LT3965/LT3965-1
8-Switch Matrix LED Dimmer
FEATURES
DESCRIPTION
Eight Independent 17V 330mΩ NMOS Switches
n Independent On/Off/Dimming Control of 1 to 4 LEDs
for Each Switch
n I2C Multidrop Serial Interface with Programmable
Open LED and Shorted LED Fault Reporting
n 16 Unique I2C Addresses
n V
DD Range: 2.7V to 5.5V and VIN Range: 8V to 60V
n Digital Programmable 256:1 PWM Dimming
n Fade Transition Between PWM Dimming States
n Optional Internal Clock Generator or External Clock
Source for PWM Dimming
n Open LED Overvoltage Protection
n Flicker Free PWM Dimming
n AEC-Q100 Qualified for Automotive Applications
The LT®3965/LT3965-1 is an LED bypass switching
device for dimming individual LEDs in a string using a
common current source. It features eight individually
controlled floating source 17V/330mΩ NMOS switches.
The eight switches can be connected in parallel and/or
in series to bypass current around one or more LEDs in
a string. The LT3965 is initialized with all switches off
(LEDs on), and the LT3965-1 is initialized with all switches
on (LEDs off)The LT3965/LT3965-1 uses the I2C serial
interface to communicate with the microcontroller. Each
of the eight channels can be independently programmed
to bypass the LED string in constant on or off, or PWM
dimming with or without fade transition. Using the fade
option provides 11-bit resolution logarithmic transition
between PWM dimming states. The LT3965/LT3965-1
provides an internal clock generator and also supports
external clock source for PWM dimming. The LT3965/
LT3965-1 reports fault conditions for each channel such
as open LED and shorted LED. The four address select
pins allow 16 LT3965/LT3965-1 devices to share the I2C
bus. The device is available in a 28-lead TSSOP package.
n
APPLICATIONS
Automotive LED Headlight Clusters
Large LED Displays
n Automated Camera Flash Equipment
n RGBW Color Mixing Lighting
n
n
All registered trademarks and trademarks are the property of their respective owners.
TYPICAL APPLICATION
Matrix LED Dimmer Powered by a Buck Mode LED Driver
750Ω
0.5Ω
VIN
40V
BIAS UVLO DETECT
Q2
Q1
BIAS
1k
49.9k
M1
1k
LED+
D4
BIAS
LED+
1µF
100V
D2
VIN
ISP
EN/UVLO
INTVCC
2.2nF
SYNC
LT3955
VREF
VMODE
FB
500mA
VLED
26V
GNDK
PGND
RT
28.7k
375kHz
DIM/SS
0.1µF
SW
VC
0.01µF
D1
IN4148
DRN8
SRC8
DRN7
SRC7
DRN6
SRC6
DRN5
SRC5
DRN4
SRC4
DRN3
SRC3
DRN2
SRC2
DRN1
1µF
GND
CTRL
1µF
50V
D3
0.1µF
100V
PWMOUT
PWM
28k
Q3
EN/UVLO
9.09k
20k
ISN
1k
L1
33µH
D5
LED–
SRC1
VIN
0.1µF
LT3965/
LT3965-1
VCC
5V
VDD
10k
10k
10k
SDA
SDA
SCL
SCL
ALERT
EN/UVLO
RTCLK
ALERT
EN/UVLO
28k
500Hz DIMMING FREQUENCY
ADDR1
ADDR2
ADDR3
ADDR4
GND
LEDREF
L1: WURTH 744066330
D1: DFLS260
D2, D3: CMSD6263S 2 IN 1 PACKAGE
D4, D5: PMEG6010CEH
M1: VISHAY Si7309DN
Q1, Q3: ZETEX FMMT593
Q2: ZETEX FMMT493
3965 TA01
Rev. B
Document Feedback
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1
LT3965/LT3965-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
VIN.............................................................................60V
VIN-SRC[8:1]...........................................................–0.3V
DRN[8:1]....................................................................60V
SRC[8:1].....................................................................60V
LEDREF......................................................................60V
DRN[8:1]-SRC[8:1] (Each Channel).................–0.3V, 25V
EN/UVLO....................................................................12V
VDD..............................................................................6V
SDA, SCL, ALERT............................. –0.3V to VDD + 0.3V
RTCLK..........................................................................6V
ADDR[4:1]....................................................................6V
Operating Junction Temperature Range (Note 2)
LT3965E/LT3965E-1/LT3965I/LT3965I-1.–40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
TOP VIEW
DRN8
1
28 SRC8
VIN
2
27 DRN7
EN/UVLO
3
26 SRC7
ALERT
4
25 DRN6
SCL
5
24 SRC6
SDA
6
23 DRN5
VDD
7
RTCLK
8
ADDR1
29
GND
22 SRC5
21 DRN4
9
20 SRC4
ADDR2 10
19 DRN3
ADDR3 11
18 SRC3
ADDR4 12
17 DRN2
LEDREF 13
16 SRC2
SRC1 14
15 DRN1
FE PACKAGE
28-LEAD PLASTIC TSSOP
θJC = 10°C/W
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
LT3965EFE#PBF
LT3965EFE#TRPBF
LT3965FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3965EFE-1#PBF
LT3965EFE-1#TRPBF
LT39651FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3965IFE#PBF
LT3965IFE#TRPBF
LT3965FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3965IFE-1#PBF
LT3965IFE-1#TRPBF
LT39651FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3965EFE#WPBF
LT3965EFE#WTRPBF
LT3965FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3965IFE#WPBF
LT3965IFE#WTRPBF
LT3965FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3965EFE-1#WPBF
LT3965EFE-1#WTRPBF
LT39651FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3965IFE-1#WPBF
LT3965IFE-1#WTRPBF
LT39651FE
28-Lead Plastic TSSOP
–40°C to 125°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.
