LTC3216
1
3216fa
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATIO
U
APPLICATIO S
U
FEATURES
DESCRIPTIO
U
s
LED Torch/Camera Light Supply for Cell Phones,
PDAs and Digital Cameras
s
Generic Lighting and/or Flash/Strobe Applications
s
High Efficiency Operation: 1x, 1.5x or 2x Boost
Modes with Automatic Mode Switching
s
Ultralow Dropout I
LED
Current Control
s
Output Current up to 1A
s
Low Noise Constant Frequency Operation*
s
Independent Low Current/High Current
Programming and Enable Pins
s
Wide V
IN
Range: 2.9V to 4.4V
s
Open/Shorted LED Protection
s
LED Disconnect in Shutdown
s
Low Shutdown Current: 2.5
A
s
4% LED Current Programming Accuracy
s
Automatic Soft-Start Limits Inrush Current
s
No Inductors
s
Tiny Application Circuit (All Components <1mm
Profile)
s
3mm
4mm 12-Lead DFN Package
1A Low Noise High Current
LED Charge Pump with
Independent Torch/Flash Current Control
The LTC
3216 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 1A from a 2.9V to
4.4V input. Low external parts count (two flying capaci-
tors, two programming resistors and two bypass capaci-
tors at V
IN
and CPO) make the LTC3216 ideally suited for
small, battery-powered applications.
Built-in soft-start circuitry prevents excessive inrush cur-
rent during start-up. High switching frequency enables the
use of small external capacitors. Independent high and
low current settings are programmed by two external
resistors. Shutdown mode and current output levels are
selected via two logic inputs.
An ultralow dropout current source maintains accurate
LED current at very low I
LED
voltages. Automatic mode
switching optimizes efficiency by monitoring the voltage
across the LED current source and switching modes only
when I
LED
dropout is detected. The LTC3216 is available in
a small 3mm
4mm 12-Lead DFN package.
Torch Mode Efficiency vs V
IN
EN1
0
1
0
1
C1
2.2
F
C2
2.2
F
C
IN
2.2
F
C
CPO
4.7
F
LED1
I
LED
V
IN
2.9V TO 4.4V
EN2
EN1
LTC3216
C1
+
C1
C2
+
C2
I
SET1
I
SET2
0 (SHUTDOWN)
200mA (TORCH)
600mA
800mA (FLASH)
EN2
0
0
1
1
3216 TA01a
LED1: LUMILEDS LXCL-PWF1 LUXEON FLASH
CPO
20k
1%
6.65k
1%
EN2 (FLASH)
EN1 (TORCH)
I
LED
V
IN
(V)
2.8
EFFICIENCY (P
LED
/PIN) (%)
100
90
80
70
60
50
40
30
20
10
0
3.2
3.6
3.8
3216 TA01b
3.0
3.4
4.0
4.2
4.4
P
LED
/PIN
LUMILEDS LXCL-PWF1
V
F
= 3V TYP AT 200mA
I
LED
= 200mA
*Protected by U.S. Patents including 6411531.
LTC3216
2
3216fa
12
11
10
9
8
7
1
2
3
4
5
6
C1
GND
C2
VIN
EN2
EN1
C2
+
C1
+
CPO
I
SET1
I
LED
I
SET2
TOP VIEW
DE12 PACKAGE
12-LEAD (4mm
3mm) PLASTIC DFN
EXPOSED PAD IS GND (PIN 13)
MUST BE SOLDERED TO PCB
13
V
IN
to GND ................................................ 0.3V to 5.5V
CPO to GND .............................................. 0.3V to 5.5V
EN2, EN1 ......................................... 0.3V to V
IN
+ 0.3V
I
CPO
, I
ILED
(Note 2) ........................................... 1500mA
CPO Short-Circuit Duration ............................. Indefinite
Operating Temperature Range (Note 3) ...40
C to 85
C
Storage Temperature Range ..................65
C to 125
C
ORDER PART
NUMBER
T
JMAX
= 125
C,
JA
= 43
C/W
LTC3216EDE
ABSOLUTE AXI U
RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
(Note 1)
ELECTRICAL CHARACTERISTICS
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. V
IN
= 3.6V, C
IN
= C1 = C2 = 2.2
F, C
CPO
= 4.7
F
Consult LTC Marketing for parts specified with wider operating temperature ranges.
