LT3497EDDB [Linear Systems]
Dual Full Function White LED Driver with Integrated Schottky Diodes; 双路全功能的白光LED驱动器，集成肖特基二极管
| 型号： | LT3497EDDB |
| 厂家： | 
Linear Systems |
| 描述： | Dual Full Function White LED Driver with Integrated Schottky Diodes |
| 文件： | 总20页 (文件大小：337K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3497
Dual Full Function White
LED Driver with Integrated
Schottky Diodes
FEATURES
DESCRIPTION
The LT®3497 is a dual full function step-up DC/DC con-
verter specifically designed to drive up to 12 white LEDs
(6whiteLEDsinseriesperconverter)fromaLi-Ioncell.Se-
riesconnectionoftheLEDsprovidesidenticalLEDcurrents
resulting in uniform brightness and eliminating the need
for ballast resistors and expensive factory calibration.
■
Drives Up to 12 White LEDs (6 in Series per
Converter) from a 3V Supply
■
Two Independent Boost Converters Capable of
Driving Asymmetric LED Strings
■
Independent Dimming and Shutdown Control of the
Two LED Strings
■
High Side Sense Allows “One Wire Current Source”
The two independent converters are capable of driving
asymmetric LED strings. Accurate LED dimming and
shutdown of the two LED strings can also be controlled
independently.TheLT3497featuresauniquehighsideLED
current sense that enables the part to function as a “one
wire current source;” one side of the LED string can be
returned to ground anywhere, allowing a simpler 1-wire
LED connection. Traditional LED drivers use a grounded
resistor to sense LED current, requiring a 2-wire connec-
tion to the LED string.
per Converter
■
Internal Schottky Diodes
■
Open LED Protection (32V)
■
2.3MHz Switching Frequency
■
±±5 ꢀeference Accuracy
■
V ꢀange: 2.±V to 10V
IN
Dual Wide 2±0:1 True Color PWMTM Dimming
ꢀequires Only 1µF Output Capacitor per Converter
Available in a 3mm × 2mm 10-Pin DFN Package
■
■
■
The 2.3MHz switching frequency allows the use of tiny
inductors and capacitors. Few external components are
neededforthedualwhiteLEDDriver:open-LEDprotection
and the Schottky diodes are all contained inside the 3mm
× 2mm DFN package. With such a high level of integra-
tion, the LT3497 provides a high efficiency dual white LED
driver solution in the smallest of spaces.
APPLICATIONS
■
Cellular Phones
■
PDAs, Handheld Computers
■
Digital Cameras
MP3 Players
■
■
GPS ꢀeceivers
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
True Color PWM is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
Li-Ion Power Driver for 4/4 White LEDs
Efficiency
V
80
IN
3V TO 5V
V
= 3.6V
IN
4/4LEDs
75
1µF
15µH
SW1
15µH
SW2
70
65
V
IN
CAP1
CAP2
60
55
50
LT3497
10Ω
10Ω
1µF
1µF
LED1
LED2
CTRL1
CTRL2
GND
3497 TA01a
OFF ON
OFF ON
0
5
10
15
20
SHUTDOWN
AND DIMMING
CONTROL 1
SHUTDOWN
AND DIMMING
CONTROL 2
LED CURRENT (mA)
3497 TA01b
3497f
1
LT3497
ABSOLUTE MAXIMUM RATINGS
PACKAGE/ORDER INFORMATION
(Note 1)
Input Voltage (VIN) ...................................................10V
SW1, SW2 Voltages..................................................3±V
CAP1, CAP2 Voltages................................................3±V
CTꢀL1, CTꢀL2 Voltages............................................10V
LED1, LED2 Voltages ................................................3±V
Operating Temperature ꢀange ................. –40°C to 8±°C
Maximum Junction Temperature .......................... 12±°C
Storage Temperature ꢀange................... –6±°C to 12±°C
TOP VIEW
1
2
3
4
5
10
9
LED1
CTRL1
GND
CAP1
SW1
11
8
V
IN
7
CTRL2
LED2
SW2
6
CAP2
DDB PACKAGE
10-LEAD (3mm × 2mm) PLASTIC DFN
= 12±°C, θ = 76°C/W, θ = 13.±°C/W
T
JMAX
JA
JC
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDEꢀED TO PCB
OꢀDEꢀ PAꢀT NUMBEꢀ
LT3497EDDB
DDB PAꢀT MAꢀKING
LCGT
Order Options Tape and ꢀeel: Add #Tꢀ
Lead Free: Add #PBF Lead Free Tape and ꢀeel: Add #TꢀPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
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 T = 25°C. V = 3V, V
= V
= 3V.