Rev. B
2
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LT3965/LT3965-1
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 40V, VDD = EN/UVLO = 5V, LEDREF = 3V, SRC = 0V, ADDR[4:1] not
connected, unless otherwise noted.
PARAMETER
CONDITIONS
VDD Input Supply Voltage
UNITS
1.3
1.8
mA
0.1
1
8
µA
µA
60
V
1
1.4
mA
All Channels VOTH[1:0] = VSTH[1:0] = “11”, LED OFF
2.5
3.3
mA
All Channels VOTH[1:0] = “11”, VSTH[1:0] = “00”,
LED ON
1.5
2
mA
EN/UVLO < 1.15V
0.1
1
µA
VIN – 3V
V
VDD Shutdown IQ
EN/UVLO < 0.4V
EN/UVLO = 1.15V
VIN Operating Voltage
All Channels VOTH[1:0] = VSTH[1:0] = “00” (Note 3)
VIN Operating IQ (Channel Not Switching)
All Channels VOTH[1:0] = VSTH[1:0] = “00”, LED ON
l
DRN[8:1] Operating Voltage
l
SRC[8:1] Operating Voltage
l
Channel LED Is On (Channel Switch Is Off)
Channel LED Is Off (Channel Switch Is On)
2.7
MAX
V
VDD Operating IQ
Current Out of SRC[8:1] Pins (Each Channel)
TYP
5.5
l
SCL = SDA =5V (I2C Bus Idle), RTCLK = 28k
VIN Shutdown IQ
MIN
8
9
40
l
l
Switch On-Resistance
VIN – 7.1V
V
13
55
µA
µA
330
Switch Leakage Current
DRN = 16V, VOTH[1:0] = 11
Switch Transition Time (tr/tf)
DRN to 10V through 50Ω Resistor
DRN[8:1] to SRC[8:1] Crowbar Protection
Clamp Voltage
LED or Switch Bypass Current is 500mA
Response Time from SW Crowbar Protection
to SW Secure Protection
mΩ
5
µA
0.5
0.65
µs
l
22
25
V
LED or Switch Bypass Current is 500mA
l
1
1.6
µs
Programmable Open LED Threshold (VOTH)
VOTH[1:0] = “00” (Note 3)
VOTH[1:0] = “01” (LT3965-1 POR State)
VOTH[1:0] = “10”
VOTH[1:0] = “11” (LT3965 POR State)
l
l
l
l
4.25
8.5
12.75
17
4.5
9
13.5
18
4.75
9.5
14.25
19
V
V
V
V
Programmable Shorted LED Threshold (VSTH)
for LEDREF = 0V
VSTH[1:0] = “00” (Note 3)
VSTH[1:0] = “01”
VSTH[1:0] = “10”
VSTH[1:0] = “11”
l
l
l
l
0.85
0.85
0.85
0.85
1
1
1
1
1.15
1.2
1.25
1.3
V
V
V
V
Programmable Shorted LED Threshold (VSTH)
for LEDREF = 3V
VSTH[1:0] = “00” (Note 3)
VSTH[1:0] = “01”
VSTH[1:0] = “10”
VSTH[1:0] = “11”
l
l
l
l
0.85
3.8
6.7
9.6
1
4
7
10
1.15
4.2
7.3
10.4
V
V
V
V
Programmable Shorted LED Threshold (VSTH)
for LEDREF ≥ 4V
VSTH[1:0] = “00” (Note 3)
VSTH[1:0] = “01”
VSTH[1:0] = “10”
VSTH[1:0] = “11”
l
l
l
l
0.85
4.7
8.5
12.3
1
5
9
13
1.15
5.3
9.5
13.7
V
V
V
V
l
1.15
1.24
1.35
EN/UVLO Threshold Voltage Falling
0.35
EN/UVLO Threshold Voltage Rising Hyst.
