Mike S
Newbie level 2
I'm having some trouble with an LED driver that I built. It uses an ISSI chip which has built in modes (high, medium, low).
http://www.issiusa.com/pdf/31LT3380.pdf
I'm trying to drive the LED at 1000 mA on High and the efficiency is somewhat poor at only 84.5%. The chip gets extremely hot within seconds, which causes it to drop to medium mode. I think this is due to the layout of the traces and the components that were selected.
Here are the details:
• Schottky Diode
Vishay B240A-E3/61T
Voltage Max - 40V
Current - 2A
Forward Voltage - 550mV @ 2A
Speed - Fast Recovery =< 500ns, > 200mA (Io)
Reverse Leakage Current - 500µA @ 40V
• Inductor
Epcos Inc. B82464A4473K
Core - Ferrite
Inductance - 47uH
Current - 1.5A
Current Saturation - 1.8A
DC Resistance - 140 mOhm Max
• Set Resistor
0.1 ohm, 1/4W, 1%
• Filtering Caps
All the filtering caps are ceramic low ESR X5R or X7R with values identical to what's shown in the datasheet.
• LED
One string of two Cree XT-E's. This is just for testing the circuit. The final design will use a single Cree XR-E.
Some measurements
Power Supply
Voltage = 9V
Current = 960mA
Watts = 8.64W
LED
Voltage = 6.71V
Current = 1.090A
Watts = 7.314W
Overall Efficiency = 84.65%
Here is the board layout.
Does anything standout which would cause the efficiency to be so low? I really wish the chip was available in something other than SO-8, but that's all that they offer. Any help would be greatly appreciated. I have little experience in electronics, but am willing to try anything to make this work.
Thanks!
http://www.issiusa.com/pdf/31LT3380.pdf
I'm trying to drive the LED at 1000 mA on High and the efficiency is somewhat poor at only 84.5%. The chip gets extremely hot within seconds, which causes it to drop to medium mode. I think this is due to the layout of the traces and the components that were selected.
Here are the details:
• Schottky Diode
Vishay B240A-E3/61T
Voltage Max - 40V
Current - 2A
Forward Voltage - 550mV @ 2A
Speed - Fast Recovery =< 500ns, > 200mA (Io)
Reverse Leakage Current - 500µA @ 40V
• Inductor
Epcos Inc. B82464A4473K
Core - Ferrite
Inductance - 47uH
Current - 1.5A
Current Saturation - 1.8A
DC Resistance - 140 mOhm Max
• Set Resistor
0.1 ohm, 1/4W, 1%
• Filtering Caps
All the filtering caps are ceramic low ESR X5R or X7R with values identical to what's shown in the datasheet.
• LED
One string of two Cree XT-E's. This is just for testing the circuit. The final design will use a single Cree XR-E.
Some measurements
Power Supply
Voltage = 9V
Current = 960mA
Watts = 8.64W
LED
Voltage = 6.71V
Current = 1.090A
Watts = 7.314W
Overall Efficiency = 84.65%
Here is the board layout.
Does anything standout which would cause the efficiency to be so low? I really wish the chip was available in something other than SO-8, but that's all that they offer. Any help would be greatly appreciated. I have little experience in electronics, but am willing to try anything to make this work.
Thanks!
Last edited:
