LTC3218EDDB#TRMPBF [Linear]
LTC3218 - 400mA Single Wire Camera LED Charge Pump; Package: DFN; Pins: 10; Temperature Range: -40°C to 85°C;
| 型号： | LTC3218EDDB#TRMPBF |
| 厂家： | 
Linear |
| 描述： | LTC3218 - 400mA Single Wire Camera LED Charge Pump; Package: DFN; Pins: 10; Temperature Range: -40°C to 85°C 泵 |
| 文件： | 总12页 (文件大小：186K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3218
400mA Single Wire
Camera LED Charge Pump
FEATURES
DESCRIPTION
The LTC®3218 is a low-noise, high-current charge pump
DC/DCconvertercapableofdrivinghighcurrentLEDsatup
to 400mA from a 2.9V to 4.5V input. A low external parts
count(oneflyingcapacitor,twoprogrammingresistorsand
■
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
two bypass capacitors at V and CPO) make the LTC3218
ideally suited for small, battery-powered applications.
IN
■
2-Second Flash Current Timeout for LED Protection
■
Automatic Soft-Start
Built-in soft-start circuitry prevents excessive inrush cur-
rentduringstart-up.Highswitchingfrequencyenablesthe
use of small external capacitors. A built-in 2-second timer
protects the LED during flash mode.
■
Output Disconnect
■
No Inductors
■
220mΩ Internal High Side Current Sense Resistor
■
Single Resistor Programming Capability
■
Output current level is programmed by an external re-
sistor. 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.
Tiny Application Circuit (3mm × 2mm DFN Package,
All Components < 1mm High)
APPLICATIONS
■
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 V
IN
2.2µF
100
90
80
70
60
50
40
CP
CM
CPO
V
2.9V TO 4.5V
IN
4.7µF
2.2µF
LTC3218
I
LED
DISABLED
ENF
ENT
ENABLED
ENABLED
LED
AOT2015
DISABLED
GND
50mA
I
I
SETT
SETF
150mA
300mA
ENF ENT
I
LED
0
0
1
1
0
1
0
1
0 (SHUTDOWN)
100mA (TORCH)
290mA
3.7 3.9
(V)
2.9 3.1 3.3 3.5
4.1 4.3 4.5
10.2k
1%
V
IN
3218 TA01b
390mA (FLASH)
3218 TA01
3218fa
1
LTC3218
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
TOP VIEW
V to GND................................................... –0.3V to 6V
IN
1
2
3
4
5
10
9
CP
V
IN
CPO to GND ................................................ –0.3V to 6V
CPO
CM
ENF, ENT .......................................... –0.3V to V + 0.3V
IN
11
8
I
GND
ENF
LED
I
, I
(Note 2)...............................................500mA
CPO ILED
7
ENT
SETT
CPO Short-Circuit Duration.............................. Indefinite
Storage Temperature Range................... –65°C to 125°C
Operating Temperature Range (Note 3) ... –40°C to 85°C
6
I
I
SETF
DDB PACKAGE
10-LEAD (3mm × 2mm) PLASTIC DFN
= 125°C, θ = 76°C/W
T
JMAX
JA
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
10-Lead (3mm × 2mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
LTC3218EDDB#PBF
LTC3218EDDB#TRPBF
LCHS
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
otherwise noted.
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25°C, V = 3.6V, C = C = 2.2
µF, C
= 4.7µF, ENF = HIGH, unless
A
IN
IN
FLY
CPO
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Power Supply
●
●
V
Operating Voltage
Operating Current
2.9
4.5
V
IN
I
I
I
= 0mA, 1x Mode
= 0mA, 2x Mode
980
1.7
µA
mA
VIN
CPO
CPO
I
Shutdown Current
ENF = ENT = LOW, V
= 0V
1.1
3
µA
VIN
CPO
LED Current
Torch Current Ratio
LED SET
I
= 50mA
765
2205
2970
850
2450
3300
7
935
2695
3630
A/A
A/A
A/A
mV
LED
(I /I
)
ENT = HIGH, ENF = LOW
Flash Current Ratio
(I /I
I
LED
= 150mA
)
ENT = LOW, ENF = HIGH
LED SET
Flash Current Ratio
(I /I
I
LED
= 150mA
)
ENT = ENF = HIGH
LED SET
I
Dropout Voltage (V
)
Mode Switching Threshold, Δ(V
– V
),
ILED
LED
ILED
CPO
I
= 100mA
LED
Mode Switching Delay (LED Warm-Up Time)
Turn-On Time
0.5
ms
µs
V
ENF, ENT to LED Current On
= 50mA
160
●
Minimum LED Forward Voltage
I
2.2
LED
3218fa
2
LTC3218
ELECTRICAL CHARACTERISTICS The
otherwise noted.
