LINER LTC3215 700ma low noise high current led charge pump Datasheet

LTC3215
700mA Low Noise High
Current LED Charge Pump
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FEATURES
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DESCRIPTIO
High Efficiency Operation: 1x, 1.5x or 2x Boost
Modes with Automatic Mode Switching
Ultralow Dropout ILED Current Control
Output Current up to 700mA
Low Noise Constant Frequency Operation*
Wide VIN Range: 2.9V to 4.4V
Open/Shorted LED Protection
LED Disconnect in Shutdown
Low Shutdown Current: 2.5µA
4% LED Current Programming Accuracy
Automatic Soft-Start Limits Inrush Current
No Inductors
Tiny Application Circuit (All Components <1mm
Profile)
3mm × 3mm 10-Lead DFN Package
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APPLICATIO S
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LED Torch/Camera Light Supply for Cell Phones,
PDAs and Digital Cameras
General Lighting and/or Flash/Strobe Applications
Built-in soft-start circuitry prevents excessive inrush current during start-up. High switching frequency enables the
use of small external capacitors. LED current is programmed with an external resistor. The LED is disconnected from VIN during shutdown.
An ultralow dropout current source maintains accurate
LED current at very low ILED voltages. Automatic mode
switching optimizes efficiency by monitoring the voltage
across the LED current source and switching modes only
when ILED dropout is detected. The LTC3215 is available in
a low profile 3mm × 3mm 10-Lead DFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
*Protected by U.S. Patent 6411531.
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The LTC®3215 is a low noise, high current charge pump
DC/DC converter designed to power high current LEDs.
The part includes an accurate programmable current
source capable of driving loads up to 700mA from a 2.9V
to 4.4V input. Low external parts count (two flying capacitors, one programming resistor and two bypass capacitors) makes the LTC3215 ideally suited for small, batterypowered applications.
TYPICAL APPLICATIO
C1
2.2µF
Efficiency vs VIN
C2
2.2µF
100
C1+
2.9V TO 4.4V
CIN
2.2µF
C1– C2+
VIN
C2–
CPO
LED1
LTC3215
ILED
DISABLE ENABLE
EN
ISET
ILED
200mA
CCPO
4.7µF
EFFICIENCY (PLED/PIN) (%)
90
70
60
50
40
30
20
10
20k
1%
ILED = 200mA
80
LED = AOT2015 HPW 1751B
VF = 3V TYP AT 200mA
0
2.8 3.0
3215 TA01a
LED1: AOT2015 HPW 1751B
3.2
3.4 3.6 3.8
VIN (V)
4.0
4.2
4.4
3215 TA01b
3215f
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LTC3215
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
VIN to GND ............................................... –0.3V to 5.5V
CPO to GND ............................................. –0.3V to 5.5V
EN ................................................... –0.3V to VIN + 0.3V
ICPO, IILED (Note 2) ........................................... 1000mA
CPO Short-Circuit Duration ............................ Indefinite
Storage Temperature Range ................. –65°C to 125°C
Operating Temperature Range (Note 3) .. –40°C to 85°C
ORDER PART
NUMBER
TOP VIEW
C2+
1
C1+
2
10 C1–
CPO
3
ILED
4
7 VIN
ISET
5
6 EN
LTC3215EDD
9 GND
11
8 C2–
DD PART
MARKING
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PIN (PIN 11) IS GND
MUST BE SOLDERED TO PCB
