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PDF LTC3783 Data sheet ( Hoja de datos )
| Número de pieza | LTC3783 | |
| Descripción | PWM LED Driver and Boost | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3783
PWM LED Driver and Boost,
Flyback and SEPIC Controller
FEATURES
DESCRIPTIO
■ True Color PWMTM Delivers Constant Color with
3000:1 Dimming Ratio
■ Fully Integrated Load FET Driver for PWM Dimming
Control of High Power LEDs
■ 100:1 Dimming from Analog Inputs
■ Wide FB Voltage Range: 0V to 1.23V
■ Constant Current or Constant Voltage Regulation
■ Low Shutdown Current: IQ = 20µA
■ 1% 1.23V Internal Voltage Reference
■ 2% RUN Pin Threshold with 100mV Hysteresis
■ Programmable Operating Frequency (20kHz to
1MHz) with One External Resistor
■ Synchronizable to an External Clock Up to 1.3fOSC
■ Internal 7V Low Dropout Voltage Regulator
■ Programmable Output Overvoltage Protection
■ Programmable Soft-Start
■ Can be Used in a No RSENSETM Mode for VDS < 36V
■ 16-Lead DFN and TSSOP Packages
U
APPLICATIO S
■ High Voltage LED Arrays
■ Telecom Power Supplies
■ 42V Automotive Systems
www■.Da2ta4SVheIent4dUu.scotrmial Controls
■ IP Phone Power Supplies
, LTC and LT are registered trademarks of Linear Technology Corporation.
True Color PWM and No RSENSE are trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Patent pending.
The LTC®3783 is a current mode LED driver and boost,
flyback and SEPIC controller that drives both an N-channel
power MOSFET and an N-channel load PWM switch.
When using an external load switch, the PWMIN input not
only drives PWMOUT, but also enables controller GATE
switching and error amplifier operation, allowing the con-
troller to store load current information while PWMIN is
low. This feature (patent pending) provides extremely fast,
true PWM load switching with no transient overvoltage or
undervoltage issues; LED dimming ratios of 3000:1 can be
achieved digitally, avoiding the color shift normally asso-
ciated with LED current dimming. The FBP pin allows
analog dimming of load current, further increasing the
effective dimming ratio by 100:1 over PWM alone.
In applications where output load current must be re-
turned to VIN, optional constant current/constant voltage
regulation controls either output (or input) current or
output voltage and provides a limit for the other. ILIM
provides a 10:1 analog dimming ratio.
For low- to medium-power applications, No RSENSE mode
can utilize the power MOSFET’s on-resistance to eliminate
the current-sense resistor, thereby maximizing efficiency.
The IC’s operating frequency can be set with an external
resistor over a 20kHz to 1MHz range and can be synchro-
nized to an external clock using the SYNC pin.
The LTC3783 is available in the 16-lead DFN and TSSOP
packages.
TYPICAL APPLICATIO
350mA PWM LED Boost Application
VIN
6V TO 16V
(< TOTAL VF OF LEDs)
1M
0.1µF
10µF
10k
LTC3783
105k
6k
RUN VIN
PWMIN OV/FB
ITH PWMOUT
SS ILIM
VREF GATE
FBP SENSE
FBN INTVCC
FREQ GND
SYNC
M1, M2: SILICONIX Si4470EY
10µF
×2 2.2µH
ZETEX ZLL51000
237k
LED*
STRING
VOUT
<25V
M1 M2 COUT
10µF
4.7µF
0.05Ω 12.4k
*LUMILEDS LHXL-BW02
0.3Ω
GND
3783 TA01a
VPWMIN
5V/DIV
VOUT
0.2V/DIV
AC COUPLED
IL
2.5A/DIV
ILED
0.5A/DIV
Typical Waveforms
1µs/DIV
3783 TA01b
3783f
1
1 page  
LTC3783
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise specified
VREF vs Temperature
1.25
VREF Line Regulation
1.235
VREF Load Regulation
1.235
1.20 1.233
1.233
1.15 1.231
1.10 1.229
1.05 1.227
1.231
