LTC3218
400mA Single Wire
Camera LED Charge Pump
FEATURES
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DESCRIPTION
Low Noise Constant-Frequency Operation
Multi-Mode Operation: 1x or 2x Boost Mode
Automatic Mode Switching
High Output Current: 150mA (Continuous), 400mA
(Pulsed) From Li-Ion/Polymer Input
2-Second Flash Current Timeout for LED Protection
Automatic Soft-Start
Output Disconnect
No Inductors
220mΩ Internal High Side Current Sense Resistor
Single Resistor Programming Capability
Tiny Application Circuit (3mm × 2mm DFN Package,
All Components < 1mm High)
The LTC®3218 is a low-noise, high-current charge pump
DC/DC converter capable of driving high current LEDs at up
to 400mA from a 2.9V to 4.5V input. A low external parts
count (one flying capacitor, two programming resistors and
two bypass capacitors at VIN and CPO) make the LTC3218
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. A built-in 2-second timer
protects the LED during flash mode.
Output current level is programmed by an external resistor. LED current is regulated using an internal high
side 220mΩ sense resistor. Automatic mode switching
optimizes efficiency by monitoring the voltage across the
charge pump and switching modes only when dropout
is detected. The part is available in a low profile 3mm ×
2mm 10-lead DFN package.
APPLICATIONS
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LED Torch/Flash Supply for DSCs/Cellphones
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 6411531.
TYPICAL APPLICATION
Efficiency vs VIN
100
2.2μF
90
VIN
2.2μF
DISABLED
DISABLED
CPO
ENF
ENABLED
ENT
ISETF
ENT
ILED
0
0
0 (SHUTDOWN)
0
1
100mA (TORCH)
1
0
290mA
1
1
390mA (FLASH)
4.7μF
LTC3218
ENABLED
ENF
CM
ILED
GND
LED
AOT2015
EFFICIENCY (%)
CP
2.9V TO 4.5V
80
70
60
50mA
150mA
300mA
50
ISETT
40
2.9
10.2k
1%
3.1
3.3
3.5
3.7
3.9
4.1
4.3
4.5
VIN (V)
3218 TA01b
3218 TA01
3218fb
1
LTC3218
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
VIN to GND ................................................... –0.3V to 6V
CPO to GND ................................................ –0.3V to 6V
ENF, ENT ........................................... –0.3V to VIN + 0.3V
ICPO, IILED (Note 2) ...............................................500mA
CPO Short-Circuit Duration .............................. Indefinite
Storage Temperature Range................... –65°C to 125°C
Operating Temperature Range (Note 3).... –40°C to 85°C
CP 1
10 VIN
CPO 2
9
CM
8
GND
ENT 4
7
ENF
ISETT 5
6
ISETF
ILED 3
11
DDB PACKAGE
10-LEAD (3mm × 2mm) PLASTIC DFN
TJMAX = 125°C, θJA = 76°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3218EDDB#PBF
LTC3218EDDB#TRPBF
LCHS
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VIN = 3.6V, CIN = CFLY = 2.2μF, CCPO = 4.7μF, ENF = HIGH, unless
otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Power Supply
●
VIN Operating Voltage
IVIN Operating Current
ICPO = 0mA, 1x Mode
ICPO = 0mA, 2x Mode
IVIN Shutdown Current
ENF = ENT = LOW, VCPO = 0V
2.9
4.5
980
1.7
●
V
μA
mA
1.1
3
μA
LED Current
Torch Current Ratio
(ILED/ISET)
ILED = 50mA
ENT = HIGH, ENF = LOW
765
850
935
A/A
Flash Current Ratio
(ILED/ISET)
ILED = 150mA
ENT = LOW, ENF = HIGH
2205
2450
2695
A/A
Flash Current Ratio
(ILED/ISET)
ILED = 150mA
ENT = ENF = HIGH
2970
3300
3630
A/A
ILED Dropout Voltage (VILED)
Mode Switching Threshold, Δ(VCPO – VILED),
ILED = 100mA
Mode Switching Delay (LED Warm-Up Time)
Turn-On Time
ENF, ENT
Minimum LED Forward Voltage
ILED = 50mA
to LED Current On
