LT3932/LT3932-1
36V, 2A Synchronous
Step-Down LED Driver
FEATURES
DESCRIPTION
±1.5% LED Current Regulation
n ±1.2% Output Voltage Regulation
n 5000:1/10000+:1 PWM Dimming at 100Hz
(LT3932/LT3932-1)
n 128:1 Internal PWM Dimming
n Spread-Spectrum Frequency Modulation
n Silent Switcher® Architecture for Low EMI
n 3.6V to 36V Input Voltage Range
n 0V to 36V LED String Voltage
n 200kHz to 2MHz with SYNC Function
n 99.9% Maximum Duty Cycle
n 20:1 Analog or Duty Cycle LED Current Control
n Open/Short LED Protection and Fault Indication
n Accurate LED Current Sense with Monitor Output
n Programmable UVLO
n Thermally Enhanced 28-Pin (4mm × 5mm) QFN
n AEC-Q100 Qualified for Automotive Applications
The LT®3932 , featuring the Silent Switcher®architecture
to minimize EMI/EMC emissions, 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.
An output voltage limit can be set with a resistor divider
to the FB pin.
n
The switching frequency is programmable from 200kHz to
2MHz by an external resistor at the RT pin or by an external clock at the SYNC/SPRD pin. With the optional spread
spectrum frequency modulation enabled, the frequency
varies from 100% to 125% to reduce EMI. The LT3932
also includes a driver for an external, high side PMOS for
PWM dimming and an internal PWM signal generator for
analog control of PWM dimming when an external signal is
not available. The LT3932-1 permits higher dimming ratios.
Additional features include 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.
APPLICATIONS
Automotive Lighting
Industrial and General Purpose Lighting
n Machine Vision Systems
n
n
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. Patents including 7199560, 7321203, 9596728, 9642200 and other patents pending.
TYPICAL APPLICATION
2A LED Driver with Internal PWM Dimming
INTVCC
VIN
20V
VIN
274k
10µF
SW
VOUT
EN/UVLO
2x1µF
30.1k
FB
LT3932
100k
100k
22nF
110k
10k
VREF
2.2µF
Internal PWM Dimming
BST
8.2µH
COUT
100µF
SW
20V/DIV
2A MAX
GND
CTRL
PWM
IL
1A/DIV
ISP
50mΩ
INTVCC
2.2µF
ISN
100k
FAULT
45.3k
2MHz
100nF
ISMON
ILED
1A/DIV
2µs/DIV
PWM = 1.078V
(8% PWM DUTY RATIO)
PWMTG
FAULT
SYNC/SPRD
SS
RT RP
PWMTG
10V/DIV
ISMON
3932 TA01b
VC
28.7k
7.8kHz
162k
9V
10nF
3932 TA01a
Rev C
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1
LT3932/LT3932-1
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
GND
BST
INTVCC
VIN
CTRL
EN/UVLO
TOP VIEW
VIN, EN/UVLO.............................................................40V
ISP, ISN, and VOUT.....................................................40V
ISP – ISN................................................................±0.3V
CTRL and FB.............................................................3.3V
PWM, SYNC/SPRD, and FAULT....................................6V
SS and VC.................................................................3.3V
SW, BST, INTVCC, VREF, ISMON, PWMTG, RT,
and RP................................................................ (Note 2)
Operating Junction Temperature Range (Notes 3, 4)
LT3932E/LT3932I............................... –40°C to 125°C
LT3932H............................................. –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
28 27 26 25 24 23
VREF
1
22 GND
SS
2
21 VIN
VC
3
FB
4
20 VIN
19 SW
ISP
5
ISN
6
ISMON
7
16 VIN
FAULT
8
15 GND
29
GND
18 SW
17 VIN
VOUT
PWMTG
PWM
SYNC/SPRD
RT
RP
9 10 11 12 13 14
UFD PACKAGE
28-LEAD (4mm × 5mm) PLASTIC QFN
θJA = 25°C/W (MEASURED ON DC2286A)
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3932EUFD#PBF
LT3932EUFD#TRPBF
3932
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LT3932IUFD#PBF
LT3932IUFD#TRPBF
3932
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LT3932HUFD#PBF
LT3932HUFD#TRPBF
3932
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 150°C
LT3932EUFD-1#PBF
LT3932EUFD-1#TRPBF
39321
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LT3932IUFD-1#PBF
LT3932IUFD-1#TRPBF
39321
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LT3932HUFD-1#PBF
LT3932HUFD-1#TRPBF
39321
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 150°C
LT3932EUFD#WPBF
LT3932EUFD#WTRPBF
3932
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LT3932IUFD#WPBF
LT3932IUFD#WTRPBF
3932
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 125°C
LT3932HUFD#WPBF
LT3932HUFD#WTRPBF
3932
28-Lead (4mm × 5mm) Plastic QFN
–40°C to 150°C
AUTOMOTIVE PRODUCTS**
Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
**Versions of this part are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. These
models are designated with a #W suffix. Only the automotive grade products shown are available for use in automotive applications. Contact your
local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for
these models.
2
Rev C
For more information www.analog.com
LT3932/LT3932-1
ELECTRICAL 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 = 5V unless otherwise noted.
PARAMETER
CONDITIONS
MIN
Input Voltage Range
VIN Pin Quiescent Current
TYP
3.6
EN/UVLO = 2V, Not Switching
EN/UVLO = 300mV, Shutdown
1.09
UNITS
36
V
2.2
2.7
2
mA
µA
1.15
1.21
V
l
EN/UVLO Threshold (Falling)
MAX
EN/UVLO Rising Hysteresis
20
mV
EN/UVLO Pin Hysteresis Current
4
µA
Reference
VREF Voltage
IVREF = 0µA
IVREF = 500µA
VREF Pin Current Limit
VREF = 1.9V, Current Out of Pin
l
1.975
1.980
2
1.998
2.020
2.016
2
V
V
mA
LED Current Regulation
CTRL-Off Threshold (Falling)
l
200
CTRL-Off Rising Hysteresis
218
228
20
−100
mV
mV
CTRL Pin Current
VCTRL = 2V
Sense Voltage (VISP−VISN)
(Analog Input)
VCTRL = 1.5V (100%), VIN = 36V, VISP = 24V
VCTRL = 750mV (50%), VIN = 36V, VISP = 24V
VCTRL = 300mV (5%), VIN = 36V, VISP = 24V
ISP Pin Current
VIN = 36V, VISP = 24V, VCTRL = 2V, Current Into Pin
50
µA
ISN Pin Current
VIN = 36V, VISN = 23.9V, VCTRL = 2V, Current Into Pin
50
µA
ISP/ISN Common Mode Range
VIN = 36V (Note 5)
Current Error Amplifier Transconductance
VIN = 36V, VISP = 24V
l
l
l
98.5
48.5
4
100
50
5
0
100
nA
101.5
51.5
6
mV
mV
mV
36
200
V
µA/V
Duty Cycle Control of LED Current
Sense Voltage (VISP−VISN)
(Duty Cycle Input)
CTRL Duty = 75% (100%), VIN = 36V, VISP = 24V
CTRL Duty = 37.5% (50%), VIN = 36V, VISP = 24V
CTRL Duty = 15% (5%), VIN = 36V, VISP = 24V
99
49
4
CTRL Pulse Input High (VIH)
100
50
5
101
51
6
1.6
V
CTRL Pulse Input Low (VIL)
0.4
CTRL Pulse Input Frequency Range
mV
mV
mV
100
V
1000
kHz
1.012
V
100
nA
Voltage Regulation
FB Regulation Voltage
VISP = VISN = 6V, VCTRL = 2V
FB Pin Current
VFB = 1V
l
0.988
1.000
−100
Voltage Error Amplifier Transconductance
480
µA/V
Power Stage
Peak Current Limit
3.0
3.6
4.2
A
Minimum Off-Time
(Note 6)
55
ns
Minimum On-Time
(Note 6)
55
ns
Bottom Switch On-Resistance
90
mΩ
Top Switch On-Resistance
90
mΩ
Oscillator
Programmed Switching Frequency (fSW)
RT = 45.3k, VSYNC/SPRD = 0V
RT = 523k, VSYNC/SPRD = 0V
Spread Spectrum Frequency Range
RT = 45.3k, VSYNC/SPRD = 3.3V
RT = 523k, VSYNC/SPRD = 3.3V
RT Pin Current Limit
VRT = 0V, Current Out of Pin
l
l
1900
180
2000
200
1900
180
34
2100
230
kHz
kHz
2650
290
kHz
kHz
µA
Rev C
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3
LT3932/LT3932-1
ELECTRICAL 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 = 5V unless otherwise noted.
