LINER LT3599EFE 4-channel 120ma led driver with â±1.5% current matching Datasheet

LT3599
4-Channel 120mA LED Driver
with ±1.5% Current Matching
Description
Features
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
True Color PWMTM Dimming Ratio Up to 3000:1
Drives Four Strings of LEDs at Up to 120mA
±1.5% Accurate LED Current Matching
Wide Input Voltage Range: 3.1V to 30V
Output Voltage Up to 44V
Regulates LED Current Even When VIN > VOUT
Disconnects LEDs in Shutdown
Programmable Maximum VOUT (Regulated)
Open/Short LED Protection and Fault Flags
Programmable LED Current Derating
Adjustable Frequency: 200kHz to 2.1MHz
Synchronizable to an External Clock
Analog Dimming Up to 20:1
Programmable Input UVLO with Hysteresis
Thermally Enhanced 32-Pin (5mm × 5mm) QFN and
28-Pin TSSOP Packages
Applications
n
n
The LT®3599 is a fixed frequency 2A step-up DC/DC
converter designed to drive four strings of 120mA LEDs
up to a 44V output voltage. The switching frequency
is programmable from 200kHz to 2.1MHz through an
external resistor.
LED dimming can be achieved with analog dimming on
the CTRL pin, and with pulse width modulation dimming
on the PWM pin. The LT3599 accurately regulates LED
current even when the input voltage is higher than the
LED output voltage.
Additional features include programmable LED current
derating, switching frequency synchronization to an external clock, LED string disable control, OPENLED alert
pin, SHORTLED alert pins and programmable maximum
output voltage when all LED strings are disconnected.
The LT3599 is available in the thermally enhanced 32-pin
(5mm × 5mm) QFN and 28-pin TSSOP packages.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. True Color PWM is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 7199560.
Automotive Navigation TFT LCD Displays
Desktop and Notebook TFT LCD Displays
Typical Application
90% Efficient 12W LED Driver
PVIN
8V TO 24V
10µH
VIN
VIN
200k
4.7µF
s2
100k
1µF
100k
33.2k
53.6k
SW
1.5
VO_SW
1M
TSET
31.6k
LED1
LED2
LED3
LED4
80.6k
GND VC
ALL FOUR LED STRINGS
1.0
FB
53.6k
DISABLE4
ISET SS
LED Current Matching
VOUT
SHORTLED
OPENLED
SHDN/UVLO
PWM
SYNC
LT3599
CTRL
RT
VREF
PWM
31.6k
VIN
MATCHING (%)
3.3µF
VIN
3.1V TO 5.5V
0.5
0
–0.5
–1.0
3599 TA01a
80mA PER STRING
–1.5
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3599 TA01b
16.5k
47nF
10k
100pF
2.2nF
3599fd
LT3599
Absolute Maximum Ratings
(Note 1)
VIN, SHDN/UVLO, OPENLED, SHORTLED...................30V
SHDN/UVLO Pin Above VIN.........................................3V
SW.............................................................................45V
VOUT, VO_SW..............................................................45V
LED1, LED2, LED3, LED4...........................................45V
PWM, SYNC, CTRL, FB, TSET, DISABLE4.....................6V
VC, SS..........................................................................3V
VREF, RT, ISET..............................................................2V
Operating Junction Temperature Range (Note 2)
LT3599E/LT3599I............................... –40°C to 125°C
LT3599H............................................. –40°C to 150°C
Maximum Junction Temperature
LT3599E/LT3599I.............................................. 125°C
LT3599H............................................................ 150°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, sec) (Note 5).......... 300°C
Pin Configuration
25 GND
LED2
5
24 VREF
LED3
6
23 SS
LED1 3
LED4
7
22 RT
LED2 4
DISABLE4
8
21 PWM
LED3 5
20 NC
LED4 6
18 PWM
17 SYNC
FE PACKAGE
28-LEAD PLASTIC TSSOP
TJMAX = 125°C, θJA = 28°C/W , θJC = 10°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
TSET
FB
VC
CTRL
15 VC
19 RT
9 10 11 12 13 14 15 16
17 TSET
16 FB
20 SS
SHORTLED 8
18 NC
ISET 13
21 VREF
33
DISABLE4 7
19 SYNC
CTRL 14
22 GND
ISET
NC 12
23 NC
OPENLED
NC 10
OPENLED 11
24 NC
VO_SW 2
NC
9
32 31 30 29 28 27 26 25
VOUT 1
NC
SHORTLED
29
NC
LED1
NC
26 NC
4
SHDN/UVLO
3
VIN
27 SHDN/UVLO
VO_SW
NC
28 VIN
2
NC
1
NC
SW
VOUT
SW
TOP VIEW
TOP VIEW
UH PACKAGE
32-LEAD (5mm s 5mm) PLASTIC QFN
TJMAX = 125°C, θJA = 34°C/W
EXPOSED PAD (PIN 33) IS GND, MUST BE SOLDERED TO PCB
order information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3599EFE#PBF
LT3599EFE#TRPBF
LT3599FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3599IFE#PBF
LT3599IFE#TRPBF
LT3599FE
28-Lead Plastic TSSOP
–40°C to 125°C
LT3599HFE#PBF
LT3599HFE#TRPBF
LT3599FE
28-Lead Plastic TSSOP
–40°C to 150°C
LT3599EUH#PBF
LT3599EUH#TRPBF
3599
32-Lead (5mm × 5mm) Plastic QFN
–40°C to 125°C
LT3599IUH#PBF
LT3599IUH#TRPBF
3599
32-Lead (5mm × 5mm) Plastic QFN
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
3599fd
LT3599
Electrical Characteristics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VSHDN = 5V, unless otherwise noted. (Note 2)
PARAMETER
CONDITIONS
MIN
Minimum Operating Voltage
l
Maximum Operating Voltage
l
Reference Voltage VREF
I(VREF ) = 0µA
l
Reference Voltage Line Regulation
I(VREF ) = 0µA, 3.1V < VIN < 30V
Maximum VREF Pin Current
(Note 3)
VREF Load Regulation
0 < I(VREF) ≤ 100µA (Max)
Feedback Voltage
1.21
1.20
TYP
MAX
2.7
3.1
V
30
V
1.227
1.24
1.25
V
V
0.01
0.03
%/V
100
µA
1
l
1.196
UNITS
mV
1.223
1.250
250
V
FB Pin Bias Current
(Note 3)
100
FB Error Amp Transconductance
∆I = 5µA
200
µmhos
nA
FB Error Amp Voltage Gain
210
V/V
Current Loop Amp Transconductance
50
µmhos
Current Loop Amp Voltage Gain
50
V/V
VC Source Current (Out of Pin)
LED1-4 = 0.4V, FB = 1V, VC = 1.5V
8