A
IN
CTRL1
CTRL2
PARAMETER
CONDITIONS
MIN
2.±
190
190
0
TYP
MAX
UNITS
V
Minimum Operating Voltage
LED Current Sense Voltage (V
LED Current Sense Voltage (V
●
●
– V
– V
)
)
V
V
V
= 16V
= 16V
200
200
2
210
210
8
mV
mV
mV
CAP1
CAP2
LED1
CAP1
LED2
CAP2
Offset Voltage (V ) Between
= |(V
– V
) – (V
– V )|
LED2
OS
) – (V
OS
CAP1
LED1
CAP2
(V
CAP1
– V
– V
) Voltages
LED2
LED1
CAP2
CAP1, LED1 Pin Bias Current
CAP2, LED2 Pin Bias Current
V
V
= 16V, V
= 16V, V
= 16V
20
20
40
40
µA
µA
V
CAP1
LED1
= 16V
CAP2
LED2
V
V
, V
Common Mode Minimum Voltage
Common Mode Minimum Voltage
2.±
2.±
8.±
CAP1 LED1
, V
V
CAP2 LED2
Supply Current
V
V
= V
= 16V, V
= V
= 1±V,
6
mA
CAP1
CTꢀL1
CAP2
LED1
LED2
= V
= 3V
CTꢀL2
V
= V
= 0V
12
2.3
92
18
µA
MHz
5
CTꢀL1
CTꢀL2
Switching Frequency
1.8
88
2.8
Maximum Duty Cycle
●
●
Converter 1 Switch Current Limit SW1
Converter 2 Switch Current Limit SW2
300
300
400
400
200
200
0.1
0.1
mA
mA
mV
mV
µA
Converter 1 V
Converter 2 V
I
I
= 200mA
= 200mA
= 16V
CESAT
CESAT
SW1
SW2
Switch 1 Leakage Current
Switch 2 Leakage Current
V
V
±
±
SW1
= 16V
µA
SW2
3497f
2
LT3497
ELECTRICAL CHARACTERISTICS The
●
denotes the specifications which apply over the full operating
= V = 3V.
temperature range, otherwise specifications are at T = 25°C. V = 3V, V
A
IN
CTRL1
CTRL2
PARAMETER
CONDITIONS
MIN
1.±
TYP
MAX
UNITS
V
●
●
●
V
CTꢀL1
V
CTꢀL2
V
CTꢀL1
V
CTꢀL1
Voltage for Full LED Current
Voltage for Full LED Current
V
= 16V
= 16V
CAP1
CAP2
V
1.±
V
or V
Voltage to Turn On the IC
100
mV
mV
nA
V
CTꢀL2
and V
Voltages to Shut Down the IC
±0
CTꢀL2
CTꢀL1, CTꢀL2 Pin Bias Current
CAP1 Pin Overvoltage Protection
CAP2 Pin Overvoltage Protection
Schottky 1 Forward Drop
100
32
●
●
30
30
34
34
32
V
I
I
= 100mA
= 100mA
0.8
0.8
V
SCHOTTKY1
Schottky 2 Forward Drop
V
SCHOTTKY2
Schottky 1 ꢀeverse Leakage Current
Schottky 2 ꢀeverse Leakage Current
V
= 2±V
= 2±V
4
4
µA
µA
ꢀ1
ꢀ2
V
Note 1: Stresses beyond those listed under Absolute Maximum ꢀatings
may cause permanent damage to the device. Exposure to any Absolute
Maximum ꢀating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LT3497E is guaranteed to meet performance specifications
from 0°C to 8±°C. Specifications over the –40°C to 8±°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
3497f
3
LT3497
(T = 25°C unless otherwise specified)
A
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Saturation Voltage
CESAT
Shutdown Current
(V
)
Schottky Forward Voltage Drop
(V
= V
= 0V)
CTRL1
CTRL2
15
12
9
450
400
350
300
250
200
150
100
50
400
350
300
250
–50°C
–50°C
125°C
25°C
125°C
25°C
125°C
25°C
200
150
6
–50°C
100
50
0
3
0
0
200 250
2
6
0
50 100 150
300 350 400
200
400
800
0
4
8
10
0
1000
600
SWITCH CURRENT (mA)
V
(V)
IN
SCOTTKY FORWARD DROP (mV)
3497 G01
3497 G03
3497 G02
Sense Voltage (V
– V
)
LED
Open-Circuit Output Clamp
Voltage
Input Current in Output Open
Circuit
CAP
vs V
CTRL
34
33
32
31
30
240
200
30
25
25°C
150°C
160
120
20
15
–50°C
–50°C
125°C
125°C
25°C
25°C
80
40
0
10
5
–50°C
0
0
2
4
6
8
10
0
500
1000
1500
2000
2
4
6
8
10
V
(mV)
V
(V)
IN
V
(V)
CTRL
IN
3497 G05
3497 G04
3497 G06
Switching Waveform
Transient Response
V
CAP
V
SW
5V/DIV
10V/DIV
V
CTRL
V
CAP
5V/DIV
50mV/DIV
I
I
L
L
100mA/DIV
200mA/DIV
3497 G07
3497 G08
V
= 3.6V
200ms/DIV
V
= 3.6V
1ms/DIV
IN
IN
FRONT PAGE
APPLICATION CIRCUIT
FRONT PAGE
APPLICATION CIRCUIT
3497f
4
LT3497
(T = 25°C unless otherwise specified)
A
TYPICAL PERFORMANCE CHARACTERISTICS
Schottky Leakage Current vs
Temperature (–50°C to 125°C)
Quiescent Current
Current Limit vs Temperature
3
2
1
0
7
6
500
450
400
350
125°C
25°C
5
4
3
2
1
0
–50°C
24V
16V
300
2
4
6
10
0
8
–50 –25
0
25
50
75 100 125
–50 –25
0
25
50
75 100 125
TEMPERATURE (°C)
TEMPERATURE (°C)
V
(V)
IN
3497 G09
3497 G11
3497 G12
Input Current in Output Open
Circuit vs Temperature
(–50°C to 125°C)
Open-Circuit Output Clamp Voltage
vs Temperature (–50°C to 125°C)
Switching Frequency vs
Temperature
36
34
32
30
30
25
20
15
2.60
V
= 3.6V
V
IN
= 3V
IN
2.50
2.40
2.30
2.20
2.10
2.00
1.90
10
5
28
0
1.80
–50 –25
0
25
50
75 100 125
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
50
75 100 125
–50 –25
0
25
75
TEMPERATURE (°C)
TEMPERATURE (°C)
3497 G13
3497 G14
3497 G15
Sense Voltage (V
– V
)
LED
CAP
Sense Voltage vs Temperature
vs V
CAP
208
204
200
196
192
188
206
202
198
194
125°C
–50°C
25°C
190
5
10
15
20
(V)
25
30
–50 –25
0
25
50
75 100 125
TEMPERATURE (°C)
V
CAP
3497 G16
3497 G17
3497f
5
LT3497
PIN FUNCTIONS
LED1 (Pin 1): Connection point for the anode of the first
CAP2 (Pin 6): Output of Converter 2. This pin is connected
LEDofthefirstsetofLEDsandthesenseresistor(ꢀ
The LED current can be programmed by:
).
to the cathode of internal Schottky diode 2. Connect the
SENSE1
outputcapacitortothispinandthesenseresistor(ꢀ
from this pin to LED2 pin.