TYP
MAX
SYNC/SPRD Threshold (Rising)
PARAMETER
1.4
1.5
SYNC/SPRD Falling Hysteresis
220
SYNC/SPRD Pin Current
CONDITIONS
MIN
VSYNC/SPRD = 3.3V
−100
UNITS
V
mV
100
nA
Soft-Start
SS Pin Charging Current
VSS = 0V
20
µA
SS Pin Discharging Current
VSS = 2V
1.25
µA
SS Lower Threshold (Falling)
200
mV
SS Higher Threshold (Rising)
1.7
V
Fault Detection
Open-Circuit Threshold (FB Rising)
l
930
Open-Circuit Falling Hysteresis
950
970
55
Short-Circuit Threshold (FB Falling)
l
180
Short-Circuit Rising Hysteresis
200
mV
220
50
FAULT Pull-Down Current
VFAULT = 200mV, VFB = 0V
100
FAULT Leakage Current
VFAULT = 3.3V, VFB = 700mV
−100
mV
mV
mV
µA
100
nA
Overvoltage Protection
FB Overvoltage Threshold (FB Rising)
1.050
FB Overvoltage Falling Hysteresis
V
48
mV
LED Current Monitor
ISMON Voltage
VISP − VISN = 100mV (100%), VISP = 12V
VISP − VISN = 10mV (10%), VISP = 12V
0.965
80
1.000
100
1.030
120
10
11
V
mV
PWM Driver
PWMTG Gate Drive (VOUT – VPWMTG)
VOUT = 12V, VPWM = 2V
PWM Threshold (Rising)
VOUT = 12V, VRP = 0V
1.4
V
PWM Falling Hysteresis
VOUT = 12V, VRP = 0V
200
mV
PWM Pin Current
VPWM = 2V
PWM to PWMTG Propagation Delay
Turn-On
Turn-Off
CPWMTG = 2.2nF (Connected from VOUT to PWMTG),
VOUT = 12V
l
−100
100
100
100
V
nA
ns
ns
Analog Control for PWM Dimming
PWM Voltage for 100% Dimming
RP = 28.7k, VREF = 2V
PWM Voltage for 0% Dimming
RP = 28.7k, VREF = 2V
PWM Dimming Accuracy
RP = 28.7k, VREF = 2V, VPWM = 1.1V
RP = 28.7k, VREF = 2V, VPWM = 1.9V
PWM Dimming Frequency
RP = 28.7k, RT = 45.3k, VSYNC/SPRD = 0V
RP = 332k, RT = 45.3k, VSYNC/SPRD = 0V
RP Pin Current Limit
VRP = 0V, Current Out of Pin
4
2.00
l
l
V
0.99
V
7.8
87
10
90
12.4
93
%
%
7.42
116
7.81
122
8.20
128
kHz
Hz
60
µA
Rev C
For more information www.analog.com
LT3932/LT3932-1
ELECTRICAL CHARACTERISTICS
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 LT3932E 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
LT3932I is guaranteed to meet performance specifications over the
−40°C to 125°C operating junction temperature range. The LT3932H is
guaranteed over the −40°C to 150°C operating junction temperature range.
Operating lifetime is derated for 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.
Note 5: The current sense error amplifier is tested with VISP = 36V, and
separately, with VISN = 0V.
Note 6: The MIN on and off times are guaranteed by design and are not
tested.
TYPICAL PERFORMANCE CHARACTERISTICS
EN/UVLO Pin Current
VIN UVLO Threshold (Rising)
5.5
3.6
1.3
5.1
3.4
1.2
1.1
1.0
VIN VOLTAGE (V)
1.4
EN/UVLO CURRENT (μA)
EN/UVLO VOLTAGE (V)
EN/UVLO Threshold (Falling)
VIN = 12V, unless otherwise noted.
4.7
4.3
0
3.5
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
0
3932 G01
2.6
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
VIN Shutdown Current
5.0
INTVCC Voltage
VIN Quiescent Current
3.5
INTVCC VOLTAGE (V)
VIN CURRENT (mA)
VIN CURRENT (nA)
3.5
3.0
2.5
2.0
1.5
1.0
0.1
0.01
–50 –25
3.4
4.0
1
VEN/UVLO = 0.3V
0
25 50 75 100 125 150
TEMPERATURE (°C)
25 50 75 100 125 150
TEMPERATURE (°C)
3932 G03
4.5
1k
10
0
3932 G02
10k
100
3.0
2.8
3.9
0.9
–50 –25
3.2
3.2
3.1
3.0
2.9
0.5
0
–50 –25
3.3
VEN/UVLO = 1V
0
25 50 75 100 125 150
TEMPERATURE (°C)
3932 G05
3932 G04
2.8
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3932 G06
Rev C
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5
LT3932/LT3932-1
TYPICAL PERFORMANCE CHARACTERISTICS
3.38
2.02
2.02
3.36
2.01
2.01
3.34
3.32
2.00
1.99
1.98
0
3
6
9
12
INTVCC CURRENT (mA)
15
1.99
1.98
1.97
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
1.97
0
0.4
0.8
1.2
1.6
VREF CURRENT (mA)
3932 G08
3932 G07
INTVCC and VREF UVLO Threshold
VREF Line Regulation
2.03
3.3
2.02
3.0
2
3932 G09
Minimum On-Time and Off-Time
75
MINIMUM OFF-TIME
MINIMUM ON-TIME
65
2.7
150°C
2.00
VOLTAGE (V)
2.01
25°C
1.99
2.4
2.1
1.98
6
12
18
24
VIN VOLTAGE (V)
45
35
1.5
0
55
1.8
–50°C
1.97
VREF Load Regulation
2.00
TIME (ns)
3.28
2.03
VREF VOLTAGE (V)
2.03
3.30
VREF VOLTAGE (V)
VREF Voltage
3.40
VREF VOLTAGE (V)
INTVCC VOLTAGE (V)
INTVCC Load Regulation
VIN = 12V, unless otherwise noted.
30
36
1.2
–50 –25
INTVCC
VREF
0
25
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
3932 G10
0
25 50 75 100 125 150
TEMPERATURE (°C)
3932 G11
3932 G12
SS Thresholds
SS Pin Pull-Up Current
RP and RT Pin Current Limit
70
2.0
24
23
40
SS VOLTAGE (V)
50
21
20
19
18
30
20
–50 –25
1.6
22
SS CURRENT (µA)
CURRENT (µA)
60
0.4
25 50 75 100 125 150
TEMPERATURE (°C)
16
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3932 G13
6
0.8
LOWER RISING
LOWER FALLING
UPPER RISING
UPPER FALLING
17
RP Current
RT Current
0
1.2
3932 G14
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3932 G15
Rev C
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LT3932/LT3932-1
TYPICAL PERFORMANCE CHARACTERISTICS
SW Frequency
PWM Duty Ratio
Internal PWM Frequency
10
260
2200
RT = 523k
200
1600
100
90
80
DUY RATIO (%)
220
1800
PWM FREQUENCY (kHz)
240
2000
110
INTERNAL PWM
RT = 45.3k
RT = 45.3k
SW FREQUENCY (kHz)
VIN = 12V, unless otherwise noted.
1
70
60
50
40
30
20
10
1400
–50 –25
100k
RP RESISTANCE (Ω)
3932 G16
1M
100
90
90
80
80
70
70
60
50
40
30
30
10
0
0
–10
–10
0.25 0.50 0.75 1 1.25 1.50 1.75
CTRL VOLTAGE (V)
2
0
270
240
180
150
120
90
120
90
30
3932 G22
0.99
1
FB VOLTAGE (V)
1.01
0
4.8
4.9
5
5.1
5.2
VISP - VISN (mV)
5.3
1.02
3932 G21
2.0
300 UNITS
VCTRL = 300mV
150
30
99.6 100.0 100.4 100.8 101.2
VISP - VISN (mV)
155°C
25°C
–50°C
180
60
99.2
0.98
ISMON Voltage
210
60
0
98.8
50
0
0.97
12.5 25 37.5 50 62.5 75 87.5 100
CTRL DUTY RATIO (%)
ISMON VOLTAGE (V)
300 UNITS
VCTRL = 1.5V
210
VCTRL = 2V
75
LED Current (5% Regulation)
300
NUMBER OF UNITS
NUMBER OF UNITS
240
155°C
25°C
–50°C
3932 G18
3932 G20
LED Current (100% Regulation)
3
25
3932 G19
270
2.5
100
40
20
1
1.5
2
PWM VOLTAGE (V)
LED Voltage Limit
50
10
0.5
125
60
20
0
3932 G17
VISP – VISN (mV)
100
VISP - VISN (mV)
VISP - VISN (mV)
110
300
–10
LED Current (Digital CTRL)
LED Current (Analog CTRL)
110
0
0
EXTERNAL PWM
0.1
10k
180
0
25 50 75 100 125 150
TEMPERATURE (°C)
5.4
3932 G23
1.5
1.0
0.5
0
0
50
100
150
200
VISP – VISN (mV)
250
300
3932 G24
Rev C
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7
LT3932/LT3932-1
TYPICAL PERFORMANCE CHARACTERISTICS
LED Current Line Regulation
3.6
49.6
3.2
2.8
2 LEDs (APPROX. 6V)
2MHz SW FREQUENCY
VCTRL = 735mV
49.2
48.8
10
30
50
70
DUTY RATIO (%)
48.0
90
FB OPENLED Threshold
RISING
FALLING
0
6
12
18
24
VIN VOLTAGE (V)
FB VOLTAGE (V)
0.95
0.90
30
0.80
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
RISING
FALLING
0.20
0
15
20
25
30
VIN VOLTAGE (V)
35
40
3932 G31
25 50 75 100 125 150
TEMPERATURE (°C)
3932 G30
Regulated FB Voltage
5 LEDs (APPROX. 15V)
4 LEDs (APPROX. 12V)
1.01
FB VOLTAGE (V)
EFFICIENCY (%)
EFFICIENCY (%)
10
0
1.02
90
85
5
100
0
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
95
80
3932 G27
150
3932 G29
95
36
50
0.10
–50 –25
400kHz
2MHz
30
200
Efficiency vs ILED
2 LEDs (APPROX. 6V, 1A)
12
18
24
VOUT VOLTAGE (V)
TOP SWITCH
BOTTOM SWITCH
250
0.25
100
85
6
Power Switch On-Resistance
0.30
Efficiency vs VIN
90
0
300
3932 G28
100
VIN = 36V
VCTRL = 750mV
2MHz SW FREQUENCY
3932 G26
0.15
0.85
80
49.0
36
FB SHORTLED Threshold
0.35
1.00
49.8
RESISTANCE (mOhm)
1.05
FB VOLTAGE (V)
0.40
50.2
49.4
3932 G25
1.10
LED Current vs VOUT
50.6
48.4
2.4
8
51.0
VISP - VISN (mV)
50.0
VISP - VISN (mV)
PEAK SW CURRENT (A)
Peak SW Current Limit
4.0
2.0
VIN = 12V, unless otherwise noted.