LBPX
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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 = C1 = C2 = 2.2µF, CCPO = 4.7µF.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
4.4
V
Input Power Supply
●
VIN Operating Voltage
2.9
IVIN Operating Current
ICPO = 0mA, 1x Mode
ICPO = 0mA, 1.5x
ICPO = 0mA, 2x Mode
300
7
9.2
IVIN Shutdown Current
EN = LOW
2.5
7
3270
3400
µA
mA
mA
µA
LED Current
●
LED Current Ratio (ILED/ISET)
ILED = 200mA to 600mA
ILED Dropout Voltage
Mode Switch Threshold, ILED = 200mA
3139
120
mV
2.5
ms
EN to LED Current On
130
µs
1x Mode Output Voltage
ICPO = 0mA
VIN
V
1.5x Mode Output Voltage
ICPO = 0mA
4.6
V
2x Mode Output Voltage
ICPO = 0mA
Mode Switching Delay (LED Warmup Time)
LED Current On Time
mA/mA
Charge Pump (CPO)
1x Mode Output Impedance
5.1
V
0.25
Ω
1.5x Mode Output Impedance
VIN = 3.4V, VCPO < 4.6V, C1 = C2 = 2.2µF
1.5
Ω
2x Mode Output Impedance
VIN = 3.2V, VCPO < 5.1V, C1 = C2 = 2.2µF
1.7
Ω
●
0.6
High Level Input Voltage (VIH)
●
1.4
Low Level Input Voltage (VIL)
●
0.4
V
Input Current (IIH)
●
–1
1
µA
Input Current (IIL)
●
–1
1
µA
CLK Frequency
0.9
1.2
MHz
EN
V
3215f
2
LTC3215
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 = C1 = C2 = 2.2µF, CCPO = 4.7µF.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
1.195
1.22
1.245
V
225
µA
ISET
VISET
●
ISET = 50µA
●
IISET
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
350mA.
Note 3: The LTC3215E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C ambient
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
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TYPICAL PERFOR A CE CHARACTERISTICS
ILED Dropout Voltage
vs LED Current
ILED Pin Current
vs ILED Pin Voltage
VIN = 3.6V
1000
ILED = 500mA
500
0.6
ILED PIN CURRENT (mA)
DROPOUT VOLTAGE (V)
0.7
0.5
0.4
0.3
0.2
800
400mA
400
300mA
300
200mA
200
0
200
400
600
LED CURRENT (mA)
0
800
0.2
0.4
0.6
0.8
ILED PIN VOLTAGE (V)
VIN = 3.9V
0.25
0.23
0.21
0.19
0.17
0.15
–40
1.8
2.0
1.6
1.8
1.4
1.6
1.2
1.0
0.8
0.6
0.4
0.2
–15
10
35
TEMPERATURE (°C)
60
85
3216 G07
10
15 20 25
RSET (kΩ)
35
30
VIN = 3V
VCPO = 4.2V
CIN = C1 = C2 = 2.2µF
CCPO = 4.7µF
0
–40
–15
35
10
TEMPERATURE (°C)
1.4
1.2
1.0
0.8
0.6
0.4
0.2
60
85
3216 G05
40
2x Mode Charge Pump
Open-Loop Output Resistance
(2VIN – VCPO)/ICPO vs Temperature
OUTPUT RESISTANCE (Ω)
OUTPUT RESISTANCE (Ω)
OUTPUT RESISTANCE (Ω)
VIN = 3.3V
VIN = 3.6V
5
1573 G06
1.5x Mode Charge Pump
Open-Loop Output Resistance
(1.5VIN – VCPO)/ICPO vs Temperature
ICPO = 200mA
0.27
0
1.0
3216 G02
1x Mode Charge Pump Open-Loop
Output Resistance vs Temperature
0.29
400
0
0
3216 G01
0.31
600
200
100mA
100
0.1
0
ILED vs RSET
600
ILED (mA)
0.8
(TA = 25°C unless otherwise specified)
VIN = 3V
VCPO = 4.8V
CIN = C1 = C2 = 2.2µF
CCPO = 4.7µF
0
–40
–15
35
10
TEMPERATURE (°C)
60
85
3216 G06
3215f
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LTC3215
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TYPICAL PERFOR A CE CHARACTERISTICS
Input Shutdown Current
vs Input Voltage
Oscillator Frequency
vs Supply Voltage
TA = 25°C
TA = –40°C
2.0
1.5
1.0
920
90
TA = 25°C
900
TA = –40°C
890
TA = 85°C
880
870
860
0.5
0
2.9
100
910
TA = 85°C
2.5
Efficiency vs VIN
930
EFFICIENCY (PLED/PIN) (%)
3.5
FREQUENCY (kHz)
INPUT SHUTDOWN CURRENT (µA)
4.0
3.0
