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PDF LT3922 Data sheet ( Hoja de datos )
| Número de pieza | LT3922 | |
| Descripción | 2A Synchronous Step-Up LED Driver | |
| Fabricantes | Linear | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LT3922 (archivo pdf) en la parte inferior de esta página. Total 30 Páginas | ||
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Features
nn ±2% LED Current Regulation
nn ±2% Output Voltage Regulation
nn 5000:1 PWM Dimming at 100Hz
nn 128:1 Internal PWM Dimming
nn Spread-Spectrum Frequency Modulation
nn Silent Switcher® Architecture for Low EMI
nn Operates in Boost, Buck Mode and Buck-Boost Mode
nn 2.8V to 36V Input Voltage Range
nn Up to 34V LED String Voltage
nn 2A, 40V Internal Switches
nn 200kHz to 2MHz with SYNC Function
nn Analog or Duty Cycle LED Current Control
nn Open/Short LED Protection and Fault Indication
nn Thermally Enhanced 28-Pin (4mm × 5mm) QFN
Applications
nn Automotive and Industrial Lighting
nn Machine Vision
L, LT, LTC, LTM, Linear Technology, the Linear logo and Silent Switcher are registered
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners. Protected by U.S. Patents, including 7199560, 7321203, and other patents
pending.
LT3922
36V, 2A Synchronous
Step-Up LED Driver
Description
The LT®3922 is a monolithic, synchronous, step-up DC/
DC converter that utilizes fixed-frequency, peak current
control and provides PWM dimming for a string of LEDs.
The LED current is programmed by an analog voltage or
the duty cycle of pulses at the CTRL pin. The LT3922 will
maintain ±2% current regulation through an external sense
resistor over a wide range of output voltages.
The switching frequency is programmable from 200kHz
to 2MHz by an external resistor at the RT pin or by an
external clock applied at the SYNC/SPRD pin. With the
optional Spread Spectrum Frequency Modulation enabled,
the frequency varies from 100% to 125% to reduce EMI.
The LT3922 also includes a driver for an external high-
side PFET for PWM dimming and an internal PWM signal
generator for analog control of PWM dimming when an
external signal is not available.
Additional features include an accurate external reference
voltage for use with the CTRL and PWM pins, an LED
current monitor, an accurate EN/UVLO pin threshold,
open-drain fault reporting for open-circuit and short-circuit
load conditions, and thermal shutdown.
Typical Application
2MHz, 93% Efficient 10W (30V, 333mA) Boost LED Driver
L1
4.7µH
0.1µF
VIN
8V TO 27V4.7µF
1M
365k
59.0k
VIN
EN/UVLO
OVLO
SW BST VOUT
GND
LT3922
VOUT
FB
VREF
1µF 100k
GND
ISP
ANALOG DIM
PWM DIM
100k
2.2µF
CTRL
PWM
SYNC/SPRD
INTVCC
FAULT
SS RT
RP
10nF
45.3k
2MHz
ISN
PWMTG
ISMON
VC
10k
1nF
0.47µF
0.47µF
1M
33.2k
4.7µF
300mΩ
M1
30V
333mA
LED
3922 TA01a
Efficiency vs VIN
100
VLED = 30V
95 fSW = 2MHz
90
85
80
75
100% PWM Duty Cycle
70
6
9 12 15 18 21 24 27 30
VIN (V)
3922 TA01b
For more information www.linear.com/LT3922
3922f
1
1 page  
LT3922
Typical Performance Characteristics VIN = 12V, TA = 25°C, unless otherwise noted.
