LM5146: Design help

Paul Connor

Part Number: LM5146
Other Parts Discussed in Thread: LM5145

Tool/software:

Some questions relating to designing with the LM5145 & LM5146 parts: -

(1) Am I right in thinking that the LM5145 and LM5146 are functionaly identical appart from the higher input voltage of the LM5146?

(2) If the design uses multiple FETs to spread the heat, should the individual FETs have gate resistors or can the gates be connected together? If resistors are required then what value?

(3) When using the SYNCIN pin to choose between DCM and FPWM, what counts as logic high. Should the pin be tied to Vcc or should a pull up resistor be used?

over 1 year ago

+1 Timothy Hegarty over 1 year ago

TI__Guru 74692 points

Hi Paul,

1. Correct, they are p2p compatible apart from input voltage rating.

2. Better to just use one good FET instead of two paralleled FETs, as it keeps the switching loop area to a minimum. See app note SNVA803 for more detail here. If paralleled FETs are deemed necessary, the high-side can have gate resistors. No need on the low-side, as it may cause Cdv/dt shoot-through.

3. There is a 20k internal pulldown, so the default state is DEM. Tie high or pullup to VCC for FPWM.

Tim