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LT3745-1

37451f

TYPICAL APPLICATION

DESCRIPTION

16-Channel 50mA LED

Driver with Buck Controller

The LT

3745-1 integrates a 16-channel LED driver with a

55V buck controller. The LED driver lights up to 75mA/36V

of LEDs in series per channel, and the buck controller gen-

erates an adaptive bus voltage supplying the parallel LED

strings. Each channel has individual 6-bit dot correction

current adjustment and 12-bit grayscale PWM dimming.

Both dot

correction and grayscale are accessible via a serial

data interface in LVDS logic. A ±4% LED current match-

ing and a 0.5µs minimum LED on-time can be achieved

at 50mA per channel.

The LT3745-1 performs full diagnostic and protection

against open/short LED and overtemperature fault. The

fault status is sent back through the serial data interface.

The 30MHz fully-buffered, cascadable LVDS serial data

interface

makes the chip extremely suitable for large screen

LCD dynamic backlighting and mono-, multi-, full-color

LED displays. The LT3745 uses a TTL/CMOS serial data

interface instead of LVDS.

16-Channel LED Driver, 1MHz Buck, 10 LEDs, 25mA to 75mA per Channel, 500Hz 12-Bit Dimming

FEATURES

APPLICATIONS

6V to 55V Power Input Voltage Range

16 Independent LED Outputs Up to 75mA/36V

±4% LED Current Matching at 50mA (Typ ±1%)

6-Bit Dot Correction Current Adjustment

12-Bit Grayscale PWM Dimming

0.5µs Minimum LED On-Time

Adaptive LED Bus Voltage for High Efficiency

Cascadable 30MHz LVDS Serial Data Interface

Full Diagnostic and Protection: Individual Open/Short

LED and Overtemperature Fault

40-Lead 6mm × 6mm QFN Package

Large Screen Display LED Backlighting

Mono-, Multi-, Full-Color LED Displays

LED Billboards and Signboards

L, LT, LT C, LTM , Linear Technology and the Linear logo are registered trademarks and

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 8058810

LVDS

EN/UVLO

SYNC

SET

SCKI

–

SDI

–

LDI

SCKO

–

SDO

–

LED13

LED14

LED15

LED00

LED01

LED02

LT3745-1

100k

42V TO 55V

3V TO 3.6V

CAP

0.47µF

GATE

GND

ISP

ISN

4.7µF

267k

10k

47µF

×2

47µH

25mΩ

PWMCK

–

LVDS

2.048MHz

LVDS CLOCK

37451 TA01

10µF

46.4k

10nF

60.4k

32.4k

Summary of content (28 pages)

