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10 Layout 10.1 Layout Guidelines The LM5026 current-sense and PWM comparators are very fast, and respond to short duration noise pulses. The components at the CS, COMP, SS, DCL, UVLO, TIME, SYNC and the RT pins should be as physically close as possible to the IC, thereby minimizing noise pick-up on the PCB tracks. Layout considerations are critical for the current-sense filter. If a current-sense transformer is used, both leads of the transformer secondary should be routed to the sense filter components and to the IC pins. The ground side of each transformer should be connected through a dedicated PCB track to the AGND pin, rather than through the ground plane. If the current-sense circuit employs a sense resistor in the drive transistor source, low inductance resistor should be used. In this case, all the noise-sensitive, low-current ground tracks should be connected in common near the IC, and then a single connection made to the power ground (sense resistor ground point). The gate drive outputs of the LM5026 should have short direct paths to the power MOSFETs in order to minimize inductance in the PCB traces. The two ground pins (AGND, PGND) must be connected together with a short direct connection to avoid jitter due to relative ground bounce. If the internal dissipation of the LM5026 produces high junction temperatures during normal operation, the use of multiple vias under the IC to a ground place can help conduct heat away from the IC. Judicious positioning of the PCB within the end product, along with use of any available air flow (forced or natural convection) can help reduce the junction temperatures.