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25°C, V = 3.6V, C = C = 2.2
µF, C
= 4.7µF, ENF = HIGH, unless
A
IN
IN
FLY
CPO
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Charge Pump (CPO)
Charge Pump Output Clamp Voltage
1:1 Mode Output Impedance
1:2 Mode Output Impedance
CLK Frequency
5.3
1.3
7
V
Ω
Ω
1
MHz
ENF, ENT
●
●
●
●
High Level Input Voltage (V )
1.4
–1
V
V
IH
Low Level Input Voltage (V )
0.4
30
1
IL
Input Current (I )
V
V
= 3.6V
= 0V
14.4
2
µA
µA
s
IH
EN
EN
Input Current (I )
IL
Flash Timeout
ENF = HIGH
ISETF, ISETT
●
●
V
I
= 110µA
SET
1.18
1.21
1.24
181
V
ISET
ISET
I
ENT = LOW, ENF = HIGH
µA
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
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 T = 25°C, unless otherwise noted.
A
I
Dropout Voltage
LED
vs LED Current
I
vs R
V Shutdown Current vs V
IN IN
LED
SET
0.009
0.008
0.007
0.006
0.005
0.004
0.003
0.002
0.001
450
400
350
300
250
200
150
100
50
3.0
2.5
2.0
1.5
1.0
0.5
0
TORCH
T = 25°C
FLASH (ENT = LOW,
ENF = HIGH)
FLASH (ENT = ENF = HIGH)
T = –40°C
T = 85°C
0
0
3.7 3.9
(V)
2.9 3.1 3.3 3.5
4.1 4.3 4.5
0
100
200
300
400
0
50 100 150
R
350
200 250 300
(kΩ)
V
LED CURRENT (mA)
IN
SET
3218 G03
3218 G01
3218 G02
3218fa
3
LTC3218
TYPICAL PERFORMANCE CHARACTERISTICS T = 25°C, unless otherwise noted.
A
2x Mode Charge Pump
1x Mode Charge Pump Open-Loop
Output Resistance vs Temperature
Open-Loop Output Resistance
(2V – V )/I
vs Temperature
Oscillator Frequency vs V
IN
CPO CPO
IN
10
9
8
7
6
5
4
3
2
1
0
1100
1080
1060
1040
1020
1000
980
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
V
= 3.6V
I
= 50mA
IN
CPO
V
= 2.9V
IN
T = –40°C
V
= 3.6V
IN
T = 25°C
T = 85°C
V
IN
= 4.5V
960
3.7 3.9
(V)
2.9 3.1 3.3 3.5
4.1 4.3 4.5
–40
–15
35
TEMPERATURE (°C)
60
85
–40
–15
35
TEMPERATURE (°C)
60
85
10
10
V
IN
3218 G05
3218 G06
3218 G04
Flash I /I Current Ratio
Flash I /I Current Ratio
LED SET
LED SET
vs I
Current
vs I
Current
LED
Torch Mode I /I Current Ratio
LED
LED SET
(ENT = LOW, ENF = HIGH)
(ENT = ENF = HIGH)
vs I
Current
LED
3500
3300
3100
2900
2700
2500
2300
2100
1900
1700
1500
1400
1300
1200
1100
1000
900
4500
4300
4100
3900
3700
3500
3300
3100
2900
2700
2500
800
700
600
500
400
100
150
250
CURRENT(mA)
300
350
400
200
50 60 70 80 90 100 110 120 130 140 150
CURRENT (mA)
100
150
250
CURRENT(mA)
300
350
400
200
I
I
I
LED
LED
LED
3218 G08
3218 G09
3218 G07
Flash Mode I
Current vs V
Flash Mode I
Current vs V
LED IN
LED
IN
Torch Mode I
Current vs V
(ENT = ENF = HIGH)
(ENT = LOW, ENF = HIGH)
LED
IN
450
400
350
300
250
200
150
100
50
160
140
120
100
80
450
400
350
300
250
200
150
100
50
R
= 10.2k
SETF
R
= 7.49k
= 10.2k
SETF
R
R
= 7.49k
= 10.2k
SETT
SETT
R
SETF
R
= 20k
SETF
R
= 20k
SETF
60
R
= 20k
SETT
R
= 40.2k
SETF
40
R
= 40.2k
SETF
R
= 40.2k
SETT
20
0
0
0
3.7 3.9
(V)
2.9 3.1 3.3 3.5