DFN PART
MARKING
3216
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Power Supply
V
IN
Operating Voltage
q
2.9
4.4
V
I
VIN
Operating Current
I
CPO
= 0mA, 1x Mode
300
A
I
CPO
= 0mA, 1.5x
7
mA
I
CPO
= 0mA, 2x Mode
9.2
mA
I
VIN
Shutdown Current
EN2 = EN1 = LOW
2.5
7
A
LED Current
LED Current Ratio (I
LED
/I
SET1/2
)
I
LED
= 200mA to 800mA
q
3120
3250
3380
mA/mA
I
LED
Dropout Voltage
Mode Switch Threshold, I
LED
= 200mA
120
mV
Mode Switching Delay
EN1 = HIGH, EN2 = LOW
150
ms
(LED Warmup Time)
EN1 = LOW or HIGH, EN2 = HIGH
2
ms
LED Current On Time
EN to LED Current On
130
s
Charge Pump (CPO)
1x Mode Output Voltage
I
CPO
= 0mA
V
IN
V
1.5x Mode Output Voltage
I
CPO
= 0mA
4.6
V
2x Mode Output Voltage
I
CPO
= 0mA
5.1
V
1x Mode Output Impedance
0.25
1.5x Mode Output Impedance
V
IN
= 3.4V, V
CPO
< 4.6V, C1 = C2 = 2.2
F
1.5
2x Mode Output Impedance
V
IN
= 3.2V, V
CPO
< 5.1V, C1 = C2 = 2.2
F
1.7
CLK Frequency
q
0.6
0.9
1.2
MHz
EN1, EN2
High Level Input Voltage (V
IH
)
q
1.4
V
Low Level Input Voltage (V
IL
)
q
0.4
V
Input Current (I
IH
)
q
1
1
A
Input Current (I
IL
)
q
1
1
A
LTC3216
3
3216fa
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
durations less than 10 seconds. Max current for continuous operation is
500mA.
Note 3: The LTC3216E is guaranteed to meet performance specifications
from 0
C to 70
C. Specifications over the 40
C to 85
C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
ELECTRICAL CHARACTERISTICS
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
I
LED
Dropout Voltage
vs LED Current
I
LED
Pin Current
vs I
LED
Pin Voltage
I
LED
vs R
SET
LED CURRENT (mA)
0
200
DROPOUT VOLTAGE (V)
400
800
600
1000
3216 G01
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
I
LED
PIN VOLTAGE (V)
0
I
LED
PIN CURRENT (mA)
600
500
400
300
200
100
0
0.2
0.4
0.6
0.8
3216 G02
1.0
TEMPERATURE (
C)
40
OUTPUT RESISTANCE (
)
10
60
85
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
3216 G05
15
35
40
10
60
85
15
35
TEMPERATURE (
C)
OUTPUT RESISTANCE (
)
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
3216 G06
I
LED
= 500mA
400mA
300mA
200mA
100mA
V
IN
= 3V
V
CPO
= 4.2V
C
IN
= C1 = C2 = 2.2
F
C
CPO
= 4.7
F
V
IN
= 3V
V
CPO
= 4.8V
C
IN
= C1 = C2 = 2.2
F
C
CPO
= 4.7
F
TEMPERATURE (
C)
40
SWITCH RESISTANCE (
)
35
85
3216 G07
15
10
60
0.31
0.29
0.27
0.25
0.23
0.21
0.19
0.17
0.15
I
CPO
= 200mA
V
IN
= 3.6V
V
IN
= 3.3V
V
IN
= 3.9V
V
IN
= 3.6V
R
SET
(k
)
I
LED
(mA)
1573 G06
1200
1000
800
600
400
200
0
0
10
20
25
5
15
30
35
40
1.5x Mode Charge Pump
Open-Loop Output Resistance
(1.5V
IN
V
CPO
)/I
CPO
vs Temperature
2x Mode Charge Pump
Open-Loop Output Resistance
(2V
IN
V
CPO
)/I
CPO
vs Temperature
1x Mode Charge Pump Open-Loop
Output Resistance vs Temperature
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
SET1
, I
SET2
V
ISET1
, V
ISET2
I
SETX
= 50
A
q
1.195
1.22
1.245
V
I
ISET1
, I
ISET2
q
321
A
T
A
= 25
C unless otherwise noted.