EN/UVLO Thresholds
1.50
RISING
1.45 FALLING
1.40
1.35
1.30
1.25
1.20
–45 –20
5 30 55 80 105 130 155
TEMPERATURE (°C)
3922 G01
EN/UVLO Pin Current
3.00
VEN/UVLO = 1.2V
2.50
2.00
1.50
1.00
0.50
0
–45 –20
5 30 55 80 105 130 155
TEMPERATURE (°C)
3922 G02
OVLO Threshold
1.35
RISING
1.30 FALLING
1.25
1.20
1.15
1.10
1.05
–45 –20
5 30 55 80 105 130 155
TEMPERATURE (°C)
3922 G03
VIN Shutdown Current
2.50
VIN = 36V
VIN = 12V
2.00 VIN = 2.7V
1.50
1.00
0.50
0
–45 –20
5 30 55 80 105 130 155
TEMPERATURE (°C)
3922 G04
VIN Quiescent Current
3.60
VIN = 36V
3.40 VIN = 12V
VIN = 2.7V
3.20
3.00
2.80
2.60
2.40
2.20
2.00
–45 –20
5 30 55 80 105 130 155
TEMPERATURE (°C)
3922 G05
INTVCC Voltage
3.2
VIN = 36V
3.1
VIN = 12V
VIN = 2.7V
3.0
2.9
2.8
2.7
2.6
2.5
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3922 G06
INTVCC Load Regulation
3.10
3.05
3.00
2.95
2.90
2.85
2.80
0
–40°C
25°C
125°C
150°C
2 4 6 8 10 12
INTVCC LOAD CURRENT (mA)
3922 G07
VREF Voltage
2.02
2.01
2.00
1.99
1.98
1.97
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3922 G08
For more information www.linear.com/LT3922
VREF Load Regulation
2.02
2.01
2.00
1.99
1.98
1.97
0
–40°C
25°C
125°C
150°C
200 400 600 800 1000
VREF LOAD CURRENT (µA)
3922 G09
3922f
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5 Page 
LT3922
Pin Functions
FAULT: Fault Pin. Connect to INTVCC through a resistance
of 100k. An internal switch pulls this pin low when any of
following conditions happen:
1. Open LED: VFB > 1.14V and (VISP – VISN) < 10mV
2. Shorted LED:
(VISP – VISN) > 150mV for more than 300us, or
(VISP – VISN) > 0.7V, or
VOUT < (VIN – 2V)
RT: Timing Resistor Pin. A resistor from this pin to GND
programs the switching frequency between 200kHz and
2MHz. Do not leave this pin open.
SYNC/SPRD: Synchronization Pin. To override the pro-
grammed switching frequency, drive this pin with an
external clock having a frequency between 200kHz and
2MHz. Even when using the external clock, select an RT
resistor that corresponds to the desired switching fre-
quency. Tie the pin to INTVCC to enable Spread Spectrum
Frequency Modulation. This pin should be tied to GND
when not in use.
RP: PWM Resistor Pin. Connect a resistor from this pin to
GND to set the frequency of the internal PWM signal. Do not
use a resistor larger than 1MΩ. If using an external PWM
pulse for LED dimming, tie this pin to GND. Refer to the
Application Information section for a detailed explanation.
PWM: PWM Input Pin. With the RP pin tied to GND, drive
this pin with a digital pulse to control PWM dimming of
the LEDs. Alternatively, when using a resistor on the RP
pin to GND, set the voltage of this pin between 1V and
2V to generate an internal pulse with duty cycle between
0% and 100%. When using an analog signal, place a 1µF
bypass capacitor between this pin and GND. Tie this pin
high when PWM dimming is not required.
PWMTG: PWM Driver Output Pin. This pin can drive the
gate of an external high-side PMOS device for PWM dim-
ming of LEDs. Do not force any voltage on this pin.
VOUT: Output Pins. Connect to the output and place output
capacitors between these pins and GND as close as pos-
sible to the package. Refer to the Application Information
section for the recommended capacitor placements.
GND (Pin 22, 23, 25, Exposed Pad Pin 29): Ground Pins.
All GND pins must be soldered to the board ground plane.
NC: No Connect Pins. These pins can be left open or con-
nected to the ground.
For more information www.linear.com/LT3922
3922f
11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet LT3922.PDF ] | |
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