4.1 4.3 4.5
3.7 3.9
(V)
3.7 3.9
V (V)
IN
2.9 3.1 3.3 3.5
4.1 4.3 4.5
2.9 3.1 3.3 3.5
4.1 4.3 4.5
V
V
IN
IN
3218 G12
3218 G10
3218 G11
3218fa
4
LTC3218
TYPICAL PERFORMANCE CHARACTERISTICS T = 25°C, unless otherwise noted.
A
Efficiency vs V
2x Mode CPO Output Ripple
IN
100
90
80
70
60
50
40
50mV/DIV
AC COUPLED
50mA
100mA
150mA
200mA
300mA
3218 G14
500ns/DIV
V
CPO
= 3.6V
IN
I
= 200mA
3.7 3.9
(V)
2.9 3.1 3.3 3.5
4.1 4.3 4.5
V
IN
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.
I
(Pin 6): LED Flash Current Programming Resistor.
SETF
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.
I
(Pin 3): LED Current Output. The LED is connected
LED
between I
(anode) and GND (cathode). The current
GND(Pin8):Ground.Thispinshouldbeconnecteddirectly
to a low impedance ground plane.
LED
out of the I
I
is connected between CPO and I
pin is set by resistors connected to the
pins. An internal, 220mΩ sense resistor
LED
and I
SETT
SETF
V (Pin 10): Power. Supply voltage for the LTC3218. V
IN
IN
LED
shouldbebypassedwithalowimpedanceceramiccapaci-
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.
tor to GND of at least 1.6µF of capacitance.
ExposedPad(Pin11):Ground. Thispadmustbesoldered
to a low impedance ground plane for optimum thermal
performance.
I
(Pin 5): LED Torch Current Programming Resistor.
SETT
A resistor connected between this pin and GND is used
to set the LED torch current level.
3218fa
5
LTC3218
BLOCK DIAGRAM
CP
1
CM
9
2
3
CPO
OSCILLATOR
220mΩ
106Ω
+
–
VOLTAGE
CLAMP
I
LED
MODE
CONTROL
V
V
10
IN
REF
CURRENT
SOURCE
CONTROL
CONTROL
LOGIC
ENT
ENF
4
7
I
I
SETF
GND
GND
11
SETT
3218 BD
5
6
8
OPERATION
this mode until the LED forward voltage (V ) approaches
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
F
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.
I
pins. The part starts up in 1x mode after a soft-start
LED
The current delivered to the LED load is controlled by the
internal programmable current source. The current is
period. In this mode, V is connected to the CPO through
IN
switches, the strengths of which are modulated to achieve
the desired LED current. This mode provides maximum
efficiencyandminimumnoise. TheLTC3218willremainin
programmed by resistors connected between the I
SETT
and I
pins and GND. The resistor values needed to
SETF
3218fa
6
LTC3218
OPERATION
attain the desired current level can be determined by
Table 1. Output Current Modes for All ENT and ENF Settings
Equations 1 and 2:
ENF
LOW
LOW
HIGH
HIGH
ENT
LOW
HIGH
LOW
HIGH
I
LED
3300 • 1.21V
SHUTDOWN
RSETF
=
=
1029/R
ILED
(1)
(2)
SETT
2965/R
3993/R
SETF
SETF
850 • 1.21V
ILED
RSETT
Thermal Protection
Overcurrent shutdown mode will prevent damage to the
part and LED by shutting down the high power sections of
The LTC3218 has built-in overtemperature protection.