10
EN/UVLO Input Bias Current Low
EN/UVLO = 1.15V
EN/UVLO Input Bias Current High
EN/UVLO = 1.33V
2.2
V
mV
2.7
3.2
µA
10
100
nA
195
500
1090
220
550
1250
Hz
Hz
Hz
RTCLK Programmable Internal Oscillator or External Clock Source
LED PWM Dimming Frequency
(=RTCLK Programmed Oscillator
Frequency/2048 or External Clock
Frequency/2048)
RTCLK = 80.6kΩ
RTCLK = 28kΩ
RTCLK = 10kΩ
l
l
l
170
450
950
Rev. B
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3
LT3965/LT3965-1
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 40V, VDD = EN/UVLO = 5V, LEDREF = 3V, SRC = 0V, ADDR[4:1] not
connected, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
RTCLK Output Voltage (Using Internal
Oscillator)
RTCLK = 28kΩ
0.83
0.88
0.93
V
0.4
V
2.5
MHz
RTCLK Input Low Threshold (RTVIL)
l
RTCLK Input High Threshold (RTVIH)
l
1.5
V
RTCLK Input Clock Frequency
RTCLK Input Clock Pulse Width High (TRTH)
100
ns
RTCLK Input Clock Pulse Width Low (TRTL)
100
ns
RTCLK Input Clock Ramp Time between RTVIL
and RTVIH (TRTRAMP)
TRTL = 10µs
2.3
µs
0.25VDD
V
Address Select
ADDR[4:1] Input Low
l
ADDR[4:1] Input High
l
0.75VDD
300
ADDR[4:1] Pull-Up Resistance to VDD
V
500
700
kΩ
0.3
0.4
V
0.1
µA
0
4
V
–100
100
nA
Alert Status Output
ALERT Output Low Voltage
IALERT = 3mA
ALERT Output High Leakage Current
ALERT = 5.5V
External LED Reference Voltage for Shorted LED Detection
LEDREF Input Linear Range
LEDREF Input Bias Current
0V ≤ LEDREF ≤ 4V
I2C Port (See Note 5 for I2C Timing Diagram)
SDA and SCL Input Threshold Rising
l
SDA and SCL Input Threshold Falling
l
SDA and SCL Input Hysteresis
l
SDA and SCL Input Current
SDA = SCL = 0V to 5.5V
SDA Output Low Voltage
ISDA = 3mA
0.7VDD
V
0.25VDD
0.05VDD
–250
V
V
250
nA
l
0.4
V
SCL Clock Operating Frequency
l
400
kHz
(Repeated) Start Condition Hold Time (tHD_STA)
l
0.6
μs
Repeated Start Condition Set-Up Time
(tSU_STA)
l
0.6
µs
Stop Condition Setup Time (tSU_STO)
l
0.6
μs
Data Hold Time Output (tHD_DAT(O))
l
0
Data Hold Time Input (tHD_DAT(I))
l
0
ns
Data Set-Up Time (tSU_DAT)
l
100
ns
SCL Clock Low Period (tLOW)
l
1.3
µs
SCL Clock High Period (tHIGH)
l
0.6
μs
900
ns
Data Rise Time (tr)
CB = Capacitance of One BUS Line (pF) (Note 4)
20 + 0.1CB
300
ns
Data Fall Time (tf)
CB = Capacitance of One BUS Line (pF) (Note 4)
20 + 0.1CB
300
ns
50
ns
1.3
µs
Input Spike Suppression Pulse Width (tSP)
Bus Free Time (tBUF)
l
Rev. B
4
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LT3965/LT3965-1
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: The LT3965E/LT3965E-1 is guaranteed to meet performance
specifications from the 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 LT3965I/LT3965I-1 is guaranteed over the full –40°C to
125°C operating junction temperature range. High junction temperatures
degrade operating lifetimes. Operating lifetime is derated at junction
temperatures greater than 125°C.
Note 3: VOTH[1:0] and VSTH[1:0] register bits are set by LT3965/LT3965-1
I2C commands. VOTH/VSTH programmed by VOTH[1:0]/VSTH[1:0] refer to
the open/shorted LED threshold between DRN and SRC of a channel. For
a channel, VIN > VSRC + VOTH + 2.5V is required for accurate open LED
detection.
Note 4: Rise and fall times are measured at 30% and 70% levels.
Note 5: I2C interface timing diagram.
SDA
tSU,DAT
tSU,STA
tHD,DATO
tHD,DATI
tSP
tHD,STA
tSP
tBUF
tSU,STO
3965 TD
SCL
tHD,STA
REPEATED START
CONDITION
REPEATED START
CONDITION
TYPICAL PERFORMANCE CHARACTERISTICS
1.8
VIN Quiescent Current
vs Temperature
2.8
VDD = 5V
2.6
VIN, IQ (mA)
VDD, IQ (mA)
1.2
ALL SWITCHES ARE OFF
2.0
1.8
VOTH[1:0] = 11, VSTH[1:0] = 00,
SWITCHES ARE OFF
1.6
1.4
1.0
VOTH[1:0] = VSTH[1:0] = 00,
SWITCHES ARE OFF
1.2
1.0
0
1.27
VOTH[1:0] = VSTH[1:0] = 11,
SWITCHES ARE ON
2.2
ALL SWITCHES ARE ON
1.4
EN/UVLO Threshold
vs Temperature
VIN = 40V, LEDREF = 3V
2.4
1.6
0.8
–50 –25
TA = 25°C, unless otherwise noted.
25 50 75 100 125 150
TEMPERATURE (°C)
0.8
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3965 G01
3965 G02
1.26
EN/UVLO THRESHOLD (V)
VDD Quiescent Current
vs Temperature
START
CONDITION
STOP
CONDITION
1.25
RISING
1.24
FALLING
1.23
1.22
1.21
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3965 G03
Rev. B
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5
LT3965/LT3965-1
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, unless otherwise noted.