PAGE 1
LT3745-1 16-Channel 50mA LED Driver with Buck Controller DESCRIPTION FEATURES n n n n n n n n n n 6V to 55V Power Input Voltage Range 16 Independent LED Outputs Up to 75mA/36V ±4% LED Current Matching at 50mA (Typ ±1%) 6-Bit Dot Correction Current Adjustment 12-Bit Grayscale PWM Dimming 0.
PAGE 2
LT3745-1 RT SS FB ISN ISP CAP GATE VIN TSET TOP VIEW ISET 40 39 38 37 36 35 34 33 32 31 EN/UVLO 1 30 SYNC LED07 2 29 LED08 LED06 3 28 LED09 LED05 4 27 LED10 41 GND LED04 5 LED03 6 26 LED11 25 LED12 LED02 7 24 LED13 LED01 8 23 LED14 LED00 9 22 LED15 SCKI– 10 21 SCKO– SCKO+ SDO– SDO+ PWMCK– PWMCK+ VCC LDI 11 12 13 14 15 16 17 18 19 20 SDI+ VIN ........................................................................... 57V CAP.................................................
PAGE 3
LT3745-1 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VCC = 3.3V, VEN/UVLO = 1.5V, VFB = 1.5V, VISP = VISN = 0V, RT = 105k, RISET = 60.4k, CCAP = 0.47µF to VIN, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS VCC UVLO Threshold VCC Rising VCC Falling 2.76 2.58 2.86 2.68 2.96 2.
PAGE 4
LT3745-1 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VCC = 3.3V, VEN/UVLO = 1.5V, VFB = 1.5V, VISP = VISN = 0V, RT = 105k, RISET = 60.4k, CCAP = 0.47µF to VIN, unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS 1.181 1.205 1.229 V 36 V 0.2 µA 25.3 50.5 74 27.3 53.
PAGE 5
LT3745-1 TIMING CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VCC = 3V to 3.6V, VEN/UVLO = 1.5V, VFB = 1.5V, VISP = VISN = 5V, VLEDxx = 1V, RT = 105k, RISET = 60.4k, CCAP = 0.47µF to VIN, CSCKO+/SCKO– = CSDO+/SDO– = 15pF, unless otherwise noted.
PAGE 6
LT3745-1 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 LT3745E-1 is guaranteed to meet performance specifications from 0°C to 125°C junction temperature.
PAGE 7
LT3745-1 TYPICAL PERFORMANCE CHARACTERISTICS 100Hz 8:1 GS Dimming TA = 25°C, unless otherwise noted. 100Hz 4096:1 GS Dimming 500Hz 4096:1 GS Dimming ILED15 50mA/DIV ILED15 50mA/DIV ILED15 50mA/DIV VOUT 2V/DIV VOUT 2V/DIV VOUT 2V/DIV VLED15 2V/DIV VLED15 2V/DIV VLED15 2V/DIV VPWMCK 0.5V/DIV VPWMCK 0.5V/DIV VPWMCK 0.
PAGE 8
LT3745-1 TYPICAL PERFORMANCE CHARACTERISTICS Buck Efficiency 95 24VIN, 12VOUT at 1MHz 0.43 4 0.42 T = 125°C 12VIN, 4VOUT at 500kHz 80 75 3 IVIN (mA) 85 IVIN (µA) EFFICIENCY (%) 90 2 48VIN, 4VOUT at 200kHz 70 T = –40°C 1 T = 125°C 0.41 T = 25°C 0.40 0.39 T = 25°C 65 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 LOAD CURRENT (A) 0 10 20 37451 G10 500 Quiescent IVIN vs VIN Shutdown IVIN vs VIN 5 100 60 TA = 25°C, unless otherwise noted. T = –40°C 30 VIN (V) 40 50 0.
PAGE 9
LT3745-1 TYPICAL PERFORMANCE CHARACTERISTICS Oscillator Frequency fOSC vs Temperature TA = 25°C, unless otherwise noted. LED Regulation Voltage vs Load Current FB Regulation Voltage vs Load Current 520 1.216 0.72 1.214 0.70 1.212 0.68 500 VLED (V) VFB (V) fOSC (kHz) 510 1.210 0.66 1.208 0.64 1.206 0.62 490 480 –50 50 75 100 –25 0 25 JUNCTION TEMPERATURE (°C) 1.204 125 400 600 800 LOAD CURRENT (mA) 200 37451 G19 Soft-Start Charge Current ISS vs Temperature 1000 0.60 1200 –10.
PAGE 10
LT3745-1 TYPICAL PERFORMANCE CHARACTERISTICS LED Current vs Dot Correction 30 ILED (mA) ILED (mA) 40 20 10 0 40 80 120 160 200 240 RISET (kΩ) 280 80 80 70 70 60 60 50 50 40 30 10 10 51.0 30 VLED (V) 50.5 ILED (mA) 16 24 32 40 48 DOT CORRECTION +1 37451 G27 LED Current Variation ILED vs Temperature 50.0 49.5 49.0 –50 8 56 125 Short LED Threshold vs VISN 20 24 16 18 12 12 0 0 8 37451 G30 16 24 VISN (V) 0 0.5 1.0 1.5 2.0 VLED (V) 2.5 3.
PAGE 11
