Page 1
Independent Torch/Flash Current Control
FEATURES
■
High Efficiency Operation: 1x, 1.5x or 2x Boost
Modes with Automatic Mode Switching
■
Ultralow Dropout I
■
Output Current up to 1A
■
Low Noise Constant Frequency Operation*
■
Independent Low Current/High Current
Current Control
LED
Programming and Enable Pins
■
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
Profile)
■
3mm × 4mm 12-Lead DFN Package
U
APPLICATIO S
■
LED Torch/Camera Light Supply for Cell Phones,
PDAs and Digital Cameras
■
Generic Lighting and/or Flash/Strobe Applications
LTC3216
1A Low Noise High Current
LED Charge Pump with
U
DESCRIPTIO
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 capacitors, two programming resistors and two bypass capacitors at VIN and CPO) make the LTC3216 ideally suited for
small, battery-powered applications.
Built-in soft-start circuitry prevents excessive inrush current 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
switching optimizes efficiency by monitoring the voltage
across the LED current source and switching modes only
when I
dropout is detected. The LTC3216 is available in
LED
a small 3mm × 4mm 12-Lead DFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Protected by U.S. Patents including 6411531.
voltages. Automatic mode
LED
TYPICAL APPLICATIO
2.9V TO 4.4V
2.2µF
EN1 (TORCH)
EN2 (FLASH)
C1
2.2µF
+C1–C2+C2–
C1
V
C
IN
IN
EN1
EN2
I
SET1ISET2
20k1%6.65k
LED1: LUMILEDS LXCL-PWF1 LUXEON FLASH
LTC3216
1%
C2
2.2µF
I
LED
CPO
EN1
0
1
0
1
U
LED1
EN2
0
0
1
1
C
CPO
4.7µF
I
LED
0 (SHUTDOWN)
200mA (TORCH)
600mA
800mA (FLASH)
3216 TA01a
Torch Mode Efficiency vs V
100
90
80
70
/PIN) (%)
60
LED
50
40
30
EFFICIENCY (P
20
10
0
2.8
3.0 3.4
3.2
I
= 200mA
LED
P
/PIN
LED
LUMILEDS LXCL-PWF1
= 3V TYP AT 200mA
V
F
4.2
3.8
4.0
3.6
VIN (V)
IN
4.4
3216 TA01b
3216fa
1
Page 2
LTC3216
WW
W
ABSOLUTE AXI U RATI GS
U
UUW
PACKAGE/ORDER I FOR A TIO
(Note 1)
VIN to GND................................................–0.3V to 5.5V
CPO to GND..............................................–0.3V to 5.5V
EN2, EN1 .........................................–0.3V to V
I
, I
CPO
(Note 2) ........................................... 1500mA
ILED
+ 0.3V
IN
CPO Short-Circuit Duration .............................Indefinite
Operating Temperature Range (Note 3)...–40°C to 85°C
Storage Temperature Range..................–65°C to 125°C
CPO
I
SET1
I
I
SET2
12-LEAD (4mm × 3mm) PLASTIC DFN
TOP VIEW
+
1
C2
+
C1
2
3
4
5
LED
6
DE12 PACKAGE
EXPOSED PAD IS GND (PIN 13)
MUST BE SOLDERED TO PCB
T
= 125°C, θJA = 43°C/W
JMAX
12
11
10
13
9
8
7
C1
GND
C2
VIN
EN2
EN1
–
–
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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
= 4.7µF
CPO
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 EN2 = EN1 = LOW 2.5 7 µA
VIN
= 0mA, 1x Mode 300 µA
CPO
= 0mA, 1.5x 7 mA
I
CPO
I
= 0mA, 2x Mode 9.2 mA
CPO
LED Current
LED Current Ratio (I
I
Dropout Voltage Mode Switch Threshold, I
LED
LED/ISET1/2
)I
= 200mA to 800mA ● 3120 3250 3380 mA/mA
LED
= 200mA 120 mV
LED
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 µs
Charge Pump (CPO)
1x Mode Output Voltage I
1.5x Mode Output Voltage I
2x Mode Output Voltage I
= 0mA V
CPO
= 0mA 4.6 V
CPO
= 0mA 5.1 V
CPO
1x Mode Output Impedance 0.25 Ω
1.5x Mode Output Impedance V
2x Mode Output Impedance V
= 3.4V, V
IN
= 3.2V, V
IN
< 4.6V, C1 = C2 = 2.2µF 1.5 Ω
CPO
< 5.1V, C1 = C2 = 2.2µF 1.7 Ω
CPO
CLK Frequency ● 0.6 0.9 1.2 MHz
EN1, EN2
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
ORDER PART
NUMBER
LTC3216EDE
DFN PART
MARKING
3216
IN
V
2
3216fa
Page 3
LTC3216
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
= 4.7µF
CPO
PARAMETER CONDITIONS MIN TYP MAX UNITS
I
, I
SET1
SET2
V
, V
ISET1
ISET2
I
, I
ISET1
ISET2
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
SETX
● 321 µA
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.
durations less than 10 seconds. Max current for continuous operation is
500mA.