RTCLK vs PWM Dimming
Frequency
EN/UVLO Hysteresis Current
vs Temperature
3.0
PWM Dimming Frequency
vs Temperature
160
540
RTCLK = 28k
120
2.6
RTCLK (kΩ)
EN/UVLO CURRENT (µA)
2.8
DIMMING FREQUENCY (Hz)
140
2.4
100
80
60
40
2.2
520
500
480
20
2.0
–50 –25
0
0
25 50 75 100 125 150
TEMPERATURE (°C)
0
200
400
600
800
DIMMING FREQUENCY (Hz)
3965 G04
Shorted LED Threshold Falling vs
LEDREF
600
14
350
300
SHORTED LED THRESHOLD (V)
500
TRANSITION TIME (ns)
SWITCH ON-RESISTANCE (mΩ)
550
400
550
RISING
500
FALLING
450
250
200
–50 –25
0
400
–50 –25
25 50 75 100 125 150
TEMPERATURE (°C)
0
1.15
1.10
1.05
1.00
–50 –25
6
VSTH[1.0] = 01
4
VSTH[1.0] = 00
2
0
1
4.8
SRC = 0V
4.6
4.5
4.4
4.3
4.2
4
5
Open LED Threshold Rising vs VIN,
Temperature for VOTH[1:0] = 01
10
–50°C
25°C
150°C
4.7
2
3
LEDREF (V)
3965 G09
OPEN LED THRESHOLD (V)
1.35
4.9
OPEN LED THRESHOLD (V)
5.0
1.20
VSTH[1.0] = 10
8
Open LED Threshold Rising vs VIN,
Temperature for VOTH[1:0] = 00
1.40
VSTH[1.0] = 11
10
3965 G08
Switch Open LED Protection
Response Time vs Temperature
1.25
VIN – SRC > 15V
12
0
25 50 75 100 125 150
TEMPERATURE (°C)
3965 G07
1.30
25 50 75 100 125 150
TEMPERATURE (°C)
3965 G06
Switching Transition Time
vs Temperature
450
0
3965 G05
Switch On-Resistance
vs Temperature
RESPONSE TIME (µs)
460
–50 –25
1000
SRC = 0V
–50°C
25°C
150°C
9
8
7
4.1
0
25 50 75 100 125 150
TEMPERATURE (°C)
3965 G10
4.0
5 10 15 20 25 30 35 40 45 50 55 60
VIN VOLTAGE (V)
3965 G11
6
5 10 15 20 25 30 35 40 45 50 55 60
VIN VOLTAGE (V)
3965 G12
Rev. B
6
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LT3965/LT3965-1
TYPICAL PERFORMANCE CHARACTERISTICS
18
OPEN LED THRESHOLD (V)
12.0
10.5
9.0
–50°C
25°C
150°C
7.5
6.0
16
14
12
10
6
5 10 15 20 25 30 35 40 45 50 55 60
VIN VOLTAGE (V)
3965 G13
4.1
4.0
3.9
3.8
7.5
6.5
6.0
3965 G15
Shorted LED Threshold Falling vs
VIN, Temperature for VSTH[1:0] = 11
11
SWITCH IS ON
30
20
10
SWITCH IS OFF
25 50 75 100 125 150
TEMPERATURE (°C)
LEDREF = 3V
SRC = 0V
10
9
8
7
6
10 15 20 25 30 35 40 45 50 55 60
VIN VOLTAGE (V)
3.0
RTCLK INPUT CLOCK FREQUENCY (MHz)
50
CURRENT OUT OF SRC (µA)
3965 G15
RTCLK Input Clock Frequency vs
Fading Time
40
5 10 15 20 25 30 35 40 45 50 55 60
VIN VOLTAGE (V)
–50°C
25°C
150°C
15
20
25
3965 G17
Current Out of SRC Pin vs
Temperature
0
–50°C
25°C
150°C
LEDREF = 3V
SRC = 0V
7.0
5.5
5 10 15 20 25 30 35 40 45 50 55 60
VIN VOLTAGE (V)
0
–50 –25
0.9
Shorted LED Threshold Falling vs
VIN, Temperature for VSTH[1:0] = 10
SHORTED LED THRESHOLD (V)
SHORTED LED THRESHOLD (V)
–50°C
25°C
150°C
LEDREF = 3V
SRC = 0V
1.0
0.8
5 10 15 20 25 30 35 40 45 50 55 60
VIN VOLTAGE (V)
55
PWM DIMMING END POINTS
0.4% AND 99.6%
2.6
50
30 35 40 45
VIN VOLTAGE (V)
50
55
60
3965 G18
RTCLK vs Fading Time
PWM DIMMING END POINTS
0.4% AND 99.6%
45
2.2
40
1.8
FADING UP
1.4
35
FADING DOWN
30
25
FADING UP
20
1.0
FADING DOWN
15
0.6
0.2
300
–50°C
25°C
150°C
LEDREF = 3V
SRC = 0V
1.1
3965 G14
Shorted LED Threshold Falling vs
VIN, Temperature for VSTH[1:0] = 01
4.2
–50°C
25°C
150°C
8
SHORTED LED THRESHOLD (V)
OPEN LED THRESHOLD (V)
13.5
1.2
SRC = 0V
SHORTED LED THRESHOLD (V)
20
SRC = 0V
Shorted LED Threshold Falling vs
VIN, Temperature for VOTH[1:0] = 00
Open LED Threshold Rising vs VIN,
Temperature for VOTH[1:0] = 11
RTCLK (kΩ)
15.0
Open LED Threshold Rising vs VIN,
Temperature for VOTH[1:0] = 10
TA = 25°C, unless otherwise noted.
10
450
750
600
900
FADING TIME (ms)
1050
3965 G19
1200
3965 G20
5
300
450
750
600
900
FADING TIME (ms)
1050
1200
3965 G21
Rev. B
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7
LT3965/LT3965-1
PIN FUNCTIONS
VIN: Input Supply Pin for LED Bypass Switches and
Fault Detectors. Must be locally by-passed with a 1µF
(or larger) capacitor placed close to this pin. For proper
channel switch bypass operation, VIN must be at least
7.1V higher than channel source voltage.
EN/UVLO: Shutdown and Undervoltage Detect Pin. An
accurate 1.24V (nominal) falling threshold with externally programmable hysteresis detects when VIN – SRC
is okay to enable the part. Rising hysteresis is generated
by an external resistor and an accurate internal 2.7µA
pull-down current. EN/UVLO going high (from below the
falling threshold to above the rising threshold) resets the
device to an initial power-on condition, which all registers
are loaded with a default value. Tie to 0.4V, or less, to disable the device and reduce VDD and VIN quiescent current
below 1µA. Typically this pin is tied to a PNP based level
shifter to ensure the part is enabled only when VIN is at
least 7.1V higher than channel source voltage.
ALERT: Alert Output for Fault Condition Report. ALERT pin
is asserted (pulled low) to indicate that an open LED fault
condition or/and a shorted LED fault condition or/and an
overheat fault condition are detected. The ALERT pin is
deasserted (released to high) after the part sends its Alert
Response Address successfully or the fault condition is
cleared by an I2C write command.
RTCLK: External PWM Clock Input and Internal Oscillator
Frequency Programming Pin. Set the internal oscillator
frequency using a resistor to GND if the internal oscillator
is used for PWM dimming. An external clock source able
to sink 500µA at 0.4V can be used for PWM dimming by
driving RTCLK above and below VIH and VIL respectively
to override the internal oscillator. Do not leave the RTCLK
pin open. Place the resistor close to the IC if a resistor is used to set the internal oscillator frequency. LED
PWM dimming frequency equals the programmed internal
oscillator frequency divided by 2048 or the external clock
frequency divided by 2048.
LEDREF: LED Reference Voltage Input. This pin is used to
set the normal operating VF of the LED. The shorted LED
threshold VSTH can be programmed through I2C Serial
Interface to one of the following four values: 1V, VLEDREF
+ 1V, 2 • VLEDREF + 1V and 3 • VLEDREF + 1V. Connecting
this pin to GND sets the shorted LED threshold to 1V.
The internal value of VLEDREF becomes fixed at 4V if more
than 4V is applied to this pin. Do not leave this pin open.
VDD: Supply Voltage for I2C Serial Port and Input Supply
Pin for Internal Bias and Logic. This pin sets the logic
reference level of I2C SCL and SDA pins. SCL and SDA
logic levels are scaled to VDD. When the VDD pin is 2.7V or
above, the I2C interface is active. The LT3965/LT3965-1
will acknowledge communications to its address and data
can be written to and read back from LT3965/LT3965-1
registers. This is true even if EN/UVLO is low. However,
when EN/UVLO goes high, the LT3965/LT3965-1 resets
all registers to default values (see Table 1 and Table 2 for
default values). Connect a 0.1μF (or larger) decoupling
capacitor from this pin to ground.
SCL: Clock Input Pin for the I2C Serial Port. The I2C logic
levels are scaled with respect to VDD.
SDA: Data Input and Output Pin for the I2C Serial Port. The
I2C logic levels are scaled with respect to VDD.
ADDR[4:1]: Programmable Address Select Pins. The
device address is 010xxxx0 for all channel mode
(ACMODE) write, 010xxxx1 for all channel mode
(ACMODE) read, 101xxxx0 for single channel mode
(SCMODE) write, and 101xxxx1 for single channel mode
(SCMODE) read. ADDR[4] is MSB and ADDR[1] is LSB.
A total of 16 LT3965/LT3965-1 devices can be connected
to the same I2C bus. ADDR[4:1] are pulled up to VDD
through a 500k resistor inside the LT3965/LT3965-1, so
ADDR[4:1] default value is 1111. Each bit of ADDR[4:1]
default value can be overwritten by connecting the pin to
the ground. For robust design, use an external resistor to
connect ADDR pins to VDD or to GND.
DRN[8:1]: Floating N-Channel FET Drain Side Pins. Tie to
VDD with a 100k resistor if not used.
SRC[8:1]: Floating N-Channel FET Source Side Pins. The
channel source voltage (SRC[8:1]) must be at least 7.1V
lower than VIN for proper channel switch bypass operation. Tie to GND if not used.
GND: Exposed Pad Pin. Solder the exposed pad directly
to ground plane (GND).