1.00
0.99
0.98
VIN = 24V
2MHz SW FREQUENCY
0
400
800
1200
ILED (mA)
1600
2000
3932 G32
0.97
–50 –25
VCTRL = 2V
VISP – VISN = 0V
0
25 50 75 100 125 150
TEMPERATURE (°C)
3932 G33
Rev C
For more information www.analog.com
LT3932/LT3932-1
TYPICAL PERFORMANCE CHARACTERISTICS
PWMTG Voltage
10
9
8
175
150
125
50
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
CPWMTG = 2.2nF (X7R)
DATA INCLUDES CAPACITANCE
VARIATION WITH TEMPERATURE
0
25 50 75 100 125 150
TEMPERATURE (°C)
C/10 Threshold
12
10
200
2.4
160
2.3
2.2
2.1
8
6
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
2.0
–50 –25
NUMBER OF UNITS
160
120
80
0
25 50 75 100 125 150
TEMPERATURE (°C)
0
8.6
9
9.4 9.8 10.2 10.6 11.0 11.4 11.8
PWM DUTY RATIO (%)
3932 G38
Internal PWM Duty Ratio (90%)
150°C
25°C
–50°C
250 UNITS
VPWM = 1.1V
150°C
25°C
–50°C
40
3932 G37
200
25 50 75 100 125 150
TEMPERATURE (°C)
Internal PWM Duty Ratio (10%)
2.5
NUMBER OF UNITS
SW CURRENT (A)
VISP - VISN (mV)
14
0
3932 G36
DA Current Limit
RISING
FALLING
16
0.900
–50 –25
3932 G35
3932 G34
18
1.000
0.950
100
75
VOUT = 20V
VPWM = 2V
RISING
FALLING
1.050
200
FB VOLTAGE (V)
PROPAGATION DELAY (ns)
VOUT – VPWMTG (V)
11
1.100
TURN–ON
TURN–OFF
225
0
FB OVLO Threshold
PWM Driver Propagation Delay
250
12
7
–50 –25
VIN = 12V, unless otherwise noted.
3932 G39
Input Voltage Transient Response
Input Voltage Transient Response
250 UNITS
VPWM = 1.9V
VIN
10V/DIV
VIN
10V/DIV
ILED
100mA/DIV
ILED
100mA/DIV
120
80
40
1ms/DIV
0
88.6 89 89.4 89.8 90.2 90.6 91.0 91.4 91.8
PWM DUTY RATIO (%)
FRONT PAGE APPLICATION
15V TO 25V INPUT VOLTAGE STEP
3 LEDs (APPROX. 9V)
3932 G41
1ms/DIV
3932 G42
FRONT PAGE APPLICATION
25V TO 15V INPUT VOLTAGE STEP
3 LEDs (APPROX. 9V)
3932 G40
Rev C
For more information www.analog.com
9
LT3932/LT3932-1
TYPICAL PERFORMANCE CHARACTERISTICS
VIN = 12V, unless otherwise noted.
Start-Up with 10% Internal PWM
Turn-On and Turn-Off
VIN
20V/DIV
VIN
20V/DIV
Start-Up with 90% Internal PWM
VIN
20V/DIV
VOUT
5V/DIV
VOUT
5V/DIV
VOUT
5V/DIV
ILED
500mA/DIV
ILED
500mA/DIV
ILED
500mA/DIV
5ms/DIV
FRONT PAGE APPLICATION
3 LEDs (APPROX. 9V)
3932 G43
5ms/DIV
3932 G44
FRONT PAGE APPLICATION WITH PWM = 1.1V
3 LEDs (APPROX. 9V)
5ms/DIV
3932 G45
FRONT PAGE APPLICATION WITH PWM = 1.9V
3 LEDs (APPROX. 9V)
PIN FUNCTIONS
VIN: Input Voltage Pins. These pins supply power to the
internal, high performance analog circuitry, and they supply the inductor current when the internal high side power
switch is on. Connect capacitors between these pins and
GND and see Selecting and Placing the Input Capacitors
in Applications Information for advice regarding their
placement.
ISN: Negative Current Sense Pin. This pin is one of the
inputs to the internal current sense error amplifier. It
should be connected to the negative side of the external
sense resistor.
EN/UVLO: Enable and Undervoltage Lockout Pin. A voltage at this pin greater than 1.15V will enable switching,
and a voltage less than 300mV is guaranteed to shut down
the internal current bias and sub-regulators. A resistor
network between this pin and VIN can be used to set the
pin voltage and automatically lockout the part when VIN is
below a certain level. No internal components pull up or
down on this pin, so it requires an external voltage bias
for normal operation. This pin may be tied directly to VIN.
CTRL: Control Pin. An analog voltage from 250mV to
1.25V at this pin programs the regulated voltage between
ISP and ISN (and therefore, the regulated current supplied
to the load). Alternatively, a digital pulse at this pin with
duty cycle from 12.5% to 62.5% can be used to program the regulated voltage. Below 200mV or 10% duty
cycle, the CTRL pin voltage disables switching. For more
detail, see Regulated LED Current in Typical Performance
Curves and Programming LED Current with the CTRL Pin
in Applications Information.
INTVCC: Internally Regulated, Low-Voltage Supply Pin.
This pin provides the power for the converter switch gate
drivers. Do not force any voltage on this pin, but bypass
it with a 2.2µF capacitor to GND.
ISP: Positive Current Sense Pin. This pin is one of the
inputs to the internal current sense error amplifier. It
should be connected to the positive side of the external
sense resistor.
10
ISMON: Output Current Monitoring Pin. This pin provides
a buffered voltage output equal to 10mV for every 1mV
between ISP and ISN.
VREF: Reference Voltage Pin. This pin provides a buffered
2V reference capable of 1mA drive. It can be used to supply resistor networks for setting the voltages at the CTRL
and PWM pins. Bypass with a 2.2μF capacitor to GND.
Rev C
For more information www.analog.com
LT3932/LT3932-1
PIN FUNCTIONS
FB: Feedback Pin. When the voltage at this pin is near 1V,
the regulated current is automatically reduced from the
programmed value. A resistor network between this pin
and VOUT can be used to set a limit for the output voltage.
If the voltage at the FB pin reaches 1.05V, an overvoltage
lockout comparator disables switching.
FAULT: Fault Pin. Connect to INTVCC through a resistance
of 100k. When the FB pin voltage is less than 200mV, an
internal switch pulls this pin low to indicate a short-circuit.
When FB is greater than 950mV and the voltage between
ISP and ISN is simultaneously less than 10mV, the switch
pulls this pin low to indicate an open-circuit.
SS: Soft-Start Pin. At startup and recovery from fault conditions, a 20μA current charges the capacitor and the FB
voltage tracks the rising voltage at this pin until the load
current reaches its programmed level. Typical values for
the capacitor are 10nF to 100nF. A resistor from SS to
INTVCC is used to select one of several fault modes. See
Soft-Start and Fault Modes in Applications Information
for more details.
VC: Compensation Pin. A capacitor connected from this
pin to GND stabilizes the current and voltage regulation.
See Stabilizing the Regulation Loop in the Applications
Information section for more details.
SW: Switch Pins. These two pins are internally connected
to the power devices and drivers. They should always be
tied together. In normal operation, the voltage of these
pins will switch between the input voltage and zero at
the programmed frequency. Do not force any voltage on
these pins.
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 programmed 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 frequency. Tie the pin to INTVCC to enable spread spectrum
frequency modulation. This pin should be tied to GND
when not in use.
BST: Boost Pin. This pin supplies the high side power
switch driver. Connect a 22nF capacitor between this
pin and SW, and connect a diode from INTVCC to BST to
charge the capacitor when the SW pin is low.
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, set the voltage of this pin between
1V and 2V to generate an internal pulse with duty ratio
between 0% and 100%. In this case, 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 dimming of LEDs. Do not force any voltage on this pin.
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 1M. If using an external
PWM pulse for LED dimming, tie this pin to GND.
VOUT: PWM Driver Supply Pin. This pin supplies an internal regulator for the driver of the external PMOS device.
Tie this pin to the output voltage even if dimming is not
required.
GND: Ground Pins. These must be soldered to the ground
plane of the circuit board.
