ZHCSNT4I February 2006 – May 2021 LM5009
PRODUCTION DATA
The LM5009 regulation and overvoltage comparators are very fast, and as such respond to short-duration noise pulses. Layout considerations are therefore critical for optimum performance. The components at pins 1, 2, 3, 5, and 6 must be as physically close as possible to the device, thereby minimizing noise pickup in the PC tracks. The two major current loops conduct currents that switch very fast and, therefore, those loops must be as small as possible to minimize conducted and radiated electromagnetic interference (EMI). The first loop is formed by CIN, through the VIN to SW pins, LIND, COUT, and back to CIN. The second current loop is formed by D1, LIND, and COUT.
If the internal dissipation of the LM5009 produces excessive junction temperatures during normal operation, good use of the PC board ground plane can help considerably to dissipate heat. The exposed pad on the bottom of the WSON-8 package can be soldered to a ground plane on the PC board, and that plane must extend out from beneath the device to help dissipate heat. Additionally, the use of wide PC board traces, where possible, can also help conduct heat away from the device. Judicious positioning of the PC board within the end product, along with the use of any available air flow (forced or natural convection) can help reduce the junction temperatures.