STCMB1 datasheet(52/59 Pages) STMICROELECTRONICS

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STCMB1 layout hints

STCMB1

52/59

DocID028958 Rev 4

Connect the pin #13 (GND) to the RTN star point making the connections as

short as possible and using a track width suitable to minimize its impedance

(larger than 1 mm). Keep this connection separated from any other GND connection,

especially if carrying high currents.

PCB tracks carrying high dV/dt signals have to be as short as possible. This

minimizes the noise radiation that might affect high impedance points working with low

level signals. Therefore, the PCB tracks connected to the boost inductor, PFC

MOSFET drain, PFC rectifier and LLC resonant tank MOSFETs and transformer have

to be routed as short as possible and their width has to be at least 1.5 mm, in order to

minimize their parasitic inductance. Pay attention also to the insulation creepage

distance.

Figure 31. STCMB1 power section and RTN connections

Place the VCC filter capacitor (ceramic, 470 nF ÷ 1 µF) close to the STCMB1

connecting it to the VCC pin (pin #15) and to the GND (pin #13).

Keep signal components as close as possible to the relevant pins. Connect the

components relevant to the FB (pin #3), COMP (pin #4), TON (pin #5) CF (pin #7), CSS

(pin #8) RFMIN (pin #9), STBY (pin #10) close to the GND pin of the STCMB1 (pin

#13). All components and traces connected to the mentioned pins have to be placed far

from traces and connections carrying signals with high dV/dt.

The tracks relevant to the whole net of the pin #3 (FB) have to be as short as

possible and far from high dV/dt signal tracks. Because of its high impedance, the

pin could pick up noise affecting the PFC operation. If an additional circuit is needed to

pull-down the pin to latch the STCMB1 in case of OTP or the open loop, it has to be

placed close to the pin itself.

Place the RC filtering components of the PFC and LLC current sensing as close

as possible to the relevant pins, ISEN_PFC and ISEN_HB. Filtering resistors in

series have to be placed nearby the pins as well. The filtering capacitors ground

connection have to be near to the pin #13 (GND), on the signal ground connection.

Components and traces connected to the mentioned pins have to be placed far from

traces and connections carrying signals with high dV/dt.

STCMB1 数据表(PDF) 52 Page - STMicroelectronics