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PDF LT3745 Data sheet ( Hoja de datos )
| Número de pieza | LT3745 | |
| Descripción | 16-Channel 50mA LED Driver | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT3745
16-Channel 50mA LED
Driver with Buck Controller
Features
n 6V to 55V Power Input Voltage Range
n 16 Independent LED Outputs Up to 75mA/36V
n ±3% LED Current Matching at 50mA (Typ ±1%)
n 6-Bit Dot Correction Current Adjustment
n 12-Bit Grayscale PWM Dimming
n 0.5µs Minimum LED On-Time
n Adaptive LED Bus Voltage for High Efficiency
n Cascadable 30MHz Serial Data Interface
n Full Diagnostic and Protection: Individual Open/Short
LED and Overtemperature Fault
n 40-Lead 6mm × 6mm QFN Package
Applications
n Large Screen Display LED Backlighting
n Mono-, Multi-, Full-Color LED Displays
n LED Billboards and Signboards
L, LT, LTC, 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.
Description
The LT®3745 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 gener-
ates 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 TTL/CMOS logic. A ±3% LED cur-
rent matching and a 0.5µs minimum LED on-time can be
achieved at 50mA per channel.
The LT3745 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, skew-balanced, cascadable
serial data interface makes the chip extremely suitable
for large screen LCD dynamic backlighting and mono-,
multi-, full-color LED displays.
Typical Application
16-Channel LED Driver, 1MHz Buck, 10 LEDs, 25mA to 75mA per Channel, 500Hz 12-Bit Dimming
VIN
42V TO 55V
0.47µF
EN
VCC
3V TO 5.5V
10µF
100k
VIN CAP
EN/UVLO
GATE
VCC
SYNC
GND
46.4k
10nF
60.4k
32.4k
2.048MHz CLOCK
TTL/CMOS
3745 TA01
RT
SS
LT3745
ISP
ISN
ISET
TSET
PWMCK
SCKI
SDI
LDI
FB
LED00
LED01
LED...02
LED13
LED14
LED15
SCKO
SDO
LDO
4.7µF
47µH 25mΩ
267k
C1
2 × 47µF
10k
..... ..... .....
TTL/CMOS
..... ..... .....
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1
1 page  
LT3745
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 5.5V, VEN/UVLO = 1.5V, VFB = 1.5V,
VotIhSPer=wVisISeNn=ot5eVd,. VLEDxx = 1V, RT = 105k, RISET = 60.4k, CCAP = 0.47µF to VIN, CSCKO = CSDO = CLDO = 15pF to GND, unless
SYMBOL
PARAMETER
CONDITIONS
MIN TYP MAX UNITS
fSCKI
fPWMCK
tWH-CKI
tWL-CKI
tWH-PWM
tWL-PWM
tWH-LDI
tSU-SDI
tHD-SDI
Data Shift Clock Frequency
PWMCK Clock Frequency
SCKI Pulse Duration
PWMCK Pulse Duration
LDI Pulse Duration
SDI-SCKI Setup Time
SCKI-SDI Hold Time
SCKI = H (Figure 3)
SCKI = L (Figure 3)
PWMCK = H (Figure 4)
PWMCK = L (Figure 4)
LDI = H (Figure 3)
SDI – SCKI ↑ (Figure 3)
SCKI ↑ – SDI (Figure 3)
l
l
l 16
l 16
l 20
l 20
l 20
l2
l2
30 MHz
25 MHz
ns
ns
ns
ns
ns
ns
ns
tSU-LDI
tHD-LDI
tPD-SCK↑
tPD-SCK↓
∆tPD-SCK
SCKI-LDI Setup Time
LDI-SCKI Hold Time
SCKI-SCKO Propagation Delay (Rising)
SCKI-SCKO Propagation Delay (Falling)
SCK Duty Cycle Change
SCKI ↓ – LDI ↑ (Figure 3)
LDI ↓ – SCKI ↑ (Figure 3)
SCKI ↑ – SCKO ↑ (Figure 3)
SCKI ↓ – SCKO ↓ (Figure 3)
∆tPD-SCK = tPD-SCK↑ – tPD-SCK↓
l5
l 15
l 17 35
l 20 40
–3
ns
ns
ns
ns
ns
tPD-SD
tPD-LD↑
tPD-LD↓
∆tPD-LD
tPD-PWM
tR-SO
tF-SO
SCKO-SDO Propagation Delay
LDI-LDO Propagation Delay (Rising)
LDI-LDO Propagation Delay (Falling)
LD Duty Cycle Change
PWMCK-LED Propagation Delay
SCKO/SDO/LDO Rise Time
SCKO/SDO/LDO Fall Time
SCKO ↑ – SDO (Figure 3)
LDI ↑ – LDO ↑ (Figure 3)
LDI ↓ – LDO ↓ (Figure 3)
∆tPD-LD = tPD-LD↑ – tPD-LD↓
PWMCK ↑ – ILED (Figure 4)
CLOAD = 15pF, 10% to 90%
CLOAD = 15pF, 90% to 10%
l 2.2
4.5
7
l 17 35
l 20 40
–3
80
4
4
ns
ns
ns
ns
ns
ns
ns
Table 1. Test Parameter Equations
∆ILEDC(%)
=
IOUTn – IOUTavg(0−15)
IOUTavg( 0 − 15)
•
100
∆I LEDD(%) =
IOUTavg(0−15) – IOUTcal
I OUTcal
•
100
IOUTcal
=
2500
•
1.205V
RISET
∆ILINE (% / V) =
IOUTn
VCC = 5.5V – IOUTn VCC = 3V
IOUTn VCC = 3V
•
100
2.5V
(1)
(2)
(3)
(4)
∆ILOAD (% / V) =
IOUTn
VOUTn = 3V – IOUTn VOUTn = 1V
IOUTn VOUTn = 1V
•
100
2V
(5)
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5 Page 
LT3745
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 op-
eration. 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. Connect the cathodes of LED strings to these pins.