Rev. B
8
For more information www.analog.com
LT3965/LT3965-1
BLOCK DIAGRAM
VIN
40V
2
LED+
VIN
CH8
C1
R3
LED
SW FAULT
8
R1
LED+
3
R2
+
–
BANDGAP
REFERENCE
INTERNAL
BIAS
VDD
5V
7
CH7
1.24V
LED
SW FAULT
POR
6
SDA
DRN7
DRIVER
SRC7
CH6
LED
SW FAULT
VDD
DRN6
SRC6
CH5
R5
5
SCL
ADDR1
9
ADDR2
10
ADDR3
11
ADDR4
12
DRN5
SCL
I2C
SERIAL
INTERFACE
ADDR1
ADDR2
LED
SW FAULT
8
REGISTERS
AND
CONTROL
LOGIC
ADDR4
SRC5
CH4
LED
SW FAULT
DRN4
ALERT
4
ALERT
SRC4
CH3
LED
SW FAULT
SET LED FAULT
1.2V
0.6V
DRN3
SRC3
CH2
+
–
LED
SW FAULT
0
PWMCLK
DRN2
0.88V
DRIVER
SRC2
CH1
8
RT
RTCLK
LED
SW FAULT
+
–
DRN1
Figure 1. Block Diagram
For more information www.analog.com
22
21
20
19
18
17
16
15
FAULT
DETECTOR
DRIVER
29
23
FAULT
DETECTOR
1
INTERNAL
OSCILLATOR
24
FAULT
DETECTOR
DRIVER
+
–
25
FAULT
DETECTOR
DRIVER
TSD SET OVERHEAT FAULT
–170°C
26
FAULT
DETECTOR
DRIVER
ADDR3
27
FAULT
DETECTOR
DRIVER
SDA
28
FAULT
DETECTOR
ENABLE
C2
R4
SRC8
EN/UVLO
IS1
2.7µA
1
FAULT
DETECTOR
DRIVER
Q1
R6
DRN8
LED FAULT
SRC1
LEDREF
13
14
3965 F01
LED–
Rev. B
9
LT3965/LT3965-1
APPLICATIONS INFORMATION
OVERVIEW
The LT3965/LT3965-1 is an 8-channel LED bypass switching device with I2C serial interface, designed for dimming
LED strings using a common current source. Each of the
eight channels can be independently programmed to
bypass the LED string in constant on or off, or dimming
with or without fade transition. Operation can be best
understood by referring to the block diagram in Figure 1.
If a resistor is connected between the RTCLK pin and the
ground, the internal oscillator is chosen and the LED dimming
frequency is set by the resistor. If the RTCLK pin is driven by
an external clock source, the external clock source is used to
override the internal oscillator and the dimming frequency
equals the external clock frequency divided by 2048.
DIFFERENCES BETWEEN LT3965 AND LT3965-1
The LT3965/LT3965-1 operates over the VDD input supply range of 2.7V to 5.5V. The eight channel switches are
powered by the VIN input supply and can be connected in
parallel and/or in series. Each of the eight channel switches
can bypass one or more LEDs up to 17V in a string.
The LT3965 and the LT3965-1 have different default
command register values, which result in different initial
switch states and different open LED threshold settings
after POR (Power On Reset). Otherwise they are the same
(see Table 1 and Table 2 for default register values).
Each channel has an LED fault detector which can be programmed to detect an open LED fault at one of the four
threshold levels: 4.5V, 9V (default setting of LT3965-1),
13.5V and 18V (default setting of LT3965). If EN/UVLO is
high, when an open LED fault is detected in a channel, the
channel switch will be turned on to bypass the faulty LED to
maintain the continuity of the string and for self protection.
The PWM dimming for this channel is interrupted until reset
by the serial interface. With a proper LED reference voltage
(>10cm)
between the LT3965/LT3965-1 and the LEDs introduce
parasitic inductance that leads to an underdamped RLC
response (ringing) in the switching voltage when channel is switching on and off. A meter of 30-gage wire can
introduce about 1µH of parasitic inductance. The ringing
can trigger open LED protection due to false open LED
detection, and cause the channel to bypass good LEDs. In
extreme cases, the ringing may exceed absolute maximum
ratings and damage the part. The parasitic inductance also
generates a step voltage waveform (relative to GND) at the
switches at the frequency of the switching regulator. The
magnitude of this step waveform depends upon the current ripple in the source and the parasitic inductance. The
fast edges of the step waveform can cause unintended
toggling of the LT3965/LT3965-1 switches.
RC snubber circuits (shown in Figure 14) can suppress
the ringing and allow use of wires up to 1 meter with
no false fault detection. The snubber should be placed
close to the IC. Please note that an 8-LED string requires
9 snubbers: one snubber across each of the 8 switches
and a snubber across all 8 switches (R9, C9). The 9th
snubber (R9, C9) softens the stepped waveform edges.
Rev. B
For more information www.analog.com
21
LT3965/LT3965-1
APPLICATIONS INFORMATION
With the snubbers, the LT3965/LT3965-1 can control the
LEDs through a 1 meter ribbon cable (9 wires total) passing 0.5A with no false faults detected. The snubber value
shown here is good for most applications.
Schottky Clamping Diode for LT3965/LT3965-1
Protection
A Schottky clamping diode (D1 shown in Figure 15) connecting the top of the LED string (LED+ node) to the VIN
pin is required to guarantee that the absolute maximum
rating VIN – SRC ≥ –0.3V is met.