Rev C
For more information www.analog.com
11
LT3932/LT3932-1
BLOCK DIAGRAM
D1
CVCC
25
26
REN2
24
INTVCC
VIN
CIN
VIN
INTERNAL VCC
REGULATOR
AND UVLO
EN/UVLO
27
20
21
R
VREF
2V REFERENCE
Q
SW
18
SYNCHRONOUS
CONTROLLER
PEAK CURRENT
COMPARATOR
19
BOTTOM SWITCH
DRIVER
DA CURRENT
+
–
+
LIMIT
8.2µH
RT
VOUT
10
RT
CIN
VIN
TOP SWITCH
DRIVER
S
1
17
22nF
REN1
CREF
16
BST
1.4V
SYNC/SPRD
11
14
200kHz TO
2MHz
OSCILLATOR
–
4.7µF
+
S/H
VOUT – 10V
REGULATOR
S/H
50mΩ
CURRENT
REGULATION
AMPLIFIER
gm = 200µS
PWMTG
PWMTG
DRIVER
13
–
+
3k
–
A/D
DETECTOR
+
CONTROL
BUFFER
+
+
–
+
CTRL
28
–
1.25V
PWM
12
3k
ISMON
INTERNAL
PWM SIGNAL
7
30k
250mV
+
–
10x
VOLTAGE
REGULATION
AMPLIFIER
gm = 480µS
ISN
6
ISP
+
+
–
5
4
1.0V
950mV
20µA
INTVCC
–
–
1.25µA
200mV
GND
15
22
23
29
SS
VC
2
3
RSS
CSS
12
RFB1
RFAULT
FAULT
+
FAULT
LOGIC
RFB2
FB
8
FAULT
COMPARATORS
FAULT
LOGIC
+
RP
9
3923 BD
INTVCC
CC
Rev C
For more information www.analog.com
LT3932/LT3932-1
OPERATION
The LT3932 is a step-down LED driver that utilizes fixedfrequency, peak-current control to accurately regulate the
current through a string of LEDs. It includes two power
switches and their drivers. The switches connect an external inductor at the SW pin alternately to the input supply and then to ground. The inductor current rises and
falls accordingly and the peak current can be regulated
by adjusting the duty ratio of the power switches through
the combined effect of the other circuit blocks.
The synchronous controller ensures the power switches
do not conduct at the same time, and a programmable
oscillator turns on the top switch at the beginning of each
switching cycle. The frequency of this oscillator is set by
an external resistor at the RT pin and can be overridden by
external pulses at the SYNC/SPRD pin. The SYNC/SPRD
pin can also be used to command spread spectrum frequency modulation (SSFM), which reduces radiated and
conducted electromagnetic interference (EMI).
The top switch is turned off by the peak current comparator which waits during the on-time for the increasing
inductor current to exceed the target set by the voltage
at the VC pin. This target is modified by a signal from the
oscillator which stabilizes the inductor current. A capacitor at the VC pin is necessary to stabilize this regulation
loop.
The target for the inductor current is derived from the
desired LED current programmed by the voltage at the
CTRL pin. The analog-to-digital detector and the control buffer convert either a DC voltage or digital pulses
at the CTRL pin into the input for the current regulation
amplifier. The other input to this amplifier comes from the
ISP and ISN pin voltages. An external current sense resistor between these pins should be placed in series with the
string of LEDs such that the voltage across it provides the
feedback to regulate the LED current. The current regulation amplifier then compares the actual LED current to the
programmed LED current and adjusts VC as necessary.
The voltage regulation amplifier overrides the current regulation amplifier, when the FB pin voltage approaches an
internal 1V reference. An external resistor network from
the LED string to the FB pin provides an indication of the
LED string voltage and allows the voltage amplifier to
prevent overvoltage of the LED string.
The FB voltage is also monitored to detect fault conditions
like open and short-circuits, which are then reported by
pulling the FAULT pin low. The response to a fault can be
selected either to try hiccup restarts or to latch-off by the
choice of an external resistor connected to the SS pin.
Refer to Applications Information for a detailed explanation of fault responses.
Finally, pulse-width-modulation (PWM) of the LED current is achieved by turning on and off an external PMOS
switch between the inductor and the string of LEDs. An
external pulse at the PWM pin controls the state of the
PWM driver, or a DC voltage at the PWM pin dictates the
duty ratio of an internal PWM pulse, whose frequency is
programmed by an external resistor at the RP pin. After
each pulse, when the PMOS switch is open, the LT3932
preserves the voltages of the capacitors at VC and VOUT
to ensure a rapid recovery for the next pulse.
Rev C
For more information www.analog.com
13
LT3932/LT3932-1
APPLICATIONS INFORMATION
The following is a guide to selecting the external components and configuring the LT3932 according to the
requirements of an application.
Programming LED Current with the CTRL Pin
The primary function of the LT3932 is to regulate the current for a string of LEDs. This current should pass through
a series current sense resistor that can be placed anywhere in the string. Then the voltage across this resistor
will be sensed by the current regulation amplifier through
the ISP and ISN pins and regulated to a level programmed
by the CTRL pin. The maximum resistor voltage that can
be programmed is 100mV, which corresponds to 2A
through the LED string when a 50mΩ current sense resistor is used.
Additionally, the LT3932 is capable of interpreting a
pulse at the CTRL pin. The high level of the pulse must
be greater than 1.6V. The low level must be less than
400mV. The frequency must be greater than 100kHz and
less than 1MHz. Then the regulated voltage between ISP
and ISN will vary with the duty ratio of the pulse as shown
in Figure 2.
In this case, the LED current is zero for duty ratios less
than 12.5% and reaches its maximum above 62.5%. The
LT3932 will cease switching if the duty ratio of the CTRL
pin pulse is less than 10%, and also for DC CTRL pin
voltages less than 200mV.
ILED
100mV
RSNS
To allow for this maximum current, the CTRL pin may
be connected directly to the VREF pin, which provides
an accurate 2V reference. Lower current levels can be
DCTRL < 10%
CTRL–OFF
50mV
RSNS
ILED
100mV
RSNS
VCTRL < 200mV
CTRL–OFF
0
12.5%
37.5%
62.5% 75%
DCTRL
3932 F02
50mV
RSNS
Figure 2. Duty Ratio CTRL Range
0
0.25V
0.75V
1.25V 1.5V
VCTRL
3932 F01
To reduce the LED current when the temperature of the
LEDs rises, use resistors with negative temperature coefficient (NTC) in the network from VREF to CTRL as shown
in Figure 3.
Figure 1. Analog CTRL Range
programmed by DC CTRL voltages between 250mV and
1.25V as shown in Figure 1.
Below 250mV, the CTRL pin commands zero LED current,
and above 1.25V, it commands the maximum. When an
independent voltage source is not available, the intermediate CTRL voltages may be derived from the 2V reference
at the VREF pin using a resistor network or potentiometer
as long as the total current drawn from the VREF pin is
less than 1mA.
14
VREF
VREF
RCTRL1
LT3932
RCTRL1
RNTC
RCTRL2
LT3932
CTRL
CTRL
RCTRL2
3932 F03
RNTC
Figure 3. Setting CTRL with NTC Resistors
Rev C
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LT3932/LT3932-1
APPLICATIONS INFORMATION
100
Setting Switching Frequency with the RT Pin
80
60
AMPLITUDE (dBuV)
The switching frequency of the LT3932 is programmed by
a resistor connected between the RT pin and GND. Values
of the RT resistor from 45.3k up to 523k program frequencies from 2MHz down to 200kHz as shown in Table 1.
Higher frequencies allow for smaller external components
but increase switching power losses and radiated EMI.
40
20
0
–20
Table 1. RT Resistance Range
SWITCHING FREQUENCY
RT
2.0MHz
45.3k
1.6MHz
59.0k
1.2MHz
80.6k
1.0MHz
97.6k
750kHz
133k
500kHz
205k
400kHz
255k
300kHz
348k
200kHz
523k
–40
WITH SSFM
WITHOUT SSFM
1
3
5
7
FREQUENCY (MHz)
9
11
3932 F04
Figure 4. Typical Average Conducted Emissions
The attenuation varies depending on the chosen switching
frequency, the range of frequencies in which interference
is measured, and whether a test measures peak, quasipeak, or average emissions. The results of several other
such emission measurements are with select Typical
Applications.
Synchronizing Switching Frequency
Understanding the Current Limit
The switching frequency can also be synchronized to an
external clock connected to the SYNC/SPRD pin. The high
level of the external clock must be at least 1.4V, and the
frequency must be between 200kHz and 2MHz. The RT
resistor is still required in this case, and the resistance
should correspond to the frequency of the external clock.
If the external clock ever stops, the LT3932 will rely on
the RT resistor to set the frequency.
The choice of switching frequency should be made knowing that, although the maximum LED current that can be
programmed with the CTRL pin is 2A, the inductor current
may exceed 2A when the frequency is high and the output
voltage is low as in a short-circuit. This is because there
is a minimum on-time for which the SW pin will be driven
high during each switching period. The inductor current
increases during this time, and if the frequency is high and
the output voltage low, there may not be enough off-time
remaining in each switching period for the inductor current to decrease back to the level at which it started. In this
case, the net inductor current would increase with each
switching period regardless of the state of the CTRL pin.
Enabling Spread Spectrum Frequency Modulation
Connecting SYNC/SPRD to INTVCC will enable spread
spectrum frequency modulation (SSFM). The switching
frequency will vary from the frequency set by the RT resistor to 125% of that frequency. If neither synchronization
nor SSFM is required, connect SYNC/SPRD to GND.
As shown in Figure 4, enabling SSFM can significantly attenuate the electromagnetic interference that
the LT3932, like all switching regulators, emits at the
switching frequency and its harmonics. This feature is
designed to help devices that include the LT3932 perform
better in the various standard industrial tests related to
interference.
To prevent large inductor currents that would damage the
LT3932, the high-side switch is not turned on until the
inductor current decreases to less than the DA current
limit, which is approximately 2.3A. While the high-side
switch is off, the current is sensed through the low-side
switch. The peak inductor current may increase to 3.6A,
but the off-time and the switching period are extended
until the inductor current reaches equilibrium as shown
in Figure 5.
Rev C
For more information www.analog.com
15
LT3932/LT3932-1
APPLICATIONS INFORMATION
Selecting an Output Capacitor
DA CURRENT LIMIT
OUTPUT SHORTED
INDUCTOR
CURRENT
500mA/DIV
100µs/DIV
3932 F05
Figure 5. Extended Off-Time at Current Limit
The DA current limit is relevant only when the output
capacitor is shorted to GND. When instead the LED string
is shorted to GND, the voltage across the external PMOS
(described later) is high enough that the required on-time
is greater than the minimum on-time. This means that, in
spite of a shorted LED string, the inductor current remains
in regulation even at the highest switching frequency.