µA
VC Sink Current (OVP Mode)
LED1-4 = 0.4V, FB = 1.5V, VC = 1.5V
15
µA
Quiescent Current
VSHDN = 5V, PWM = 0V, Not Switching, VC = 0.7V
3
4.8
mA
Quiescent Current in Shutdown
VSHDN = 0V
0
1
µA
LED Current
RISET = 13.3k
99
102
mA
LED String Current Matching
100mA LED Current
±0.25
±1.5
%
LED Open Detection Threshold (VLED–GND)
FB > 1.25V
0.3
0.4
V
1.5
2.2
V
96
l
LED Short Detection Threshold (VOUT –VLED)
0.8
LED Regulation Voltage
0.77
LED1-4 Leakage Current
VLED1-4 = 45V
CTRL Pin Bias Current
VCTRL = 0.8V (Note 3)
Switching Frequency
RT = 324k
RT = 53.6k
RT = 20k
176
0.9
1.82
TSET Voltage
Maximum Switch Duty Cycle
RT = 324k
RT = 53.6k
RT = 20k
l
V
0.1
1
µA
100
200
nA
198
1
2.06
220
1.1
2.3
kHz
MHz
MHz
595
mV
97
85
70
98
90
80
%
%
%
2
2.5
Switch Current Limit
(Note 4)
Switch VCESAT
ISW = 0.5A
0.10
Switch Leakage Current
VSW = 45V, FB = 1.3V
0.2
5
µA
SHDN/UVLO Pin Threshold (VSD_SHDN)
Shutdown
0.3
0.7
0.95
V
SHDN/UVLO Pin Threshold (VSD_ UVLO)
Rising
1.28
1.36
1.44
V
SHDN/UVLO Pin Hysteresis Current
SHDN = VSD_UVLO – 50mV
SHDN = VSD_UVLO + 50mV
2.5
4
0
5.5
µA
µA
Soft-Start Current
SS = 1V (Note 3)
µA
1
0.4
A
V
11
PWM Input High Threshold
PWM Input Low Threshold
3
V
V
3599fd
LT3599
Electrical Characteristics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, VSHDN = 5V, unless otherwise noted. (Note 2)
PARAMETER
CONDITIONS
PWM Pin Bias Current
PWM = 3.3V
MIN
TYP
MAX
0.1
2
µA
1.7
V
SYNC Input High Threshold
SYNC Input Low Threshold
SYNC Pin Bias Current
0.8
SYNC = 0V (Note 3)
SYNC = 3.3V
V
25
0.1
VO_SW Switch Resistance
OPENLED Pull-Down Current
PWM = 5V; LEDx < 0.2V, OPENLED = 0.3V
1
SHORTLED Pull-Down Current
PWM = 5V, SHORTLED = 0.3V
1
DISABLE4 Input High Threshold
DISABLE4 Input Low Threshold
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 LT3599E 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
LT3599I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
50
1
µA
µA
1000
Ω
mA
mA
1.15
0.4
UNITS
V
V
Note 3: Current flows out of pin.
Note 4: Current limit guaranteed by design and/or correlation to static test.
Current limit is independent of duty cycle and is guaranteed by design.
Note 5: TSSOP package only.
3599fd
LT3599
Typical Performance Characteristics TA = 25°C unless otherwise specified
1.45
SHDN/UVLO Pin Turn-On
Threshold (VSD_UVLO)
SHDN/UVLO Pin
(Hysteresis) Current
500
6
VIN Current (Shutdown)
SHDN/ UVLO (V)
1.40
1.35
1.30
1.25
–50 –25
0
25
50
75
4
3
2
0
25
50
75
10000
VREF (mV)
VIN = 30V
1230
VIN = 3V
1220
25
50
75
2.5
2.1MHz
2.0
1.5
1MHz
1.0
0.5
JUNCTION TEMPERATURE (°C)
100
100
VTSET THRESHOLD (mV)
ISS (µA) (OUT OF PIN)
1.2
11
10
9
7
–50 –25
1000
800
750
700
650
600
550
0
25
50
75
100 125 150
JUNCTION TEMPERATURE (°C)
3599 G07
100
RT (k)
850
8
0.4
0.8
1.0
0.6
CTRL PIN VOLTAGE (V)
10
900
12
0.2
Switching Frequency vs RT
TSET Pin Threshold
vs Junction Temperature
13
ISET = 13.3k
20
100 125 150
3599 G06
Soft-Start Pin Current
40
75
3599 G05
LED Current vs CTRL Pin
60
50
1000
25 50 75 100 125 150
0
JUNCTION TEMPERATURE (°C)
3599 G04
80
25
0.2MHz
0
–50 –25
100 125 150
SWITCHING FREQUENCY (kHz)
SWITCHING FREQUENCY (MHz)
1240
0
3599 G03
Switching Frequency
0
VIN = 3V
JUNCTION TEMPERATURE (°C)
3.0
1210
–50 –25
VIN = 30V
150
3599 G02
VREF
LED CURRENT (mA)
200
JUNCTION TEMPERATURE (°C)
1250
0
250
0
–50 –25
100 125 150
3599 G01
0
300
50
AFTER PART TURN-OFF
JUNCTION TEMPERATURE (°C)
120
350
100
1
0
–50 –25
100 125 150
400
JUST BEFORE PART TURN-ON
VIN CURRENT (nA)
SHDN /UVLO PIN CURRENT (µA)
450
5
3599 G08
500
0
25
50
75
100
125
JUNCTION TEMPERATURE (°C)
150
3599 G09
3599fd
LT3599
Typical Performance Characteristics TA = 25°C unless otherwise specified
2500
VC Pin Active and Clamp Voltages
LED Current vs PWM Duty Cycle
Switch Saturation Voltage
100
0.40
VC HIGH
0.35
2000
VC (V)
1500
VC ACTIVE
1000
500
0.30
VCESAT (V)
LED CURRENT (mA)
10
1
0.25
0.20
0.15
0.10
0.1
0.05
0
–50 –25
0
25
50
75
0.01
0.01
100 125 150
0.1
1
10
PWM DUTY CYCLE (%)
JUNCTION TEMPERATURE (°C)
3599 G10
0
100
0
0.5
1
1.5
ISW (A)
2
3599 G12
3599 G11
Switch Current Limit
LED Current vs Temperature
Feedback Pin Voltage
2.8
2.5
1250
101
1245
2.0
1.6
1.2
0.8
0.4
–50 –25
1240
1235
LED CURRENT (mA)
FEEDBACK PIN VOLTAGE (mV)
SWITCH CURRENT (A)
2.4
1230
1225
1220
1215
100
99
98
1210
1205
0
25
50
75
100 125 150
JUNCTION TEMPERATURE (°C)
1200
25 50 75 100 125 150
–50 –25 0
JUNCTION TEMPERATURE (°C)
3599 G13
97
–50 –25
0
25
50
100 125 150
3599 G15
3599 G14
LED Current Waveforms
(0.1% PWM) (10ms Period)
75
JUNCTION TEMPERATURE (°C)
LED Current Waveforms
(90% PWM) (10ms Period)
PWM
5V/DIV
PWM
5V/DIV
SW
20V/DIV
SW
20V/DIV
ILED1
50mA/DIV
ILED1
50mA/DIV
2µs/DIV
3599 G16
100µs/DIV
3599 G17
3599fd
LT3599
Pin Functions
CTRL: LED Current Control. If the CTRL pin is not used,
tie this pin to VREF.
DISABLE4: Allows Disabling Channel 4. Connect to VREF
to disable channel 4. If channel 4 is disabled, the LED4 pin
should be connected to the LED3 pin. Connect DISABLE4
to ground to allow operation of channel 4.
Exposed Pad: Ground. The ground for the IC should be
soldered to a continuous copper ground plane under the
LT3599 die.
FB: Feedback Pin for Overvoltage Protection. Reference
voltage is 1.223V. Connect the resistive divider tap here.
Minimize trace area at FB. Set VOUT according to VOUT =
1.223(1 + R2/R1) when overvoltage protection occurs.
GND: Analog Ground. Tie directly to local ground plane.
Connect RT, ISET and TSET resistors between this local
ground plane and their respective pins.