For the boost-buck configuration, where the voltage at
the LED string bottom (LED– node) may go below 0V, a
Schottky clamping diode (D2 shown in Figure 15) connecting the IC ground to the LED– node is required to
keep SRC ≥ –0.3V.
In applications with wires longer than 30cm, there is
potential for an open or shorted LED to cause ringing at
channel DRN-SRC beyond the absolute maximum rating
of –0.3V. The LT3965/LT3965-1 can be protected by placing Schottky clamping diodes (D3 to D10 shown in Figure
15) near the IC across channel pins.
LED+
DRN8
SRC8
D1
C8
10nF
R8
10Ω
D8
VIN
D7
C9
10nF
R9
10Ω
SRC3
DRN2
SRC2
DRN1
SRC1
•
• UP TO 1 METER
•
D3
SRC7
DRN6
D4
SRC6
DRN5
D5
D3
LT3965/ SRC5
LT3965-1 DRN4
D6
D2
SRC4
DRN3
D7
SRC3
DRN2
D8
SRC2
DRN1
D9
•
•
•
C2
10nF
R2
10Ω
C1
10nF
R1
10Ω
IF NEEDED
SRC8
DRN7
DRN7
LT3965/LT3965-1
DRN8
D1
3965 F14
LED–
LED+
D10
Figure 14. RC Snubbers In Long Wire Application
GND
SRC1
D2
LED–
3965 F15
Figure 15. Clamping Diode For LT3965/LT3965-1 Protection
Rev. B
22
For more information www.analog.com
LT3965/LT3965-1
TYPICAL APPLICATIONS
Matrix LED Dimmer Powered by a Dual Buck Mode LED Driver with a Boost Pre-Regulator
BIAS = VOUT + INTVCC + 5V
VOUT
ISP1
5V
ISP2
ALERT SDA SCL
0.50Ω
500mA
22µF
4V
0.50Ω
500mA
10k
ISN1
ISN2
10k
TG1
10k
D6
M4
1µF
50V
D10
D11
D4
D5
500mA
0.1µF
16V
0.1µF
16V
0.1µF
50V
VLED
26V
0.1µF
50V
SYNC
VIN
9V TO 30V
L3
15µH
+
33µF
50V
D3
10µF
50V
10µF
50V
×2
M3
SRC1
LED1–
VDD VIN
10µF
50V
×2
43.2k
D1
SCL
SDA
SDA
ALERT
L1
33µH
ALERT
LT3965/
LT3965-1
CH1
49.9k
1M
1µF
50V
GATE3 SENSEP3 SENSEN3
VIN
TG3
ISP3 ISN3
LT3965/
LT3965-1
CH2
VOUT
1k
Q1
EN/UVLO
EN/UVLO
ADDR1
ADDR1
9.09k
ADDR2
ADDR2
ADDR3
ADDR3
ADDR4
ADDR4
LEDREF
LEDREF
RTCLK
RTCLK
5V
M1
VIN
0.1µF
10V
DRN8
SRC8
DRN7
SRC7
DRN6
SRC6
DRN5
SRC5
DRN4
SRC4
DRN3
SRC3
DRN2
SRC2
DRN1
500mA
VLED
26V
SRC1
GND
LED2–
D9
350kHz SYNC
OUT
SET
499k
10k
RT
SENSEN1 SENSEP1 GATE1
SS3
47.5k
SYNC GATE2 SENSEP2 SENSEN2
TG1-2
ISP1-2
FLT1-3 SW1 SW2
L4
47µH
1µF
INTVCC
L1, L2: WURTH ELECTRONICS 7447789133
L3: WURTH ELECTRONICS 7443551151
L4: COOPER BUSSMANN SD25-470-R
10µF
50V
×2
ISN1-2
SS1-2
0.22µF
D2
0.05Ω
LT3797
EN/UVLO
PWM1-3 VREF CTRL3 CTRL1-2
69.8k
44.2k
FBH2
M2
DIV
0.05Ω
FBH3
1M
L2
33µH
LTC6900
GND
60.4k
0.02Ω
LED2+
BIAS
GND
M5
1µF
50V
SCL
D8
44.2k
1M
FBH1
D7
1µF
VIN VDD
DRN8
SRC8
DRN7
SRC7
DRN6
SRC6
DRN5
SRC5
DRN4
SRC4
DRN3
SRC3
DRN2
SRC2
DRN1
TG2
5V
1µF
10V
LED1+
INTVCC
22µF
4V
D1, D2: DIODES DFLS260
D3: DIODES PDS360
D4, D5, D10, D11: CENTRAL SEMI CMSD6263S
2 IN 1 PACKAGE
D6, D7: NXP SEMI PMEG6010CEH
D8, D9: NXP SEMI PMEG4010CEH
Q1: ZETEX FMMT591
M1, M2: VISHAY Si7308DN
M3: VISHAY Si7850DP
M4, M5: VISHAY Si7309DN
BOOST
INTVCC
10µF
0.1µF
INTVCC
GND VC1-2
FBH1-2
VC3
5.7k
2.2nF
15k
1nF
22nF
3965 TA02
Rev. B
For more information www.analog.com
23
LT3965/LT3965-1
PACKAGE DESCRIPTION
FE Package
28-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1663 Rev L)
Exposed Pad Variation EB
9.60 – 9.80*
(.378 – .386)
4.75
(.187)
4.75
(.187)