)
SENSE2
200mV
RSENSE1
ILED1
=
SW2 (Pin 7): Switch Pin. Minimize trace area at this pin
to minimize EMI. Connect the inductor at this pin.
CTRL1 (Pin 2): Dimming and Shutdown Pin. Connect
CTꢀL1 below ±0mV to disable converter 1. As the pin volt-
ageisrampedfrom0Vto1.±V,theLEDcurrentrampsfrom
V
(Pin 8): Input Supply Pin. This pin must be locally
IN
bypassed.
0 to (I
= 200mV/ꢀ
). The CTꢀL1 pin must not
SW1 (Pin 9): Switch Pin. Minimize trace area at this pin
to minimize EMI. Connect the inductor at this pin.
LED1
be left floating.
SENSE1
GND (Pin 3): Connect the GND pin to the PCB system
CAP1(Pin10):OutputofConverter1.Thispinisconnected
ground plane.
to the cathode of internal Schottky diode 1. Connect the
outputcapacitortothispinandthesenseresistor(ꢀ
from this pin to LED1 pin.
)
SENSE1
CTRL2 (Pin 4): Dimming and Shutdown Pin. Connect
CTꢀL2 below ±0mV to disable converter 2. As the pin volt-
ageisrampedfrom0Vto1.±V,theLEDcurrentrampsfrom
Exposed Pad (Pin 11): Ground. Must be soldered to
PCB.
0 to (I
= 200mV/ꢀ
). The CTꢀL2 pin must not
LED2
be left floating.
SENSE2
LED2 (Pin 5): Connection point for the anode of the first
LED of the second set of LEDs and the sense resistor
(ꢀ ). The LED current can be programmed by:
SENSE2
200mV
RSENSE2
ILED2
=
3497f
6
LT3497
BLOCK DIAGRAM
3497f
7
LT3497
OPERATION
Main Control Loop
A1, sets the correct peak current level in inductor L1 to
keep the output in regulation. The CTꢀL1 pin is used to
adjust the LED current.
TheLT3497usesaconstantfrequency, currentmodecon-
trol scheme to provide excellent line and load regulation.
It incorporates two identical, but fully independent PWM
converters. Operationcanbebestunderstoodbyreferring
to the Block Diagram in Figure 1. The oscillator, start-up
biasandthebandgapreferencearesharedbetweenthetwo
converters. The control circuitry, power switch, Schottky
diode etc., are identical for both the converters.
Ifonlyoneoftheconvertersisturnedon,theotherconverter
will stay off and its output will remain charged up to V
IN
(input supply voltage). The LT3497 enters into shutdown
when both CTꢀL1 and CTꢀL2 pins are pulled lower than
±0mV. The CTꢀL1 and CTꢀL2 pins perform independent
dimming and shutdown control for the two converters.
At power up, the capacitors at CAP1 and CAP2 pins are
Minimum Output Current
chargeduptoV (inputsupplyvoltage)viatheirrespective
IN
The LT3497 can drive a 4-LED string at 2mA LED current
without pulse skipping. As current is further reduced, the
device may begin skipping pulses.
inductor and the internal Schottky diode. If either CTꢀL1
and CTꢀL2 or both are pulled higher than 100mV, the
bandgap reference, the start-up bias and the oscillator
are turned on.
This will result in some low frequency ripple, although the
average LED current remains regulated down to zero. The
photo in Figure 2 details circuit operation driving 4 white
LEDs at 2mA. Peak inductor current is less than ±0mA and
the regulator operates in discontinuous mode, meaning
the inductor current reaches zero during the discharge
phase. After the inductor current reaches zero, the SW
pin exhibits ringing due to the LC tank circuit formed
by the inductor in combination with the switch and the
diode capacitance. This ringing is not harmful; far less
spectral energy is contained in the ringing than in the
switch transitions.
The main control loop can be understood by following the
operationofconverter1.Atthestartofeachoscillatorcycle,
the power switch, Q1, is turned on. A voltage proportional
to the switch current is added to a stabilizing ramp and the
resulting sum is fed into the positive terminal of the PWM
comparator, A2. When this voltage exceeds the level at the
negative input of A2, the PWM logic turns off the power
switch. The level at the negative input of A2 is set by the
error amplifier, A1, and is simply an amplified version of
the difference between the V
and V
voltage and
CAP1
LED1
the bandgap reference. In this manner the error amplifier,
I
L
50mA/DIV
V
SW
10V/DIV
3497 F02
V
= 4.2V
200ns/DIV
IN
I
= 2mA
LED
4 LEDs
Figure 2. Switching Waveforms
3497f
8
LT3497
APPLICATIONS INFORMATION
DUTY CYCLE
15µH MURATA LQH32CN150K53
15µH MURATA LQH2MCN150K02
15µH COOPER SD3112-150
15µH TOKO 1001AS-150M TYPE D312C
15µH SUMIDA CDRH2D11/HP
The duty cycle for a step-up converter is given by:
80
75
70
VOUT + VD – V
VOUT + VD – VCESAT
IN
D=
where:
65
60
55
50
45
V
= Output voltage
OUT
V = Schottky forward voltage drop
V
V = Input voltage
D
= Saturation voltage of the switch
CESAT
IN
The maximum duty cycle achievable for LT3497 is 885
when running at 2.3MHz switching frequency. Always
ensure that the converter is not duty-cycle limited when
powering the LEDs at a given frequency.
