch/Camera Light Supply for Cell Phones,
PDAs and Digital Cameras

■

General Lighting and/or Flash/Strobe Applications

LTC3215

700mA Low Noise High

Current LED Charge Pump

U

DESCRIPTIO

The LTC®3215 is a low noise, high current charge pump
DC/DC converter designed to power high current LEDs.
The part includes an accurate programmable current
source capable of driving loads up to 700mA from a 2.9V
to 4.4V input. Low external parts count (two flying capaci­tors, one programming resistor and two bypass capaci­tors) makes the LTC3215 ideally suited for small, battery­powered applications.

Built-in soft-start circuitry prevents excessive inrush cur­rent during start-up. High switching frequency enables the
use of small external capacitors. LED current is pro­grammed with an external resistor. The LED is discon­nected from V

An ultralow dropout current source maintains accurate
LED current at very low I
switching optimizes efficiency by monitoring the voltage
across the LED current source and switching modes only
when I

LED

a low profile 3mm × 3mm 10-Lead DFN package.

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

*Protected by U.S. Patent 6411531.

during shutdown.

IN

voltages. Automatic mode

LED

dropout is detected. The LTC3215 is available in

TYPICAL APPLICATIO

2.9V TO 4.4V

2.2µF

C1

2.2µF

+C1–C2+C2–

C1

V

C

IN

IN

ENDISABLE ENABLE

I

SET

LED1: AOT2015 HPW 1751B

C2

2.2µF

LTC3215

20k
1%

CPO

I

LED

U

3215 TA01a

LED1

I

LED

200mA

C

CPO

4.7µF

100

90

80

70

) (%)

IN

/P

60

LED

50

40

30

EFFICIENCY (P

20

LED = AOT2015 HPW 1751B

10

= 3V TYP AT 200mA

V

F

0

2.8

3.0 3.4

3.2

Efficiency vs V

I

LED

3.6

3.8

VIN (V)

IN

= 200mA

4.0

4.2

3215 TA01b

4.4

3215f

1

LTC3215

WW

W

ABSOLUTE AXI U RATI GS

U

UUW

PACKAGE/ORDER I FOR ATIO

(Note 1)

VIN to GND ............................................... –0.3V to 5.5V

CPO to GND ............................................. –0.3V to 5.5V

EN ................................................... – 0.3V to V

I

, I

CPO

(Note 2) ........................................... 1000mA

ILED

+ 0.3V

IN

CPO Short-Circuit Duration ............................ Indefinite

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

Operating Temperature Range (Note 3) .. – 40°C to 85°C

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at TA = 25°C. V

PARAMETER CONDITIONS MIN TYP MAX UNITS

Input Power Supply

VIN Operating Voltage ● 2.9 4.4 V

I

Operating Current I

VIN

I

Shutdown Current EN = LOW 2.5 7 µA

VIN

LED Current

LED Current Ratio (I

I

Dropout Voltage Mode Switch Threshold, I

LED

Mode Switching Delay (LED Warmup Time) 2.5 ms

LED Current On Time EN to LED Current On 130 µs

Charge Pump (CPO)

1x Mode Output Voltage I

1.5x Mode Output Voltage I

2x Mode Output Voltage I

1x Mode Output Impedance 0.25 Ω

1.5x Mode Output Impedance V

2x Mode Output Impedance V

CLK Frequency ● 0.6 0.9 1.2 MHz

EN

High Level Input Voltage (VIH) ● 1.4 V

Low Level Input Voltage (VIL) ● 0.4 V

Input Current (IIH) ● –1 1 µA

Input Current (IIL) ● –1 1 µA

)I

LED/ISET

The ● denotes the specifications which apply over the full operating

= 3.6V, CIN = C1 = C2 = 2.2µF, C

IN

= 0mA, 1x Mode 300 µA

CPO

= 0mA, 1.5x 7 mA

I

CPO

I

= 0mA, 2x Mode 9.2 mA

CPO

= 200mA to 600mA ● 3139 3270 3400 mA/mA

LED

= 0mA V

CPO

= 0mA 4.6 V

CPO

= 0mA 5.1 V

CPO

= 3.4V, V

IN

= 3.2V, V

IN

CPO

CPO

C2

C1

CPO

I

LED

I

SET

10-LEAD (3mm × 3mm) PLASTIC DFN

Consult LTC Marketing for parts specified with wider operating temperature ranges.

< 4.6V, C1 = C2 = 2.2µF 1.5 Ω

< 5.1V, C1 = C2 = 2.2µF 1.7 Ω

TOP VIEW

+

1

+

2

11

3

4

5

DD PACKAGE

T

= 125°C, θJA = 43°C/W

JMAX

EXPOSED PIN (PIN 11) IS GND

MUST BE SOLDERED TO PCB

= 200mA 120 mV

LED

10

9

8

7

6

–

C1

GND

–

C2

V

IN

EN

= 4.7µF.

CPO

ORDER PART

NUMBER

LTC3215EDD

DD PART

MARKING

LBPX

IN

V

2

3215f

LTC3215

ELECTRICAL CHARACTERISTICS

temperature range, otherwise specifications are at TA = 25°C. V

The ● denotes the specifications which apply over the full operating

= 3.6V, CIN = C1 = C2 = 2.2µF, C

IN

CPO

= 4.7µF.

PARAMETER CONDITIONS MIN TYP MAX UNITS

I

SET

V

ISET

I

ISET

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Note 2: Based on long-term current density limitations. Assumes an
operating duty cycle of ≤ 10% under absolute maximum conditions for

I

= 50µA ● 1.195 1.22 1.245 V

SET

● 225 µA

Note 3: The LTC3215E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C ambient
operating temperature range are assured by design, characterization and
correlation with statistical process controls.

durations less than 10 seconds. Max current for continuous operation is
350mA.

UW

TYPICAL PERFOR A CE CHARACTERISTICS

I

Dropout Voltage

LED

vs LED Current

0.8
VIN = 3.6V

0.7

0.6

0.5

0.4

0.3

DROPOUT VOLTAGE (V)

0.2

0.1

0

0 200

LED CURRENT (mA)

400 800600

3216 G01

I

Pin Current

LED

vs I

Pin Voltage

LED

600

500

400

300

PIN CURRENT (mA)

200

LED

I

100

0

0

0.2 0.4 0.6 0.8
I

PIN VOLTAGE (V)

LED

(TA = 25°C unless otherwise specified)

I

vs R

LED

1000

I

= 500mA

LED

800

400mA

300mA

200mA

100mA

1.0

3216 G02

600

(mA)

LED

I

400

200

0

0

515

SET

35

(kΩ)

30

25

40

1573 G06

10

20

R

SET

1x Mode Charge Pump Open-Loop
Output Resistance vs Temperature

0.31
I

= 200mA

CPO

OUTPUT RESISTANCE (Ω)

0.29

0.27

0.25

0.23

0.21

0.19

0.17

0.15

VIN = 3.6V

–15 10 60

–40

VIN = 3.3V

35

TEMPERATURE (°C)

VIN = 3.9V

3216 G07

1.5x Mode Charge Pump
Open-Loop Output Resistance
(1.5VIN – V

1.8

1.6

1.4

1.2

1.0

0.8

0.6

OUTPUT RESISTANCE (Ω)

VIN = 3V

0.4

0.2

85

V

CPO

= C1 = C2 = 2.2µF

C

IN

C

CPO

0

–40

= 4.2V

= 4.7µF

–15 35

)/I

CPO

TEMPERATURE (°C)

vs Temperature

CPO

10

85

60

3216 G05

2x Mode Charge Pump
Open-Loop Output Resistance

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

OUTPUT RESISTANCE (Ω)