GND (Pins 10, 12, 19, 21): Ground Pin.
SCKI (Pin 11): Serial Interface TTL/CMOS Logic Clock
Input Pin.
SDI (Pin 13): Serial Interface TTL/CMOS Logic Data Input
Pin.
LDI (Pin 14): Serial Interface TTL/CMOS Logic Latch Input
Pin. An asynchronous input signal at this pin latches the
serial data in the shift registers into the proper registers
and the status information is ready to shift out with the
coming clock pulses. See more details in the Operation
section.
VCC (Pin 15): Logic and Control Supply Pin. The pin powers
serial data interface and internal control circuitry. Must be
locally bypassed with a capacitor to ground.
PWMCK (Pin 16): Grayscale PWM Dimming TTL/CMOS
Logic Clock Pin. Individual PWM dimming signal is gener-
ated by counting this clock pulse from zero to the bits in
its 12-bit grayscale PWM register.
LDO (Pin 17): Serial Interface TTL/CMOS Logic Latch
Output Pin.
SDO (Pin 18): Serial Interface TTL/CMOS Logic Data
Output Pin.
SCKO (Pin 20): Serial Interface TTL/CMOS Logic Clock
Output Pin.
SYNC (Pin 30): Switching Frequency Synchronization Pin.
Synchronizes the internal oscillator frequency to an exter-
nal clock applied to the SYNC pin. The SYNC pin is TTL/
CMOS logic compatible. Tie to ground or VCC if not used.
RT (Pin 31): Timing Resistor Pin. Programs the switching
frequency from 200kHz to 1MHz. See Table 2 for the rec-
ommended RT values for common switching frequencies.
SS (Pin 32): Soft-Start Pin. Placing a capacitor here pro-
grams soft-start timing to limit inductor inrush current
during startup. The soft-start cycle will not begin until all
the VCC, EN/UVLO, and (VIN - VCAP) voltages are higher
than their respective UVLO thresholds.
FB (Pin 33): Feedback Pin. The pin is regulated to the
internal bang-gap reference 1.205V during startup and
precharging phases. Connect to a resistor divider from
the buck converter output to program the maximum LED
bus voltage. See more details in the Applications Informa-
tion section.
ISN (Pin 34): Negative Inductor Current Sense Pin. The
pin is connected to one terminal of the external inductor
current sensing resistor and the buck converter output
supplying parallel LED channels.
ISP (Pin 35): Positive Inductor Current Sense Pin. The pin
is connected to the inductor and the other terminal of the
external inductor current sensing resistor.
CAP (Pin 36): VIN Referenced Regulator Supply Capacitor
Pin. The pin holds the negative terminal of an internal VIN
referenced 6.8V linear regulator used to bias the gate driver
circuitry. Must be locally bypassed with a capacitor to VIN.
GATE (Pin 37): Gate Driver Pin. The pin drives an external
P-channel power MOSFET with a typical peak current of
1A. Connect this pin to the gate of the power MOSFET with
a short and wide PCB trace to minimize trace inductance.
VIN (Pin 38): Power Input Supply Pin. Must be locally
bypassed with a capacitor to ground.
TSET (Pin 39): Temperature Threshold Setting Pin. A
resistor to ground programs overtemperature threshold.
See more details in the Applications Information section.
ISET (Pin 40): Nominal LED Current Setting Pin. A resistor
to ground programs the nominal LED current for all the
channels. See more details in the Applications Informa-
tion section.
Exposed Pad (Pin 41): Ground Pin. Must be soldered to a
continuous copper ground plane to reduce die temperature
and to increase the power capability of the device.
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11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LT3745.PDF ] | |
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