(TA = 25°C unless otherwise specified)
840
3.3
3.5 3.7 3.9 4.1
INPUT VOLTAGE (V)
4.3
3.1
2.9
4.5
3.3 3.5 3.7 3.9 4.1
SUPPLY VOLTAGE (V)
4.3
3216 G04
400mA
70
600mA
60
50
40
30
20
10 LED = LXCL-PWF1 LUMILED
VF = 3V TYP AT 200mA
0
2.8 3.0 3.2 3.4 3.6 3.8
VIN (V)
850
3.1
200mA
80
4.5
4.0
4.2
4.4
3216 G11
3216 G03
ISET/ILED Current Ratio
vs ILED Current
Efficiency vs VIN
100
3400
3350
80
70
CURRENT RATIO
EFFICIENCY (PLED/PIN) (%)
90
60
50
40
100mA
200mA
400mA
AOT2015 HPW 1751B
VF = 3V TYP AT 100mA
30
20
10
0
2.8 3.0
3.2
3300
25°C
–40°C
3250
85°C
3200
3150
3100
3.4 3.6 3.8
VIN (V)
4.0
4.2
0
4.4
600
200
400
ILED CURRENT (mA)
3215 G16
3215 G15
Charge Pump Mode Switching
and Input Current (ILED = 400mA)
2x Mode CPO Output Ripple
1.5x Mode CPO Output Ripple
800
VCPO
1V/DIV
VCPO
50mV/DIV
A/C COUPLED
VCPO
20mV/DIV
A/C COUPLED
IVIN
500mA/
DIV
EN2
5V/DIV
VIN = 3.6V
ICPO = 200mA
500ns/DIV
3216 G12
VIN = 3.6V
ICPO = 400mA
500ns/DIV
3216 G13
VIN = 3V
1ms/DIV
3215 G14
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LTC3215
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PI FU CTIO S
C2+, C1+, C2–, C1– (Pins 1, 2, 8, 10): Charge Pump
Flying Capacitor Pins. A 2.2µF X5R or X7R ceramic
capacitor should be connected from C1+ to C1– and from
C2+ to C2 –.
CPO (Pin 3): Output. CPO is the output of the Charge
Pump. This pin may be enabled or disabled using the EN
input. A 4.7µF X5R or X7R ceramic capacitor is required
from CPO to GND.
ILED (Pin 4): Output. ILED is the LED current source output.
The LED is connected between CPO (anode) and ILED
(cathode). The current into the ILED pin is set by the
programming resistor connected from ISET to GND.
ISET (Pin 5): LED Current Programming Resistor Pin. The
ISET pin will servo to 1.22V. A resistor connected between
this pin and GND is used to set the LED current level.
Connecting a resistor of 2k or less will cause the LTC3215
to enter overcurrent shutdown mode.
EN (Pin 6): Input. The EN is used to enable the part or put
it into shutdown mode.
VIN (Pin 7): Power. Supply voltage for the LTC3215. VIN
should be bypassed with a 2.2µF or greater low impedance
ceramic capacitor to GND.
GND (Pin 9): Charge Pump Ground. This pin should be
connected directly to a low impedance ground plane.
EXPOSED PAD (Pin 11): Control Signal Ground. This pad
must be soldered to a low impedance ground plane for
optimum thermal and electrical performance.
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BLOCK DIAGRA
2
10
C1+
1
C1–
8
C2+
C2–
CPO
3
1X MODE: CPO = VIN
1.5X MODE: CPO = 4.6V
2X MODE: CPO = 5.1V
OSCILLATOR
–
+
MODE
CONTROL
7
6
VREF
ILED
DROPOUT
DETECTOR
4
VIN
EN
CONTROL
LOGIC
CURRENT
SOURCE
CONTROL
ISET
GND
9
5
GND
11
3215 BD
3215f
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LTC3215
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OPERATIO
The LTC3215 uses a fractional switched capacitor charge
pump to power a high current LED with a programmed
regulated current. The part starts up into the 1x mode. In
this mode, VIN is directly connected to CPO. This mode
provides maximum efficiency and minimum noise. The
LTC3215 will remain in this mode until the LED current
source begins to dropout. When dropout is detected, the
LTC3215 will switch to 1.5x mode after a soft-start period.