0.4

0.2

(2VIN – V

VIN = 3V
V

CPO

= C1 = C2 = 2.2µF

C

IN

C

CPO

0

–40

)/I

CPO

CPO

= 4.8V

= 4.7µF

–15 35

10

TEMPERATURE (°C)

vs Temperature

85

60

3216 G06

3215f

3

LTC3215

UW

TYPICAL PERFOR A CE CHARACTERISTICS

(TA = 25°C unless otherwise specified)

Input Shutdown Current
vs Input Voltage

4.0

3.5

3.0

2.5

2.0

1.5

1.0

INPUT SHUTDOWN CURRENT (µA)

0.5

TA = 85°C

0

2.9 4.5

TA = 25°C

3.3

3.7

INPUT VOLTAGE (V)

TA = –40°C

4.13.1 3.5 3.9

Efficiency vs V

100

90

80

70

) (%)

IN

/P

60

LED

50

40

100mA

30

EFFICIENCY (P

200mA

20

400mA

AOT2015 HPW 1751B

10

= 3V TYP AT 100mA

V

F

0

2.8

3.0 3.4

3.2

4.3

3216 G04

IN

3.6

VIN (V)

930

920

910

900

890

880

870

FREQUENCY (kHz)

860

850

840

4.0

3.8

Oscillator Frequency
vs Supply Voltage

TA = 25°C

TA = –40°C

TA = 85°C

3.1 3.5 3.9

2.9 4.5

3.3

3.7

SUPPLY VOLTAGE (V)

4.1

4.3

3216 G03

I

SET/ILED

vs I

3400

3350

3300

3250

3200

CURRENT RATIO

3150

3100

4.2

4.4

3215 G15

0

Current Ratio

Current

LED

85°C

200 400

I

LED

Efficiency vs V

100

90

80

70

) (%)

IN

/P

60

LED

50

40

30

EFFICIENCY (P

20

LED = LXCL-PWF1 LUMILED

10

= 3V TYP AT 200mA

V

F

0

2.8

3.0 3.4

25°C

–40°C

CURRENT (mA)

200mA

3.2

600

IN

VIN (V)

3215 G16

3.6

800

400mA

3.8

600mA

4.0

4.2

4.4

3216 G11

V

CPO

50mV/DIV

A/C COUPLED

4

1.5x Mode CPO Output Ripple

I

IN

CPO

= 3.6V

= 200mA

500ns/DIVV

3216 G12

V

CPO

20mV/DIV

A/C COUPLED

2x Mode CPO Output Ripple

IN

I

CPO

= 3.6V

= 400mA

500ns/DIVV

3216 G13

Charge Pump Mode Switching
and Input Current (I

V

CPO

1V/DIV

I

VIN

500mA/

DIV

EN2

5V/DIV

= 3V 1ms/DIV

V

IN

= 400mA)

LED

3215 G14

3215f

LTC3215

U

UU

PI FU CTIO S

C2+, C1+, C2–, C1– (Pins 1, 2, 8, 10): Charge Pump
Flying Capacitor Pins. A 2.2µF X5R or X7R ceramic
capacitor should be connected from C1+ to C1– and from

+

to C2–.

C2

CPO (Pin 3): Output. CPO is the output of the Charge
Pump. This pin may be enabled or disabled using the EN
input. A 4.7µF X5R or X7R ceramic capacitor is required
from CPO to GND.

I

(Pin 4): Output. I

LED

The LED is connected between CPO (anode) and I
(cathode). The current into the I
programming resistor connected from I

is the LED current source output.

LED

pin is set by the

LED

to GND.

SET

LED

I

(Pin 5): LED Current Programming Resistor Pin. The

SET

pin will servo to 1.22V. A resistor connected between

I

SET

this pin and GND is used to set the LED current level.
Connecting a resistor of 2k or less will cause the LTC3215
to enter overcurrent shutdown mode.

EN (Pin 6): Input. The EN is used to enable the part or put
it into shutdown mode.

V

(Pin 7): Power. Supply voltage for the LTC3215. V

IN

IN

should be bypassed with a 2.2µF or greater low impedance
ceramic capacitor to GND.