The
q
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25
C. V
IN
= 3.6V, C
IN
= C1 = C2 = 2.2
F, C
CPO
= 4.7
F
LTC3216
4
3216fa
V
IN
(V)
2.8
EFFICIENCY (PLED/PIN) (%)
100
90
80
70
60
50
40
30
20
10
0
3.2
3.6
3.8
3216 G11
3.0
3.4
4.0
4.2
4.4
LED = LXCL-PWF1 LUMILEDS
3216 G12
3216 G13
V
CPO
50mV/DIV
A/C COUPLED
500ns/DIV
V
CPO
20mV/DIV
A/C COUPLED
500ns/DIV
V
IN
= 3.6V
I
CPO
= 200mA
V
IN
= 3.6V
I
CPO
= 400mA
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
INPUT SHUTDOWN CURRENT (
A)
3216 G04
INPUT VOLTAGE (V)
2.9
4.5
3.3
3.7
4.1
3.1
3.5
3.9
4.3
T
A
= 85
C
T
A
= 40
C
T
A
= 25
C
FREQUENCY (kHz)
930
920
910
900
890
880
870
860
850
840
3216 G03
SUPPLY VOLTAGE (V)
2.9
4.5
3.3
3.7
4.1
3.1
3.5
3.9
4.3
T
A
= 85
C
T
A
= 40
C
T
A
= 25
C
600mA
I
LED
= 800mA
400mA
200mA
1ms/DIV
EN2
5V/DIV
I
VIN
500mA/DIV
V
CPO
1V/DIV
3216 G14
V
IN
= 3V
I
LED
CURRENT(mA)
0
CURRENT RATIO
200
400 500
900
3216 G15
100
300
600 700 800
3400
3350
3300
3250
3200
3150
3100
T
A
= 85
C
T
A
= 40
C
T
A
= 25
C
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Efficiency vs V
IN
1.5x Mode CPO Output Ripple
2x Mode CPO Output Ripple
Input Shutdown Current
vs Input Voltage
Oscillator Frequency
vs Supply Voltage
Charge Pump Mode Switching
and Input Current
T
A
= 25
C unless otherwise noted.
I
SET
/I
LED
Current Ratio vs I
LED
Current
LTC3216
5
3216fa
U
U
U
PI FU CTIO S
C2
+
, C1
+
, C2
, C1
(Pins 1, 2, 10, 12): Charge Pump
Flying Capacitor Pins. A 2.2
F X5R or X7R ceramic
capacitor should be connected from C1
+
to C1
and from
C2
+
to C2
.
CPO (Pin 3): Output. CPO is the output of the Charge
Pump. This pin may be enabled or disabled using the EN1
and EN2 inputs. A 4.7
F X5R or X7R ceramic capacitor is
required from CPO to GND.
I
SET1
/I
SET2
(Pins 4, 6): LED Current Programming Resis-
tor Pins. The I
SET1
and I
SET2
pins will servo to 1.22V.
Resistors connected between each of these pins and GND
are used to set the high and low LED current levels.
Connecting a resistor of 2k
or less will cause the
LTC3216 to enter overcurrent shutdown mode.