Any subsequent dropout detected will cause the part to
enter 2x mode. The part may be reset to 1x mode by
bringing the part into shutdown mode and then reenabling
the part.
A two phase nonoverlapping clock activates the charge
pump switches. In the 2x mode, the flying capacitors are
charged on alternate clock phases from VIN. While one
capacitor is being charged from VIN, the other is stacked
on top of VIN and connected to the output. Alternatively, in
the 1.5x mode the flying capacitors are charged in series
during the first clock phase, and stacked in parallel on top
of VIN on the second clock phase. This sequence of
charging and discharging the flying capacitors continues
at a free running frequency of 900kHz (typ).
The current delivered to the LED load is controlled by the
internal programmable current source. The value of this
current may be selected by choosing the appropriate
programming resistor. The resistor is connected between
the ISET pin and GND. The resistor value needed to attain
the desired current level can be determined by Equation 1.
RSET = 3990/ILED
(1)
A resistor value of 2k or less (e.g., a short-circuit) will
cause the LTC3215 to enter overcurrent shutdown mode.
This mode will prevent damage to the part by shutting
down the high power sections of the chip.
Regulation is achieved by sensing the voltage at the CPO
pin and modulating the charge pump strength based on
the error signal. The CPO regulation voltages are set
internally, and are dependent on the charge pump mode as
shown in Table 1.
Table 1. Charge Pump Output Regulation Voltages
CHARGE PUMP MODE
VCPO
1.5x
4.6V
2x
5.1V
In shutdown mode all circuitry is turned off and the
LTC3215 draws a very low current from the VIN supply.
Furthermore, CPO is weakly connected to VIN. The LTC3215
enters shutdown mode when the EN pin is brought low.
Since EN is a high impedance CMOS input it should never
be allowed to float. To ensure that its state is defined, it
must always be driven with valid logic levels.
Thermal Protection
The LTC3215 has built-in overtemperature protection.
Thermal shutdown circuitry will shutdown the ILED output
when the junction temperature exceeds approximately
150°C. It will re-enable the ILED output once the junction
temperature drops back to approximately 135°C. The
LTC3215 will cycle in and out of thermal shutdown indefinitely without latch up or damage until the heat source is
removed.
Soft-Start
To prevent excessive inrush current during start-up and
mode switching, the LTC3215 employs built-in soft-start
circuitry. Soft-start is achieved by increasing the amount
of current available to the output charge storage capacitor
linearly over a period of approximately 250µs.
Charge Pump Strength
When the LTC3215 operates in either the 1.5x mode or 2x
mode, the charge pump can be modeled as a Theveninequivalent circuit to determine the amount of current
available from the effective input voltage and effective
open-loop output resistance, ROL(Figure 1).
3215f
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LTC3215
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OPERATIO
ROL
1.5VIN
OR
2VIN
+
+
–
CPO
3215 F01
–
Figure 1. Charge Pump Open-Loop Thevenin-Equivalent Circuit
ROL is dependent on a number of factors including
the oscillator frequency, flying capacitor values and
switch resistances.
From Figure 1, we can see that the output current is
proportional to:
(1.5VIN – CPO)/ROL or (2VIN – CPO)/ROL
(2)
in the 1.5x mode or 2x mode respectively.
LED Current Programming
The LTC3215 includes an accurate, programmable current source that is capable of driving LED currents up to
350mA continuously and up to 700mA for pulsed operation. Pulsed operation may be achieved by toggling the EN
pin. In either continuous or pulsed operation, proper
board layout is required for effective heat sinking.