GND (Pin 9): Charge Pump Ground. This pin should be
connected directly to a low impedance ground plane.

EXPOSED PAD (Pin 11): Control Signal Ground. This pad
must be soldered to a low impedance ground plane for
optimum thermal and electrical performance.

BLOCK DIAGRA

V

IN

7

W

OSCILLATOR

2

+

C1

MODE

CONTROL

10

–

C1

1X MODE: CPO = V

1.5X MODE: CPO = 4.6V
2X MODE: CPO = 5.1V

–

+

V

REF

1 8

+

C2

IN

DROPOUT

DETECTOR

–

C2

CPO

3

I

LED

4

EN

6

CONTROL

LOGIC

GND

CURRENT

SOURCE

CONTROL

I

SET

5

GND

119

3215 BD

3215f

5

LTC3215

OPERATIO

U

The LTC3215 uses a fractional switched capacitor charge
pump to power a high current LED with a programmed
regulated current. The part starts up into the 1x mode. In
this mode, VIN is directly connected to CPO. This mode
provides maximum efficiency and minimum noise. The
LTC3215 will remain in this mode until the LED current
source begins to dropout. When dropout is detected, the
LTC3215 will switch to 1.5x mode after a soft-start period.
Any subsequent dropout detected will cause the part to
enter 2x mode. The part may be reset to 1x mode by
bringing the part into shutdown mode and then reenabling
the part.

A two phase nonoverlapping clock activates the charge
pump switches. In the 2x mode, the flying capacitors are
charged on alternate clock phases from VIN. While one
capacitor is being charged from VIN, the other is stacked
on top of VIN and connected to the output. Alternatively, in
the 1.5x mode the flying capacitors are charged in series
during the first clock phase, and stacked in parallel on top
of VIN on the second clock phase. This sequence of
charging and discharging the flying capacitors continues
at a free running frequency of 900kHz (typ).

Table 1. Charge Pump Output Regulation Voltages

CHARGE PUMP MODE V

1.5x 4.6V

2x 5.1V

In shutdown mode all circuitry is turned off and the
LTC3215 draws a very low current from the VIN supply.
Furthermore, CPO is weakly connected to VIN. The LTC3215
enters shutdown mode when the EN pin is brought low.
Since EN is a high impedance CMOS input it should never
be allowed to float. To ensure that its state is defined, it
must always be driven with valid logic levels.

Thermal Protection

The LTC3215 has built-in overtemperature protection.
Thermal shutdown circuitry will shutdown the I
when the junction temperature exceeds approximately
150°C. It will re-enable the I
temperature drops back to approximately 135°C. The
LTC3215 will cycle in and out of thermal shutdown indefi­nitely without latch up or damage until the heat source is
removed.

output once the junction

LED

CPO

LED

output

The current delivered to the LED load is controlled by the
internal programmable current source. The value of this
current may be selected by choosing the appropriate
programming resistor. The resistor is connected between
the I
the desired current level can be determined by Equation 1.

A resistor value of 2k or less (e.g., a short-circuit) will
cause the LTC3215 to enter overcurrent shutdown mode.
This mode will prevent damage to the part by shutting
down the high power sections of the chip.

Regulation is achieved by sensing the voltage at the CPO
pin and modulating the charge pump strength based on
the error signal. The CPO regulation voltages are set
internally, and are dependent on the charge pump mode as
shown in Table 1.

pin and GND. The resistor value needed to attain

SET

R

= 3990/I

SET

LED

(1)

Soft-Start

To prevent excessive inrush current during start-up and
mode switching, the LTC3215 employs built-in soft-start
circuitry. Soft-start is achieved by increasing the amount
of current available to the output charge storage capacitor
linearly over a period of approximately 250µs.

Charge Pump Strength

When the LTC3215 operates in either the 1.5x mode or 2x
mode, the charge pump can be modeled as a Thevenin­equivalent circuit to determine the amount of current
available from the effective input voltage and effective
open-loop output resistance, ROL(Figure 1).