ISET: Programs Led Current for Each String. A resistor
to ground programs LED currents between 30mA and
120mA.
LED1-4: LED String Output. Connect the bottom cathode
of each LED string to these pins.
OPENLED: Open LED Flag. An open-collector output when
any LED string opens.
NC: No Connect Pins. Can be left open or connected to
any ground plane.
PWM: Input Pin for PWM Dimming Control. Above 1V
allows converter switching, and below 0.4V disables
switching with VC pin level maintained. A PWM signal
driving the PWM pin provides accurate dimming control.
The PWM signal can be driven from 0V to 5V. If unused,
the pin should be connected to VREF.
RT: A Resistor to Ground Which Programs Switching
Frequency Between 200kHz and 2.1MHz. For SYNC function, choose the resistor to program a frequency 20%
slower than the SYNC pulse frequency. Do not leave this
pin open.
SHDN/UVLO: The SHDN/UVLO pin has an accurate 1.36V
threshold and can be used to program an undervoltage
lockout (UVLO) threshold for system input supply using a
resistor divider from supply to ground. A 4µA pin current
hysteresis allows programming of undervoltage lockout
(UVLO) hysteresis. 1.36V turns the part on and removes a
4µA sink current from the pin. SHDN/UVLO = 0V reduces
VIN current < 0.1µA. SHDN/UVLO can be directly connected
to VIN. Do not leave this pin open.
SHORTLED: Indicates a high side short (LED pin shorted
to VOUT). This is an open-collector output.
SS: Soft-Start Pin. Place a soft-start capacitor here. Upon
start-up, a 11µA current charges the capacitor. Use a larger
capacitor for a slower start-up.
SW: Switch Pin. This is the collector of the internal NPN
power switch. Minimize the metal trace area connected
to this pin to minimize EMI.
SYNC: Frequency Synchronization Pin. This input allows for
synchronizing the operating frequency to an external clock.
The RT resistor should be chosen to program a switching
frequency 20% slower than SYNC pulse frequency. This
pin should be grounded if this feature is not used.
TSET: Programs LT3599 junction temperature breakpoint,
beyond which LED currents will begin to decrease. An
internal VPTAT threshold (see Block Diagram) increases
with junction temperature. When VPTAT exceeds TSET pin
voltage, LED currents are decreased. If the function is not
required, connect TSET pin to VREF pin. If the TSET pin is
not used, tie this pin to VREF.
VC: Error Amplifier Output Pin. Tie the external compensation network to this pin.
VIN : Input Supply Pin. Must be locally bypassed with a
capacitor to ground.
VO_SW: Drain of an Internal PMOS. The internal PMOS
disconnects the feedback resistors from the VOUT pin
during shutdown and when the PWM pin is low.
VOUT: Output Pin. This pin provides power to all LEDs.
VREF : Bandgap Voltage Reference. Internally set to 1.227V.
This pin can supply up to 100µA. Can be used to program
the CTRL pin voltage using resistor dividers to ground.
3599fd
LT3599
Block Diagram
SHDN/UVLO
1.4V
VIN
RT
–
+
SYNC
SW
OSCILLATOR
1.227 VREF
SLOPE
SOFT-START LOGIC
+
3
VC
–
S
Q1
Q
R
A2
+
SS
A3
––
VOUT
PWM
PMOS
PWM DIMMING
LOGIC
+
VO_SW
VREF
R2
OVP gm
VREF
FB
–
R1
+
CTRL
–
1V
+
TSET
–
VPTAT
+
0.7V
LED gm
–
SHORTLED
OPENLED, SHORTLED
DETECTION
OPENLED
LED1
LED2
LED DRIVE
CIRCUITRY
A1
LED3
LED4
ISET
LED4 DISABLE
DISABLE4
GND
3599 F01
Figure 1. Block Diagram
3599fd
LT3599
Operation
The LT3599 uses a constant-frequency, peak current mode
control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the
Block Diagram in Figure 1.
To turn on the LT3599, the VIN pin must exceed 3.1V and
the SHDN/UVLO pin must exceed 1.4V. The SHDN/UVLO
pin threshold allows programming of an undervoltage
lockout (UVLO) threshold for the system input supply using a simple resistor divider. A 4µA current flows into the
SHDN/UVLO pin before the part turns on and is removed
after the part turns on. This current hysteresis allows the
programming of hysteresis for the UVLO threshold. See
“Shutdown Pin and Programming Undervoltage Lockout”
in the Applications Information section. For part switching,
the PWM pin must exceed 1V (typical). For micropower
shutdown, the SHDN/UVLO pin at 0V reduces VIN supply
current to approximately ~0µA.
LT3599 has a built-in boost converter which converts the
input voltage to a higher output voltage for driving LEDs.
The LED strings are connected to current sources where
the current level is set with an external resistor on the
ISET pin. The LED1 to LED4 voltages are monitored for
output voltage regulation. During normal operation, when
all LEDs are used, the lowest LED pin voltage (LED1 to
LED4) is used to regulate the output voltage to ensure all
LED strings have enough voltage to run the programmed
current.
If the user prefers only three strings, then LED string 4 can
be disabled through the DISABLE4 pin and by connecting
LED4 to any other LED pin. If the user prefers only two
strings, then two pins are connected in parallel (i.e., LED1,2
and LED3,4 can be connected together in operation).
The basic loop uses a pulse from an internal oscillator
to set the SR latch and turn on the internal power NPN
switch Q1. The signal at the noninverting input of the PWM
comparator (A2) is proportional to the sum of the switch
current and oscillator ramp. When this signal exceeds the
VC voltage, the PWM comparator resets the latch. The
switch is then turned off, causing the inductor current
to lift the SW pin and turn on an external Schottky diode
connected to the output. Inductor current flows via the
Schottky diode charging the output capacitor. The switch
is turned on again at the next reset cycle of the internal
oscillator. During normal operation, the VC voltage controls
the peak switch current limit and, hence, the inductor
current available to the output LEDs.
Dimming of the LEDs is accomplished by either PWM dimming or analog dimming. PWM dimming is achieved by
pulsing the LED current using the PWM pin. For constant
color LED dimming, the LT3599 provides up to a 3000:1
wide PWM dimming range by allowing the duty cycle of the
PWM pin to be reduced from 100% to as low as 0.033%.
When the PWM pin is low, switching is disabled and the
error amplifier is turned off so that it does not drive the VC
pin. Also, all internal loads on the VC pin are disabled so
that the state of the VC pin is maintained on the external
compensation capacitor. This feature reduces transient
recovery time. When the PWM input again transitions
high, the peak switch current returns to the correct value.
In applications where the user can sacrifice OPENLED,
SHORTLED fault flag diagnostics, the dimming ratios can
be as high as 3000:1. Analog dimming of LED currents is
accomplished by varying the level of CTRL pin voltage.
This method, however, changes LED color since dimming
is achieved by changing LED current. For CTRL pin voltage
less than 1V, LED current is defined as:
 1330 
ILED = VCTRL • 
( Amps)
 RISET 
The LT3599 uses the FB pin to provide overvoltage protection when all LED strings are open. There is an internal
PMOS switch between VOUT and VO_SW that is controlled
by the PWM signal. During the PWM off-period, this
PMOS is turned off, allowing for higher dimming range
and lower current during shutdown. A resistor divider is
connected between the VO_SW pin and ground, which sets
the overvoltage protection voltage.
