STCMB1 datasheet(53/59 Pages) STMICROELECTRONICS

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DocID028958 Rev 4

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STCMB1

STCMB1 layout hints

Connect the RTN of signal components directly to the STCMB1 GND pin (pin

#13). RTN of signal components relevant to the pins FB (pin #3), COMP (pin #4), TON

(pin #5) CF (pin #7), CSS (pin #8) RFMIN (pin #9), STBY (pin #10) must not be

involved in any different return path, it must be kept separated. Use ground tracks width

more than 1 mm.

Figure 32. Control circuitry hints

Connect the feedback optocoupler emitter to the signal RTN, close to the GND

connection of oscillator components. Both optocoupler tracks have to be placed far

from traces and pins operating with high voltage and high dV/dt.

10. Connect heatsinks to Power GND close to each relevant MOSFET source.

Connect the PFC MOSFET heatsink to primary GND, close to the PFC MOSFET

source. Connect the half-bridge MOSFETs heatsink, if present, to primary GND too and

close to the LLC low-side MOSFET source. Never leave heatsinks floating.

11. Place an external copper band contacting the ferrite core of the boost inductor

and connect it to GND. Grounding the core of the PFC inductor decreases the EMI

(radiated noise) from the PFC inductor caused by the dV/dt; it improves the EMC

performance of the SMPS.

12. Place the bootstrap capacitor close to the pins #20 and #18 of STCMB1. Do not

place tracks relevant to the pins VBOOT, HVG an OUT close to signal pins or tracks,

especially CF and other oscillator pins may be affected by disturbances because such

pins operates with high voltage and high dV/dt. Furthermore,

Minimum insulation distances of these tracks and relevant components, with

respect to other low voltage parts, have be checked too.

If an external bootstrap diode is needed, please locate it close to the STCMB1

pins minimizing the length of the tracks.

STCMB1 Datasheet(PDF) 53 Page - STMicroelectronics