6

3215f

OPERATIO

2.2µF 2.2µF

4.7µF

1µF

I

LED

V

IN

2.9V TO 4.4V

2.2µF

EN

LTC3215

C1

+C1–C2+C2–

I

SET

3215 F02b

CPO

1k

9.31k
1%

9.31k
1%

PWM

LTC3215

U

R

OL

+

1.5V

IN

+

OR

–

2V

IN

3215 F01

CPO

–

Figure 1. Charge Pump Open-Loop Thevenin-Equivalent Circuit

ROL is dependent on a number of factors including
the oscillator frequency, flying capacitor values and
switch resistances.

From Figure 1, we can see that the output current is
proportional to:

(1.5V

– CPO)/ROL or (2VIN – CPO)/R

IN

OL

(2)

in the 1.5x mode or 2x mode respectively.

LED Current Programming

The LTC3215 includes an accurate, programmable cur­rent source that is capable of driving LED currents up to
350mA continuously and up to 700mA for pulsed opera­tion. Pulsed operation may be achieved by toggling the EN
pin. In either continuous or pulsed operation, proper
board layout is required for effective heat sinking.

The current may be programmed using a single external
resistor. Equation 1, used to calculate the resistor value
from the desired current level is repeated below:

For applications requiring multiple current levels, several
schemes may be used to change the resistance for the

resistor. Figure 2 shows two such schemes. The

R

SET

circuit in Figure 2a uses the I/O output of a microcontroller
to switch a second resistor (R2) in parallel or series with
R1, changing the effective I

current. Alternatively, the

SET

circuit in Figure 2b uses a pulse-width modulator (PWM)
to vary the current through R

, which changes the LED

SET

current.

Mode Switching

The LTC3215 will automatically switch from 1x mode to

1.5x mode, and subsequently from 1.5x mode to 2x mode
whenever a dropout condition is detected at the I

LED

pin.
The part will wait approximately 2ms before switching to
the next mode. This delay allows the LED to warm up and
reduce its forward voltage which may remove the dropout
condition.

In order to reset the part back into 1x mode, the LTC3215
must be brought into shutdown (EN = LOW). Immediately
after the part has been brought to shutdown, it may be
enabled into the 1x mode via the EN pin. An internal
comparator will not allow the main switches to connect V

IN

and CPO in 1x mode until the voltage at the CPO pin has
decayed to less than or equal to the voltage at the VIN pin.

R

= 3990/I

SET

ON/OFF

TORCH/FLASH

LED

2.9V TO 4.4V

2.2µF

V

IO

V

IO

= [(1.22V/R1) – ((VIO – 1.22V)/R2)] • 3270

= [(1.22V/(R1 • R2/(R1 + R2))] • 3270

R2

*I

TORCH

I

FLASH

µP

(1)

2.2µF 2.2µF

+C1–C2+C2–

C1

V

IN

LTC3215

EN

I

SET

R1

(2a) (2b)

CPO

I

LED

3215 F02a

I

LED

4.7µF

*

Figure 2

3215f

7

LTC3215

WUUU

APPLICATIO S I FOR ATIO

VIN, CPO Capacitor Selection

The value and type of capacitors used with the LTC3215
determine several important parameters such as regulator
control loop stability, output ripple, charge pump strength
and minimum start-up time.

To reduce noise and ripple, it is recommended that low
equivalent series resistance (ESR) ceramic capacitors be
used for both C

VIN

and C

. Tantalum and aluminum

CPO

capacitors are not recommended because of their high ESR.

The value of C

directly controls the amount of output

CPO

ripple for a given load current. Increasing the size of
C

will reduce the output ripple at the expense of higher

CPO

start-up current. The peak-to-peak output ripple for 1.5x
mode is approximately given by the expression:

V

RIPPLE(P-P)

Where f

OSC

cally 900kHz) and C

= I

OUT

/(3f

OSC

• C

) (3)

CPO

is the LTC3215’s oscillator frequency (typi-

is the output storage capacitor.