If the LED1-4 pin voltage is below 0.3V, the string is treated
as an open LED string. As a result, an OPENLED flag is
set. If a LED string is opened during regular operation,
the output voltage will regulate to the optimum voltage
for the remaining connected strings.
If a short occurs between VOUT and any LED pin during
operation, the LT3599 immediately turns off the shorted
channel and sets a SHORTLED flag. Disabling the channel
protects the LT3599 from high power thermal dissipation
and ensures reliable operation.
3599fd
LT3599
Operation
SHORTLED and OPENLED detection are disabled during
the start-up phase to avoid false flag generation. If an LED
string is open during normal operation, it will no longer
be used to regulate the output voltage. The output voltage
will regulate itself to find the LED string with the lowest
LED pin voltage. Fault detection (SHORTLED, OPENLED)
is updated when the PWM pin is high and latched when
the PWM pin is low.
During start-up, 11µA of current charges the external
soft-start capacitor. The SS pin directly limits the rate
of voltage rise on the VC pin, which in turn, limits the
peak switch current. Soft-start also enables switching
frequency foldback to provide a clean start-up for the
LT3599. Switch current limit protects the power switch
and external components.
Applications Information
Inductor Selection
Capacitor Selection
Table 1 lists several inductors that work well with the
LT3599, however, there are many other manufacturers and
devices that can be used. Consult each manufacturer for
detailed information on their entire range of parts. Ferrite
core inductors should be used to obtain the best efficiency.
Choose an inductor that can handle the necessary peak
current without saturating. Also, ensure that the inductor
has a low DCR (copper wire resistance) to minimize I2R
power losses. Values between 4.7µH and 22µH will suffice
for most applications.
Low ESR (equivalent series resistance) ceramic capacitors should be used at the output to minimize the output
ripple voltage. Use only X5R or X7R dielectrics, as these
materials retain their capacitance over wider voltage and
temperature ranges than other dielectrics. A 4.7µF to 10µF
output capacitor is sufficient for most high output current
designs. Table 2 lists some suggested manufacturers.
Consult the manufacturers for detailed information on
their entire selection of ceramic parts.
Inductor manufacturers specify the maximum current
rating as the current where inductance falls by a given
percentage of its nominal value. An inductor can pass a
current greater than its rated value without damaging it.
Consult each manufacturer to determine how the maximum
inductor current is measured and how much more current
the inductor can reliably conduct.
Taiyo Yuden
(408) 573-4150
www.t-yuden.com
AVX
(843) 448-9411
www.avxcorp.com
Murata
(770) 436-1300
www.murata.com
Kemet
(408) 986-0424
www.kemet.com
Table 1. Recommended Inductors
MAX DCR CURRENT
(Ω)
RATING (A)
Table 2. Recommended Ceramic Capacitor Manufacturers
Diode Selection
PART
L
(µH)
B1015AS-100M
817FY-4R7M
10
4.7
0.07
0.06
2.2
2.26
TOKO
www.toko.com
744065100
74454068
74454010
10
6.8
10
0.04
0.055
0.065
3
2.2
2
Würth Electronics
www.we-online.com
CDH115-100
CDH74NP-120L
CDH74NP-150L
10
12
15
0.028
0.065
0.083
3
2.45
2.10
Sumida
www.sumida.com
IHLP2020-BZ
IHLP2525-BD
10
10
0.184
0.116
2.3
2.5
Vishay
www.vishay.com
VENDOR
Schottky diodes, with their low forward voltage drop and
fast switching speed, should be used for all LT3599 applications. Table 3 lists several Schottky diodes that work
well. The diode’s average current rating must exceed the
application’s average output current. The diode’s maximum
reverse voltage must exceed the application’s output voltage. A 2A diode is sufficient for most designs. For PWM
dimming applications, be aware of the reverse leakage
current of the diode. Lower leakage current will drain the
output capacitor less, allowing for higher dimming range.
3599fd
10
LT3599
Applications Information
The companies below offer Schottky diodes with high
voltage and current ratings. Standard silicon diodes (PN
junction diodes) should not be used.
Table 3. Suggested Diodes
The output voltage should be set 10% higher than the
normal LED string operating voltage. Under normal
operation, LED1 to LED4 pin voltages are monitored and
provide feedback information to the converter for output
voltage regulation given the programmed LED current.
The output voltage regulation loop is activated only when
all LEDs are open.
MAX
CURRENT
(A)
MAX REVERSE
VOLTAGE
(V)
B250A
DFLS240
B240A
B350A
B340A
2
2
2
3
3
50
40
40
50
40
Diodes, Inc.
www.diodes.com
Programming Maximum LED Current
HSM150G
HSM150J
HSM350G
1
1
3
50
50
50
Microsemi
www.microsemi.com
Maximum LED current can be programmed by placing a
resistor between the ISET pin and ground (RISET). The ISET
pin resistor can be selected from 11k to 44.2k.
PART
MANUFACTURER
The LED current can be programmed according to the
following equation:
Overvoltage Protection
The LT3599 uses the FB pin to provide overvoltage protection. A resistor divider is connected between the VO_SW
pin and ground (Figure 2). There is an internal PMOS
switch between VOUT and VO_SW, which is controlled by
the PWM signal. The PMOS switch addition prevents the
feedback resistor divider from draining the output capacitor during PWM off-period, allowing for a higher dimming
range without falsely tripping the OPENLED flag. It also
reduces the system current in shutdown. This PMOS has
about 1k resistance, so select FB resistor values taking
this resistance into account.
To set the maximum output voltage, select the values
of R1 and R2 (see Figure 2) according to the following
equation:
ILED ≈
1330
( Amps) (CTRL > 1V)
RISET
See Table 4 and Figure 3 for resistor values and corresponding programmed LED current.
LED current can also be adjusted by programming the
CTRL pin voltage.
Table 4. RISET Value Selection for LED Current
LED CURRENT (mA)
RESISTOR ON ISET PIN (k)
30mA
44.2
50mA
26.7
99mA
13.3
120mA
11
 R2 
VOUT(MAX) = 1.223V  1+ 
 R1
120
100
LT3599
VOUT
VO_SW
R2
ILED (mA)
80
60
40
20
FB
R1
3599 F02
Figure 2. Overvoltage Protection Voltage Feedback Connections
0
0
20
40
60 80 100 120 140 160
RISET (k)
3599 F03
Figure 3. RISET Value Selection for LED Current
3599fd
11
LT3599
Applications Information
LED Current Dimming
Two different types of dimming control can be used with
the LT3599. The LED brightness can be set either by analog
dimming (CTRL pin voltage adjustment between 0V and 1V)
or PWM dimming (PWM pin duty cycle adjustment).
For some applications, the preferred method of brightness
control is to use a variable DC input voltage. The CTRL
pin voltage can be adjusted to set the dimming of the LED
string (see Figures 4 and 5). As the voltage on the CTRL
pin increases from 0V to 1V, the LED current increases
from 0 to the programmed LED current level. Once the
CTRL pin voltage increases beyond 1V, it has no effect on
the LED current.
For True Color PWM dimming, the LT3599 provides
up to a 3000:1 PWM dimming range by allowing the duty
cycle of the PWM pin to be reduced from 100% to as
120
ISET = 13.3k
LED CURRENT (mA)
100
low as 0.033% at a PWM frequency of 100Hz (Figure 6).
Dimming by PWM duty cycle, allows for constant LED
color to be maintained over the entire dimming range.