The inductor must be rated for the current limit regardless
of the intended application. Its value, in most applications,
should be selected such that the inductor current ripple is
not more than 25% of the maximum output current. When
that current is 2A, for example, the minimum inductance
can be calculated using the following equation:
VOUT
VIN(MAX)
•
VIN(MAX) – VOUT 1MHz
•
fSW
1V
However, for high output voltages even the above equation
would suggest an inductance value that is too small. For
stability, the LT3932 requires an inductance greater than:
L = 1µH •
VOUT 1MHz
•
1V
fSW
Choose the larger of the values given by these equations.
The manufacturers featured in Table 2 are recommended
sources of inductors.
Table 2. Inductor Manufacturers
MANUFACTURER
WEBSITE
Würth Elektronik
www.we-online.com
Coilcraft
www.coilcraft.com
16
COUT = 100µF •
1V 1MHz
•
VOUT fSW
However, applications may still be stable with more or
less capacitance, and more capacitance may improve LED
current waveforms for large PWM dimming ratios.
Use X7R or X5R ceramic capacitors as they retain their
capacitance better than other capacitor types over a wide
voltage and temperature range. Sources of quality ceramic
and electrolytic capacitors are listed in Table 3.
Table 3. Capacitor Manufacturers
Selecting an Inductor
L = 2µH •
Some applications are sensitive to ripple current in the
LED string. In those cases, a capacitor at the output will
absorb part of the inductor current ripple and thereby
reduce the LED current ripple. Typically, the value of this
capacitance is inversely proportional to the switching frequency and the output voltage as shown below:
MANUFACTURER
WEBSITE
Murata Manufacturing
www.murata.com
Garrett Electronics
www.garrettelec.com
AVX
www.avx.com
Nippon Chemi-Con
www.chemi-con.co.jp/e
Stabilizing the Regulation Loop
Stabilizing the regulation loop typically requires only a
capacitor CC connected from the VC pin to GND. For most
designs, values between 1nF and 10nF are suitable. When
using an output capacitor COUT larger than 10µF, as is
needed for large PWM dimming ratios, a resistor RC in
series with CC may be necessary. Larger values of COUT
require larger values of RC. See Typical Applications for
some examples.
Selecting and Placing the Input Capacitors
Although they do not impact stability, several capacitors
are necessary between VIN and GND to properly bypass
the input supply voltage. At least 10μF is required in
total, although it does not have to be composed entirely
of ceramic capacitors placed very close to the VIN pins.
However, it is important that a ceramic capacitor be placed
Rev C
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LT3932/LT3932-1
APPLICATIONS INFORMATION
as close as possible to each of the pairs of VIN pins (Pins
16 and 17 as well as 20 and 21) and their adjacent GND
pins as shown in Figure 6. These two capacitors should be
at least 1μF if possible. Because the SW pins lie between
the VIN pins, it is convenient to join the VIN pins using a
trace on the second layer of the circuit board.
Another 1μF capacitor should be placed very close to the
remaining VIN pin (Pin 26), which supplies the internal
control circuitry.
8
7
6
5
4
3
2
1
9
28
10
27
11
26
29
12
GND
VIN
25
13
24
14
23
15 16 17 18 19 20 21 22
1µF
CERAMIC
GND
1µF
VIN
VIN
GND
1µF
CERAMIC
GND
100nF
BST
SW
TOP LAYER
3932 F06
BOTTOM LAYER
Figure 6. Placement of Input Capacitors
Selecting a MOSFET for PWM Dimming
Pulse-Width-Modulation (PWM) dimming of the LED current is an effective way to control the brightness of the
light without varying its color. The brightness can also be
adjusted more accurately this way than by varying the
current level.
The LT3932 features a PWMTG driver that is intended
for a high-voltage PMOS switch in position to effectively
PWM dim a string of LEDs from the output capacitor and
current sense resistor. When the switch is open and the
string is disconnected, the LED current will be zero. In
contrast to a low-side NMOS driver, this feature eliminates
the need for a dedicated return path for the LED current
in automotive applications or other grounded chassis
systems.
The gate driver for this PMOS draws power through the
VOUT pin, which must be connected even in applications
that do not require PWM dimming. When the PWM pin
voltage is greater than 1.4V, the driver will pull the gate
of the PMOS to a maximum of 10V below the VOUT pin. If
VOUT is below 10V, the gate drive is necessarily reduced.
For constant current applications, leave PWMTG open,
connect the load directly after the current sense resistor,
and connect PWM to INTVCC. In these cases, analog dimming may be implemented with the CTRL pin.
The drain-source voltage rating of the chosen PMOS
should be greater than the maximum output voltage.
Typically the output voltage is a little higher than the sum
of the forward voltages of the LEDs in the string. However,
when the string is broken, the output voltage will begin
to increase due to the imbalance of inductor current and
load current. As described in detail later, the LT3932 will
not reduce the inductor current nor limit the output voltage until the FB pin voltage approaches 1V. Therefore, the
maximum output voltage is ultimately determined by the
resistor network between FB and VOUT.
In most applications, the gate-source voltage rating of
the PMOS should be at least 10V. The only exceptions
to this rule are applications for which the output voltage
is always less than 10V. The PWMTG driver will try to
pull the gate of the PMOS down to 10V below VOUT, but
it cannot pull the gate below GND. Therefore, when the
maximum output voltage is less than 10V, the PMOS gate
source voltage rating will be sufficient if it is merely equal
to or greater than the output voltage.
Finally, the drain current rating of the PMOS must exceed
the programmed LED current. Assuming this condition
and the conditions above are met, the only electrical
parameter to be considered is the on-resistance. Other
parameters such as gate charge are less important
because PWM dimming frequencies are typically too low
for efficiency to be affected noticeably by gate charging
loss or transition loss.
Rev C
For more information www.analog.com
17
LT3932/LT3932-1
APPLICATIONS INFORMATION
Table 4 lists recommended manufacturers of PMOS
devices.
Table 4. PMOS Manufacturers
MANUFACTURER
WEBSITE
Infineon
www.infineon.com
Vishay Intertechnology
www.vishay.com
NXP Semiconductors
www.nxp.com
Selecting an RP Resistor for Internal PWM Dimming
If the RP pin is tied to GND, an external pulse-width modulated signal at the PWM pin will control PWM dimming
of the LED load. The signal will enable the PWMTG driver
and turn on the external PMOS device when it is higher
than 1.4V.
However, the LT3932 is capable of PWM dimming even
when an external PWM signal is not available. In this case,
an internal PWM signal with frequency set by a resistor at
the RP pin and duty ratio set by a DC voltage at the PWM
pin will control the PWMTG driver. The RP resistor should
be one of the seven values listed in Table 5. For each of
these values, the PWM frequency is a unique ratio of the
switching frequency.
Table 5. Internal PWM Dimming Frequencies
RP
28.7k
47.5k
76.8k
118k
169k
237k
332k
2MHz
7.81kHz
3.91kHz
1.95kHz
977Hz
488Hz
244Hz
122Hz
SWITCHING FREQUENCY
1MHz
500KHz
3.91kHz
1.95kHz
1.95kHz
977Hz
977Hz
488Hz
488Hz
244Hz
244Hz
122Hz
122Hz
61Hz
61Hz
31Hz
250KHz
977Hz
488Hz
244Hz
122Hz
61Hz
31Hz
15Hz
When using the internal PWM signal, set the voltage at
the PWM pin between 1V and 2V. The PWMTG driver will
stay off if PWM is below 1V, and it will stay on if PWM
is above 2V. Between 1V and 2V there are 128 evenly
spaced thresholds corresponding to 128 discrete PWM
duty ratios from 0% to 100%. This range of 1V to 2V has
been chosen so that the PWM voltage may be set using
a potentiometer or a resistor network and the 2V reference available at the VREF pin. Place a small 1µF ceramic
capacitor near the PWM pin to ground.
18
There are a couple of exceptions to the PWM dimming
behavior described above. First, once initiated, the PWM
on-time will will last at least four switching cycles regardless of the signal at the PWM pin and the resistor at the
RP pin. This ensures that the current regulation loop has
enough time to reach equilibrium but still allows for a
5000:1 dimming ratio when the PWM frequency is 100Hz
and the switching frequency is 2MHz. The LT3932-1 does
not enforce this four-cycle limit so that dimming ratios
of 10000:1 or greater are possible in some applications.
Second, to avoid excessive start-up times, after the first
PWM pulse, PWMTG will stay on until the SS pin voltage
reaches 1.7V or the LED current has reached 10% of the
full-scale current.
PWM Dimming with Very Long Off Times
To enhance PWM dimming, the VOUT and VC pin voltages
are driven when the PWM pulse (internal or external) is
at a logic low to maintain the charge on the capacitors at
those pins. Consequently, when PWM returns to a logic
high state, the LED current can quickly reach the regulated
level even if PWM was low for a very long time. This feature facilitates machine vision applications which require
a synchronized strobe light or brief illuminating flashes
on short delay.
Monitoring LED Current
The ISMON pin provides an amplified and buffered monitor of the voltage between the ISP and ISN pins. The
gain of the internal amplifier is ten, and the speed is fast
enough to track the pulse-width modulated LED current.
However, as shown in Figure 7, the ISMON voltage can be
filtered with a resistor-capacitor network to monitor the
average LED current instead.