I
LED
(Pin 5): Output. I
LED
is the LED current source output.
The LED is connected between CPO (anode) and I
LED
(cathode). The current into the I
LED
pin is set via the EN1
and EN2 inputs, and the programming resistors con-
nected from I
SET2
and I
SET1
to GND.
EN1/EN2 (Pins 7, 8): Inputs. The EN1 and EN2 pins are
used to select which current level is being supplied to the
LED, as well as to put the part into shutdown mode. The
truth table for these pins is as follows:
Truth Table
EN1
EN2
MODE
0
0
Shutdown
1
0
Low Current
0
1
High Current
1
1
Low + High Current
V
IN
(Pin 9): Power. Supply voltage for the LTC3216. V
IN
should be bypassed with a 2.2
F or greater low impedance
ceramic capacitor to GND.
GND (Pin 11): Charge Pump Ground. This pin should be
connected directly to a low impedance ground plane.
EXPOSED PAD (Pin 13): Control Signal Ground. This pad
must be soldered to a low impedance ground plane for
optimum thermal and electrical performance.
BLOCK DIAGRA
W
2
3
5
13
11
12
4
6
+
1
10
1X MODE: CPO = V
IN
1.5X MODE: CPO = 4.6V
2X MODE: CPO = 5.1V
V
REF
DROPOUT
DETECTOR
CURRENT
SOURCE
CONTROL
CONTROL
LOGIC
MODE
CONTROL
OSCILLATOR
8
9
7
GND
CPO
I
LED
GND
I
SET2
I
SET1
V
IN
EN1
EN2
C1
+
C1
C2
+
C2
3216 BD
LTC3216
6
3216fa
The LTC3216 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, V
IN
is directly connected to CPO. This mode
provides maximum efficiency and minimum noise. The
LTC3216 will remain in this mode until the LED current
source begins to dropout. When dropout is detected, the
LTC3216 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 V
IN
. While one
capacitor is being charged from V
IN
, the other is stacked
on top of V
IN
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 V
IN
on the second clock phase. This sequence of
charging and discharging the flying capacitors continues
at a free running frequency of 900kHz (typ).
The current delivered to the LED load is controlled by the
internal programmable current source. Three discrete
current settings (Low, High and Low + High) are available
and may be selected via the EN2 and EN1 pins. The values
of these currents may be selected by choosing the appro-
priate programming resistors. Each resistor is connected
between the I
SET2
or I
SET1
pin and GND. The resistor
values needed to attain the desired current levels can be
determined by equation 1.
R
SET1/2
= 3965/I
LED
(1)
A resistor value of 2k
or less (i.e. a short-circuit) will
cause the LTC3216 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.
Table 1. Charge Pump Output Regulation Voltages
Charge Pump Mode
V
CPO
1.5x
4.6V
2x
5.1V
In shutdown mode all circuitry is turned off and the
LTC3216 draws a very low current from the V
IN
supply.
Furthermore, CPO is weakly connected to V
IN
. The LTC3216
enters shutdown mode when both the EN1 and EN2 pins
are brought low. Since EN1 and EN2 are high impedance
CMOS inputs they should never be allowed to float. To
ensure that their states are defined they must always be
driven with valid logic levels.
Thermal Protection
The LTC3216 has built-in overtemperature protection.
Thermal shutdown circuitry will shutdown the I
LED
output
when the junction temperature exceeds approximately
150
C. It will re-enable the I
LED
output once the junction
temperature drops back to approximately 135
C. The
LTC3216 will cycle in and out of thermal shutdown indefi-
nitely without latch up or damage until the heat source is
removed.
Soft-Start
To prevent excessive inrush current during start-up and
mode switching, the LTC3216 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 250
s.
Charge Pump Strength
When the LTC3216 operates in either the 1.5x mode or 2x
mode, the charge pump can be modeled as a Thevenin-
equivalent circuit to determine the amount of current
available from the effective input voltage and effective
open-loop output resistance, R
OL
(Figure 1).