For LT3599 PWM dimming control during startup and
normal operation, observe the following guidelines:
(1) STARTUP
LT3599 VOUT start-up requires the SHDN/UVLO pin to be
asserted from off to on and the PWM on-time to be above
a minimum value. The lowest PWM on-time allowed for
fault detection is ≈20µs. The lowest PWM on-time allowed
for reaching VOUT regulation is typically 20µs but might be
greater depending on external circuit parameters. Once LED
current is in regulation, PWM on-time can be reduced as
low as 3µs depending on external component selection.
(2) VOUT Collapse
If during normal operation VOUT collapses due to a fault
or because PWM on-time is too low, a re-start is required
(see STARTUP in item (1)).
80
VREF
60
R2
40
LT3599
CTRL
20
R1
0
0
0.2
0.4
0.8
1.0
0.6
CTRL PIN VOLTAGE (V)
1.2
3599 F05
3599 F04
Figure 4. LED Current vs CTRL Voltage
Figure 5. LED Current vs CTRL
TPWM
TONPWM
(= 1/fPWM)
PWM
INDUCTOR
CURRENT
LED
CURRENT
MAX ILED
3599 F06
Figure 6. LED Current Using PWM Dimming
3599fd
12
LT3599
Applications Information
Programming LED Current Derating
vs Temperature
Programming LED Current Derating Using the CTRL Pin
A useful feature of the LT3599 is its ability to program
a derating curve for maximum LED current versus temperature. LED data sheets provide curves of maximumallowable LED current versus temperature to warn against
exceeding this current limit and damaging the LED. The
LT3599 allows the output LEDs to be programmed for
maximum allowable current while still protecting the
LEDs from excessive currents at high temperature. This is
achieved by programming a voltage at the CTRL pin with
a negative temperature coefficient using a resistor divider
with temperature dependent resistance (Figure 7). As the
temperature increases, the CTRL voltage will fall below the
internal 1V voltage reference, causing LED currents to be
controlled by the CTRL pin voltage. The LED current curve
breakpoint and slope versus temperature is defined by the
choice of resistor ratios and use of temperature-dependent
resistance in the divider for the CTRL pin.
A variety of resistor networks and NTC resistors with
different temperature coefficients can be used for programming CTRL to achieve the desired CTRL curve vs
temperature.
Table 5 shows a list of manufacturers/distributors of NTC
resistors. There are several other manufacturers available and the chosen supplier should be contacted for
more detailed information. If an NTC resistor is used to
indicate LED temperature, it is effective only if the resistor
is connected as closely as possible to the LED strings.
LED derating curves shown by manufacturers are listed
for ambient temperature. The NTC resistor should have
the same ambient temperature as the LEDs. Since the
temperature dependency of an NTC resistor can be nonlinear over a wide range of temperatures, it is important
to obtain a resistor’s exact values over temperature from
the manufacturer. Hand calculations of CTRL voltage can
then be performed at each given temperature, resulting
in the CTRL versus temperature plotted curve. Several
iterations of resistor value calculations may be required
to achieve the desired breakpoint and slope of the LED
current derating curve.
Table 5. NTC Resistor Manufacturers/Distributors
Murata Electronics North America
(770) 436-1300
www.murata.com
TDK Corporation
(516) 535-2600
www.tdk.com
Digi-Key
(800) 344-4539
www.digikey.com
If calculating the CTRL voltage at various temperatures
gives a downward slope that is too strong, alternative
resistor networks can be chosen (B, C, D in Figure 7)
which use temperature-independent resistance to reduce
the effects of the NTC resistor overtemperature.
Murata Electronics provides a selection of NTC resistors
with complete data over a wide range of temperatures.
In addition, a software tool is available which allows the
user to select from different resistor networks and NTC
resistor values, and then simulate the exact output voltage
curve (CTRL behavior) over temperature. Referred to as
the “Murata Chip NTC Thermistor Output Voltage Simulator,” users can log onto www.murata.com/designlib and
download the software followed by instructions for creating an output voltage VOUT (CTRL) from a specified VCC
supply (VREF). At any time during the selection of circuit
parameters, the user can access data on the chosen NTC
resistor by clicking on a link to the Murata catalog.
RY
VREF
R2
RY
LT3599
CTRL
R1
(OPTION A TO D)
RNTC
RNTC
A
RX RNTC
B
RNTC
C
RX
D
3599 F07
Figure 7 . LED Current Derating vs Temperature Using NTC Resistor
3599fd
13
LT3599
Applications Information
Using the TSET Pin for Thermal Protection
The LT3599 contains a special programmable thermal
regulation loop that limits the internal junction temperature
of the part. Since the LT3599 topology consists of a single
boost converter with four linear current sources, any LED
string voltage mismatch will cause additional power to be
dissipated in the package. This topology provides excellent
current matching between LED strings and allows a single
power stage to drive a large number of LEDs, but at the
price of additional power dissipation inside the part (which
means a higher junction temperature). Being able to limit
the maximum junction temperature allows the benefits of
this topology to be fully realized. This thermal regulation
feature provides important protection at high ambient temperatures, and allows a given application to be optimized
for typical, not worst case, ambient temperatures with the
assurance that the LT3599 will automatically protect itself
and the LED strings under worst-case conditions.
The operation of the thermal loop is simple. As the ambient temperature increases, so does the internal junction
temperature of the part. Once the programmed maximum
junction temperature is reached, the LT3599 begins to
linearly reduce the LED current, as needed, to try and
maintain this temperature. This can only be achieved
when the ambient temperature stays below the desired
maximum junction temperature. If the ambient temperature continues to rise past the programmed maximum
junction temperature, the LEDs’ current will be reduced
to approximately 5% of the full LED current.
While this feature is intended to directly protect the LT3599,
it can also be used to derate the LED current at high temperatures. Since there is a direct relationship between the
LED temperature and LT3599 junction temperature, the
TSET function also provides some LED current derating
at high temperatures.
VREF
R2
LT3599
TSET
R1
3599 F08
Figure 8. Programming the TSET Pin
Two external resistors program the maximum IC junction
temperature using a resistor divider from the VREF pin, as
shown in Figure 8. Choose the ratio of R1 and R2 for the
desired junction temperature. Table 6 shows commonly
used values for R1 and R2 (see TSET graph).
Table 6. Resistor Values to Program Maximum IC Junction
Temperature
TJ (°C)
R1 (k)
R2 (k)
100
80.6
53.6
105
82.5
53.6
110
82.5
51.1
115
84.5
51.1
120
84.5
49.9
135
84.5
44.2
145
90.9
44.2
Programming Switching Frequency
The switching frequency of the LT3599 is set between
200kHz and 2.1MHz by an external resistor connected
between the RT pin and ground (see Table 7). Do not
leave this pin open.
Selecting the optimum switching frequency depends
on several factors. Inductor size is reduced with higher
frequency, but efficiency drops due to higher switching
losses. In addition, some applications require very high duty
cycles to drive a large number of LEDs from a low supply.
Low switching frequency allows a greater operational duty
cycle and, hence, a greater number of LEDs to be driven.
In each case, the switching frequency can be tailored to
provide the optimum solution. When programming the
switching frequency, the total power losses within the IC
should be considered.