●
2.2
7
mV
0.5
ms
160
μs
V
3218fb
2
LTC3218
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VIN = 3.6V, CIN = CFLY = 2.2μF, CCPO = 4.7μF, ENF = HIGH, unless
otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Charge Pump (CPO)
Charge Pump Output Clamp Voltage
5.3
V
1:1 Mode Output Impedance
1.3
Ω
1:2 Mode Output Impedance
7
Ω
CLK Frequency
1
MHz
CPO Short Circuit Detection
Threshold Voltage
ENT = HIGH
●
0.6
1.5
V
Test Current
ENT = ENF = LOW, VCPO = 0V
●
20
50
mA
High Level Input Voltage (VIH)
●
1.4
Low Level Input Voltage (VIL)
●
ENF, ENT
Input Current (IIH)
VEN = 3.6V
●
Input Current (IIL)
VEN = 0V
●
Flash Timeout
ENF = HIGH
V
14.4
–1
0.4
V
30
μA
1
μA
2
s
ISETF, ISETT
VISET
ISET = 110μA
●
IISET
ENT = LOW, ENF = HIGH
●
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: Based on long-term current density limitations. Assumes an
operating duty cycle of ≤ 10% under Absolute Maximum Conditions
400
0.007
0.006
300
0.005
0.004
250
200
0.003
150
0.002
100
0.001
50
0
0
0
200
300
100
LED CURRENT (mA)
400
3218 G01
0
50
100
181
μA
VIN Shutdown Current vs VIN
TORCH
FLASH (ENT = LOW,
ENF = HIGH)
FLASH (ENT = ENF = HIGH)
350
V
150 200
RSET (kΩ)
250
300
350
3.0
T = 25°C
VIN SHUTDOWN CURRENT (μA)
0.008
ILED (mA)
DROPOUT VOLTAGE (V)
450
1.24
TA = 25°C, unless otherwise noted.
ILED vs RSET
0.009
1.21
for durations less than 10 seconds. Maximum current for continuous
operation is 150mA.
Note 3: The LTC3218E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C ambient
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
TYPICAL PERFORMANCE CHARACTERISTICS
ILED Dropout Voltage
vs LED Current
1.18
2.5
2.0
T = –40°C
1.5
T = 85°C
1.0
0.5
0
2.9
3.1
3.3
3.5
3.7
3.9
4.1
4.3
4.5
VIN (V)
3218 G02
3218 G03
3218fb
3
LTC3218
TYPICAL PERFORMANCE CHARACTERISTICS
2x Mode Charge Pump
Open-Loop Output Resistance
(2VIN – VCPO)/ICPO vs Temperature
1x Mode Charge Pump Open-Loop
Output Resistance vs Temperature
10
1.6
VIN = 2.9V
1.4
1.2
VIN = 3.6V
1.0
VIN = 4.5V
0.8
0.6
0.4
0.2
0
–40
–15
35
10
TEMPERATURE (°C)
60
VIN = 3.6V
9
1080
8
T = –40°C
7
6
5
4
3
1040
1020
T = 85°C
980
1
–15
35
10
TEMPERATURE (°C)
60
960
2.9
85
3100
4100
1100
2900
3900
CURRENT RATIO
4300
1200
CURRENT RATIO
4500
3300
2700
2500
2300
2100
2900
2700
1500
100
150
250
300
200
ILED CURRENT(mA)
350
160
450
140
400
ILED (mA)
ILED (mA)
80
RSETT = 20k
0
2.9
3.3
3.5
3.7
3.9
4.1
4.3
4.5
350
350
300
300
250
RSETF = 20k
200
VIN (V)
0
2.9
RSETF = 10.2k
250
200
RSETF = 20k
150
RSETF = 40.2k
RSETF = 40.2k
100
50
3.1
3.3
3.5
3.7
3.9
4.1
4.3
4.5
VIN (V)
3218 G10
400
RSETF = 7.49k
400
50
3.1
350
450
RSETF = 10.2k
100
20
250
300
200
ILED CURRENT(mA)
Flash Mode ILED Current vs VIN
(ENT = LOW, ENF = HIGH)
150
RSETT = 40.2k
150
3218 G09
ILED (mA)
RSETT = 7.49k
120
40
2500
100
Flash Mode ILED Current vs VIN
(ENT = ENF = HIGH)
Torch Mode ILED Current vs VIN
60
400
3218 G08
3218 G07
4.5
3100
1700
RSETT = 10.2k
4.3
3300
500
100
4.1
3700
1900
50 60 70 80 90 100 110 120 130 140 150
ILED CURRENT (mA)
3.9
3500
600
400
3.7
Flash ILED/ISET Current Ratio
vs ILED Current
(ENT = ENF = HIGH)
Flash ILED/ISET Current Ratio
vs ILED Current
(ENT = LOW, ENF = HIGH)
3500
700
3.5
3218 G06
1300
800
3.3
VIN (V)
1400
900
3.1
3218 G05
Torch Mode ILED/ISET Current Ratio
vs ILED Current
1000
T = 25°C
2
3218 G04
CURRENT RATIO
1060
1000
0
–40
85
Oscillator Frequency vs VIN
1100
FREQUENCY (kHz)
ICPO = 50mA
OPEN-LOOP OUTPUT RESISTANCE (Ω)
OPEN-LOOP OUTPUT RESISTANCE (Ω)
1.8
TA = 25°C, unless otherwise noted.