5
10
20
0
15
3497 F03
LED CURRENT (mA)
Figure 3. Efficiency Comparison of Different Inductors
and a 1µF output capacitor are sufficient for most applica-
tions. Table 2 shows a list of several ceramic capacitor
manufacturers. Consult the manufacturers for detailed
information on their entire selection of ceramic parts.
INDUCTOR SELECTION
A 1±µH inductor is recommended for most LT3497 ap-
plications. Although small size and high efficiency are
major concerns, the inductor should have low core losses
at 2.3MHz and low DCꢀ (copper wire resistance). Some
inductors in this category with small size are listed in
Table 1. The efficiency comparison of different inductors
is shown in Figure 3.
Table 2: Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden
(800) 368-2496
www.t-yuden.com
AVX
(803) 448-9411
www.avxcorp.com
Murata
(714) 8±2-2001
www.murata.com
Table 1: Recommended Inductors
MAX
DCR
(Ω)
CURRENT
RATING
(mA)
L
(µH)
OVERVOLTAGE PROTECTION
PART
VENDOR
LQH32CN1±0K±3
LQH2MCN1±0K02
LQH32CN100K±3
LQH2MCN100K02
1±
1±
10
10
0.±8
1.6
0.3
1.2
300
200
4±0
22±
Murata
The LT3497 has an internal open-circuit protection
circuit for both converters. In the cases of output open
circuit, when the LEDs are disconnected from the circuit
www.murata.com
SD3112-1±0
1±
0.6±4
440
Cooper
www.cooperet.com
or the LEDs fail open circuit, the converter V
voltage
CAP
is clamped at 32V (typ). Figure 4a shows the transient
response of the front page application step-up converter
with LED1 disconnected. With LED1 disconnected, the
converter starts switching at the peak inductor current
limit. The converter output starts ramping up and finally
gets clamped at 32V (typ). The converter will then switch
at low inductor current to regulate the converter output
1001AS-1±0M
(TYPE D312C)
1±
1±
0.80
360
410
Toko
www.toko.com
CDꢀH2D11/HP
0.739
Sumida
www.sumida.com
CAPACITOR SELECTION
The small size of ceramic capacitors make them ideal for
LT3497applications.UseonlyX±ꢀandX7ꢀtypesbecause
theyretaintheircapacitanceoverwidertemperatureranges
thanothertypessuchasY±VorZ±U.A1µFinputcapacitor
at the clamp voltage. The V
and input current during
CAP
output open circuit are shown in the Typical Performance
Characteristics.
3497f
9
LT3497
APPLICATIONS INFORMATION
For low DCꢀ inductors, which are usually the case for this
application, the peak inrush current can be simplified as
follows:
V
CAP
10V/DIV
r
α =
2•L
I
SW
200mA/DIV
1
L •C
r2
ω =
–
4•L2
3497 F04a
V
= 3.6V
500µs/DIV
IN
FRONT PAGE
APPLICATION CIRCUIT
LEDs DISCONNECTED
AT THIS INSTANT
V –0.6
α π
• exp – •
⎛
⎝
⎞
IN
IPK
=
⎜
⎟
⎠
L •ω
ω 2
Figure 4a. Transient Response of Switcher 1 with LED1
Disconnected from the Output
where L is the inductance, r is the DCꢀ of the inductor
and C is the output capacitance.
I
L1
50mA/DIV
Table 3 gives inrush peak currents for some component
selections.
V
SW1
20V/DIV
Table 3: Inrush Peak Currents
I
L2
50mA/DIV
V
(V)
r (Ω)
L (µH)
C
(µF)
I (A)
P
IN
OUT
V
4.2
0.±8
1.6
1±
1±
1±
1±
1
0.828
0.682
0.794
0.803
SW2
20V/DIV
4.2
4.2
4.2
1
1
1
3497 F04b
V
= 3.6V
200ms/DIV
0.8
IN
4 LEDs
0.739
LED 2 DISCONNECTED
Figure 4b. Switching Waveforms with Output 1 Open Circuit
PROGRAMMING LED CURRENT
The LED current of each LED string can be set indepen-
dently by the choice of resistors ꢀ and ꢀ
In the event one of the converters has an output open
circuit, its output voltage will be clamped at 32V. However,
the other converter will continue functioning properly.
The photo in Figure 4b shows circuit operation with
converter 2 output open circuit and converter 1 driving
4 LEDs at 20mA. Converter 2 starts switching at a lower
peakinductorcurrentandbeginsskippingpulses, thereby
reducing its input current.
,
SENSE2
SENSE1
respectively. For each LED string, the feedback resistor
(ꢀ ) and the sense voltage (V – V ) control the
SENSE
CAP
LED
LED current.
For each independent LED string, the CTꢀL pin controls
the sense reference voltage as shown in the Typical
Performance Characteristics. For CTꢀL higher than 1.±V,
the sense reference is 200mV, which results in full LED
current. In order to have accurate LED current, precision
resistorsarepreferred(15isrecommended).Theformula
INRUSH CURRENT
The LT3497 has built-in Schottky diodes. When supply
voltage is applied to the V pin, an inrush current flows
IN
and Table 4 for ꢀ
selection are shown below.