Table 7. Switching Frequency
SWITCHING FREQUENCY (MHz)
RT (k)
2.1
20
2.0
21.5
1.5
31.6
1.0
53.6
0.5
121
0.4
154
0.3
210
0.2
324
3599fd
14
LT3599
Applications Information
Switching Frequency Synchronization
The nominal operating frequency of the LT3599 is programmed using a resistor from the RT pin to ground
and can be controlled over a 200kHz to 2.1MHz range. In
addition, the internal oscillator can be synchronized to an
external clock applied to the SYNC pin. The synchronizing
clock signal input to the LT3599 must have a frequency
between 240kHz and 1.5MHz, a pulse on-time of at least
150ns, a pulse off-time of at least 300ns, a low state below
0.8V and a high state above 1.7V. Synchronization signals
outside of these parameters will cause erratic switching
behavior. For proper operation, an RT resistor should be
chosen to program a switching frequency 20% slower
than the SYNC pulse frequency. Synchronization occurs
at a fixed delay after the rising edge of SYNC.
The SYNC pin should be grounded if the clock synchronization feature is not used. When the SYNC pin is grounded,
the internal oscillator generates switching frequency to
the converter.
Shutdown and Programming Undervoltage Lockout
The LT3599 has an accurate 1.4V shutdown threshold
at the SHDN/UVLO pin. This threshold can be used in
conjunction with a resistor divider from the system input
supply to define an accurate undervoltage lockout (UVLO)
threshold for the system (Figure 10). A pin current hysteresis allows programming of the hysteresis voltage for
this UVLO threshold. Just before the part turns on, 4µA
flows into the SHDN/UVLO pin. After the part turns on, 0µA
flows from the SHDN/UVLO pin. Calculation of the on/off
thresholds for a system input supply using the LT3599
SHDN/UVLO pin can be made as follows :
 R1
VS(OFF) = 1.4  1+ 
 R2 
VS(ON) = VS(OFF) + (4µA • R1)
A simple open drain transistor can be added to the resistor
divider network at the SHDN/UVLO pin to independently
control the turn off of the LT3599.
With the SHDN/UVLO pin connected directly to the VIN pin,
an internal undervoltage lockout threshold of approximately
2.7V exists for the VIN pin. This prevents the converter
from operating in an erratic mode when supply voltage is
too low. The LT3599 provides a soft-start function when
recovering from such faults as SHDN < 1.4V and/or VIN
< 2.7V. See “Soft-Start” in the Applications Information
section for details.
Soft-Start and Switching Frequency Foldback
To limit inrush current and output voltage overshoot during start-up/recovery from a fault condition, the LT3599
provides a soft-start pin, SS. The SS pin is used to program
switch current ramp-up timing using a capacitor to ground.
The LT3599 monitors system parameters for the following
faults: VIN < 2.7V or SHDN < 1.4. On detection of any of
these faults, the LT3599 stops switching immediately and
SWITCHING FREQUENCY (kHz)
10000
VS
LT3599
R1
11
SHDN/UVLO
–
1000
OFF
100
10
100
RT (k)
Figure 9. Switching Frequency
ON
R2
4µA
1.4V
+
1000
3599 F11
3599 F10
Figure 10. Programming Undervoltage
Lockout (UVLO) with Hysteresis
3599fd
15
LT3599
Applications Information
a soft-start latch is set causing the SS pin to be discharged
(see the Soft-Start Pin Timing Diagram in Figure 11). All
faults are detected internally and do not require external
components. When all faults no longer exist and the SS
pin has been discharged to at least 0.25V, the soft-start
latch is reset and an internal 11µA supply charges the SS
pin. During start-up or recovery from a fault, the SS pin
ramp up controls the ramp up of switch current limit.
Soft-start ramp rate is given by:
∆VSS ISS
=
(ISS = 11µA typ)
∆T
CSS
A 10nF capacitor from the SS pin to ground will therefore
provide a 1V/ms ramp rate on the SS pin.
In addition, during soft-start, switching frequency is reduced to protect the inductor from high currents.
SW
but continues to ramp upwards. If the soft-start ramp
voltage was held every time PWM goes low, this would
cause very slow start-up of LED displays for applications
using very high PWM dimming ratios.
OPENLED FLAG
The OPENLED pin is an open-collector output and needs
an external resistor tied to a supply (see Figure 12). If any
LED string is open during normal operation, the OPENLED
pin will be pulled down.
The open LED detection is enabled only when the PWM
signal is enabled. There is a delay for OPENLED flag generation when the PWM signal is enabled to avoid generating
a spurious flag signal.
During start-up (see the Operation section), the open LED
detection is disabled.
SHORTLED FLAG
SS
FAULTS TRIGGERING
SOFT-START LATCH
WITH SW TURNED OFF
IMMEDIATELY:
VIN < 2.7V
OR
SHDN < 1.4V
0.3V (ACTIVE THRESHOLD)
0.25V (RESET THRESHOLD)
0.15V
SOFT-START
LATCH SET
SOFT-START
LATCH RESET:
SS < 0.25V
AND
VIN > 2.7V
AND
SHDN > 1.4V
AND
PWM > 1V (FOR >200ns)
3599 F12
Figure 11. Soft-Start Pin Timing Diagram
A useful feature of the LT3599 is that it waits for the first
PWM pin active high (minimum 200ns pulse width) before
it allows the soft-start of VC pin to begin. This feature
ensures that during start-up of the LT3599 the soft-start
ramp has not timed out before PWM is asserted high.
Without this ‘wait for PWM high’ feature, systems which
apply PWM after VIN and SHDN are valid, can potentially
turn on without soft-start and experience high inductor
currents during wake up of the converter’s output voltage.
It is important to note that when PWM subsequently goes
low, the soft-start ramp is not held at its present voltage
The SHORTLED pin is an open-collector output, and needs
an external resistor tied to a supply (see Figure 12). If
any LED pin is shorted to VOUT during normal operation,
the SHORTLED pin will be pulled down. In addition, the
shorted LED string (channel) is immediately disabled,
thereby protecting the LT3599.
The short LED detection is enabled only when the PWM
signal is enabled. There is a delay for SHORTLED flag generation when the PWM signal is enabled to avoid spurious
signal being generated.
During start-up, the SHORTLED flag is disabled (see the
Operation section).
LT3599
R1
R2
OPENLED
SHORTLED
3599 F13
Figure 12. OPENLED and SHORTLED Connection
3599fd
16
LT3599
Applications Information
Loop Compensation
programming current with a 100% PWM dimming ratio,
at least 280mW is dissipated within the IC due to current
sources. Thermal calculations shall include the power
dissipation on current sources in addition to conventional
switch DC loss, switch AC loss and input quiescent loss.
For best efficiency, it is recommended that all channels
have the same number of LEDs, and each string has a
similar voltage drop across the LEDs.
The LT3599 has an internal transconductance error
amplifier for LED current regulation whose VC output
compensates the control loop. During overvoltage, the
VC node also compensates the control loop. The external
inductor, output capacitor, and the compensation resistor
and capacitor determine the loop stability. The inductor
and output capacitor are chosen based on performance,
size and cost. The compensation resistor and capacitor
at VC are selected to optimize control loop stability. For
typical LED applications, a 10nF compensation capacitor
in series with a 2k resistor at VC is adequate.
Board Layout Considerations
As with all switching regulators, careful attention must be
paid to the PCB board layout and component placement.
To prevent electromagnetic interference (EMI) problems,
proper layout of high frequency switching paths is essential. Minimize the length and area of all traces connected to the switching node pin (SW). Always use a
ground plane under the switching regulator to minimize
interplane coupling. Good grounding is essential in LED
fault detection. Recommended component placement is
shown in Figure 13.
Thermal Consideration
The LT3599 provides four channels for LED strings with
internal NPN devices serving as constant-current sources.