OPERATIO
U
LTC3216
7
3216fa
R
OL
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
IN
CPO)/R
OL
or (2V
IN
CPO)/R
OL
(2)
in the 1.5x mode or 2x mode respectively.
Current Levels
The LTC3216 may be programmed to have three discrete
current levels. These are the LOW, HIGH and LOW + HIGH
current levels. The LOW and HIGH currents are set by the
resistors connected between I
SET1
and I
SET2
pins, respec-
tively, to GND. The LOW + HIGH current mode supplies a
current that is equal to sum of the LOW and HIGH currents.
Due to the low output impedance of this part, care should
be taken in selecting current levels. This part can supply up
to 500mA continuously, and up to 1A for pulsed operation
with a 10% duty cycle. Pulsed operation may be achieved
by toggling the EN1 and EN2 bits. In either continuous or
pulsed operation, proper board layout is required for
effective heat sinking.
Mode Switching
The LTC3216 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.
In the LOW current mode, the part will wait approximately
150ms after dropout is detected before switching to the
next mode. In the HIGH and LOW + HIGH current modes,
the part will wait approximately 2ms before switching to
the next mode. These delays allow 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 LTC3216
must be brought into shutdown (EN1 = EN2 = LOW).
Immediately after the part has been brought to shutdown,
it may be set to the desired output current level via the EN1
and EN2 pins. 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 V
IN
pin.
Figure 1. Charge Pump Open-Loop Thevenin-Equivalent Circuit
OPERATIO
U
+
+
CPO
R
OL
1.5V
IN
OR
2V
IN
LTC3216
8
3216fa
V
IN
, CPO Capacitor Selection
The style and value of capacitors used with the LTC3216
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
CPO
. Tantalum and aluminum
capacitors are not recommended because of their high
ESR.
The value of C
CPO
directly controls the amount of output
ripple for a given load current. Increasing the size of
C
CPO
will reduce the output ripple at the expense of higher
start-up current. The peak-to-peak output ripple for 1.5x
mode is approximately given by the expression:
V
RIPPLE(P-P)
= I
OUT
/(3f
OSC
C
CPO
)
(3)
Where f
OSC
is the LTC3216's oscillator frequency (typi-
cally 900kHz) and C
CPO
is the output storage capacitor.
Both the style and value of the output capacitor can
significantly affect the stability of the LTC3216. As shown
in the block diagram, the LTC3216 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
2.2
F of actual capacitance over all conditions.
Likewise, excessive ESR on the output capacitor will tend
to degrade the loop stability of the LTC3216. The closed
loop output resistance of the LTC3216 is designed to be
76m
. For a 100mA load current change, the error signal
will change by about 7.6mV. If the output capacitor has
76m
or more of ESR, the closed-loop frequency re-
sponse will cease to roll off in a simple one-pole fashion
and poor load transient response of 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
CPO
controls the amount of output ripple, the value of
C
VIN
controls the amount of ripple present at the input pin
(V
IN
). The input current to the LTC3216 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 capaci-
tors are again recommended for their exceptional ESR
performance. Input noise can be further reduced by pow-
ering the LTC3216 through a very small series inductor as
shown in Figure 2. 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.
APPLICATIO S I FOR ATIO
W
U
U
U
Figure 2. 10nH Inductor Used for Input Noise Reduction
(Approximately 1cm of Wire)
V
IN
GND
LTC3216
2.2
F
0.1
F
10nH
3216 F02
Flying Capacitor Selection
Warning: Polarized capacitors such as tantalum or alumi-
num should never be used for the flying capacitors since
their voltage can reverse upon start-up of the LTC3216.