SENSE
through the inductor and the Schottky diode and charges
uptheCAPvoltage.BoththeSchottkydiodesintheLT3497
can sustain a maximum current of 1A. The selection of
inductor and capacitor value should ensure the peak of
the inrush current to be below 1A.
200mV
ILED
RSENSE
=
3497f
10
LT3497
APPLICATIONS INFORMATION
Table 4: R
Value Selection for 200mV Sense
SENSE
I
(mA)
R
(Ω)
LT3497
R1
100k
LED
SENSE
PWM
10kHz TYP
±
40
CTRL1,2
C1
0.1µF
3497 F05
10
1±
20
20
13.3
10
Figure 5. Dimming Control Using a Filtered PWM Signal
Direct PWM Dimming
DIMMING CONTROL
Changing the forward current flowing in the LEDs not only
changestheintensityoftheLEDs,italsochangesthecolor.
The chromaticity of the LEDs changes with the change in
forward current. Many applications cannot tolerate any
shift in the color of the LEDs. Controlling the intensity of
the LEDs with a direct PWM signal allows dimming of the
LEDs without changing the color. In addition, direct PWM
dimming offers a wider dimming range to the user.
Therearethreedifferenttypesofdimmingcontrolcircuits.
The LED current can be set by modulating the CTꢀL pin
with a DC voltage, a filtered PWM signal or directly with
a PWM signal.
Using a DC Voltage
Forsomeapplications,thepreferredmethodofbrightness
control is a variable DC voltage to adjust the LED current.
The CTꢀL pin voltage can be modulated to set the dim-
ming of the LED string. As the voltage on the CTꢀL pin
increases from 0V to 1.±V, the LED current increases from
Dimming the LEDs via a PWM signal essentially involves
turning the LEDs on and off at the PWM frequency. The
typical human eye has a limit of ~60 frames per second.
By increasing the PWM frequency to ~80Hz or higher,
the eye will interpret that the pulsed light source is con-
tinuously on. Additionally, by modulating the duty cycle
(amount of “on time”) the intensity of the LEDs can be
controlled. The color of the LEDs remains unchanged in
this scheme since the LED current value is either zero or
a constant value.
0 to I . As the CTꢀL pin voltage increases beyond 1.±V,
LED
it has no effect on the LED current.
The LED current can be set by:
200mV
ILED
≈
≈
when VCTRL >1.5V
RSENSE
VCTRL
6.25• RSENSE
ILED
when VCTRL <1.25V
Figure6showsaLi-ionpowered4/4whiteLEDdriver.Direct
PWM dimming method requires an external NMOS tied
between the cathode of the lowest LED in the string and
ground as shown in Figure 6. Si2318DS MOSFETs can be
used since its sources are connected to ground. The PWM
signal is applied to the (CTꢀL1 and CTꢀL2) control pins of
the LT3497 and the gate of the MOSFET. The PWM signal
should traverse between 0V to ±V to ensure proper turn
on and off of the converters and the NMOS transistors (Q1
and Q2). When the PWM signal goes high, LEDs are con-
Feedback voltage variation versus control voltage is given
in the Typical Performance Characteristics.
Using a Filtered PWM Signal
A filtered PWM can be used to control the brightness of
the LED string. The PWM signal is filtered (Figure ±) by a
ꢀC network and fed to the CTꢀL1, CTꢀL2 pins.
The corner frequency of ꢀ1, C1 should be much lower
than the frequency of the PWM signal. ꢀ1 needs to be
much smaller than the internal impedance in the CTꢀL
pins which is 10MΩ (typ).
nected to ground and a current of I = (200mV/ꢀ
)
LED
SENSE
flows through the LEDs. When the PWM signal goes low,
the LEDs are disconnected and turn off. The low PWM
input applied to the LT3497 ensures that the respective
3497f
11
LT3497
APPLICATIONS INFORMATION
Example:
ƒ = 100Hz, t
converter turns off. The MOSFETs ensure that the LEDs
quickly turn off without discharging the output capacitors
which in turn allows the LEDs to turn on faster. Figures 7
and 8 show the PWM dimming waveforms and efficiency
for the Figure 6 circuit.
= 40μs
SETTLE
t
= 1/ƒ = 1/100 = 0.01s
PEꢀIOD
Dim ꢀange = t
/t
= 0.01s/40μs = 2±0:1
PEꢀIOD SETTLE
Min Duty Cycle = t
/t
• 100
SETTLE PEꢀIOD
= 40μs/0.01s = 0.45
The time it takes for the LEDs current to reach its pro-
grammed value sets the achievable dimming range for a
given PWM frequency. For example, the settling time of
the LEDs current in Figure 7 is approximately 40μs for a
3V input voltage. The achievable dimming range for this
application and 100Hz PWM frequency can be determined
using the following method.
Duty Cycle ꢀange = 1005→0.45 at 100Hz
Thecalculationsshowthatfora100Hzsignalthedimming
range is 2±0 to 1. In addition, the minimum PWM duty
cycle of 0.45 ensures that the LEDs current has enough
3V TO 5V
1µF
L1
15µH
L2
15µH
SW1
V
SW2
IN
CAP1
CAP2
R
R
SENSE2
10Ω
SENSE1
10Ω
LT3497
1µF
1µF
LED1
LED2
CTRL1
CTRL2
GND
Q1
Si2318DS
Q2
Si2318DS
5V
0V
5V
0V
100k
100k
3497 F06
PWM
FREQ
PWM
FREQ
Figure 6. Li-Ion to 4/4 White LEDs with Direct PWM Dimming
80
V
= 3.6V
IN
I
LED
4/4 LEDs
20mA/DIV
78
76
74
72
70
I
L
200mA/DIV
PWM
5V/DIV
3497 F07
V
= 3.6V
2ms/DIV
IN
4 LEDs
Figure 7. Direct PWM Dimming Waveforms
0
5
10
15
20
3497 F08
LED CURRENT (mA)
Figure 8. Efficiency
3497f
12
LT3497
APPLICATIONS INFORMATION
time to settle to its final value. Figure 9 shows the avail-
able dimming range for different PWM frequencies with
a settling time of 40μs.