When LED strings are regulated, the lowest LED pin voltage is 0.7V. The higher the programmed LED current, the
more power dissipation in the LT3599. For 100mA LED
BYPASS
CAPACITOR
POWER VIN
SOLDER EXPOSED PAD (PIN 29)
TO THE ENTIRE COPPER GROUND
PLANE UNDERNEATH THE DEVICE.
GROUND
CONNECT MULTIPLE GROUND PLANES
THROUGH VIAS UNDERNEATH THE IC
INDUCTOR
LT3599
SCHOTTKY DIODE
COUT
LED +
(VOUT)
R
R
R
SW
1
VOUT
2
POWER
GROUND
28
VIN
27
SHDN/UVLO
CVIN
3
26
NC
LED1
4
25
GND
LED2
5
24
VREF
LED3
6
23
SS
CSS
22
RT
RT
21
PWM
VO_SW
LED4
7
DISABLE4
8
EXPOSED
PAD
(PIN 29)
CVREF
SHORTLED
9
20
NC
NC
10
19
SYNC
OPENLED
11
18
NC
NC
12
17
TSET
ISET
13
16
FB
R
R
15
VC
RC
CC
CTRL
14
Cf
3599 F13
Figure 13. Recommended Component Placement
3599fd
17
LT3599
Typical Applications
12W LED Driver
1MHz Boost, 80mA per String, 10 LEDs per String
L1
10µH
PVIN
8V TO 24V
C1
3.3µF
25V
R1
200k
R4
100k
C2
4.7µF
50V
s2
VIN
3.1V TO 5.5V
VIN
VIN
D1
C3
1µF
6.3V
R5
100k
PWM
R2
31.6k
R3
33.2k
R6
53.6k
R7
53.6k
R8
80.6k
VIN
VOUT
VO_SW
SHORTLED
OPENLED
SHDN/UVLO
PWM
SYNC
LT3599
CTRL
RT
VREF
TSET
DISABLE4
ISET SS
R9
16.5k
C1: MURATA GRM21BR71E335K
C2: MURATA GRM31CR71H475K
D1: DIODES INC. DFLS240
L1: VISHAY IHLP2020BZER100M01
SW
FB
R11
31.6k
LED1
LED2
LED3
LED4
GND VC
C4
47nF
R10
1M
RC
10k
CC
2.2nF
80mA PER STRING
100pF
3599 TA02a
PWM Dimming Range 1000:1
(10ms Period)
Efficiency
100
PVIN = 24V
95
PWM
5V/DIV
EFFICIENCY (%)
90
PVIN = 12V
85
80
ILED
TOTAL
200mA/DIV
75
70
65
60
10µs/DIV
40
80
120 160 200 240 280
TOTAL LED CURRENT (mA)
3599 TA02c
320
3599 TA02b
3599fd
18
LT3599
Typical Applications
12W LED Driver
400kHz Boost, Two LED Strings, 200mA per String, 8 LEDs per String
L1
22µH
PVIN
9V TO 16V
C1
3.3µF
25V
VIN
R3
464k
R1
200k
R4
100k
VIN
R12
64.9k
R5
100k
C3
1µF
6.3V
PWM
R6
154k
C2
4.7µF
50V
s3
VIN
3.1V TO 5.5V
R2
64.9k
CTRL
D1
R7
53.6k
R8
80.6k
C1: MURATA GRM21BR71E335K
C2: MURATA GRM31CR71H475K
D1: DIODES INC. DFLS240
L1: VISHAY IHLP2525CZER220M11
VIN
SW
VOUT
VO_SW
SHORTLED
OPENLED
SHDN/UVLO
PWM
SYNC
LT3599
CTRL
RT
VREF
DISABLE4
ISET SS
R9
13.3k
FB
R11
39.2k
LED1
LED2
LED3
LED4
TSET
R10
1M
8 LEDs/
STRING
200mA PER STRING
GND VC
C4
47nF
RC
3.01k
CC
10nF
100pF
3599 TA03a
3599fd
19
LT3599
Typical Applications
7W LED Driver
SEPIC (Survives Output Short to Ground)
300kHz, Three Strings, 100mA per String, 6 LEDs per String
10Ω
L1
22µH
PVIN
8V TO 16V
D1
C1
3.3µF
25V
VIN
VIN
R1
200k
R4
100k
C3
1µF
6.3V
PWM
R2
31.6k
R3
33.2k
R6
210k
C6
1µF
25V
VIN
3.1V TO 5.5V
R5
100k
C7
4.7µF
25V
R7
53.6k
R8
80.6k
C1: MURATA GRM21BR71E335K
C2: MURATA GRM31CR71H475K
D1: DIODES INC. B360A
L1, L2: VISHAY IHLP2525CZER220M11
L2
22µH
VIN SW
VOUT
VO_SW
SHORTLED
OPENLED
SHDN/UVLO
PWM
SYNC
LT3599
CTRL
RT
VREF
DISABLE4
TSET
ISET
R9
13.3k
SS
C2
4.7µF
50V
s2
R10
1M
6 LEDs/
STRING
FB
R11
49.9k
LED1
LED2
LED3
LED4
100mA PER STRING
GND VC
C4
47nF
RC
10k
CC
2.2nF
100pF
3599 TA04a
3599fd
20
LT3599
Typical Applications
8W LED Driver
2MHz Boost, Three Strings, 100mA per String, 7 LEDs per String
L1
4.7µH
PVIN
8V TO 16V
C1
3.3µF
25V
VIN
R1
200k
VIN
R4
100k
C3
1µF
6.3V
R5
100k
PWM
R2
31.6k
R3
33.2k
VIN
3.1V TO 5.5V
R6
21.5k
R7
53.6k
R8
80.6k
VIN
SW
VOUT
VO_SW
SHORTLED
OPENLED
SHDN/UVLO
PWM
SYNC
LT3599
CTRL
RT
VREF
DISABLE4
C2
4.7µF
50V
s2
R10
1M
7 LEDs/
STRING
FB
R11
43.2k
LED1
LED2
LED3
LED4
100mA PER STRING
TSET
ISET
C1: MURATA GRM21BR71E335K
C2: MURATA GRM31CR71H475K
D1: DIODES INC. DFLS240
L1: SUMIDA CDRH4D22HPNP-4R7N
D1
R9
13.3k
SS
GND VC
C4
47nF
RC
10k
CC
2.2nF
100pF
3599 TA05a
3599fd
21
LT3599
Typical Applications
2.1 MHz Boost, Four Strings, 80mA per String, 7 LEDs per String
L1
4.7µH
PVIN
9V TO 16V
C1
3.3µF
25V
R1
200k
R4
100k
C3
1µF
6.3V
R5
100k
PWM
R2
32.4k
R3
32.4k
C2
4.7µF
50V
s2
VIN
3.1V TO 5.5V
VIN
VIN
D1
R6
20k
R7
53.6k
R8
80.6k
C1: MURATA GRM21BR71E335K
C2: MURATA GRM31CR71H475K
D1: DIODES INC. DFLS240
L1: SUMIDA CDRH4D22HPNP-4R7N
VIN
SW
VOUT
VO_SW
SHORTLED
OPENLED
SHDN/UVLO
PWM
SYNC
LT3599
CTRL
RT
VREF
FB
R9
16.5k
7 LEDs/
STRING
R11
43.2k
LED1
LED2
LED3
LED4
TSET
DISABLE4
ISET
SS
R10
1M
VC
GND
C4
47nF
80mA PER STRING
RC
10k
CC
2.2nF
100pF
3599 TA06a
PWM Dimming 3000:1
(10ms Period)
PWM
5V/DIV
ILED
TOTAL
200mA/DIV
10µs/DIV
3599 TA07
3599fd
22
LT3599
Package Description
FE Package
28-Lead Plastic TSSOP (4.4mm)
(Reference LTC DWG # 05-08-1663)
Exposed Pad Variation EB
9.60 – 9.80*
(.378 – .386)
4.75
(.187)
4.75
(.187)
28 2726 25 24 23 22 21 20 19 18 1716 15
6.60 ±0.10
2.74
(.108)
4.50 ±0.10
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 0204
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
3599fd