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
400 800600
LED CURRENT (mA)
1x Mode Charge Pump Open-Loop
Output Resistance vs Temperature
0.31
I
= 200mA
CPO
SWITCH 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)
1000
3216 G01
VIN = 3.9V
85
3216 G07
I
Pin Current
LED
vs I
Pin Voltage
LED
600
500
400
300
PIN CURRENT (mA)
200
LED
I
100
0
0.2 0.4 0.6 0.8
0
I
PIN VOLTAGE (V)
LED
1.5x Mode Charge Pump
Open-Loop Output Resistance
1.8
1.6
1.4
1.2
1.0
0.8
0.6
OUTPUT RESISTANCE (Ω)
0.4
0.2
0
–40
(1.5VIN – V
VIN = 3V
V
= 4.2V
CPO
= C1 = C2 = 2.2µF
C
IN
= 4.7µF
C
CPO
–15 35
)/I
CPO
CPO
10
TEMPERATURE (°C)
vs Temperature
TA = 25°C unless otherwise noted.
I
LED
1200
I
= 500mA
LED
400mA
300mA
200mA
100mA
1.0
3216 G02
1000
800
(mA)
600
LED
I
400
200
0
0
2x Mode Charge Pump
Open-Loop Output Resistance
(2VIN – V
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
OUTPUT RESISTANCE (Ω)
VIN = 3V
0.4
V
CPO
C
IN
0.2
C
CPO
85
60
3216 G05
0
–40
vs R
SET
10
R
SET
)/I
CPO
CPO
= 4.8V
= C1 = C2 = 2.2µF
= 4.7µF
–15 35
10
TEMPERATURE (°C)
20
25515
(kΩ)
35
30
vs Temperature
60
40
1573 G06
85
3216 G06
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3
Page 4
LTC3216
UW
TYPICAL PERFOR A CE CHARACTERISTICS
TA = 25°C unless otherwise noted.
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
I
SET/ILED
Current
3400
3350
3300
3250
CURRENT RATIO
3200
930
920
910
900
890
880
870
FREQUENCY (kHz)
860
850
4.3
3216 G04
840
Current Ratio vs I
TA = –40°C
TA = 85°C
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
LED
1.5x Mode CPO Output Ripple
TA = 25°C
V
50mV/DIV
A/C COUPLED
CPO
Efficiency vs V
100
90
80
70
60
50
40
30
EFFICIENCY (PLED/PIN) (%)
20
10
0
2.8
200mA
LED = LXCL-PWF1 LUMILEDS
3.0 3.4
3.2
IN
3.6
VIN (V)
400mA
3.8
600mA
I
LED
4.0
= 800mA
4.2
3216 G11
4.4
V
20mV/DIV
A/C COUPLED
3150
3100
100 300
0
200
500 900
400
CURRENT(mA)
I
LED
2x Mode CPO Output Ripple
CPO
V
IN
I
CPO
= 3.6V
= 400mA
500ns/DIV
600
700
800
3216 G15
3216 G13
V
1V/DIV
I
500mA/DIV
EN2
5V/DIV
V
I
CPO
IN
= 3.6V
= 200mA
500ns/DIV
Charge Pump Mode Switching
and Input Current
CPO
VIN
VIN = 3V
1ms/DIV
3216 G12
3216 G14
4
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Page 5
LTC3216
U
UU
PI FU CTIO S
C2+, C1+, C2–, C1– (Pins 1, 2, 10, 12): Charge Pump
Flying Capacitor Pins. A 2.2µF 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 4.7µF X5R or X7R ceramic capacitor is
required from CPO to GND.
I
SET1/ISET2
tor Pins. The I
Resistors connected between each of these pins and GND
are used to set the high and low LED current levels.
Connecting a resistor of 2kΩ or less will cause the
LTC3216 to enter overcurrent shutdown mode.
I
LED
The LED is connected between CPO (anode) and I
(cathode). The current into the I
and EN2 inputs, and the programming resistors connected from I
(Pins 4, 6): LED Current Programming Resis-
and I
SET1
(Pin 5): Output. I
and I
SET2
LED
pins will servo to 1.22V.
SET2
is the LED current source output.
pin is set via the EN1
LED
to GND.