0
2.9
3.1
3.3
3.5
3.7
3.9
4.1
4.3
4.5
VIN (V)
3218 G11
3218 G12
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4
LTC3218
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs VIN
TA = 25°C, unless otherwise noted.
2x Mode CPO Output Ripple
100
EFFICIENCY (%)
90
80
50mV/DIV
AC COUPLED
70
60
50mA
100mA
150mA
200mA
300mA
50
40
2.9
3.1
3.3
3.5
3.7
3.9
4.1
4.3
VIN = 3.6V
ICPO = 200mA
500ns/DIV
3218 G14
4.5
VIN (V)
3218 G13
PIN FUNCTIONS
CP, CM (Pin 1, Pin 9): Charge Pump Flying Capacitor. A
2.2μF X5R or X7R ceramic capacitor should be connected
from CP to CM.
ISETF (Pin 6): LED Flash Current Programming Resistor.
A resistor connected between this pin and GND is used
to set the LED flash current level.
CPO (Pin 2): Output of the Charge Pump. This pin may
be enabled or disabled using the ENT and ENF inputs.
A 4.7μF X5R or X7R ceramic capacitor is required from
CPO to GND.
ENF (Pin 7): Input. The ENF pin is used to enable the
part into flash mode and bring it into shutdown mode.
An internal 250kΩ resistor pulls this pin to GND when
left floating. A safety timer will disable the part if this pin
is held high for more than 2 seconds.
ILED (Pin 3): LED Current Output. The LED is connected
between ILED (anode) and GND (cathode). The current
out of the ILED pin is set by resistors connected to the
ISETT and ISETF pins. An internal, 220mΩ sense resistor
is connected between CPO and ILED
ENT (Pin 4): Input. The ENT pin is used to enable the
part into torch mode and bring it into shutdown mode.
An internal 250kΩ resistor pulls this pin to GND when
left floating.
GND (Pin 8): Ground. This pin should be connected directly
to a low impedance ground plane.
VIN (Pin 10): Power. Supply voltage for the LTC3218. VIN
should be bypassed with a low impedance ceramic capacitor to GND of at least 1.6μF of capacitance.
Exposed Pad (Pin 11): Ground. This pad must be soldered
to a low impedance ground plane for optimum thermal
performance.
ISETT (Pin 5): LED Torch Current Programming Resistor.
A resistor connected between this pin and GND is used
to set the LED torch current level.
3218fb
5
LTC3218
BLOCK DIAGRAM
CP
CM
1
9
2 CPO
OSCILLATOR
220mΩ
106Ω
+
VOLTAGE
CLAMP
–
MODE
CONTROL
VIN 10
ENT 4
ENF 7
3 ILED
CONTROL
LOGIC
VREF
CURRENT
SOURCE
CONTROL
ISETF
ISETT
5
6
GND
8
GND
11
3218 BD
OPERATION
The LTC3218 uses a switched capacitor charge pump to
power a high current LED with a programmed regulated
current. Current regulation is achieved using an internal
current sense resistor connected between the CPO and
ILED pins. The part starts up in 1x mode after a soft-start
period. In this mode, VIN is connected to the CPO through
switches, the strengths of which are modulated to achieve
the desired LED current. This mode provides maximum
efficiency and minimum noise. The LTC3218 will remain in
this mode until the LED forward voltage (VF) approaches
the maximum CPO voltage possible in this mode. When
this dropout condition occurs, the LTC3218 will switch to
2x mode after a soft-start period.
