LT3922EUFD Datasheet, PDF (1/30 Pages) Linear Integrated Systems – 36V, 2A Synchronous Step-Up LED Driver

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
V_IN
8V TO 27V
4.7µF
1M
365k
59.0k
V_IN
EN/UVLO
OVLO
SW BST _VOUT
GND
LT3922
V_OUT
FB
V_REF
GND
1µF
100k
ISP
ANALOG DIM
PWM DIM
100k
2.2µF
CTRL
PWM
SYNC/SPRD
INTV_CC
FAULT
SS RT
RP
10nF
45.3k
2MHz
ISN
PWMTG
ISMON
V_C
10k
1nF
0.47µF
0.47µF
1M
33.2k
4.7µF
300mΩ
M1
30V
333mA
LED
3922 TA01a
Efficiency vs V_IN
100
V_LED = 30V
f_SW = 2MHz
95
90
85
80
75
100% PWM Duty Cycle
70
6
9 12 15 18 21 24 27 30
V_IN (V)
3922 TA01b
For more information www.linear.com/LT3922
3922f
1