LT3932
ISMON
RMON
CMON
3932 F07
Figure 7. ISMON Filter Configuration
Rev C
For more information www.analog.com
LT3932/LT3932-1
APPLICATIONS INFORMATION
The resistor should be 1M. The capacitance can be as
large or small as needed without affecting the stability of
the internal amplifier. For example, when the PWM frequency is 200Hz, a 100nF capacitor combined with the
1M resistor would limit the ripple on ISMON to 1%.
VOUT
LT3932
RFB2
FB
RFB1
R
VOUT(MAX) = 1V • 1+ FB2
RFB1
3932 F08
Figure 8. FB Resistor Configuration
Selecting the FB Resistors
Two resistors should be selected to form a network
between the output voltage and the FB pin as shown in
Figure 8.
This network forms part of a voltage regulation loop when
FB is nearly 1V. In this case, the LT3932 will override
the programmed LED current to lower the output voltage
and limit FB to 1V. This resistor configuration therefore
determines the maximum output voltage.
Note that this voltage limit may be reached inadvertently
if it is set too close to the typical output voltage and the
output capacitor is too small. To avoid interference with
the current regulation, the feedback resistors should be
chosen such that FB is about 700mV when the LEDs are
conducting.
For a 12V string of LEDs, design for a maximum output
voltage of about 17V. Start with a 10k resistor for RFB1.
To calculate the value of RFB2, add 10k for every volt of
difference between FB (1V) and the maximum output voltage. In this case, the nearest standard 1% value for RFB2
would be 162k.
In this way, the LT3932 can also be configured as a voltage regulator instead of an LED driver. It will regulate the
output voltage near the programmed maximum as long as
the load current is less than the current level programmed
by CTRL.
Understanding FB Overvoltage Lockout
It is possible that the FB voltage can exceed the 1V limit.
If the output voltage is near the maximum when the LED
string opens, it may take too long for the feedback loop
to adjust the inductor current and avoid overcharging
the output. However, if the FB voltage exceeds the 1.05V
Overvoltage Lockout Threshold, the LT3932 will immediately stop switching and resume only when FB decreases
to 1V.
This threshold may be routinely exceeded when the
LT3932 is being operated as a voltage regulator and the
load current decreases rapidly. In this case, the pause in
switching limits the output overshoot and ensures that the
voltage is back in regulation as quickly as possible. For
safe operation, choose RFB2 and RFB1 values to ensure
the output voltage is not greater than VIN when the FB
voltage is 1.05V.
Open and Shorted LED Fault Detection and Response
The resistor network formed by RFB1 and RFB2 also defines
the criteria for two fault conditions with respect to the LED
string: short and open-circuits. For the LT3932, a shortcircuit is when FB is less than 200mV. An open-circuit
is when FB is greater than 950mV and simultaneously
the difference between ISP and ISN is less than 10mV
(the C/10 threshold). The latter condition ensures that the
output current is low (as it should be in an open-circuit)
not just that output voltage is high as it may be when the
LEDs are conducting a large current.
In both cases, a fault is indicated by an internal device
pulling the voltage at the FAULT pin low. There is nothing
internal that pulls this voltage high, so an external resistor between INTVCC and FAULT is necessary as shown in
Figure 9. This configuration allows multiple FAULT pins
and similar pins on other parts to be connected and share
a single resistor.
INTVCC
RFAULT
LT3932
FAULT
3932 F09
Figure 9. FAULT Resistor Configuration
Rev C
For more information www.analog.com
19
LT3932/LT3932-1
APPLICATIONS INFORMATION
Soft-Start and Fault Modes
The SS pin has two functions. First, it allows the user to
program the output voltage startup ramp rate. An internal
20μA current pulls up the SS pin to INTVCC. Connecting
an external capacitor CSS from the SS pin to GND, as
shown in Figure 10, will generate a linear ramp voltage.
The LT3932 regulates the FB pin voltage to track the SS
pin voltage until VOUT is high enough to drive the LED at
the commanded current level.
INTVCC
RSS
LT3932
SS
CSS
3932 F10
Figure 10. SS Capacitor and Resistor Configuration
The SS pin is also used as a fault timer. After a fault is
detected, an internal 1.25μA current sink will begin to
discharge the soft-start capacitor and lower the voltage
at the SS pin. When the voltage falls from 3.3V to 1.7V,
all switching will cease, but the SS pin will continue to
discharge. Switching will not resume until SS reaches
200mV. At this point, the 20μA current will recharge the
soft-start capacitor, and the LT3932 will try to switch
again. If the fault persists when SS returns to 1.7V, the
process will repeat as shown in Figure 11.
The charging rate of the soft-start capacitor is much faster
than the discharging rate, so while the fault persists, the
LT3932 will only attempt switching for a relatively short
part of the cycle before being interrupted. Although the
LT3932 can safely endure a short-circuit while continuously switching, this hiccup action saves power. The frequency of the hiccups is inversely proportional to CSS and
100nF yields about 8Hz.
The operating point of a voltage regulator supplying light
loads will frequently satisfy the criteria for an open-circuit,
and the hiccup behavior would therefore be very disruptive. So when the LT3932 is configured as a voltage regulator, a resistor RSS should be connected between INTVCC
and SS as shown in Figure 10.
The current that pulls down the SS pin during a fault is so
weak that if RSS is 1M, the voltage at the SS pin will never
reach 1.7V. Therefore, the LT3932 will not stop switching or start to hiccup. With this resistor, the LT3932 will
continue switching and rely on overvoltage and overcurrent protection to guarantee safe operation in the event
of open-circuits and short-circuits.
If the resistor is changed to 2M, then the SS pin may be
discharged to less than 1.7V, but not less than 200mV as
shown in Figure 12. The LT3932 will consequently cease
switching permanently until being reset by the EN/UVLO
pin or by powering off. Some applications may demand
this behavior so that short and open-circuits can be investigated manually before resuming normal operation.
This latch-off behavior is the third of three ways that the
LT3932 can be programmed to respond to faults—the
other two being continuous operation and the default hiccup behavior.
FAULT DETECTED
FAULT DETECTED
CONTINUOUS
RSS = 1MEG
SS
1V/DIV
SS
1V/DIV
FAULT CLEARED
10ms/DIV
3932 F11
Figure 11. Hiccup Response to Fault
20
LATCH–OFF
RSS = 2MEG
10ms/DIV
3932 F12
Figure 12. Latch-Off Response to a Fault
Rev C
For more information www.analog.com
LT3932/LT3932-1
APPLICATIONS INFORMATION
Dimming with External Drivers
Continuous operation in response to a fault also enables
the LT3932 to operate with external switches that shunt
some or all of the LEDs in the string. The LT3965 8-switch
Matrix LED Dimmer, for example, is designed to shunt
a changing combination of up to eight LEDs in a single
string with independent PWM dimming signals. See
Typical Applications for more details.
Programming the EN/UVLO Threshold
An external voltage source can be used to set the voltage
at the EN/UVLO pin to enable or disable the LT3932. The
LT3932 will stop switching, disable the PWMTG driver,
and reset the SS pin when the voltage at EN/UVLO drops
below 1.15V, but internal circuitry will continue drawing
current. Full shutdown is guaranteed when EN/UVLO is
below 300mV, and in full shutdown the LT3932 will draw
less than 2μA. For applications in which the level of the
source driving EN/UVLO changes slowly, 20mV of hysteresis has been added to the 1.15V enable threshold.
Alternatively, a resistor network can be placed between
VIN and EN/UVLO as shown in Figure 13. In this case,
EN/UVLO automatically falls below 1.15V and disables
VIN
REN2
LT3932
EN/UVLO
REN1
3932 F13
Figure 13. EN/UVLO Resistor Configuration
switching when VIN falls below a certain level, called the
Undervoltage Lockout (UVLO) threshold, which is defined
by resistors REN1 and REN2. Additionally, a 4μA current
is designed to flow into EN/UVLO when the pin voltage
is below the threshold. This current provides additional
hysteresis. To define the hysteresis (VHYST) and the UVLO
threshold (VUVLO) select REN1 and REN2 according to the
following equations:
REN2 =
VHYST VUVLO
–
4µA 480µA
REN1 =
1.15 • REN2
VUVLO – 1.15
For example, to program a 10V threshold with 1V of
hysteresis, use 226k and 29.4k for REN2 and REN1,
respectively.
Planning for Thermal Shutdown
The LT3932 automatically stops switching when the
internal temperature is too high. The temperature limit is
guaranteed to be higher than the operational temperature
of the part. During thermal shutdown, all switching is terminated, SS is forced low, and the LEDs are disconnected
using the PWMTG driver.
The exposed pad on the bottom of the package must be
soldered to a ground plane. Vias placed directly under the
package are necessary to dissipate heat. Following these
guidelines, the official four-layer demo board DC2286A
reduces thermal resistance θJA to 25°C/W, but with a compromised board design θJA could be 40°C/W or higher.
Rev C
For more information www.analog.com
21
LT3932/LT3932-1
APPLICATIONS INFORMATION
Designing the Printed Circuit Board
Note that large switched currents flow through the local
input capacitors and the VIN and GND pins. The loops
traveled by these currents should be made as small as
possible by keeping the capacitors as close as possible
to these pins. These capacitors, as well as the inductor,
should be placed on the same side of the board as the
LT3932 and connected on the same layer. Other large,
bulk input capacitors can be safely placed farther from
the chip and on the other side of the board.
Create a Kelvin ground network by keeping the ground
connection for all of the other components separate.
It should only join the ground for the input and output
capacitors and the return path for the LED current at the
exposed pad.
22
There are a few other aspects of the board design that
improve performance. An unbroken ground plane on
the second layer dissipates heat, but also reduces noise.
