I am currently trying to use the LMR61428 boost converter IC with the configuration in the attached schematic and having an heating problem with the inductor. The inductor gets very hot very fast even though it is able to carry more current than the intended peak current. The IC is able to function but it shutdowns itself as thermal management starts to work. Is there anything wrong the with schematic or the component selection. The Mosfet is controlled by a microcontroller ATTINY84. The input voltage for the system is 8 volts. Inductor used in PCB Schematic

  • \$\begingroup\$ What is value of RZ? . \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 24 '19 at 17:49
  • \$\begingroup\$ What does the board layout look like? Do you have thermal relief via's? Large pad to dissipate heat? \$\endgroup\$ – Ron Beyer Jun 24 '19 at 17:50
  • \$\begingroup\$ @SunnyskyguyEE75 RZ is around 5 ohms. \$\endgroup\$ – Berkays Jun 24 '19 at 19:05
  • \$\begingroup\$ @RonBeyer Here is the relevant PCB layout Board \$\endgroup\$ – Berkays Jun 24 '19 at 19:11

There are a few design flaws overlooked from the datasheet.

  1. Output is 11.6V = Vdd =Bootstrap which exceeds > 5.5V and
  2. Ipk inductor = 1.5 output may exceed L rating 2.9A which may be caused by 1.) and
  3. Switch Current up to 2.85A "spec" = is not same as = I out max at a 11.6V boost voltage.
  4. Your heater load RX is not given.
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  • \$\begingroup\$ Thank you for your answer. Do you think removing the R21 connection and connecting to 5V will solve the problem? According to the datasheet, maximum switching current for 12 volt output is not specified. Can you explain what the difference is between 2.85A and I out max at 11.6V boost voltage? \$\endgroup\$ – Berkays Jun 24 '19 at 20:07
  • \$\begingroup\$ No . the datasheet says what’s needed for Bootstrap there. A 5Vdc supply or LDO. If it switches current while boosting voltage, Inductor current peak must be higher according to datasheet. And max input current cannot be exceeded while your load is already demanding 2.4A \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 24 '19 at 20:14
  • \$\begingroup\$ I got the bootstrap pin directly connected to a 5V output. Now heating problem for the inductor seems to be solved. However this time the linear voltage regulator in the circuit is now getting really hot (U2). Could you help on this as well? PCB, Schematic \$\endgroup\$ – Berkays Jun 24 '19 at 22:14
  • \$\begingroup\$ Didn't you follow the datasheet. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 24 '19 at 22:42
  • \$\begingroup\$ Not such a SIMPLE design® if not followed exactly. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jun 24 '19 at 22:51

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