23
LT3599
Package Description
UH Package
32-Lead Plastic QFN (5mm × 5mm)
(Reference LTC DWG # 05-08-1693 Rev D)
0.70 p0.05
5.50 p0.05
4.10 p0.05
3.50 REF
(4 SIDES)
3.45 p 0.05
3.45 p 0.05
PACKAGE OUTLINE
0.25 p 0.05
0.50 BSC
RECOMMENDED SOLDER PAD LAYOUT
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
5.00 p 0.10
(4 SIDES)
BOTTOM VIEW—EXPOSED PAD
0.75 p 0.05
R = 0.05
TYP
0.00 – 0.05
R = 0.115
TYP
PIN 1 NOTCH R = 0.30 TYP
OR 0.35 s 45° CHAMFER
31 32
0.40 p 0.10
PIN 1
TOP MARK
(NOTE 6)
1
2
3.50 REF
(4-SIDES)
3.45 p 0.10
3.45 p 0.10
(UH32) QFN 0406 REV D
0.200 REF
NOTE:
1. DRAWING PROPOSED TO BE A JEDEC PACKAGE OUTLINE
M0-220 VARIATION WHHD-(X) (TO BE APPROVED)
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 0.20mm 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
0.25 p 0.05
0.50 BSC
3599fd
24
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LT3599
Revision History
(Revision history begins at Rev D)
REV
DATE
DESCRIPTION
D
01/10
Updated Typical Applications
PAGE NUMBER
Added H-Grade to Abs Max Ratings and Order Information
Updated Typical Performance Characteristics
1, 18, 19, 20, 21, 22
2
5, 6
Revised Pin Functions
7
Updated Table 6 and Deleted Text in Programming Switching Frequency Section
14
Added to Related Parts Table
26
3599fd
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
25
LT3599
Related Parts
PART NUMBER DESCRIPTION
COMMENTS
LT3463/
LT3463A
Dual Output, Boost/Inverter, 250mA ISW, Constant
Off-Time, High Efficiency Step-Up DC/DC Converter with
Integrated Schottkys
VIN: 2.3V to 15V, VOUT(MAX) = ±40V, IQ = 40µA, ISD < 1µA, 3mm × 3mm
DFN-10 Package
LT3466/
LT3466-1
Dual Constant Current, 2MHz, High Efficiency White LED
Boost Regulator with Integrated Schottky Diode
VIN: 2.7V to 24V, VOUT(MAX) = 40V, IQ = 5µA, ISD < 16µA, 3mm × 3mm
DFN-10 Package
LT3474
36V, 1A (ILED), 2MHz, Step-Down LED Driver
VIN: 4V to 36V, VOUT(MAX) = 13.5V, True Color PWM Dimming = 400:1,
ISD < 1µA, TSSOP-16E Package
LT3475
Dual 1.5A (ILED), 36V, 2MHz, Step-Down LED Driver
VIN: 4V to 36V, VOUT(MAX) = 13.5V, True Color PWM Dimming = 3000:1,
ISD < 1µA, TSSOP-20E Package
LT3476
Quad Output 1.5A, 2MHz High Current LED Driver with
1000:1 Dimming
VIN: 2.8V to 16V, VOUT(MAX) = 36V, True Color PWM Dimming = 1000:1,
ISD < 3µA, 5mm × 7mm QFN-10 Package
LT3477
3A, 42V, 3MHz Boost, Buck-Boost, Buck LED Driver
VIN: 2.5V to 25V, VOUT(MAX) = 40V, Dimming = Analog/PWM,
ISD < 1µA, QFN and TSSOP-20E Packages
LT3478/
LT3478-1
High Current LED Driver
VIN: 2.8V to 36V, VOUT(MAX) = 42V, True Color PWM Dimming = 3000:1,
ISD < 10µA, TSSOP-16E Package
LT3486
Dual 1.3A, 2MHz High Current LED Driver
VIN: 2.5V to 24V, VOUT(MAX) = 36V, True Color PWM Dimming = 1000:1,
ISD < 1µA, 5mm × 3mm DFN and TSSOP-16E Packages
LT3496
45V, 2.1MHz 3-Channel (ILED = 1A) Full Featured
LED Driver
VIN: 3V to 30V (40VMAX), VOUT(MAX) = 45V, True Color PWM Dimming =
3000:1, ISD < 1µA, 4mm × 5mm QFN-28 Package
LT3497
Dual 2.3MHz, Full Function LED Driver with Integrated
Schottkys and 250:1 True Color PWM Dimming
VIN: 2.5V to 10V, VOUT(MAX) = 32V, IQ = 6mA, ISD < 12µA, 2mm × 3mm
DFN-10 Package
LT3498
2.3MHz, 20mA LED Driver and OLED Driver with
Integrated Schottkys
VIN: 2.5V to 12V, VOUT(MAX) = 32V, IQ = 1.65mA, ISD < 9µA, 2mm × 3mm
DFN-12 Package
LT3518/
LT3517
2.3A/1.3A 45V, 2.5MHz Full Featured LED Driver with True VIN: 3V to 30V (40VMAX), VOUT(MAX) = 42V, True Color PWM Dimming =
Color PWM Dimming
3000:1, ISD < 5µA, 4mm × 4mm QFN-16 Package
LT3590
48V Buck Mode LED Driver
LT3591
Constant Current, 1MHz, High Efficiency White LED Boost VIN: 2.5V to 12V, VOUT(MAX) = 40V, IQ = 4mA, ISD < 9µA, 2mm × 3mm
Regulator with Integrated Schottky Diode and 80:1 True
DFN-8 Package
Color PWM Dimming
LT3595
45V, 2.5MHz 16-Channel Full Featured LED Driver
VIN: 4.5V to 45V, VOUT(MAX) = 45V, True Color PWM Dimming = 5000:1,
ISD < 1µA, 5mm × 9mm QFN-56 Package
LT3598
44V, 1.5A, 2.5MHz Boost 6-Channel LED Driver
VIN: 3V to 30V, VOUT(MAX) = 44V, True Color PWM Dimming = 3000:1,
ISD < 1µA, 4mm × 4mm QFN-24 Package
LT3754
16-Channel × 50mA LED Driver
VIN: 6V to 40V, VOUT(MAX) = 60V, 3,000:1 True Color PWM Dimming,
ISD < 2µA, 5mm × 5mm QFN-32 Package
LT3760
8-Channel × 100mA LED Driver
VIN: 6V to 40V, VOUT(MAX) = 60V, 3,000:1 True Color PWM Dimming,
ISD < 2µA, TSSOP-28E Package
VIN: 4.5V to 55V, VOUT(MAX) = 5V, IQ = 700µA, ISD < 15µA,
2mm × 2mm DFN-6 and SC70 Packages
3599fd
26 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
LT 0110 REV D • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 2009