Thermal shutdown circuitry will shut down the part when
the junction temperature exceeds approximately 165°C. It
willre-enablethepartoncethejunctiontemperaturedrops
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.
thechip. ChoosinganR
orR
valueof5korgreater
SETF
SETT
will ensure that the part stays out of this mode.
Regulation is achieved by sensing the voltage at the I
LED
pin and modulating the charge pump strength based on
the error signal.
InshutdownmodeallcircuitryisturnedoffandtheLTC3218
drawsaverylowcurrentfromtheV supply.Theoutputis
IN
ENF Timeout
disconnected from V and is pulled down by a resistance
IN
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 cur-
rent from being delivered to the LED. Normal operation
can be restored by bringing the part into shutdown and
re-enabling it.
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 cur-
rent source that is capable of driving LED currents up to
150mAcontinuouslyandupto400mAforpulsedoperation.
Pulsed operation may be achieved by toggling the ENT or
ENFpins. Ineithercontinuousorpulsedoperation, proper
board layout is required for effective heat sinking.
Short-Circuit Protection
When ENF or ENT are brought high, the part will connect
The output current of the LTC3218 is programmed using
V and CPO through a weak pull-up. If the CPO capacitor
IN
external resistors connected between the I
and I
SETT
SETF
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.
pins and GND. The output current modes are shown in
Table1,whereR isconnectedbetweenI andGND,
SETT
SETT
and R
is connected between I
and GND.
ESTF
SETF
Soft-Start
Since the LTC3218 has three separate LED current ratios
built in, it can be programmed using a single resistor by
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.
connecting I
and I
together, and then connecting
SETT
SETF
the pins to the resistor.
3218fa
7
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 deter-
mine the amount of current available from the effective
input voltage and effective open-loop output resistance,
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 condi-
tion. 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.
R
(Figure 1).
OL
R
is dependent on a number of factors including the
OL
oscillator frequency, flying capacitor values and switch
resistances. From Figure 1, we can see that the output
current is proportional to:
2V − CPO
IN
ROL
(3)
in 2x mode.
R
OL
+
+
2V
IN
CPO
–
–
3218 F01
Figure 1. Charge Pump Open-Loop Thevenin-Equivalent Circuit
APPLICATIONS INFORMATION
V , CPO Capacitor Selection
Wheref
istheLTC3218’soscillatorfrequency(typically
CPO
IN
OSC
1MHz) and C
is the output storage capacitor.
The value and type of capacitors used with the LTC3218
determineseveralimportantparameterssuchasregulator
control loop stability, output ripple, charge pump strength
and minimum start-up time.
Both the style and value of the output capacitor can sig-
nificantly 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 cur-
rent 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.
To reduce noise and ripple, it is recommended that low
equivalent series resistance (ESR) ceramic capacitors be
used for both C and C . Tantalum and aluminum ca-
VIN
CPO
pacitors 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
CPO
will reduce the output ripple at the expense of higher start-
up current. The peak-to-peak output ripple for 2x mode is
approximately given by the expression:
Likewise, excessive ESR on the output capacitor will tend
to degrade the loop stability of the LTC3218. To prevent
poorloadtransientresponseandinstability, theESRofthe
output capacitor should be kept below 80mΩ. Multilayer
IOUT
2fOSC • CCPO
VRIPPLE
=
(P−P)
ceramic chip capacitors typically have exceptional ESR
3218fa
8
LTC3218
APPLICATIONS INFORMATION
performance. MLCCs combined with a tight board layout
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
causingthemtolose60%ormoreoftheircapacitancewhen
the rated voltage is applied. Therefore, when comparing
differentcapacitors,itisoftenmoreappropriatetocompare
the amount of achievable capacitance for a given case size
ratherthancomparingthespecifiedcapacitancevalue.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.
will yield very good stability. As the value of C
controls
CPO
the amount of output ripple, the value of C controls the
VIN
amount of ripple present at the input pin (V ). The input
IN
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
recommendedfortheirexceptionalESRperformance.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.