3V TO 5V
1µF
L1
15µH
L2
15µH
10000
SW1
V
SW2
IN
CAP1
CAP2
R
10Ω
R
SENSE2
SENSE1
1µF
1µF
PULSING MAY BE VISIBLE
LT3497
1000
100
10
10Ω
LED1
LED2
CTRL1
CTRL2
GND
5V
0V
5V
0V
PWM
FREQ
PWM
FREQ
Q1
Si2318DS
Q2
Si2318DS
1
100k
100k
10
100
1000
10000
PWM FREQUENCY (Hz)
3497 F10
3497 F09
Figure 10. Li-Ion to 4/4 White LEDs with Both PWM Dimming
and Analog Dimming
Figure 9. Dimming Ratio vs Frequency
The dimming range can be further extended by changing
the amplitude of the PWM signal. The height of the PWM
signalsetsthecommandedsensevoltageacrossthesense
resistor through the CTꢀL pin. In this manner both analog
dimming and direct PWM dimming extend the dimming
range for a given application. The color of the LEDs no
longer remains constant because the forward current of
the LED changes with the height of the CTꢀL signal. For
the 4-LED application described above, the LEDs can be
dimmedfirst,modulatingthedutycycleofthePWMsignal.
Once the minimum duty cycle is reached, the height of the
PWMsignalcanbedecreasedbelow1.±Vdownto100mV.
TheuseofbothtechniquestogetherallowstheaverageLED
current for the 4-LED application to be varied from 20mA
down to less than 20µA. Figure 10 shows the application
for dimming using both analog dimming and PWM dim-
ming. A potentiometer must be added to ensure that the
gate of the NMOS receives a logic-level signal, while the
CTꢀL signal can be adjusted to lower amplitudes.
lower battery voltage. This technique allows the LEDs to
be powered off two alkaline cells. Most portable devices
have a 3.3V supply voltage which can be used to power
the LT3497. The LEDs can be driven straight from the
battery, resulting in higher efficiency.
Figure 11 shows 3/3 LEDs powered by two AA cells.
The battery is connected to the inductors and the chip is
powered off a 3.3V logic supply voltage.
3.3V
2 AA CELLS
2V TO 3.2V
C2
1µF
C1
1µF
L1
15µH
L2
15µH
SW1
V
SW2
IN
CAP1
CAP2
R
R
SENSE2
10Ω
SENSE1
10Ω
LT3497
LED1
LED2
CTRL1
CTRL2
GND
C3
1µF
C4
1µF
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 2
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 1
LOW INPUT VOLTAGE APPLICATIONS
3497 F11
C1, C2: TAIYO YUDEN LMK212BJ105MG
C3, C4: TAIYO YUDEN GMK212BJ105KG
L1, L2: MURATA LQH32CN150K53
The LT3497 can be used in low input voltage applica-
tions. The input supply voltage to the LT3497 must be
2.±V or higher. However, the inductors can be run off a
Figure 11. 2 AA Cells to 3/3 White LEDs
3497f
13
LT3497
APPLICATIONS INFORMATION
the switching node. Place the output capacitors (C
BOARD LAYOUT CONSIDERATIONS
OUT1
and C
) next to the output pins (CAP1 and CAP2).
OUT2
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To prevent electromagnetic interference (EMI) problems,
properlayoutofhighfrequencyswitchingpathsisessential.
Minimize the length and area of all traces connected to
the switching node pins (SW1 and SW2). Keep the sense
voltage pins (CAP1, CAP2, LED1 and LED2) away from
The placement of a bypass capacitor on V needs to be
IN
in close proximity to the IC to filter EMI noise from SW1
and SW2. Always use a ground plane under the switching
regulator to minimize interplane coupling. ꢀecommended
component placement is shown in Figure 12.