The current delivered to the LED load is controlled by the
internal programmable current source. The current is
programmed by resistors connected between the ISETT
and ISETF pins and GND. The resistor values needed to
3218fb
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LTC3218
OPERATION
attain the desired current level can be determined by
Equations 1 and 2:
3300 • 1 . 21V
R SETF =
(1)
ILED
R SETT
850 • 1 . 21V
=
ILED
(2)
Overcurrent shutdown mode will prevent damage to the
part and LED by shutting down the high power sections of
the chip. Choosing an RSETF or RSETT value of 5k or greater
will ensure that the part stays out of this mode.
Regulation is achieved by sensing the voltage at the ILED
pin and modulating the charge pump strength based on
the error signal.
In shutdown mode all circuitry is turned off and the LTC3218
draws a very low current from the VIN supply. The output is
disconnected from VIN and is pulled down by a resistance
of approximately 90kΩ. The LTC3218 enters shutdown
mode when the ENF and ENT pins are brought low.
LED Current Programming
The LTC3218 includes an accurate, programmable current source that is capable of driving LED currents up to
150mA continuously and up to 400mA for pulsed operation.
Pulsed operation may be achieved by toggling the ENT or
ENF pins. In either continuous or pulsed operation, proper
board layout is required for effective heat sinking.
The output current of the LTC3218 is programmed using
external resistors connected between the ISETT and ISETF
pins and GND. The output current modes are shown in
Table 1, where RSETT is connected between ISETT and GND,
and RESTF is connected between ISETF and GND.
Since the LTC3218 has three separate LED current ratios
built in, it can be programmed using a single resistor by
connecting ISETT and ISETF together, and then connecting
the pins to the resistor.
Table 1. Output Current Modes for All ENT and ENF Settings
ENF
ENT
ILED
LOW
LOW
SHUTDOWN
LOW
HIGH
1029/RSETT
HIGH
LOW
2965/RSETF
HIGH
HIGH
3993/RSETF
Thermal Protection
The LTC3218 has built-in overtemperature protection.
Thermal shutdown circuitry will shut down the part when
the junction temperature exceeds approximately 165°C. It
will re-enable the part once the junction temperature drops
back to approximately 150°C. The LTC3218 will cycle in
and out of thermal shutdown indefinitely without latchup
or damage until the heat source is removed.
ENF Timeout
The ENF input is used to select the high current setting for
use as a camera flash. To prevent damage to the LED, the
ENF pin has a 2-second timeout. If the LTC3218 is enabled
for greater than approximately 2 seconds using the ENF
pin, the part will enter a low-power mode, preventing current from being delivered to the LED. Normal operation
can be restored by bringing the part into shutdown and
re-enabling it.
Short-Circuit Protection
When ENF or ENT are brought high, the part will connect
VIN and CPO through a weak pull-up. If the CPO capacitor
fails to charge up to over 1V (i.e., CPO is shorted), the chip
will not be enabled. Similarly, during operation if CPO is
pulled down below 1V, the part will be disabled.
Soft-Start
To prevent excessive inrush current during start-up and
mode switching, the LTC3218 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 80μs.
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LTC3218
OPERATION
Charge Pump Strength
Mode Switching
When the LTC3218 operates in 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,
ROL (Figure 1).
The LTC3218 will automatically switch from 1x mode to
2x mode whenever the LED forward voltage approaches
the maximum CPO voltage for that mode. The part will
wait approximately 500μs 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. The part may be reset to 1x mode by bringing the part
into shutdown by setting the ENF and ENT pins low. Once
these pins are low, either one or both may be immediately
brought high to re-enable the part.
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:
2VIN − CPO
ROL
(3)
in 2x mode.
ROL
+
–
2VIN
+
CPO
–
3218 F01
Figure 1. Charge Pump Open-Loop Thevenin-Equivalent Circuit
APPLICATIONS INFORMATION
VIN, CPO Capacitor Selection
The value and type of capacitors used with the LTC3218
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 CVIN and CCPO. Tantalum and aluminum capacitors are not recommended because of their high ESR.
