2
dc2345af
DEMO MANUAL DC2345A
QUICK START PROCEDURE
Demonstration circuit DC2345A is easy to set up to evaluate
the performance of the LT8391 Follow the procedure below:
1. With power off, connect a string of LEDs that will run
with forward voltage less than or equal to 25V (at 2A)
to the LED+ and GND banana jacks on the PCB as
shown in Figure 1.
2. Connect the EN/UVLO terminal to GND.
3. Set JP1 to EXT/ON and JP3 to ON for 100% always-on
LED operation. Set JP2 to NO SPREAD/SYNC to run
without SSFM or external synchronization.
4. With power off, connect the input power supply to the
EMIVIN and GND banana jacks. Make sure that the DC
input voltage will not exceed 60V.
5. Turn the input power supply on and make sure the
voltage is between 4V and 60V for proper operation.
6. Release the EN/UVLO-to-GND connection.
7. Observe the LED string running at the programmed
LED current.
8. To change the brightness with analog dimming, simply
attach a voltage source to either the CTRL1 or CTRL2
terminal and set the voltage between 0V and 1.5V. See
data sheet for details.
9. To change brightness with external PWM dimming, set
JP1 to EXT/ON and JP3 to EXT. Attach a 3V rectangular
waveform with varying duty cycle to the PWM terminal.
10. To change brightness with internally-generated PWM
dimming, set JP1 to INT and JP3 to INT. Adjust the
setting of the VR1 variable resistor with a small flat-
head screwdriver to toggle between 0% and 100%
PWM dimming duty cycle in 1/128 steps.
11. To enable spread spectrum frequency modulation, set
JP2 to SPREAD ON.
PERFORMANCE SUMMARY
Specifications are at T
A
= 25°C
PARAMETER
CONDITIONS
MIN
TYP
MAX
Input Voltage EMIVIN Range
Operating V
LED
= 25V
4V
60V
Switching Frequency
R3 = 100k
400kHz
I
LED
R1 = 0.05Ω 7.0V < PV
IN
< 60V V
LED
= 25V
2.0A
V
LED
range
R5 = 1M R6 = 34.8k
26V
Open LED Voltage V
OUT
R5 = 1M R6 = 34.8k
29.7V
Typical Efficiency (100% PWM DC)
PV
IN
= 14V V
LED
= 25V I
LED
= 2.0A
97%
Internally-Generated PWM Dimming Range
Operating JP3 = INT JP1 = INT
1/128
100%
Internally-Generated PWM Dimming Frequency
Operating JP3 = INT JP1 = INT R16 = 200k
200Hz
Peak Switch Current Limit Boost Region
R2 = 0.004Ω
12.5A
Peak Switch Current Limit Buck Region
R2 = 0.004Ω
12.5A