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 2.2
F of actual capacitance for
each of the flying capacitors. Capacitors of different mate-
rials 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
LTC3216
9
3216fa
from 40
o
C to 85
o
C 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 compare the amount of achievable capaci-
tance for a given case size rather than comparing the
specified capacitance value. For example, over rated volt-
age and temperature conditions, a 1
F, 10V, Y5V ceramic
capacitor in a 0603 case may not provide any more
capacitance than a 0.22
F, 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 LTC3216, 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 capaci-
tors are not close to the LTC3216 (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 LTC3216 pins. For a high quality
AC ground, it should be returned to a solid ground plane
that extends all the way to the LTC3216.
Power Efficiency
To calculate the power efficiency (
) of a white LED driver
chip, the LED power should be compared to the input
power. The difference between these two numbers repre-
sents lost power whether it is in the charge pump or the
current sources. Stated mathematically, the power effi-
ciency is given by:
P
P
LED
IN
(4)
The efficiency of the LTC3216 depends upon the mode in
which it is operating. Recall that the LTC3216 operates as
a pass switch, connecting V
IN
to CPO, until dropout is
detected at the I
LED
pin. This feature provides the optimum
efficiency available for a given input voltage and LED
forward voltage. When it is operating as a switch, the
efficiency is approximated by:
=
P
P
V
I
V
I
V
V
LED
IN
LED
LED
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 LTC3216 is negligible and the expression above is
valid.
Once dropout is detected at the I
LED
pin, the LTC3216
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:
IDEAL
LED
IN
LED
LED
IN
LED
LED
IN
P
P
V
I
V
I
V
V
=
.
.
1 5
1 5
(6)
APPLICATIO S I FOR ATIO
W
U
U
U
LTC3216
10
3216fa
TYPICAL APPLICATIO S
U
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:
IDEAL
LED
IN
LED
LED
IN
LED
LED
IN
P
P
V
I
V
I
V
V
=
2
2
(7)
Thermal Management
For higher input voltages and maximum output current,
there can be substantial power dissipation in the LTC3216.
If the junction temperature increases above approximately
150
C, the thermal shutdown circuitry will automatically
deactivate the output. To reduce maximum junction tem-
perature, 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.
LTC3216
11
3216fa
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PACKAGE DESCRIPTIO
U
4.00
0.10
(2 SIDES)
3.00
0.10
(2 SIDES)
NOTE:
1. DRAWING PROPOSED TO BE A VARIATION OF VERSION
(WGED) 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
0.38
0.10
BOTTOM VIEW--EXPOSED PAD
1.70
0.10
(2 SIDES)
0.75
0.05
R = 0.115
TYP
R = 0.20
TYP
0.25
0.05
3.30
0.10
(2 SIDES)
1
6
12
7
0.50
BSC
PIN 1
NOTCH
PIN 1
TOP MARK
(NOTE 6)
0.200 REF
0.00 0.05
(UE12/DE12) DFN 0603
0.25
0.05
3.30
0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
1.70
0.05
(2 SIDES)
2.20
0.05
0.50
BSC
0.65
0.05
3.50
0.05
PACKAGE OUTLINE
DE Package
12-Lead Plastic DFN (4mm
3mm)
(Reference LTC DWG # 05-08-1695)
LTC3216
12
3216fa
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
q
FAX: (408) 434-0507
q
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2004
LT/LT 0305 REV A PRINTED IN USA
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1.1A (I
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DC/DC Converter with Integrated Soft-Start
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LT3479
3A, Full Featured DC/DC Converter with Soft-Start and
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Inrush Current Protection
DFN, TSSOP Packages
High Power Camera Light and Flash
C1
2.2
F
C2
2.2
F
C
IN
2.2
F
C
CPO
4.7
F
I
LED
(TOTAL) =
200mA/400mA
2.9V TO 4.4V
R
SET1
= 20k
1%
R
SET2
= 10k
1%
3216 TA02
I
LED
V
IN
EN2
EN1
LTC3216
C1
+
C1
C2
+
C2
I
SET1
I
SET2
CPO
EN1 (TORCH)
EN2 (FLASH)
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