SET1
LED
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
(Pin 9): Power. Supply voltage for the LTC3216. V
IN
IN
should be bypassed with a 2.2µF 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
V
IN
EN2
EN1
W
9
8
7
OSCILLATOR
CONTROL
LOGIC
GND
C1
+
2
MODE
CONTROL
–
C1
12
1X MODE: CPO = V
1.5X MODE: CPO = 4.6V
2X MODE: CPO = 5.1V
–
+
V
REF
+
C2
1 10
IN
DROPOUT
DETECTOR
CURRENT
SOURCE
CONTROL
SET2ISET1
–
C2
3
CPO
5
I
LED
3216 BD
1311
46
GNDI
3216fa
5
Page 6
LTC3216
OPERATIO
U
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, VIN 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 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).
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 appropriate programming resistors. Each resistor is connected
between the I
SET2
or I
pin and GND. The resistor
SET1
values needed to attain the desired current levels can be
determined by equation 1.
R
SET1/2
= 3965/I
LED
(1)
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
1.5x 4.6V
2x 5.1V
CPO
In shutdown mode all circuitry is turned off and the
LTC3216 draws a very low current from the VIN supply.
Furthermore, CPO is weakly connected to VIN. 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
output once the junction
LED
temperature drops back to approximately 135°C. The
LTC3216 will cycle in and out of thermal shutdown indefinitely 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 250µs.
A resistor value of 2kΩ 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
6
Charge Pump Strength
When the LTC3216 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).
3216fa
Page 7
OPERATIO
LTC3216
U
R
OL
1.5V
IN
+
OR
–
2V
IN
Figure 1. Charge Pump Open-Loop Thevenin-Equivalent Circuit
+
CPO
–
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:
(1.5VIN – CPO)/ROL or (2VIN – 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
pins, respec-
SET2
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 VIN 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.
3216fa
7
Page 8
LTC3216
WUUU
APPLICATIO S I FOR ATIO
VIN, 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
. 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 LTC3216’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 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
2.2µF 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
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 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
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 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 capacitors are again recommended for their exceptional ESR
performance. Input noise can be further reduced by powering 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.
10nH
Figure 2. 10nH Inductor Used for Input Noise Reduction
(Approximately 1cm of Wire)
V
IN
GND
LTC32162.2µF0.1µF
3216 F02
Flying Capacitor Selection
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 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 2.2µF 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
8
3216fa
Page 9
WUUU
APPLICATIO S I FOR ATIO
LTC3216
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 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
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 LTC3216 depends upon the mode in
which it is operating. Recall that the LTC3216 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
LED
η≡ = ≈
P
IN
•
VI
LED 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 LTC3216 is negligible and the expression above is
valid.
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 capacitors 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.
Once dropout is detected at the I
pin, the LTC3216
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)
3216fa
9
Page 10
LTC3216
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:
η
IDEAL
P
LED
≡= ≈
P
VI
LED LED
VIVV
IN
•• •22
IN LED
•
LED
IN
(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 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
3216fa
Page 11
PACKAGE DESCRIPTIO
LTC3216
U
DE Package
12-Lead Plastic DFN (4mm × 3mm)
(Reference LTC DWG # 05-08-1695)
0.65 ±0.05
3.50 ±0.05
1.70 ±0.05
(2 SIDES)2.20 ±0.05
PACKAGE OUTLINE
0.25 ± 0.05
3.30 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
4.00 ±0.10
(2 SIDES)
PIN 1
TOP MARK
(NOTE 6)
0.200 REF
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
0.50
BSC
3.00 ±0.10
(2 SIDES)
0.75 ±0.05
R = 0.20
TYP
1.70 ± 0.10
(2 SIDES)
0.00 – 0.05
R = 0.115
TYP
0.25 ± 0.05
3.30 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
127
16
0.50
BSC
0.38 ± 0.10
PIN 1
NOTCH
(UE12/DE12) DFN 0603
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.
3216fa
11
Page 12
LTC3216
TYPICAL APPLICATIO
U
High Power Camera Light and Flash
2.9V TO 4.4V
2.2µF
EN1 (TORCH)
EN2 (FLASH)
C1
2.2µF
+C1–C2+C2–
C1
V
SET1
EN1
EN2
= 20k
1%
IN
I
SET1ISET2
C
IN
R
LTC3216
R
1%
2.2µF
I
LED
SET2
C2
CPO
= 10k
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
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 Converter with Integrated Soft-Start ThinSOT Package
LT3479 3A, Full Featured DC/DC Converter with Soft-Start and VIN: 2.5V to 24V, V
Inrush Current Protection DFN, TSSOP Packages
OUT(MAX)
I
(TOTAL) =
LED
200mA/400mA
C
CPO
4.7µF
3216 TA02
= 36V, IQ = 1.8mA, ISD <1µA
OUT(MAX)
= 35V, IQ = 0.9mA, ISD 6µA
= 5.5V, IQ = 50uA, ISD <1µA
OUT(MAX)
= 5.5V, IQ = 50uA, 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 = 5mA, ISD <1µA
OUT(MAX)
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com
3216fa
LT/LT 0305 REV A • PRINTED IN USA
LINEAR TECHN OLOGY CO RPORATION 2004
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