Table 1 shows a list of ceramic capacitor manufacturers
and how to contact them.
Table 1. Recommended Capacitor Vendors
AVX
www.avxcorp.com
www.kemet.com
www.murata.com
www.t-yuden.com
www.vishay.com
www.tdk.com
Kemet
Murata
Taiyo Yuden
Vishay
TDK
10nH
V
IN
0.1µF
2.2µF
LTC3218
GND
3218 F02
Layout Considerations and Noise
Figure 2. 10nH Inductor Used for Input Noise Reduction
(Approximately 1cm of Wire)
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.
Flying Capacitor Selection
Warning: Polarized capacitors such as tantalum or
aluminum should never be used for the flying capaci-
tors since their voltage can reverse upon start-up of the
LTC3218. Ceramic capacitors should always be used for
the flying capacitors.
The flying capacitor pins, CP and CM, will have very high
edge rate waveforms. The large dv/dt on these pins can
coupleenergycapacitivelytoadjacentPCBruns.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
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
X7Rmaterialwillretainmostofitscapacitancefrom–40°C
that extends all the way to the LTC3218.
3218fa
9
LTC3218
APPLICATIONS INFORMATION
The following guidelines should be followed when design-
ing 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:
• The Exposed Pad should be soldered to a large copper
planethatisconnectedtoasolid,lowimpedanceground
plane using plated, through-hole vias for proper heat
sinking and noise protection.
• Input and output capacitors (C and C ) must also
IN
CPO
PLED
be placed as close to the part as possible.
η ≡
P
IN
• 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
seriesswitches.Thismodeprovidestheoptimumefficiency
availableforagiveninputvoltageandLEDforwardvoltage.
The efficiency is approximated by:
• V , CPO and I traces must be made as wide as pos-
IN
LED
sible. 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.
PLED
VLED •ILED VLED
η ≡
=
≈
P
V •IIN
V
IN
IN
IN
since the input current will be very close to the LED current.
C
FLY
C
CPO
PIN 1
C
IN
R
R
SETF
SETT
3218 F03
Figure 3. Example Board Layout
3218fa
10
LTC3218
APPLICATIONS INFORMATION
At moderate to high output power, the quiescent current
of the LTC3218 is negligible and the expression above is
valid.
Thermal Management
For higher input voltages and maximum output current,
therecanbesubstantialpowerdissipationintheLTC3218.
Ifthejunctiontemperatureincreasesaboveapproximately
165°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.
