I'm working on a project where we have a 24VDC input and I'm using the TL2575-33 switching regulator to get that down to 3.3VDC. This is the power supply for a relatively small and simple PCB with two other TI RF chips (CC2530 w/ CC2591 amplifier) and a power metering chip. The problem we're having is that when we test the TL2575 through-hole package in the lab on a perf board, the heat the TL2575 puts off is enough to burn your finger. I'm using all the suggested parts as given in the datasheet with the components as close to the TL2575 as they can be.
Based on our calculations for current, we are going to need around 100 mA normally with a peak consumption around 200-230mA when at full RF power. I have a schottky diode rated at 1A and 40V, the caps are at the recommended values and are rated for 50V and the inductor is 680uH. I also tried a 1000uH inductor but still had the same heat problems. To test I hook up a load resistor that simulates 200mA of current.
On the test bench when running at a lower input voltage the heat is not bad but when i get up to around 18-24VDC it starts getting really hot, which i expect. But what I'm wondering is, when I use the DDPACK-5 package and put it on my board, will it be scorching hot still and is this acceptable? Should I have a ground plane around it to help dissipate the heat? I'm assuming I should get a heat sink as well but will this solve my heat problems to a reasonable point?
Thanks in advance for the help,
Some things sound strange, others are not clear. When you say the thru-hole package, is that the PDIP one?
Your output power is 3.3V x 200mA , approx. 0.65W. With an efficiency of between 70 to 80%, the heat disipated by the device should be of no more than 0.2W. Even with the very bad thermal resistance of the PDIP package, that would ammount to a temp. increase of no more than 20°C.
It is also not so good that the temperature raises so much for high Vin. The efficiency of the device doesn't change so much... and I have the impression that it gets BETTER as Vin increases.
You should check all your design carefully. Measure output voltage and output current for several input voltages. Something fishy is going there, according to what you told.
Yes, we are using the PDIP package for testing and we're going to use the TO-263 package when we make our PCB. According to what you said, we're going to have to revisit our circuit again to double check everything it sounds like. Thank you for the advice so far and i'll post more questions if I have them. We basically wanted some verification that this shouldn't be happening...
Hello John,Be sure to connect all three grounds together on the PDIP package. It is important to do so.
Measure the input and outputs voltages and current to calculate efficiency and power loss.Look at pin 3 (output) with an oscilloscope, this node is very informative.~ -1V is inductor discharging through diode (switch off)~+VCC is internal switch charging inductor.~+3.3V is inductor current zero (switch off)Regards,Ron Michallick
Regards,Ronald MichallickLinear Applications
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