VIA TO
GROUND PLANE
C
OUT2
SW2
L2
CAP2
LED2
CTRL2
5
10
9
C
IN
4
VIA TO
GROUND
PLANE
V
IN
8
3
2
1
GND
7
L1
6
CTRL1
CAP1
LED1
SW1
C
OUT1
3497 F12
VIAS TO
GROUND PLANE
Figure 12. Recommended Component Placement
TYPICAL APPLICATIONS
Li-Ion to 1/2 White LEDs
Conversion Efficiency
V
IN
3V TO 5V
70
V
= 3.6V
IN
1/2LEDs
C3
1µF
65
60
55
50
45
40
35
30
C1
C2
1µF
1µF
L1
L2
10µH
10µH
SW1
V
SW2
IN
CAP1
CAP2
R
R
SENSE2
10Ω
SENSE1
10Ω
LT3497
3497 TA02a
LED1
CTRL1
LED2
CTRL2
GND
OFF ON
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 1
SHUTDOWN
AND DIMMING
CONTROL 2
10
0
5
15
20
LED CURRENT (mA)
3497 TA02b
C1, C2: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN LMK212BJ105MG
L1, L2: MURATA LQH32CN100K53
3497f
14
LT3497
TYPICAL APPLICATIONS
Li-Ion to 2/2 White LEDs
Conversion Efficiency
V
IN
3V TO 5V
70
65
V
= 3.6V
IN
C3
1µF
2/2 LEDs
C1
1µF
C2
1µF
L1
L2
10µH
10µH
60
55
SW1
V
SW2
IN
CAP1
CAP2
R
R
SENSE2
SENSE1
LT3497
50
45
40
10Ω
10Ω
LED1
LED2
3497 TA12a
CTRL1
CTRL2
GND
OFF ON
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 1
SHUTDOWN
AND DIMMING
CONTROL 2
0
5
10
15
20
LED CURRENT (mA)
3497 TA12b
C1, C2: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN LMK212BJ105MG
L1, L2: MURATA LQH32CN100K53
Li-Ion to 2/2 White LEDs
Conversion Efficiency
3V TO 5V
80
75
70
65
60
55
50
45
40
C3
1µF
V
= 3.6V
IN
2/2LEDs
L1
L2
10µH
10µH
SW1
V
SW2
IN
CAP1
CAP2
C1
1µF
C2
1µF
R
R
SENSE2
SENSE1
LT3497
10Ω
10Ω
LED1
CTRL1
LED2
CTRL2
GND
OFF ON
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 1
SHUTDOWN
AND DIMMING
CONTROL 2
3497TA13a
10
0
5
15
20
LED CURRENT (mA)
C1, C2: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN LMK212BJ105MG
L1, L2: MURATA LQH32CN100K53
3497 TA13b
3497f
15
LT3497
TYPICAL APPLICATIONS
Li-Ion to 2/4 White LEDs
Conversion Efficiency
V
IN
80
75
70
3V TO 5V
V
= 3.6V
IN
2/4LEDs
C3
1µF
C1
1µF
L1
10µH
L2
15µH
65
60
55
50
45
SW1
V
SW2
IN
CAP1
CAP2
C2
R
R
SENSE2
SENSE1
LT3497
1µF
10Ω
10Ω
LED1
CTRL1
LED2
CTRL2
GND
3497 TA03a
OFF ON
OFF ON
5
10
20
0
15
SHUTDOWN
AND DIMMING
CONTROL 1
SHUTDOWN
AND DIMMING
CONTROL 2
LED CURRENT (mA)
3497 TA03b
C1, C2: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN LMK212BJ105MG
L1: MURATA LQH32CN100K53
L2: MURATA LQH32CN150K53
Li-Ion to 3/3 White LEDs
Conversion Efficiency
V
IN
3V TO 5V
80
75
70
V
= 3.6V
3/3LEDs
IN
C3
1µF
L1
15µH
L2
15µH
SW1
V
SW2
IN
65
60
55
50
45
CAP1
CAP2
C1
C2
1µF
1µF
R
R
SENSE2
SENSE1
LT3497
10Ω
10Ω
LED1
CTRL1
LED2
CTRL2
3497 TA04a
GND
OFF ON
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 1
SHUTDOWN
AND DIMMING
CONTROL 2
5
10
20
0
15
LED CURRENT (mA)
3497 TA04b
C1, C2: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN LMK212BJ105MG
L1, L2: MURATA LQH32CN150K53
3497f
16
LT3497
TYPICAL APPLICATIONS
Li-Ion to 4/6 White LEDs
V
Conversion Efficiency
IN
3V TO 5V
80
75
V
= 3.6V
IN
C3
1µF
4/6LEDs
L1
15µH
L2
15µH
70
65
SW1
V
SW2
IN
CAP1
CAP2
C1
1µF
R
R
SENSE2
SENSE1
LT3497
C2
10Ω
10Ω
1µF
60
55
50
LED1
CTRL1
LED2
CTRL2
GND
OFF ON
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 1
SHUTDOWN
AND DIMMING
CONTROL 2
3497 TA05a
0
5
10
15
20
LED CURRENT (mA)
C1, C2: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN LMK212BJ105MG
L1, L2: MURATA LQH32CN150K53
3497 TA05b
Li-Ion to 5/5 White LEDs
Conversion Efficiency
V
IN
3V TO 5V
80
75
V
= 3.6V
IN
C3
1µF
5/5LEDs
L1
15µH
L2
15µH
70
65
SW1
V
SW2
IN
CAP1
CAP2
C1
1µF
C2
1µF
R
R
SENSE2
10Ω
SENSE1
10Ω
LT3497
60
55
50
LED1
CTRL1
LED2
CTRL2
GND
OFF ON
OFF ON
3497 TA06a
SHUTDOWN
AND DIMMING
CONTROL 1
SHUTDOWN
AND DIMMING
CONTROL 2
0
5
10
15
20
LED CURRENT (mA)
C1, C2: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN LMK212BJ105MG
L1, L2: MURATA LQH32CN150K53
3497 TA06b
3497f
17
LT3497
TYPICAL APPLICATIONS
Li-Ion to 6/6 White LEDs
V
IN
Conversion Efficiency
3V TO 5V
80
75
C3
1µF
V
= 3.6V
IN
6/6LEDs
L1
15µH
L2
15µH
SW1
V
SW2
70
65
IN
CAP1
CAP2
R
R
SENSE2
SENSE1
LT3497
C1
1µF
C2
10Ω
10Ω
1µF
LED1
CTRL1
LED2
CTRL2
60
55
50
GND
OFF ON
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 1
SHUTDOWN
AND DIMMING
CONTROL 2
3497 TA07a
0
5
10
15
20
LED CURRENT (mA)
C1, C2: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN LMK212BJ105MG
L1, L2: MURATA LQH32CN150K53
3497 TA07b
2-Cell Li-Ion Movie and Flash Mode/6 White LEDs Control
V
IN
Conversion Efficiency
6V TO 9V
C3
85
80
75
70
1-100mA LED/6 LEDs
1µF
L2
15µH
R
SENSE1
1Ω
C1
4.7µF
CAP1
LED1
V
IN
SW2
CAP2
R
SENSE2
L1
15µH
LT3497
D1
C2
1µF
10Ω
SW1
LED2
CTRL1
CTRL2
GND
FLASH
OFF ON
1.5V
MOVIE
SHUTDOWN
AND DIMMING
CONTROL 2
V
680mV
CTRL1
3497 TA08a
65
6
6.5
7
7.5
(V)
8
8.5
9
MODE
MOVIE 100mA
FLASH 200mA
I
LED
C1: TAIYO YUDEN LMK212BJ475KD
C2: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN LMK212BJ105MG
D1: AOT-2015 HPW1751B
V
IN
3497 TA08b
L1, L2: MURATA LQH32CN150K53
3497f
18
LT3497
PACKAGE DESCRIPTION
DDB Package
10-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1722 Rev Ø)
0.64 0.05
(2 SIDES)
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)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
0.40 0.10
3.00 0.10
(2 SIDES)
TYP
6
R = 0.05
TYP
10
2.00 0.10
PIN 1 BAR
(2 SIDES)
TOP MARK
PIN 1
R = 0.20 OR
(SEE NOTE 6)
0.25 × 45°
0.64 0.05
(2 SIDES)
0.25 0.05
CHAMFER
5
1
(DDB10) DFN 0905 REV Ø
0.75 0.05
0.200 REF
0.50 BSC
2.39 0.05
(2 SIDES)
0 – 0.05
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
3497f
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.