The current may be programmed using a single external
resistor. Equation 1, used to calculate the resistor value
from the desired current level is repeated below:
RSET = 3990/ILED
Mode Switching
The LTC3215 will automatically switch from 1x mode to
1.5x mode, and subsequently from 1.5x mode to 2x mode
whenever a dropout condition is detected at the ILED pin.
The part will wait approximately 2ms before switching to
the next mode. This delay allows the LED to warm up and
reduce its forward voltage which may remove the dropout
condition.
In order to reset the part back into 1x mode, the LTC3215
must be brought into shutdown (EN = LOW). Immediately
after the part has been brought to shutdown, it may be
enabled into the 1x mode via the EN pin. An internal
comparator will not allow the main switches to connect 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.
(1)
2.2µF
C1+
2.2µF
C1– C2+
VIN
2.9V TO 4.4V
µP
VIO
For applications requiring multiple current levels, several
schemes may be used to change the resistance for the
RSET resistor. Figure 2 shows two such schemes. The
circuit in Figure 2a uses the I/O output of a microcontroller
to switch a second resistor (R2) in parallel or series with
R1, changing the effective ISET current. Alternatively, the
circuit in Figure 2b uses a pulse-width modulator (PWM)
to vary the current through RSET, which changes the LED
current.
2.2µF
C2–
C1+
2.9V TO 4.4V
CPO
2.2µF
4.7µF
LTC3215
ILED
ON/OFF
R2
C1– C2+
VIN
C2–
CPO
2.2µF
4.7µF
LTC3215
ILED
ILED*
EN
VIO
2.2µF
EN
ISET
ISET
TORCH/FLASH
9.31k
1%
R1
1k
3215 F02b
PWM
9.31k
1%
3215 F02a
*ITORCH = [(1.22V/R1) – ((VIO – 1.22V)/R2)] • 3270
IFLASH = [(1.22V/(R1 • R2/(R1 + R2))] • 3270
(2a)
1µF
(2b)
Figure 2
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LTC3215
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APPLICATIO S I FOR ATIO
VIN, CPO Capacitor Selection
The value and type of capacitors used with the LTC3215
determine several important parameters such as regulator
control loop stability, output ripple, charge pump strength
and minimum start-up time.
To reduce noise and ripple, it is recommended that low
equivalent series resistance (ESR) ceramic capacitors be
used for both 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
start-up current. The peak-to-peak output ripple for 1.5x
mode is approximately given by the expression:
VRIPPLE(P-P) = IOUT/(3fOSC • CCPO)
(3)
charging phase or the output charging phase but will drop
to zero during the clock nonoverlap times. Since the
nonoverlap time is small (~15ns), these missing “notches”
will result in only a small perturbation on the input power
supply line. Note that a higher ESR capacitor such as
tantalum will have higher input noise due to the input
current change times the ESR. Therefore, ceramic capacitors are again recommended for their exceptional ESR
performance. Input noise can be further reduced by powering the LTC3215 through a very small series inductor as
shown in Figure 3. A 10nH inductor will reject the fast
current notches, thereby presenting a nearly constant
current load to the input power supply. For economy, the
10nH inductor can be fabricated on the PC board with
about 1cm (0.4") of PC board trace.
Flying Capacitor Selection
Where fOSC is the LTC3215’s oscillator frequency (typically 900kHz) and CCPO is the output storage capacitor.
Both the style and value of the output capacitor can
significantly affect the stability of the LTC3215. As shown
in the block diagram, the LTC3215 uses a control loop to
adjust the strength of the charge pump to match the
current required at the output. The error signal of this loop
is stored directly on the output charge storage capacitor.
The charge storage capacitor also serves as the dominant
pole for the control loop. To prevent ringing or instability,
it is important for the output capacitor to maintain at least
2.2µF of actual capacitance over all conditions.
