LT3922 Datasheet PDF - Linear

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LT3922
Linear

Part Number LT3922
Description 2A Synchronous Step-Up LED Driver
Page 30 Pages


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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
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LT3922
Absolute Maximum Ratings
(Note 1)
VIN and EN/UVLO.......................................................40V
ISP, ISN, and VOUT.....................................................40V
ISP – ISN..................................................................0.3V
CTRL and FB.............................................................3.3V
OVLO, PWM, SYNC/SPRD, and FAULT.........................6V
SS and VC.................................................................3.3V
SW.............................................................................40V
BST............................................................................43V
BST – SW....................................................................3V
INTVCC, VREF, ISMON, PWMTG, RT, and RP....... (Note 2)
Operating Junction Temperature Range (Notes 3, 4)
LT3922E/LT3922I................................... –40 to 125°C
LT3922H................................................. –40 to 150°C
Storage Temperature Range.......................–60 to 150°C
Pin Configuration
TOP VIEW
28 27 26 25 24 23
SW 1
22 GND
BST 2
INTVCC 3
21 VOUT
20 PWMTG
VIN 4
EN/UVLO 5
29 19 PWM
GND 18 RP
OVLO 6
17 SYNC/SPRD
VREF 7
CTRL 8
16 RT
15 FAULT
9 10 11 12 13 14
UFD PACKAGE
28-LEAD (4mm × 5mm) PLASTIC QFN
θJA = 34°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
Order Information http://www.linear.com/product/LT3922#orderinfo
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3922EUFD#PBF
LT3922EUFD#TRPBF
3922
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LT3922IUFD#PBF
LT3922IUFD#TRPBF
3922
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LT3922HUFD#PBF
LT3922HUFD#TRPBF
3922
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
E lectrical Characteristics The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VIN = 12V, VEN/UVLO = 2V unless otherwise noted.
PARAMETER
CONDITIONS
MIN TYP MAX
Input Voltage Range
2.8 36
VIN Pin Quiescent Current
EN/UVLO Threshold (Falling)
VEN/UVLO = 1.5V, Not Switching
VEN/UVLO = 0.1V, Shutdown
1.260
2.9
1.330
4
1
1.400
EN/UVLO Rising Hysteresis
25
EN/UVLO Pin Current
Input OVLO Threshold (Rising)
VEN/UVLO = 1.2V
1.145
2
1.205
1.265
Input OVLO Falling Hysteresis
50
OVLO Pin Current
VOVLO = 1.0V
–100 100
UNITS
V
mA
µA
V
mV
µA
V
mV
nA
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LT3922
E lectrical Characteristics The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VIN = 12V, VEN/UVLO = 2V unless otherwise noted.
PARAMETER
CONDITIONS
MIN TYP MAX
Reference
VREF Voltage
VREF Pin Current Limit
LED Current Regulation
IVREF = 0µA
IVREF = 500µA
VREF = 0V, Current Out of Pin
l 1.97 2 2.03
1.985 2 2.015
3.2
CTRL-Off Threshold (Falling)
l 200 210 220
CTRL-Off Rising Hysteresis
15
CTRL Pin Current
Sense Voltage
(Analog Input)
(VISP−VISN)
ISP Pin Current
ISN Pin Current
Current Error Amplifier Transconductance
Duty Cycle Control of LED Current
VCTRL = 2V
VVCCTTRRLL
=
=
20V.75(1V0(05%0%), )V,IVSPIS=P
24V
= 24V
VCTRL = 0.3V (5%), VISP = 24V
VISP = 24.1V, VISN = 24V, VCTRL = 2V
VISP = 24.1V, VISN = 24V , VCTRL = 2V
VISP = 24V
−100 100
l 98
100 102
l 48.5 50 51.5
l4 5 6
75
75
140
Sense Voltage (VISP−VISN)
(Duty Cycle Input)
CTRL Pulse Input High (VIH)
CTRL Pulse Input Low (VIL)
CTRL Pulse Input Frequency Range
CTRL Duty = 75% (100%), VISP = 24V
CTRL Duty = 37.5% (50%), VISP = 24V
CTRL Duty = 15% (5%), VISP = 24V
99 100 101