Likewise minimizing the area of the SW and BST nodes
reduces noise. The traces for FB and VC should be kept
short to lessen the susceptibility to noise of these high
impedance nodes. Matched kelvin connections from the
external current sense resistor RS to the ISP and ISN
pins are essential for current regulation accuracy. The
2.2μF INTVCC and VREF capacitors as well as the 22nF
BST capacitor should be placed as closely as possible to
their respective pins. A capacitor for the CTRL pin and,
when the internal dimming feature is used, the PWM pin,
can compensate for compromised layouts. Finally, a diode
with anode connected to ground and cathode to the drain
of the PWMTG MOSFET can protect that device from overvoltage caused by excessive inductance in the LED string.
Please refer to the demo board layout of the LT3932 for
an example of how to implement these recommendations.
Rev C
For more information www.analog.com
LT3932/LT3932-1
TYPICAL APPLICATIONS
2A LED Driver with Duty Cycle LED Current
D1
INTVCC
VIN
36V
VIN
ENABLE
CIN1
10µF
EN/UVLO
CREF
2.2µF
RFAULT
100k
FAULT
CBST
22nF
L1
150µH
SW
CIN2
2×1µF
3.3V
0V
3.3V
0V
CVCC
2.2µF
BST
VOUT
CTRL
LT3932
FB
PWM
VREF
GND
RFB2
287k
RFB1
10k
COUT
2×10µF
L1: WURTH 7447709151
M1: VISHAY Si4447ADY
RS: OHMITE LVK12R050D
COUT1: MURATA GRM32ER71H106K
D1: NEXPERIA BAT46WJ
2A MAX
ISP
RS
50mΩ
INTVCC
ISN
FAULT
PWMTG
SYNC/SPRD
SS
CSS
100nF
ISMON
RT RP
RT
523k
200kHz
M1
ISMON
LED1
VC
CC
10nF
LED8
3932 TA02
Digital CTRL 50%,
Digital PWM 100%
Digital CTRL 25%,
Digital PWM 100%
CTRL
5V/DIV
CTRL
5V/DIV
PWM
2V/DIV
PWM
2V/DIV
LED CURRENT
1A/DIV
LED CURRENT
1A/DIV
500ns/DIV
3932 TA02a
500ns/DIV
Digital CTRL 25%,
Digital PWM 50%
Digital CTRL 25%,
Digital PWM 25%
CTRL
5V/DIV
CTRL
5V/DIV
PWM
5V/DIV
PWM
5V/DIV
LED CURRENT
500mA/DIV
LED CURRENT
500mA/DIV
5ms/DIV
3932 TA02b
3932 G33
5ms/DIV
3932 TA02d
Rev C
For more information www.analog.com
23
LT3932/LT3932-1
TYPICAL APPLICATIONS
24V Voltage Regulator with Spread Spectrum
D1
INTVCC
VIN
29V TO 36V
CIN1
10µF
CIN2
2×1µF
VIN
REN2
576k
BST
SW
EN/UVLO
REN1
23.7k
VOUT
LT3932
FB
ISP
SYNC/SPRD
RSS
1M
CSS
10nF
PWMTG NOT USED
ISMON
RT
RP
VC
RC
20k
CC
10nF
RT
45.3k
2MHz
L1: COILCRAFT XAL5050-153
RS: OHMITE LVK12R050D
COUT: GRM32ER71H106K
D1: NEXPERIA BAT46WJ
3932 TA03
Efficiency
95
2.0
94
1.5
93
1.0
500
1000
1500
OUTPUT CURRENT (mA)
VOUT
1V/DIV
2.5
ON-CHIP LOSS (W)
EFFICIENCY (%)
Load Step Response (100mA to 1A)
3.0
EFFICIENCY (29VIN)
LOSS (29VIN)
EFFICIENCY (36VIN)
LOSS (36VIN)
0
COUT
2 × 10µF
VOUT
24V, 2A MAX
FAULT
SS
L1
15µH
RS
50mΩ
ISN
INTVCC
RFAULT
100k
CVCC
2.2µF
92
RFB2
10k
GND
CTRL
PWM
96
RFB1
226k
VREF
CREF
2.2µF
97
CBST
22nF
ILOAD
500mA/DIV
100µs/DIV
3932 TA03b
0.5
2000
3932 TA03a
24
Rev C
For more information www.analog.com
LT3932/LT3932-1
TYPICAL APPLICATIONS
D1
INTVCC
VIN
8V TO 36V
FB1
VIN
CIN2
4.7µF
50V
1206
CIN1
2x100nF
50V
0402
CIN3
33µF
50V
ELYT.
CIN4
1µF
50V
0603
CIN5
2x470nF
50V
0402
CREF
2.2µF
BST
CBST
22nF
REN2
232k
REN1
39.2k
L1
2.2µH
SW
EN/UVLO
VOUT
LT3932
VREF
RFB2
69.8k
FB
CTRL
PWM
RFB1
10k
GND
COUT
4.7µF
16V
0805
1A MAX
ISP
RS
100mΩ
ISN
INTVCC
RS: SUSUMU KRL1220D-M-R100-F
D1: NXP PMEG4010CEJ
FB1,2: WURTH 742792040
L1: WURTH 74438323022
M1: VISHAY Si2399DS
D1: NEXPERIA BAT46WJ
CVCC
10µF
PWMTG
FB2
SS
RT
RP
VC
RC
24.9k
CC
150pF
RT
45.3k
2MHz
CSS
1nF
ISMON, FAULT NOT USED
M1
SYNC/SPRD
CB2
100nF
16V
0402
LED1
LED2
D1
3932 TA07
CISPR25 Peak Radiated Emissions Test
80
70
70
60
60
AMPLITUDE (dBµV/m)
AMPLITUDE (dBµV)
CISPR25 Peak Conducted Emissions Test
80
50
40
30
20
10
0
–10
–20
0.1
10
FREQUENCY (MHz)
DC2286A DEMO BOARD
14V INPUT TO 6V OUTPUT AT 1A
50
40
30
20
10
0
CLASS 5 PEAK LIMIT
MEASURED EMISSIONS
AMBIENT NOISE
1
CLASS 5 PEAK LIMIT
MEASURED EMISSIONS
AMBIENT NOISE
–10
100
–20
200
3932 TA07a
0
100
200
300
400
500
600
FREQUENCY (MHz)
DC2286A DEMO BOARD
14V INPUT TO 6V OUTPUT AT 1A
CISPR25 Average Conducted Emissions Test
80
60
50
40
30
20
10
40
30
20
10
0
–10
–10
1
10
FREQUENCY (MHz)
DC2286A DEMO BOARD
14V INPUT TO 6V OUTPUT AT 1A
100
1000
3932 TA07b
50
0
–20
0.1
900
CLASS 5 AVERAGE LIMIT
MEASURED EMISSIONS
AMBIENT NOISE
70
AMPLITUDE (dBµV/m)
AMPLITUDE (dBµV)
60
800
CISPR25 Average Radiated Emissions Test
80
CLASS 5 AVERAGE LIMIT
MEASURED EMISSIONS
AMBIENT NOISE
70
700
200
3932 TA07c
–20
0
100
200
300
400
500
600
FREQUENCY (MHz)
DC2286A DEMO BOARD
14V INPUT TO 6V OUTPUT AT 1A
700
800
900
1000
3932 TA07d
Rev C
For more information www.analog.com
25
LT3932/LT3932-1
TYPICAL APPLICATIONS
2A LED Driver with Internal PWM Dimming
D1
INTVCC
VIN
12V TO 24V
VIN
BST
REN2
274k
CIN2
2×1µF
REN1
29.4k
RFB2
110k
LT3932
VREF
CREF
2.2µF
COUT
100µF
RFB1
10k
CTRL
RREF2
100k
PWM
ISP
RS
50mΩ
ISN
RFAULT
100k
FAULT
2A MAX
GND
INTVCC
CVCC
2.2µF
L1: WURTH 74404064082
M1: INFINEON IRF7204
RS: OHMITE LVK12R050D
COUT: AVX TPME107M020R0035
D1: NEXPERIA BAT46WJ
VOUT
FB
RREF1
100k
L1
8.2µH
SW
EN/UVLO
CIN1
10µF
CBST
22nF
PWMTG
FAULT
ISMON
M1
ISMON
LED1
SYNC/SPRD
SS
CSS
100nF
RT RP
RT
45.3k
2MHz
VC
RP
28.7k
7.8kHz
LED2
RC
162k
LED3
CC
10nF
3932 TA06
Internal PWM Dimming
SW
20V/DIV
SW
20V/DIV
PWMTG
10V/DIV
PWMTG
10V/DIV
IL
1A/DIV
IL
1A/DIV
ILED
1A/DIV
ILED
1A/DIV
PWM = 1.078V
26
Internal PWM Dimming
2µs/DIV
3932 TA06a
PWM = 1.132V
2µs/DIV
3932 TA06b
Rev C
For more information www.analog.com
LT3932/LT3932-1
TYPICAL APPLICATIONS
Multiple String Drivers from Single Boosted 36V Input
VBUCK
36V, 5A MAX
L0
4.2µH
D0
M0
VIN
GATE
SHDN/UVLO
SENSE
R0
4mΩ
SYNC
RSHDN1
12.1k
LT3757
GND
RFB1
348k
COUT
35µF
50V
+
VIN
6V MIN FOR OPERATION
10V MIN FOR FULL CURRENT
CIN
10µF
RSHDN2
48.7k
RT
FBX
COUT
5µF
RFB2
16.2k
L0: WÜRTH 7443630420
M0: INFINEON BSZ040N04LS
R0: VISHAY WSLP25124L000F
D0: ONSEMI MBR1240MFS
INTVCC
SS
VC
RC
10k
CC
10nF
CVCC
4.7µF
CSS
100nF
RT
30.9k
400MHz
+2 LT3932 (1A EACH)
D2
D1
INTVCC
INTVCC
CIN1
10µF
VIN
CIN2
2×1µF
BST
SW
ENABLE1
3.3V
0V
CREF
2.2µF
EN/UVLO
PWM
RCTRL2
49.9k
RCTRL1
30.1k
3.3V
0V
VOUT
LT3932
VREF
CTRL
FB
GND
CSS
100nF
CIN2
2×1µF
CIN1
10µF
RFB1
110k
RFB2
10k
VIN
BST
SW
ENABLE2
3.3V
0V
COUT
4.7µF
EN/UVLO
VOUT
LT3932
PWM
1A MAX
GND