CPO

Both the style and value of the output capacitor can
significantly affect the stability of the LTC3215. As shown
in the block diagram, the LTC3215 uses a control loop to
adjust the strength of the charge pump to match the
current required at the output. The error signal of this loop
is stored directly on the output charge storage capacitor.
The charge storage capacitor also serves as the dominant
pole for the control loop. To prevent ringing or instability,
it is important for the output capacitor to maintain at least

2.2µF of actual capacitance over all conditions.

Likewise, excessive ESR on the output capacitor will tend
to degrade the loop stability of the LTC3215. The closed
loop output resistance of the LTC3215 is designed to be
76mΩ. For a 100mA load current change, the error signal
will change by about 7.6mV. If the output capacitor has
76mΩ or more of ESR, the closed-loop frequency re­sponse will cease to roll off in a simple one-pole fashion
and poor load transient response or instability could
result. Multilayer ceramic chip capacitors typically have
exceptional ESR performance. MLCCs combined with a
tight board layout will yield very good stability. As the value
of C
C

controls the amount of output ripple, the value of

CPO

controls the amount of ripple present at the input pin

VIN

(VIN). The input current to the LTC3215 will be relatively
constant while the charge pump is on either the input

charging phase or the output charging phase but will drop
to zero during the clock nonoverlap times. Since the
nonoverlap time is small (~15ns), these missing “notches”
will result in only a small perturbation on the input power
supply line. Note that a higher ESR capacitor such as
tantalum will have higher input noise due to the input
current change times the ESR. Therefore, ceramic capaci­tors are again recommended for their exceptional ESR
performance. Input noise can be further reduced by pow­ering the LTC3215 through a very small series inductor as
shown in Figure 3. A 10nH inductor will reject the fast
current notches, thereby presenting a nearly constant
current load to the input power supply. For economy, the
10nH inductor can be fabricated on the PC board with
about 1cm (0.4") of PC board trace.

Flying Capacitor Selection

10nH

2.2µF0.1µF

Figure 3. 10nH Inductor Used for Input Noise Reduction
(Approximately 1cm of Wire)

V

IN

GND

LTC3215

3215 F03

Warning: Polarized capacitors such as tantalum or alumi­num should never be used for the flying capacitors since
their voltage can reverse upon start-up of the LTC3215.
Ceramic capacitors should always be used for the flying
capacitors.

The flying capacitors control the strength of the charge
pump. In order to achieve the rated output current it is
necessary to have at least 2.2µF of actual capacitance for
each of the flying capacitors. Capacitors of different mate­rials lose their capacitance with higher temperature and
voltage at different rates. For example, a ceramic capacitor
made of X7R material will retain most of its capacitance from
–40oC to 85oC whereas a Z5U or Y5V style capacitor
will lose considerable capacitance over that range. Z5U and
Y5V capacitors may also have a very poor voltage coeffi­cient causing them to lose 60% or more of their capacitance
when the rated voltage is applied. Therefore, when compar­ing different capacitors, it is often more appropriate to

3215f

8

WUUU

APPLICATIO S I FOR ATIO

LTC3215

compare the amount of achievable capacitance for a given
case size rather than comparing the specified capacitance
value. For example, over rated voltage and temperature
conditions, a 1µF, 10V, Y5V ceramic capacitor in a 0603 case
may not provide any more capacitance than a 0.22µF, 10V,
X7R available in the same case. The capacitor
manufacturer’s data sheet should be consulted to determine
what value of capacitor is needed to ensure minimum
capacitances at all temperatures and voltages.

Table 2 shows a list of ceramic capacitor manufacturers
and how to contact them.

Table 2. Recommended Capacitor Vendors

AVX www.avxcorp.com

Kemet www.kemet.com

Murata www.murata.com

Taiyo Yuden www.t-yuden.com

Vishay www.vishay.com

TDK www.tdk.com

Layout Considerations and Noise

Due to its high switching frequency and the transient
currents produced by the LTC3215, careful board layout is
necessary. A true ground plane and short connections to
all capacitors will improve performance and ensure proper
regulation under all conditions.