19
LT3497
TYPICAL APPLICATION
2 Li-Ion to 8/8 White LEDs
Conversion Efficiency
V
IN
6V TO 9V
85
80
75
V
= 7.2V
IN
C3
1µF
8/8LEDs
L1
15µH
L2
15µH
SW1
V
SW2
IN
70
65
60
55
50
CAP1
CAP2
R
R
SENSE2
SENSE1
LT3497
10Ω
10Ω
LED1
CTRL1
LED2
CTRL2
C1
1µF
C2
1µF
GND
OFF ON
OFF ON
SHUTDOWN
AND DIMMING
CONTROL 1
SHUTDOWN
AND DIMMING
CONTROL 2
5
10
20
0
15
LED CURRENT (mA)
3497 TA11b
C1, C2: TAIYO YUDEN GMK212BJ105KG
C3: TAIYO YUDEN LMK212BJ105MG
L1, L2: MURATA LQH32CN150K53
3497 TA11a
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT1937
Constant Current, 1.2MHz, High Efficiency White LED
Boost Regulator
Up to 4 White LEDs, VIN: 2.5V to 10V, VOUT(MAX) = 34V,
IQ = 1.9mA, ISD < 1µA, ThinSOTTM/SC70 Packages
LTC3200-5
LTC3201
Low Noise, 2MHz Regulated Charge Pump White LED Driver
Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 8mA, ISD < 1µA,
ThinSOT Package
Low Noise, 1.7MHz Regulated Charge Pump White LED Driver Up to 6 White LEDs, VIN: 2.7V to 4.5V, IQ = 6.5mA,
SD < 1µA, MS Package
I
LTC3202
Low Noise, 1.5MHz Regulated Charge Pump White LED Driver Up to 8 White LEDs, VIN: 2.7V to 4.5V, IQ = 5mA, ISD < 1µA,
MS Package
LTC3205
High Efficiency, Multidisplay LED Controller
Up to 4 (Main), 2 (Sub) and RGB, VIN: 2.8V to 4.5V,
IQ = 50µA, ISD < 1µA, 24-Lead QFN Package
LT3465/LT3465A
Constant Current, 1.2MHz/2.7MHz, High Efficiency White LED Up to 6 White LEDs, VIN: 2.7V to 16V, VOUT(MAX) = 34V,
Boost Regulator with Integrated Schottky Diode IQ = 1.9mA, ISD < 1µA, ThinSOT Package
LT3466/LT3466-1 Dual Full Function, 2MHz Diodes White LED Step-Up Converter Up to 20 White LEDs, VIN: 2.7V to 24V, VOUT(MAX) = 39V,
with Built-In Schottkys
DFN, TSSOP-16 Packages
LT3486
LT3491
Dual 1.3A White LED Converter with 1000:1 True Color PWM
Dimming
Drives Up to 16 100mA White LEDs. VIN: 2.5V to 24V,
V
OUT(MAX) = 36V, DFN, TSSOP Packages
Drives Up to 6 20mA White LEDs, VIN: 2.5V to 12V,
OUT(MAX) = 27V, 8-Lead SC70 Package
White LED Driver in SC70 with Integrated Schottky
V
ThinSOT is a trademark of Linear Technology Corporation.
3497f
LT 1206 • PRINTED IN USA
20 LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 9±03±-7417
●
●
© LINEAR TECHNOLOGY CORPORATION 2006
(408) 432-1900 FAX: (408) 434-0±07 www.linear.com
相关型号：
LT3497EDDB#TR
IC LED DISPLAY DRIVER, PDSO10, 3 X 2 MM, PLASTIC, MO-229WECD-1, DFN-10, Display Driver
Linear
LT3497EDDB#TRPBF
LT3497 - Dual Full Function White LED Driver with Integrated Schottky Diodes; Package: DFN; Pins: 10; Temperature Range: -40°C to 85°C
Linear
LT3500EDD#PBF
LT3500 - Monolithic 2A Step-Down Regulator Plus Linear Regulator/Controller; Package: DFN; Pins: 12; Temperature Range: -40°C to 85°C
Linear
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