Likewise, excessive ESR on the output capacitor will tend
to degrade the loop stability of the LTC3215. The closed
loop output resistance of the LTC3215 is designed to be
76mΩ. For a 100mA load current change, the error signal
will change by about 7.6mV. If the output capacitor has
76mΩ or more of ESR, the closed-loop frequency response will cease to roll off in a simple one-pole fashion
and poor load transient response or instability could
result. Multilayer ceramic chip capacitors typically have
exceptional ESR performance. MLCCs combined with a
tight board layout will yield very good stability. As the value
of 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 LTC3215 will be relatively
constant while the charge pump is on either the input
8
10nH
VIN
0.1µF
LTC3215
2.2µF
GND
3215 F03
Figure 3. 10nH Inductor Used for Input Noise Reduction
(Approximately 1cm of Wire)
Warning: Polarized capacitors such as tantalum or aluminum should never be used for the flying capacitors since
their voltage can reverse upon start-up of the LTC3215.
Ceramic capacitors should always be used for the flying
capacitors.
The flying capacitors control the strength of the charge
pump. In order to achieve the rated output current it is
necessary to have at least 2.2µF of actual capacitance for
each of the flying capacitors. Capacitors of different materials lose their capacitance with higher temperature and
voltage at different rates. For example, a ceramic capacitor
made of X7R material will retain most of its capacitance from
– 40oC to 85oC whereas a Z5U or Y5V style capacitor
will lose considerable capacitance over that range. Z5U and
Y5V capacitors may also have a very poor voltage coefficient causing them to lose 60% or more of their capacitance
when the rated voltage is applied. Therefore, when comparing different capacitors, it is often more appropriate to
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LTC3215
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APPLICATIO S I FOR ATIO
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
pins can couple energy capacitively to adjacent PCB runs.
Magnetic fields can also be generated if the flying capacitors are not close to the LTC3215 (i.e., the loop area is
large). To decouple capacitive energy transfer, a Faraday
shield may be used. This is a grounded PCB trace between
the sensitive node and the LTC3215 pins. For a high quality
AC ground, it should be returned to a solid ground plane
that extends all the way to the LTC3215.
The following guidelines should be followed when designing a PCB layout for the LTC3215.
• The Exposed Pad should be soldered to a large copper
plane that is connected to a solid, low impedance
ground plane using plated, through-hole vias for proper
heat sinking and noise protection.
• Input and output capacitors (CIN and CCPO) must also
be placed as close to the part as possible.
• The flying capacitors must also be placed as close to the
part as possible. The traces running from the pins to the
capacitor pads should be as wide as possible.
Layout Considerations and Noise
Due to its high switching frequency and the transient
currents produced by the LTC3215, careful board layout is
necessary. A true ground plane and short connections to
all capacitors will improve performance and ensure proper
regulation under all conditions.
The flying capacitor pins C1+, C2+, C1– and C2– will have
very high edge rate waveforms. The large dv/dt on these
• 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.
C1
PIN 1
C2
CIN
RSET
CCPO
3215 F04
Figure 4. Example Board Layout
3215f
9
LTC3215
U
W
U U
APPLICATIO S I FOR ATIO
Power Efficiency
To calculate the power efficiency (η) of a white LED driver
chip, the LED power should be compared to the input
power. The difference between these two numbers represents lost power whether it is in the charge pump or the
current sources. Stated mathematically, the power efficiency is given by:
P
η ≡ LED
PIN
ηIDEAL ≡
(4)
The efficiency of the LTC3215 depends upon the mode in
which it is operating. Recall that the LTC3215 operates as
a pass switch, connecting VIN to CPO, until dropout is
detected at the ILED 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:
η≡
PLED VLED • ILED VLED
=
≈
PIN
VIN • IIN
VIN
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:
(5)
since the input current will be very close to the LED
current.
At moderate to high output power, the quiescent current
of the LTC3215 is negligible and the expression above is
valid.
Once dropout is detected at the ILED pin, the LTC3215
enables the charge pump in 1.5x mode.