The flying capacitor pins C1+, C2+, C1– and C2– will have
very high edge rate waveforms. The large dv/dt on these

pins can couple energy capacitively to adjacent PCB runs.
Magnetic fields can also be generated if the flying capaci­tors are not close to the LTC3215 (i.e., the loop area is
large). To decouple capacitive energy transfer, a Faraday
shield may be used. This is a grounded PCB trace between
the sensitive node and the LTC3215 pins. For a high quality
AC ground, it should be returned to a solid ground plane
that extends all the way to the LTC3215.

The following guidelines should be followed when design­ing a PCB layout for the LTC3215.

• The Exposed Pad should be soldered to a large copper

plane that is connected to a solid, low impedance
ground plane using plated, through-hole vias for proper
heat sinking and noise protection.

• Input and output capacitors (CIN and C

) must also

CPO

be placed as close to the part as possible.

• The flying capacitors must also be placed as close to the

part as possible. The traces running from the pins to the
capacitor pads should be as wide as possible.

•VIN, CPO and I

traces must be made as wide as

LED

possible. This is necessary to minimize inductance,
as well as provide sufficient area for high current
applications.

• LED pads must be large and should be connected to as

much solid metal as possible to ensure proper heat
sinking.

C1

C

CPO

PIN 1

RSET

Figure 4. Example Board Layout

C2

C

IN

3215 F04

3215f

9

LTC3215

WUUU

APPLICATIO S I FOR ATIO

Power Efficiency

To calculate the power efficiency (η) of a white LED driver
chip, the LED power should be compared to the input
power. The difference between these two numbers repre­sents lost power whether it is in the charge pump or the
current sources. Stated mathematically, the power effi­ciency is given by:

P

LED

η≡

P

IN

(4)

The efficiency of the LTC3215 depends upon the mode in
which it is operating. Recall that the LTC3215 operates as
a pass switch, connecting VIN to CPO, until dropout is
detected at the I

pin. This feature provides the optimum

LED

efficiency available for a given input voltage and LED
forward voltage. When it is operating as a switch, the
efficiency is approximated by:

P

η≡ = ≈

P

VI

LEDINLED LED

•

VIVV

•

IN IN

LED

IN

(5)

since the input current will be very close to the LED
current.

At moderate to high output power, the quiescent current
of the LTC3215 is negligible and the expression above is
valid.

Once dropout is detected at the I

pin, the LTC3215

LED

enables the charge pump in 1.5x mode.

In 1.5x boost mode, the efficiency is similar to that of a
linear regulator with an effective input voltage of 1.5 times
the actual input voltage. This is because the input current
for a 1.5x charge pump is approximately 1.5 times the load
current. In an ideal 1.5x charge pump, the power efficiency
would be given by:

η

IDEAL

P

LED

≡ = ≈

P

IN

VI

•

LED LED

VIVV

•. .15 15

IN LED

LED

IN

(6)

Similarly, in 2x boost mode, the efficiency is similar to that
of a linear regulator with an effective input voltage of 2
times the actual input voltage. In an ideal 2x charge pump,
the power efficiency would be given by:

η

IDEAL

P

LED

≡ = ≈

P

IN

VI

•

LED LED

VIVV

•• •22

IN LED

LED

IN

(7)

Thermal Management

For higher input voltages and maximum output current,
there can be substantial power dissipation in the LTC3215.
If the junction temperature increases above approximately
150°C, the thermal shutdown circuitry will automatically
deactivate the output. To reduce maximum junction tem­perature, a good thermal connection to the PC board is
recommended. Connecting the Exposed Pad to a ground
plane and maintaining a solid ground plane under the
device can reduce the thermal resistance of the package
and PC board considerably.