28 27 26 2524 23 22 21 20 1918 17 16 15
6.60 ±0.10
4.50 ±0.10
2.74
(.108)
SEE NOTE 4
0.45 ±0.05
EXPOSED
PAD HEAT SINK
ON BOTTOM OF
PACKAGE
6.40
2.74
(.252)
(.108)
BSC
1.05 ±0.10
0.65 BSC
RECOMMENDED SOLDER PAD LAYOUT
4.30 – 4.50*
(.169 – .177)
0.09 – 0.20
(.0035 – .0079)
0.50 – 0.75
(.020 – .030)
NOTE:
1. CONTROLLING DIMENSION: MILLIMETERS
2. DIMENSIONS ARE IN MILLIMETERS
(INCHES)
3. DRAWING NOT TO SCALE
1 2 3 4 5 6 7 8 9 10 11 12 13 14
0.25
REF
1.20
(.047)
MAX
0° – 8°
0.65
(.0256)
BSC
0.195 – 0.30
(.0077 – .0118)
TYP
0.05 – 0.15
(.002 – .006)
FE28 (EB) TSSOP REV L 0117
4. RECOMMENDED MINIMUM PCB METAL SIZE
FOR EXPOSED PAD ATTACHMENT
*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.150mm (.006") PER SIDE
Rev. B
24
For more information www.analog.com
LT3965/LT3965-1
REVISION HISTORY
REV
DATE
DESCRIPTION
A
04/17
Added LT3965-1 Option
PAGE NUMBER
All
Clarified Block Diagram
9
B
12/19
Added Automotive Products
2
Rev. B
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
25
LT3965/LT3965-1
TYPICAL APPLICATION
Matrix LED Dimmer Powered by a Boost-Buck LED Driver
D4
D5
1µF
50V
0.1µF
100V
VIN
SW
5V
100k
10k
LT3965/
LT3965-1
VDD
10µF
10V EN/UVLO
10k
D3
BIAS
10V
EN/UVLO
SDA
SDA
SCL
SCL
ALERT
ALERT
350kHz SYNC
(170Hz PWM)
RTCLK
ADDR1
ADDR2
ADDR3
ADDR4
LEDREF
ISN 4V ISP
22µF
M1
0.25Ω
LED+
DRN8
SRC8
DRN7
SRC7
DRN6
SRC6
DRN5
SRC5
DRN4
SRC4
DRN3
SRC3
DRN2
SRC2
DRN1
BIAS UVLO DETECT
BIAS
49.9k
LED+
1k
Q2
8 LEDs
25V
500mA
EN/UVLO
9.09k
365k
SRC1
GND
TG
LED–
10k
Q1
5V
D6
D2
LT3470
5V REGULATOR
VIN
6V TO 18V
L1
22µH
10µF
25V
EN/UVLO
D1
FB
OVLO
TG
VREF
130k
LT3952
PWM
CTRL
69.8k
1.5k
6.8nF
ISP
ISN
ISMON
DIM
SYNC/SPRD
IVINCOMP
OPENLED
SHORTLED
INTVCC
VC
4.7µF
50V
VIN IVINP IVINN SW
GND
64.9k
0.1µF
SW
1µF
25V
249k
D1, D6: DIODES DFLS260
D2, D3: NXP SEMI PMEG6010CEH
D4, D5: CENTRAL SEMI CMSD6263S
2 IN 1 PACKAGE
L1: WURTH 74437349220 22µH
L2: WURTH 74408943330 33µH
Q1, Q2: ZETEX FMMT591
M1: VISHAY Si7415DN
L2
33µH
SS
RT
0.1µF
340k
14.7k
TG
ISP
ISN
ISMON
350kHz
SYNC
DIV
INTVCC
V+
0.1µF
GND
LTC6900
OUT
SET
60.4k
OPENLED
SHORTLED
INTVCC
100k
100k
2.2µF
3965 TA03
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT3795
High Side 110V, 1MHz LED Driver with 3000:1 PWM
VIN: 4.5V to 110V, VOUT(MAX) = 110V, 3000:1 PWM, 20:1 Analog, ISD < 1µA,
Dimming with Spread Spectrum Frequency Modulation TSSOP-28E Package
LT3952
60V, 4A LED Driver with 4000:1 PWM Dimming with
Spread Spectrum
VIN: 3V to 42V, VOUT(MAX) = 60V, 4000:1 PWM, 20:1 Analog, ISD < 1µA,
TSSOP-28E Package
LT3797
Triple Output LED Driver Controller with 3000:1 PWM
Dimming
VIN: 2.5V to 90V, VOUT(MAX) = 100V, 3000:1 PWM, 20:1 Analog, ISD < 1µA,
7mm × 8mm QFN-52 Package
LT3756/LT3756-1/ High Side 100V, 1MHz LED Controller with 3000:1
LT3756-2
PWM Dimming
VIN: 6V to 100V, VOUT: 5V to 100V, 3000:1 PWM, 20:1 Analog, ISD < µA,
3mm × 3mm QFN-16 and MSOP-16E Packages
Rev. B
26
12/19
www.analog.com
For more information www.analog.com
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