LT3745-1 PIN FUNCTIONS EN/UVLO (Pin 1): Enable and Undervoltage Lockout (UVLO) Pin. The pin can accept a digital input signal to enable or disable the chip. Tie to 0.35V or lower to shut down the chip or tie to 1.34V or higher for normal operation. This pin can also be connected to VIN through a resistor divider to program a power input UVLO threshold. If both the enable and UVLO functions are not used, tie this pin to VCC pin. LED00 to LED15 (Pins 2 to 9, 22 to 29): LED Driver Output Pins.
PAGE 12
CVCC VCC RFB1 RFB2 CSS 19 18 21 20 11 10 13 12 14 17 16 33 15 1 32 SDO– SDO+ SCKO– UV SCKO SDO SHIFT REGISTER C1 x SCKI SDI C0 192 PRECHG VSS < 1V PG + GM1 – OT 1.210V 192 R S REFERENCE BIAS (VIN-VCAP) AND UVLO STATUS INFO (FAULT LEDXX) SCKO+ SCKI + SCKI– SDI+ SDI– LDI PWMCK– PWMCK+ FB VCC EN/UVLO SS 12µA Q 16X 6 12 POR ISP – 6 12 FAULT LEDXX DC REGISTER FS GS REGISTER FS FS + – 6.
PAGE 13
LT3745-1 OPERATION The LT3745-1 integrates a single constant-frequency current-mode nonsynchronous buck controller with sixteen linear current sinks. The buck controller generates an adaptive output LED bus voltage to supply parallel LED strings and the sixteen linear current sinks regulate and modulate individual LED strings. Its operation is best understood by referring to the Block Diagram. Start-Up The LT3745-1 enters shutdown mode when the EN/UVLO pin is lower than 0.35V.
PAGE 14
LT3745-1 OPERATION LT3745-1 LVDS Topology #1 CONTROLLER LDO SCKO+ CHIP 1 LDI SCKI+ SCKO+ 100Ω SCKO– SDO+ 100Ω SCK-– SDI+ SCKO– SDO+ SDI– SDO– 100Ω SDO– CHIP 2 LDI SCKI+ SCKO+ CHIP N LDI SCKI+ SCKO+ 100Ω SCK-– SDI+ SCKO– SDO+ SDI– SDO– 100Ω SCK-– SDI+ SCKO– SDO+ SDI– SDO– 100Ω SDI– 100Ω SDI+ SCKI– 100Ω SCKI+ LDI LT3745-1 LVDS Topology #2 CONTROLLER LDO SCKO+ SCKO– SDO+ CHIP 1 LDI SCKI+ SCKO+ CHIP 2 LDI SCKI+ SCKO+ CHIP N LDI SCKI+ SCKO+ SCK-– SDI+ SCKO– SDO+ SCK-– SDI+ SCKO– SDO+
PAGE 15
LT3745-1 OPERATION x x MSB DC 15, 6 BITS 0 0 0 0 0 S15 LSB x LSB x x x x x x x C1 LSB MSB MSB DC 15, 6 BITS C1 0 0 0 0 0 S0 0 GS 0, 12 BITS MSB x GS 15, 12 BITS DC 0, 6 BITS MSB LSB LSB x LSB MSB 194 BITS DC 0, 6 BITS C0 GS FRAME C0 DC FRAME F0 STATUS FRAME 37451 F02 COMMAND REGISTER: STATUS REGISTER: C1: ENABLE LED CHANNELS - ENABLE = 1, DISABLE = 0 C0: FRAME SELECT - GS FRAME = 0, DC FRAME = 1 S0-S15: LED 0-15 FAULT - FAULT = 1, OK = 0 F0: OT - OVER
PAGE 16
LT3745-1 OPERATION the SDI pins into the 194-bit shift register SR[0:193]. After 194 clock cycles, all the 194-bit data sit in the right place waiting for the LDI signal. An asynchronous LDI high signal latches the 1-bit FS register, 1-bit EN register, and individual 12-bit GS registers (when FS = 0) or 6-bit DC registers (when FS = 1) for each channel.
PAGE 17
LT3745-1 OPERATION LED bus voltage and should be programmed high enough to supply the worst-case LED string across temperature, current, and manufacturing variation. all the LED channels being not active (i.e., either fault or off) before the 3585th PWMCK clock, the PRECHG signal will go high immediately. Adaptive-Tracking-Plus-Precharging To better explain the operation of the adaptive-trackingplus-precharging technique, a simplified application system with 3-channel LED array is presented in Figure 5.
PAGE 18
LT3745-1 OPERATION down to 4.2V to maintain the minimum active LED pin voltage equal to 0.7V again. Similarly, at the next time instant t2, the output LED bus voltage is tracked down to 3.8V. In this manner, the adaptive-tracking technique eliminates unnecessary power dissipation across the current sinks and yields superior system efficiency when compared to a constant 4.6V output voltage.
PAGE 19
LT3745-1 APPLICATIONS INFORMATION Globally, the LT3745-1 converts a higher input voltage to a single lower LED bus voltage (VOUT) supplying 16 parallel LED strings with the adaptive-tracking-plus-precharging technique. Locally, the part regulates and modulates the current of each string to an independent dot correction and grayscale PWM dimming setting sent by LVDS logic serial data interface.