10

3215f

PACKAGE DESCRIPTIO

LTC3215

U

DD Package

10-Lead Plastic DFN (3mm × 3mm)

(Reference LTC DWG # 05-08-1698)

0.675 ±0.05

3.50 ±0.05

1.65 ±0.05
(2 SIDES)2.15 ±0.05

PACKAGE
OUTLINE

0.25 ± 0.05

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

PIN 1

TOP MARK

(SEE NOTE 6)

0.200 REF

NOTE:

1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT

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

0.50
BSC

2.38 ±0.05
(2 SIDES)

3.00 ±0.10
(4 SIDES)

0.75 ±0.05

0.00 – 0.05

1.65 ± 0.10
(2 SIDES)

R = 0.115

TYP

2.38 ±0.10
(2 SIDES)

BOTTOM VIEW—EXPOSED PAD

106

15

0.25 ± 0.05

0.50 BSC

0.38 ± 0.10

(DD10) DFN 1103

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

3215f

11

LTC3215

TYPICAL APPLICATIO

ON/OFF

U

High Power Camera Light and Flash

2.2µF 2.2µF

+C1–C2+C2–

C1

V

IN

EN

µP

2.9V TO 4.4V

2.2µF

2.8V

LTC3215

CPO

I

LED

I

LED

200mA/500mA

4.7µF

2.8V

TORCH/FLASH

30k

1%

I

SET

10.5k
1%

3215 TA02

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LT1618 Constant Current, 1.4MHz, 1.5A Boost Converter VIN: 1.6V to 18V, V

MS Package

LT1961 1.5A (ISW), 1.25MHz, High Efficiency Step-Up VIN: 3V to 25V, V

DC/DC Converter MS8E Package

LTC3205 250mA, 1MHz, Multi-Display LED Controller VIN: 2.8V to 4.5V, V

DFN Package

LTC3206 400mA, 800kHz, Multi-Display LED Controller VIN: 2.8V to 4.5V, V

DFN Package

LTC3216 1A Low Noise High Current LED Charge Pump with VIN: 2.9V to 4.4V, V

Independent Flash/Torch Current Control DFN Package

LTC3440/LTC3441 600mA/1.2A I

, 2MHz/1MHz, Synchronous VIN: 2.4V to 5.5V, V

OUT

Buck-Boost DC/DC Converter MS/DFN Packages

LTC3443 600mA/1.2A I

, 600kHz, Synchronous VIN: 2.4V to 5.5V, V

OUT

Buck-Boost DC/DC Converter DFN Package

LTC3453 1MHz, 800mA Synchronous Buck-Boost V

: 2.7V to 5.5V, V

IN(MIN)

High Power LED Driver QFN Package

LT3467/LT3467A 1.1A (ISW), 1.3/2.1MHz, High Efficiency Step-Up VIN: 2.4V to 16V, V

DC/DC Converters with Integrated Soft-Start ThinSOT Package

LT3479 3A, 42V, 3.5MHz Boost Converter VIN: 2.5V to 24V, V

DFN, TSSOP Packages

OUT(MAX)

= 36V, IQ = 1.8mA, ISD < 1µA

OUT(MAX)

= 35V, IQ = 0.9mA, ISD < 6µA

= 5.5V, IQ = 50µA, ISD < 1µA

OUT(MAX)

= 5.5V, IQ = 50µA, ISD < 1µA

OUT(MAX)

= 5.5V, IQ = 300µA, ISD < 2.5µA

OUT(MAX)

= 5.25V, IQ = 25µA/50µA, ISD <1µA

OUT(MAX)

= 5.25V, IQ = 28µA, ISD <1µA

OUT(MAX)

: 2.7V to 4.5V, IQ = 2.5mA, ISD < 6µA

IN(MAX)

= 40V, IQ = 1.2mA, ISD < 1µA

OUT(MAX)

= 40V, IQ = 2µA, ISD < 1µA

OUT(MAX)

12

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone] ● www.linear.com

3215f

LT/TP 0305 1K • PRINTED IN USA

© LINEAR TECHNOLOGY CORPORATION 2005