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|  | alexey.sevastyanov
on 05/04 at 12:58 AM
| Category(s): | Technical Questions |
| Subject: | issues with LM3743 controller |
| Message: (Notified via email on every direct response) |
Hi,
I have some issues with the implementation of LM3740 voltage controller. We have used this DC-DC converter in PCB design as a power supply for FPGA (converting 5 V to 1.0 V). After we have designed and assembled our board we have found next issue. Without any load our converter output voltage is near our target (0.98 V) but circuit consumed current is changing quickly in the interval between 2 and 50 mA. Voltage at the converter FB pin is equal to 0.786 V. When we connect the load to this convertor (we used 2 Ohm load) converter output voltage is fall down to 0.6 V with the circuit consumed current changing quickly again (current interval: 370-410 mA). Voltage at the converter FB pin is about 0.5 V.
Our schematic is similar to Example Circuit 1 that is in LM3740 datasheet page 24, Figure 12, (http://www.national.com/ds/LM/LM3743.pdf). In attachment you can find our full bill of material for this converter with part numbers and datasheets url?s (most of the parts is similar to Example Circuit 1 BOM). Part reference designators are for Figure 12 of LM3740 datasheet. For PCB layout we used application note AN-1450 (http://www.national.com/an/AN/AN-1450.pdf) as a reference.
Please suggest solutions that can resolve this issue!
Thanks in advance,
Alexey Sevastyanov
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