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DEMO MANUAL DC1772A
performance summary
PARAMETER
Input Voltage PVIN Range
Switching Frequency
I
LED
Low PVIN I
(CTRL Foldback)
LED
V
Range
LED
Open LED Voltage
Typical Efficiency
PVIN Under Voltage Lockout (Falling Turn-Off)
PVIN Under Voltage Lockout (Rising Turn-On)
INTVCC
Peak Switch Current Limit
PWMOUT Dimming Duty Cycle
Internal PWM Dimming Frequency
Quick start proceDure
Demonstration circuit 1772A is easy to set up to evaluate
the performance of the LT3761EMSE. Follow the proce-
dure below:
1. Connect a string of LEDs that will run with forward volt-
age less than 60V, but greater than PVIN, to the LED+
and LED– terminals on the PCB as shown in Figure 1.
2. Connect the EN/UVLO terminal to GND.
3. With power off, connect the input power supply to the
PVIN and GND terminals. Make sure that the PVIN DC
input voltage will not exceed 60V (or V
4. Connect the DIM terminal to a voltage between 0V and
7.7V to set the internal PWMOUT dimming duty cycle.
If this terminal is left floating the converter will run with
approximately 12% PWMOUT dimming duty cycle. Pull
the PWM terminal high to INTVCC to set the converter
at 100% duty cycle.
2
Specifications are at T
CONDITION
Operating
R6 = 29.4k
RS2 = 0.25Ω 10V < PVIN < V
RS2 = 0.25Ω PVIN = 8.5V
RS2 = 0.25Ω PVIN = 9V
R3 = 1M R4 = 18.2k
R3 = 1M R4 = 18.2k
PVIN = 14V V
= 60V I
LED
LED
R1 = 499k and R2 = 90.9k
R1 = 499k and R2 = 90.9k
Operating
RS1 = 0.008Ω
VDIM = 7.7V
VDIM = 4V
VDIM = 1.5V
VDIM = 0.4V
C8 = 0.047µF 0V < VDIM < 7.7V
5. Turn the input power supply on and make sure the
voltage is between 8V and 60V (or V
6. Release the EN/UVLO-to-GND connection.
7. Observe the LED string running at the programmed
LED current and brightness related to the programmed
PWMOUT duty cycle.
8. To change the brightness with PWM dimming, simply
vary the VDIM voltage between 0V and 7.7V with the
PWM terminal floating.
).
LED
9. To change the brightness with analog dimming, simply
attach a voltage source on the CTRL terminal and reduce
the voltage below 1.2V.
10. Observe the reduction of brightness in the LED string
when PWM or analog dimming.
= 25°C
A
(60V)
LED
= 1A PWM = INTVCC
VALUE (TYPICAL)
8V to V
(Up to 60V)
LED
350kHz
1A
930mA
975mA
PVIN < V
< 60V
LED
69.8V
94%
8V
9.1V
7.85V
12.5A
96%
50%
10%
4.3%
300Hz
).
LED
dc1772af
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