The value of CCPO directly controls the amount of output
ripple for a given load current. Increasing the size of CCPO
will reduce the output ripple at the expense of higher startup current. The peak-to-peak output ripple for 2x mode is
approximately given by the expression:
IOUT
VRIPPLE(P −P) =
2fOSC • CCPO
Where fOSC is the LTC3218’s oscillator frequency (typically
1MHz) and CCPO is the output storage capacitor.
Both the style and value of the output capacitor can significantly affect the stability of the LTC3218. As shown in
the Block Diagram, the LTC3218 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
3μF of actual capacitance over all conditions.
Likewise, excessive ESR on the output capacitor will tend
to degrade the loop stability of the LTC3218. To prevent
poor load transient response and instability, the ESR of the
output capacitor should be kept below 80mΩ. Multilayer
ceramic chip capacitors typically have exceptional ESR
3218fb
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LTC3218
APPLICATIONS INFORMATION
performance. MLCCs combined with a tight board layout
will yield very good stability. As the value of CCPO controls
the amount of output ripple, the value of CVIN controls the
amount of ripple present at the input pin (VIN). The input
current to the LTC3218 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 LTC3218
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 (0.4ʺ) of
PC board trace.
10nH
VIN
0.1μF
2.2μF
LTC3218
to 85°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 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 1 shows a list of ceramic capacitor manufacturers
and how to contact them.
Table 1. 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
GND
3218 F02
Figure 2. 10nH Inductor Used for Input Noise Reduction
(Approximately 1cm of Wire)
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
LTC3218. Ceramic capacitors should always be used for
the flying capacitors.
The flying capacitor controls the strength of the charge
pump. In order to achieve the rated output current it is
necessary to have at least 1.6μF of actual capacitance for
the flying capacitor. 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 –40°C
Layout Considerations and Noise
Due to the high switching frequency and the transient
currents produced by the LTC3218, 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. An example of
such a layout is shown in Figure 3.
The flying capacitor pins, CP and CM, 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 LTC3218 (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 LTC3218 pins. For a high quality
AC ground, it should be returned to a solid ground plane
that extends all the way to the LTC3218.
3218fb
9
LTC3218
APPLICATIONS INFORMATION
The following guidelines should be followed when designing a PCB layout for the LTC3218.
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 sense resistor. Stated mathematically, the power
efficiency is given by:
P
η ≡ LED
PIN
• 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 CCPO) must also
be placed as close to the part as possible.
• The flying capacitor 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.
The efficiency of the LTC3218 depends on the mode in
which it is operating. In 1x mode, the LTC3218 regulates
the output down to the LED forward voltage required to
achieve the desired current by varying the strength of the
series switches. This mode provides the optimum efficiency
available for a given input voltage and LED forward voltage.
The efficiency is approximated by:
P
V
•I
V
η ≡ LED = LED LED ≈ LED
PIN
VIN • IIN
VIN
• VIN, CPO and ILED traces must be made as wide as 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.
since the input current will be very close to the LED current.
CFLY
CCPO
PIN 1
CIN
RSETT
RSETF
3218 F03
Figure 3. Example Board Layout
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10
LTC3218
APPLICATIONS INFORMATION
At moderate to high output power, the quiescent current
of the LTC3218 is negligible and the expression above is
valid.
Once dropout is detected at the ILED pin, the LTC3218
enables the charge pump in 2x mode.
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:
P
V
V
•I
ηIDEAL ≡ LED = LED LED ≈ LED
PIN
VIN • 2 • ILED 2VIN
Thermal Management
For higher input voltages and maximum output current,
there can be substantial power dissipation in the LTC3218.
If the junction temperature increases above approximately
165°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.
PACKAGE DESCRIPTION
DDB Package
10-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1722 Rev Ø)
0.64 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
R = 0.05
TYP
R = 0.115
TYP
6
0.40 ± 0.10
10
0.70 ±0.05
2.55 ±0.05
1.15 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
2.39 ±0.05
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
2.00 ±0.10
(2 SIDES)
0.75 ±0.05
0.64 ± 0.05
(2 SIDES)
5
0.25 ± 0.05
0 – 0.05
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
1
(DDB10) DFN 0905 REV Ø
0.50 BSC
2.39 ±0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) 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
3218fb
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.