Once dropout is detected at the I
pin, the LTC3218
LED
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:
PLED
V
LED •ILED
VLED
ηIDEAL
≡
=
≈
P
V • 2 •ILED 2V
IN IN
IN
PACKAGE DESCRIPTION
DDB Package
10-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1722 Rev Ø)
R = 0.115
0.64 0.05
(2 SIDES)
0.40 0.10
3.00 0.10
(2 SIDES)
TYP
6
R = 0.05
TYP
10
0.70 0.05
2.55 0.05
1.15 0.05
2.00 0.10
PIN 1 BAR
(2 SIDES)
TOP MARK
PIN 1
R = 0.20 OR
(SEE NOTE 6)
0.25 × 45°
PACKAGE
OUTLINE
0.64 0.05
(2 SIDES)
0.25 0.05
CHAMFER
5
1
(DDB10) DFN 0905 REV Ø
0.25 0.05
0.50 BSC
0.75 0.05
0.200 REF
0.50 BSC
2.39 0.05
(2 SIDES)
2.39 0.05
(2 SIDES)
0 – 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
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
3218fa
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
LTC3218
RELATED PARTS
2.2µF
CP
CM
CPO
V
2.9V TO 4.5V
IN
ENF ENT
I
LED
4.7µF
2.2µF
0
0
1
1
0
1
0
1
0 (SHUTDOWN)
50mA (TORCH)
260mA
LTC3218
I
LED
DISABLED
ENF
ENT
ENABLED
ENABLED
350mA (FLASH)
LED
AOT2015
DISABLED
GND
I
I
SETT
SETF
20.5k
1%
11.4k
1%
3218 TA02
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
LTC3200-5
LTC3201
LTC3202
Low Noise, 2MHz Regulated Charge Pump
White LED Driver
Up to 6 White LEDs, V : 2.7V to 4.5V, V
= 5V, I = 8mA, I ≤ 1µA,
Q SD
IN
OUT(MAX)
OUT(MAX)
OUT(MAX)
ThinSOTTM Package
Low Noise, 1.7MHz Regulated Charge Pump
White LED Driver
Up to 6 White LEDs, V : 2.7V to 4.5V, V
= 5V, I = 6.5mA, I ≤ 1µA, 10-Lead
Q SD
IN
MS Package
Low Noise, 1.5MHz Regulated Charge Pump
White LED Driver
Up to 8 White LEDs, V : 2.7V to 4.5V, V
= 5V, I = 5mA, I ≤ 1µA, 10-Lead
Q SD
IN
MS Package
LTC3205
LTC3206
Multidisplay LED Controller
92% Efficiency, V : 2.8V to 4.5V, I = 50µA, I ≤ 1µA, 4mm × 4mm QFN Package
IN Q SD
2
I C Multidisplay LED Controller
92% Efficiency, 400mA Continuous Output Current. Up to 11 White LEDs in
4mm × 4mm QFN Package
LTC3208
LTC3209
High Current Software Configurable
Multidisplay LED Controller
95% Efficiency, V : 2.9V to 4.5V, V
: 5.5V, I = 280µA, I < 1µA,
OUT(MAX) Q SD
IN
5mm × 5mm QFN-32 Package
600mA MAIN/CAM LED Controller
Up to 8 LEDs, 94% Efficiency, V : 2.9V to 4.5V, 1x/1.5x/2x Boost Modes,
IN
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
LTC3210-3
LTC3214
LTC3215
LTC3216
MAIN/CAM LED Controller with 32-Step
Brightness Control
Drives 4 MAIN LEDs, 3mm × 3mm QFN Package
MAIN/CAM LED Controller with 32-Step
Brightness Control
Drives 3 MAIN LEDs, 3mm × 3mm QFN Package
500mA Camera LED Charge Pump
94% Efficiency, V : 2.9V to 4.5V, I = 300µA, I < 2.5µA, 500mA Output Current,
IN Q SD
10-Lead 3mm × 3mm DFN Package
700mA Low Noise High Current LED
Charge Pump
V : 2.9V to 4.4V, V
= 5.5V, I = 300µA, I < 2.5µA, 3mm × 3mm
OUT(MAX) Q SD
IN
DFN Package
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
LTC3251
600mA Low Noise Multi-LED Camera Light
V : 2.9V to 4.4V, I = 400µA, Four Outputs, 3mm × 3mm 16-Lead DFN Package
IN Q
500mA (I ), 1MHz to 1.6MHz Spread
85% Efficiency, V : 3.1V to 5.5V, V : 0.9V to 1.6V, I = 9µA, I ≤1µA,
OUT
IN
OUT
Q
SD
Spectrum Step-Down Charge Pump
10-Lead MS Package
LTC3440
600mA (I ), 2MHz Synchronous Buck-
95% Efficiency, V : 2.5V to 5.5V, V
= 2.5V, I = 25µA, I ≤1µA,
OUT(MIN) Q SD
OUT
IN
Boost DC/DC Converter
10-Lead MS Package
ThinSOT is a trademark of Linear Technology Corporation.
3218fa
LT 0207 REV A • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
12
●
●
© LINEAR TECHNOLOGY CORPORATION 2007
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
相关型号：
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LTC3219EUD#TRPBF
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