49 50 51
456
1.6
0.4
10 200
Voltage Regulation
FB Regulation Voltage
FB Pin Current
VCTRL = 2V
FB in Regulation
l 1.175
−100
1.200
1.225
100
Voltage Error Amplifier Transconductance
1000
INTVCC Regulator
INTVCC Voltage
INTVCC Pin Current Limit
Power Stage
VINTVCC = 0V, Current Out of Pin
2.7 3 3.3
20
Peak Current Limit
2.0 2.3 2.6
Bottom Switch Minimum Off-Time
l 15 25 35
Bottom Switch On-Resistance
140
Top Switch On-Resistance
155
Oscillator
Programmed Switching Frequency (fSW)
Spread Spectrum Frequency Range
RT Pin Current Limit
SYNC/SPRD Threshold (Rising)
RRTT
=
=
4459.93kk,,VVSSYYNNCC/S/SPPRRDD==00VV
RRTT
=
=
4459.93kk,,VVSSYYNNCC/S/SPPRRDD==33VV
VRT = 0V, Current Out of Pin
l 1880 2000 2120
l 175 210 245
1880 2650
175 306
75
1.4 1.5
SYNC/SPRD Falling Hysteresis
0.2
SYNC/SPRD Pin Current
VSYNC/SPRD = 5V
−100 100
UNITS
V
V
mA
mV
mV
nA
mV
mV
mV
µA
µA
µA/V
mV
mV
mV
V
V
kHz
V
nA
µA/V
V
mA
A
ns
kHz
kHz
kHz
kHz
µA
V
V
nA
For more information www.linear.com/LT3922
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LT3922
E lectrical Characteristics The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VIN = 12V, VEN/UVLO = 2V unless otherwise noted.
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
Soft-Start
SS Pin Charging Current
SS Pin Discharging Current
SS Lower Threshold
VSS = 1V
VSS = 2V
20 µA
2 µA
0.2 V
SS Higher Threshold
1.7 V
Fault Detection
Open-Circuit Threshold (FB Rising)
Open-Circuit Falling Hysteresis
VISP = VISN = 20V
l 1.117
1.140
50
1.163
V
mV
LED Short-Circuit Threshold (VISP − VISN)
FAULT Pull-Down Current
FAULT Leakage Current
Overvoltage Protection
VISP = 20V
VFAULT = 0.2V, VFB = 1.25V
VFAULT = 3V, VFB = 0.7V
150
0.8
−100
100
mV
mA
nA
FB Overvoltage Threshold (Rising)
l 1.240
1.266
1.292
V
FB Overvoltage Falling Hysteresis
22 mV
LED Current Monitor
ISMON Voltage
PWM Driver
VISP − VISN = 100mV (100%), VISP = 24V
VISP − VISN = 10mV (10%), VISP = 24V
l 0.980
l 80
1.000
100
1.020
120
V
mV
PWMTG Gate Drive (VOUT – VPWMTG)
PWM Threshold (Rising)
VOUT = 20V, VPWM = 1.5V
9 10 11
1.4
V
V
PWM Falling Hysteresis
0.2 V
PWM Pin Current
PWM to PWMTG Propagation Delay
Turn-On
Turn-Off
VPWM = 2V
CPWMTG = 2.1nF (Connected from VOUT to PWMTG)
VOUT = 20V
−100
110
140
100
nA
ns
ns
Internal PWM Dimming
PWM Voltage for 100% PWM Dimming
PWM Voltage for 0% PWM Dimming
PWM Dimming Accuracy
PWM Dimming Frequency
RP Pin Current Limit
RP = 28.7k, VREF = 2V
RP = 28.7k, VREF = 2V
RP = 28.7k, VREF = 2V, VPWM = 1.1V
RP = 28.7k, VREF = 2V, VPWM = 1.9V
RP = 28.7k, RT = 45.3k, VSYNC/SPRD = 0V
RP = 332k, RT = 45.3k, VSYNC/SPRD = 0V
VRP = 0V, Current Out of Pin
2.00
0.99
7.5 10.5 13.5
89 92 95
7.34 7.81 8.28
115 122 129
65
V
V
%
%
kHz
Hz
µA
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Do not apply a positive or negative voltage source to these pins,
otherwise permanent damage may occur.
Note 3: The LT3922E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the −40°C
to 125°C operating junction temperature range are assured by design,
characterization and correlation with statistical process controls. The
LT3922I is guaranteed to meet performance specifications over the
−40°C to 125°C operating junction temperature range. The LT3922H is
guaranteed over the −40°C to 150°C operating junction temperature range.
Operating lifetime is derated at junction temperatures greater than 125°C.
Note 4: This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. The maximum
rated junction temperature will be exceeded when this protection is active.
Continuous operation above the specified absolute maximum operating
junction temperature may impair device reliability or permanently damage
the device.
3922f
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