PAGE 20
LT3745-1 APPLICATIONS INFORMATION Obviously, lower frequency operation accommodates both extremely high and low VOUT to VIN ratios. Besides these common considerations, the specific application also plays an important role in switching frequency choice. In a noise-sensitive system, the switching frequency is usually chosen to keep the switching noise out of a sensitive frequency band.
PAGE 21
LT3745-1 APPLICATIONS INFORMATION current ripple of 30% to 40% offers a good compromise between inductor performance and inductor size and cost. However, for high duty cycle applications, a ∆IL value of ~20% should be used to prevent sub-harmonic oscillation due to insufficient slope compensation. 22mA current capability of the internal regulator limits the maximum QG(MAX) it can deliver to: The largest inductor ripple current occurs at the highest VIN.
PAGE 22
LT3745-1 APPLICATIONS INFORMATION CIN, CVCC, and CCAP Capacitor Selection A local input bypass capacitor CIN is required for buck converters because the input current is pulsed with fast rise and fall times. The input capacitor selection criteria are based on the voltage rating, bulk capacitance, and RMS current capability. The capacitor voltage rating must be greater than VIN(MAX).
PAGE 23
LT3745-1 APPLICATIONS INFORMATION look carefully through the data sheet to find out what the actual capacitance is under operating conditions (applied voltage and temperature). A physically larger capacitor, or one with a higher voltage rating, may be required. Undervoltage Lockout (UVLO) and Shutdown LT3745-1 has three UVLO thresholds with hysteresis for the EN/UVLO, VCC, and CAP pins.
PAGE 24
LT3745-1 APPLICATIONS INFORMATION ILED(NOM) must be set between 10mA and 50mA. Typical RISET resistor values for various nominal LED currents are listed in Table 3. Table 3. Nominal LED Current ILED(NOM) vs. RISET Value ILED(NOM) (mA) RISET* (kΩ) 10 301 20 150 30 100 40 75 50 60.4 * Recommend 1% Standard Values control the amount of LED on-/off-time by pulse width modulation (PWM). The LT3745-1 can adjust the brightness for each channel independently.
PAGE 25
LT3745-1 APPLICATIONS INFORMATION When the RTSET is placed at the TSET pin, a current equal to the current flowing through the RISET passes the RTSET, generating a voltage VTSET at the TSET pin, which is calculated as: VTSET = 1.205V • R TSET R ISET Then the VTSET is compared to an internal proportionalto-absolute-temperature voltage VPTAT, VPTAT = 1.72mV • (TJ + 273.15) where TJ is the LT3745-1 junction temperature in °C. When VPTAT is higher than VTSET, an overtemperature flag OT = 1 is set.
PAGE 26
LT3745-1 TYPICAL APPLICATION VIN 10V TO 40V VIN CAP GATE EN/UVLO EN VCC 3V TO 3.6V 4.7µF 50V 0.47µF 16V 100k VCC RT 105k D1 SYNC SS GND LT3745-1 10nF 23.2k C1 220µF 10k ISN FB ISET 60.4k ISP 4V MAXIMUM OUTPUT VOLTAGE 25mΩ ... 10µF 10V M1 L1 22µH TSET 32.4k LED00 LED01 LED02 LED03 409.6kHz LVDS CLOCK PWMCK+ PWMCK– LED04 LED05 .. .
PAGE 27
LT3745-1 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. UJ Package 40-Lead Plastic QFN (6mm × 6mm) (Reference LTC DWG # 05-08-1728 Rev Ø) 0.70 0.05 6.50 0.05 5.10 0.05 4.42 0.05 4.50 0.05 (4 SIDES) 4.42 0.05 PACKAGE OUTLINE 0.25 0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED 6.00 0.10 (4 SIDES) 0.75 0.05 R = 0.10 TYP R = 0.115 TYP 39 40 0.40 0.
PAGE 28
LT3745-1 TYPICAL APPLICATION VIN 42V TO 55V VIN EN VCC 3V TO 3.6V 4.7µF 100V 0.47µF 16V CAP GATE EN/UVLO 100k 10µF 10V VCC M1 L1 47µH D1 SYNC GND 33.4V MAXIMUM OUTPUT VOLTAGE 25mΩ 267k C1 47µF ×2 . .. RT 46.4k SS ISP LT3745-1 10nF LED00 TSET LVDS .. .. . .. .. . .. .. . .. .. . .. .. . LED01 32.4k 2.048MHz LVDS CLOCK .. .. . FB ISET 60.4k 10k ISN LED02 PWMCK+ PWMCK– SCKI+ SCKI– SDI+ SDI– LDI .. .