VIN = 12V
1.229
VIN = 2.5V
1.227
1.00
–50
0 50 100
TEMPERATURE (°C)
150
3783 G01
IQ vs Temperature (PWMIN Low)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
–75 –25 25 75 125
www.DataSheet4U.coTmEMPERATURE (°C)
175
3783 G04
RUN Thresholds vs VIN
1.6
1.5
RUN HIGH
1.4
1.3
RUN LOW
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0
10 20 30
VIN (V)
40
3783 G07
1.225
0
10 20 30
VIN (V)
40
3783 G02
IQ vs VIN (PWMIN Low)
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
0
0 10 20 30
VIN (V)
40 50
3783 G05
RUN Thresholds vs Temperature
1.40
1.38
RUN HIGH
1.36
1.34
1.32
1.30
1.28
1.26 RUN LOW
1.24
1.22
–50
0 50 100
TEMPERATURE (°C)
150
3783 G08
1.225
01 2 345
IREF (mA)
3783 G03
Dynamic IQ vs Frequency
30
CL = 3300pF
IQ(TOT) = 1.3mA + QG • f
25
20
15
10
5
0
0 0.5 1
FREQUENCY (MHz)
RT vs Frequency
1000
1.5
3783 G06
100
10
1
1 10 100 1000 10000
FREQUENCY (kHz)
3783 G09
3783f
5
5 Page 
U
OPERATIO
INTVCC Regulator Bypassing and Operation
An internal, P-channel low dropout voltage regulator pro-
duces the 7V supply which powers the gate drivers and
logic circuitry within the LTC3783 as shown in Figure 3.
The INTVCC regulator can supply up to 50mA and must be
bypassed to ground immediately adjacent to the IC pins
with a minimum of 4.7µF low ESR or ceramic capacitor.
Good bypassing is necessary to supply the high transient
currents required by the MOSFET gate driver.
For input voltages that don’t exceed 8V (the absolute
maximum rating for INTVCC is 9V), the internal low drop-
out regulator in the LTC3783 is redundant and the INTVCC
pin can be shorted directly to the VIN pin. With the INTVCC
pin shorted to VIN, however, the divider that programs the
regulated INTVCC voltage will draw 15µA from the input
supply, even in shutdown mode. For applications that
require the lowest shutdown mode input supply current,
do not connect the INTVCC pin to VIN. Regardless of
whether the INTVCC pin is shorted to VIN or not, it is always
necessary to have the driver circuitry bypassed with a
4.7µF low ESR ceramic capacitor to ground immediately
adjacent to the INTVCC and GND pins.
LTC3783
In an actual application, most of the IC supply current is
used to drive the gate capacitance of the power MOSFET.
As a result, high input voltage applications in which a large
power MOSFET is being driven at high frequencies can
cause the LTC3783 to exceed its maximum junction tem-
perature rating. The junction temperature can be esti-
mated using the following equations:
IQ(TOT) = IQ + f • QG
PIC = VIN • (IQ + f • QG)
TJ = TA + PIC • θJA
The total quiescent current IQ(TOT) consists of the static
supply current (IQ) and the current required to charge and
discharge the gate of the power MOSFET. The 16-lead FE
package has a thermal resistance of θJA = 38°C/W and the
DHD package has an θJA = 43°C/W
As an example, consider a power supply with VIN = 12V
and VOUT = 25V at IOUT = 1A. The switching frequency is
300kHz, and the maximum ambient temperature is 70°C.
The power MOSFET chosen is the Si7884DP, which has a
maximum RDS(ON) of 10mΩ (at room temperature) and a
www.DataSheet4U.com
1.230V
R2
–
+
VIN
P-CH
R1 7V INTVCC
LOGIC
DRIVER
GATE
INPUT
SUPPLY
6V TO 36V
CIN
CVCC
4.7µF
X5R
6V-RATED
M1 POWER
MOSFET
GND
3783 F03
GND
PLACE AS CLOSE AS
POSSIBLE TO DEVICE PINS
Figure 3. Bypassing the LDO Regulator and Gate Driver Supply
3783f
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3783.PDF ] | |
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