CTRL
PWMTG
ISMON
RT
RP
VC
RT
45.3k
2MHz
L1: WURTH 74437336100
M1: INFINEON IRF7204
RS1: OHMITE LVK12R050D
COUT: MURATA GRM32ER714475K
D1: NEXPERIA BAT46WJ
RFB1
287k
RFB2
10k
L2
15µH
COUT
4.7µF
1A MAX
M1
RS2
100mΩ
SYNC/SPRD
RFAULT
100k
CSS
100nF
ISN
INTVCC
PWMTG
RT
M2
ISMON
FAULT
SS
CVCC
2.2µF
CC
10nF
CBST
22nF
ISP
3.3V
0V
ISN
FAULT
FB
VREF
CREF
2.2µF
RS1
50mΩ
INTVCC
SS
CVCC
2.2µF
L1
10µH
ISP
SYNC/SPRD
RFAULT
100k
CBST
22nF
RP
VC
RT
45.3k
2MHz
L2: COILCRAFT LPS8045B-153
M2: VISHAY Si2319CDS
RS2: OHMITE LVK12R100D
COUT: MURATA GRM32ER71H475K
D2: NEXPERIA BAT46WJ
8×
LED
CC
10nF
3932 TA05
Rev C
For more information www.analog.com
27
LT3932/LT3932-1
PACKAGE DESCRIPTION
UFD Package
28-Lead Plastic QFN (4mm × 5mm)
(Reference LTC DWG # 05-08-1712 Rev C)
0.70 ±0.05
4.50 ±0.05
3.10 ±0.05
2.50 REF
2.65 ±0.05
3.65 ±0.05
PACKAGE OUTLINE
0.25 ±0.05
0.50 BSC
3.50 REF
4.10 ±0.05
5.50 ±0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 ±0.10
(2 SIDES)
R = 0.05
TYP
0.75 ±0.05
PIN 1 NOTCH
R = 0.20 OR 0.35
× 45° CHAMFER
2.50 REF
R = 0.115
TYP
27
28
0.40 ±0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
5.00 ±0.10
(2 SIDES)
3.50 REF
3.65 ±0.10
2.65 ±0.10
(UFD28) QFN 0816 REV C
0.200 REF
0.00 – 0.05
0.25 ±0.05
0.50 BSC
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGHD-3).
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
28
Rev C
For more information www.analog.com
LT3932/LT3932-1
REVISION HISTORY
REV
DATE
DESCRIPTION
A
02/18
Added LT3932-1 to data sheet.
1
Added 10000:1 PWM dimming ratio for LT3932-1 with supporting text in Features and Description.
1
Added machine vision systems to Applications.
1, 22, 24, 25, 28
On Figure, added Schottky Diode from INTVCC to BST pin, changed boost capacitor from 100nF to 22nF.
1, 12, 22, 23, 24,
25, 26, 28
Changed θJA from 43°C/W to 25°C/W (based on demo board measurement).
2
Sense voltage VCTRL changed from 2V to 1.5V. ISN pin current VISN value changed from 24V to 23.9V.
3
LED Current and LED Voltage Limit Graphs y-axis corrected to mV units.
7
DA Limit graph retitled to “DA Current Limit”, input step changed from 20V upper limit to 25V on Input Voltage
Transient Response graph.
9
Added additional BST pin description text; corrected BST capacitor value from 100nF to 22nF.
11
DA Current Limit added to Block Diagram.
12
Text added to describe DA Current Limit.
15
Added LT3932-1 text regarding four-cycle limit and machine vision usage.
18
Added text regarding θJA equals 25°C/W using DC2286 demo board, corrected boost capacitor value.
21
Corrected Typical Application figure, reduced VOUT from 30V to 24V, changed digital CTRL 50% graph y-axis
from 5A/DIV to 5V/DIV.
22
Added Diode D1: Nexperia BAT46WJ.
C
07/18
05/21
1
Relabeled Soft-Start pin from S to SS.
Add new Efficiency graph.
B
PAGE NUMBER
23
22, 24, 25, 26, 28
Three revised UVLO graphs in Typical Performance Characteristics.
5
EN/UVLO description; Changed text from “A resistor network between this pin and GND” to “. . . this pin and VIN.”
10
VREF description; Changed buffered reference drive current from 2mA to 1mA.
10
Corrected RSS from 1mΩ to 1M.
24
Changed Inductor L1 value from 7438323022 to 74438323022.
25
Increased Inductor value from 8.2µH to 10µH.
27
Changed Inductor; New Product Number; changed L1 From 7440463082 to 74437336100.
27
Added AEC-Q100 statement.
1
Added Automotive Products in Order Information table.
2
Rev C
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
subject to change without notice. No license For
is granted
implication or
otherwise under any patent or patent rights of Analog Devices.
more by
information
www.analog.com
29
LT3932/LT3932-1
TYPICAL APPLICATION
700mA Matrix LED Driver with Individual Dimming for 6 LEDs
D1
INTVCC
VIN
32V
VIN
BST
REN2
249k
CIN1
10µF
50V
CIN2
2x1µF
50V
0402
VOUT
D7
RFB2
267k
LT3932
VREF
RFB1
10k
RREF2
110k
GND
CTRL
REN4
249k
RDD
100k
700mA
VIN
EN/UVLO
REN3
10.7k
D8
D7
ISP
RREF1
105k
VDD
COUT
22nF
FB
CREF
2.2µF
L1: WURTH 74437349330
D1-7: NXP PMEG4010CEJ
RS: OHMITE LVK12R100DER
D1: NEXPERIA BAT46WJ
L1
33µH
SW
EN/UVLO
REN1
10.2k
CBST
22nF
S8
RS
100mΩ
S7
LT3965
ISN
D6
D6
PWM
START
SYNC/SPRD
SS
RPWM
10k
RSS
1M
CSS
10nF
VDD
RSDA
10k
S6
INTVCC
CVCC
2.2µF
LED6
RT
RP
RT
287k
350kHz
D2
VC
D2
LED2
CC
330pF
S2
D1
D1
LED1
S1
RSCL
10k
RALERT
10k
SDA
SCL
CVDD
2.2µF
ALERT
PWMCLK
350kHz
ADDR1-4 GND LEDREF
3.3V
0V
PWMTG, FAULT, AND ISMON NOT USED
3932 TA04
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
LT3922
40V, 2A, 2MHz, Synchronous Boost LED Driver
VIN: 2.7V to 40V, VOUT(MAX) = 40V, 5000:1 True Color PWM™ Dimming,
5mm × 5mm QFN and TSSOP-28E
LT3965
8-Switch Matrix LED Dimmer
VIN: 8V to 60V, Digital Programmable 256:1 PWM Dimming, I2C Multidrop Serial
Interface TSSOP-28E Package
LT3956
80V, 3.3A 1MHz, Step-Up/Down LED Driver
VIN: 4.5V to 80V, VOUT(MAX) = 80V, 3000:1 True Color PWM Dimming,
5mm × 6mm QFN
LT3474
36V, 1A, 2MHz, Step-Down LED Driver
VIN: 4V to 36V, VOUT(MAX) = 13.5V, 400:1 True Color PWM Dimming, TSSOP-16E
LT3475
Dual 36V, 1.5A, 2MHz, Step-Down LED Driver
VIN: 4V to 36V, VOUT(MAX) = 13.5V, 3000:1 True Color PWM Dimming, TSSOP-20E
LT3476
Quad 36V, 1.5A, 2MHz, Step-Up/Down LED Driver VIN: 2.8V to 16V, VOUT(MAX) = 36V, 1000:1 True Color PWM Dimming,
5mm × 7mm QFN
LT3477
42V, 3A, 3.5MHz, Step-Up/Down LED Driver
VIN: 2.5V to 25V, VOUT(MAX) = 40V, 4mm × 4mm QFN and TSSOP-20E
LT3478
42V, 4.5A, 2.5MHz, Step-Up/Down LED Driver
VIN: 2.5V to 26V, VOUT(MAX) = 42V, 3000:1 True Color PWM Dimming, TSSOP-16E
LTM8040
36V, 1A, μModule, Step-Down LED Driver
VIN: 4V to 36V, VOUT(MAX) = 13V, 250:1 True Color PWM Dimming,
9mm × 15mm × 4.32mm LGA
LTM8042
36V, 1A, μModule, Step-Up/Down LED Driver
VIN: 3V to 30V, VOUT(MAX) = 36V, 3000:1 True Color PWM Dimming,
9mm × 15mm × 2.82mm LGA
LT3757
40V, 1MHz, Step-Up Controller
VIN: 2.9V to 40V, Positive and Negative Output Voltages,
3mm × 3mm DFN and MSOP-10E
30
Rev C
05/21
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For more information www.analog.com
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