11
LTC3218
RELATED PARTS
2.2μF
CP
ENF
ENT
ILED
0
0
0 (SHUTDOWN)
0
1
50mA (TORCH)
1
0
260mA
1
1
350mA (FLASH)
2.9V TO 4.5V
VIN
2.2μF
DISABLED
DISABLED
CM
CPO
4.7μF
LTC3218
ENABLED
ENF
ENABLED
ENT
ILED
GND
ISETF
20.5k
1%
LED
AOT2015
ISETT
11.4k
1%
3218 TA02
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
LTC3200-5
Low Noise, 2MHz Regulated Charge Pump
White LED Driver
Up to 6 White LEDs, VIN: 2.7V to 4.5V, VOUT(MAX) = 5V, IQ = 8mA, ISD ≤ 1μA,
ThinSOTTM Package
LTC3201
Low Noise, 1.7MHz Regulated Charge Pump
White LED Driver
Up to 6 White LEDs, VIN: 2.7V to 4.5V, VOUT(MAX) = 5V, IQ = 6.5mA, ISD ≤ 1μA, 10-Lead
MS Package
LTC3202
Low Noise, 1.5MHz Regulated Charge Pump
White LED Driver
Up to 8 White LEDs, VIN: 2.7V to 4.5V, VOUT(MAX) = 5V, IQ = 5mA, ISD ≤ 1μA, 10-Lead
MS Package
LTC3205
Multidisplay LED Controller
92% Efficiency, VIN: 2.8V to 4.5V, IQ = 50μA, ISD ≤ 1μA, 4mm × 4mm QFN Package
LTC3206
I2C Multidisplay LED Controller
92% Efficiency, 400mA Continuous Output Current. Up to 11 White LEDs in
4mm × 4mm QFN Package
LTC3208
High Current Software Configurable
Multidisplay LED Controller
95% Efficiency, VIN: 2.9V to 4.5V, VOUT(MAX): 5.5V, IQ = 280μA, ISD < 1μA,
5mm × 5mm QFN-32 Package
LTC3209
600mA MAIN/CAM LED Controller
Up to 8 LEDs, 94% Efficiency, VIN: 2.9V to 4.5V, 1x/1.5x/2x Boost Modes,
4mm × 4mm QFN Package
LTC3210/
LTC3210-1
500mA MAIN/Camera LED Controller
Up to 5 LEDs, 95% Efficiency, VIN: 2.9V to 4.5V, 1x/1.5x/2x Boost Modes, Exponential
Brightness Control, “-1” Version Has 64-Step Linear Brightness Control, 3mm × 3mm
QFN Package
LTC3210-2
MAIN/CAM LED Controller with 32-Step
Brightness Control
Drives 4 MAIN LEDs, 3mm × 3mm QFN Package
LTC3210-3
MAIN/CAM LED Controller with 32-Step
Brightness Control
Drives 3 MAIN LEDs, 3mm × 3mm QFN Package
LTC3214
500mA Camera LED Charge Pump
94% Efficiency, VIN: 2.9V to 4.5V, IQ = 300μA, ISD < 2.5μA, 500mA Output Current,
10-Lead 3mm × 3mm DFN Package
LTC3215
700mA Low Noise High Current LED
Charge Pump
VIN: 2.9V to 4.4V, VOUT(MAX) = 5.5V, IQ = 300μA, ISD < 2.5μA, 3mm × 3mm
DFN Package
LTC3216
1A Low Noise High Current White LED Driver
93% Efficiency, 1A Output Current, 12-Lead 3mm × 4mm DFN Package, Independent
Low/High Current Programming
LTC3217
600mA Low Noise Multi-LED Camera Light
VIN: 2.9V to 4.4V, IQ = 400μA, Four Outputs, 3mm × 3mm 16-Lead DFN Package
LTC3251
500mA (IOUT), 1MHz to 1.6MHz Spread
Spectrum Step-Down Charge Pump
85% Efficiency, VIN: 3.1V to 5.5V, VOUT: 0.9V to 1.6V, IQ = 9μA, ISD ≤1μA,
10-Lead MS Package
LTC3440
600mA (IOUT), 2MHz Synchronous BuckBoost DC/DC Converter
95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN) = 2.5V, IQ = 25μA, ISD ≤1μA,
10-Lead MS Package
ThinSOT is a trademark of Linear Technology Corporation.
12 Linear Technology Corporation
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LT 1207 REV B • PRINTED IN USA
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