PLED
V •I
V
= LED LED ≈ LED
PIN
VIN • 1.5ILED 1.5VIN
(6)
Similarly, in 2x boost mode, the efficiency is similar to that
of a linear regulator with an effective input voltage of 2
times the actual input voltage. In an ideal 2x charge pump,
the power efficiency would be given by:
ηIDEAL ≡
PLED
V •I
V
= LED LED ≈ LED
PIN
VIN • 2 • ILED 2 • VIN
(7)
Thermal Management
For higher input voltages and maximum output current,
there can be substantial power dissipation in the LTC3215.
If the junction temperature increases above approximately
150°C, the thermal shutdown circuitry will automatically
deactivate the output. To reduce maximum junction temperature, a good thermal connection to the PC board is
recommended. Connecting the Exposed Pad to a ground
plane and maintaining a solid ground plane under the
device can reduce the thermal resistance of the package
and PC board considerably.
3215f
10
LTC3215
U
PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1698)
0.675 ±0.05
3.50 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
PACKAGE
OUTLINE
0.25 ± 0.05
0.50
BSC
2.38 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
TYP
6
3.00 ±0.10
(4 SIDES)
0.38 ± 0.10
10
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD10) DFN 1103
5
0.200 REF
1
0.25 ± 0.05
0.50 BSC
0.75 ±0.05
0.00 – 0.05
2.38 ±0.10
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
3215f
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
LTC3215
U
TYPICAL APPLICATIO
High Power Camera Light and Flash
2.2µF
C1+
2.9V TO 4.4V
µP
2.8V
2.2µF
C1– C2+
VIN
C2–
CPO
2.2µF
4.7µF
LTC3215
ILED
ON/OFF
EN
2.8V
30k
1%
ILED
200mA/500mA
ISET
TORCH/FLASH
10.5k
1%
3215 TA02
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1618
Constant Current, 1.4MHz, 1.5A Boost Converter
VIN: 1.6V to 18V, VOUT(MAX) = 36V, IQ = 1.8mA, ISD < 1µA
MS Package
LT1961
1.5A (ISW), 1.25MHz, High Efficiency Step-Up
DC/DC Converter
VIN: 3V to 25V, VOUT(MAX) = 35V, IQ = 0.9mA, ISD < 6µA
MS8E Package
LTC3205
250mA, 1MHz, Multi-Display LED Controller
VIN: 2.8V to 4.5V, VOUT(MAX) = 5.5V, IQ = 50µA, ISD < 1µA
DFN Package
LTC3206
400mA, 800kHz, Multi-Display LED Controller
VIN: 2.8V to 4.5V, VOUT(MAX) = 5.5V, IQ = 50µA, ISD < 1µA
DFN Package
LTC3216
1A Low Noise High Current LED Charge Pump with
Independent Flash/Torch Current Control
VIN: 2.9V to 4.4V, VOUT(MAX) = 5.5V, IQ = 300µA, ISD < 2.5µA
DFN Package
LTC3440/LTC3441
600mA/1.2A IOUT, 2MHz/1MHz, Synchronous
Buck-Boost DC/DC Converter
VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 25µA/50µA, ISD <1µA
MS/DFN Packages
LTC3443
600mA/1.2A IOUT, 600kHz, Synchronous
Buck-Boost DC/DC Converter
VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 28µA, ISD <1µA
DFN Package
LTC3453
1MHz, 800mA Synchronous Buck-Boost
High Power LED Driver
VIN(MIN): 2.7V to 5.5V, VIN(MAX): 2.7V to 4.5V, IQ = 2.5mA, ISD < 6µA
QFN Package
LT3467/LT3467A
1.1A (ISW), 1.3/2.1MHz, High Efficiency Step-Up
DC/DC Converters with Integrated Soft-Start
VIN: 2.4V to 16V, VOUT(MAX) = 40V, IQ = 1.2mA, ISD < 1µA
ThinSOT Package
LT3479
3A, 42V, 3.5MHz Boost Converter
VIN: 2.5V to 24V, VOUT(MAX) = 40V, IQ = 2µA, ISD < 1µA
DFN, TSSOP Packages
3215f
12
Linear Technology Corporation
LT/TP 0305 1K • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2005