STCMB1 datasheet(28/59 Pages) STMICROELECTRONICS

28 / 59 page

Application information

STCMB1

28/59

DocID028958 Rev 4

In the left picture a feedback disconnection event has been captured: we can see that when

the FB pin drops below the threshold the converters stops switching and the HV start-up is

activated keeping the STCMB1 correctly powered to retain the latch condition. The latch

condition can be cleared by unplugging the ac mains voltage.

7.14

PFC gate driver

The GD_PFC gate driver has a DMOS structure driving the MOSFET gate. The current

capability is 0.3 A at the MOSFET turn-on and 0.7 A at turn-off, giving typical rise and fall

times of 60 ns and 30 ns respectively, so it is able to drive MOSFETs with suitable size for

high efficiency transition mode PFCs.

The driver has no any voltage clamping of the gate voltage thus the MOSFET will be driven

with a driving voltage at the VCC level. For this reason the VCC will have to be limited in all

operating or fault condition to a safe level, to avoid any premature aging or damaging of the

MOSFETs gate oxide.

Active pull-down circuitry prevents any undesired MOSFET turn-on that might occur in very

noisy environment and allows removing the typical gate-source resistance or using

a higher value.

7.15

Resonant HB section

The STCMB1 embeds an advanced double-ended controller specific for the resonant half-

bridge topology. Its detailed block diagram is illustrated in Figure 7 on page 19.

Normally, in this converter the MOSFETs of the half-bridge leg are alternately switched on

and off (180 ° out-of-phase) for exactly the same time. This is commonly referred to as an

operation at “50% duty cycle”, although the real duty cycle, e.g.: the ratio of the on-time of

either switch to the switching period, is actually less than 50%. The reason is that there is

a deadtime TD inserted between the turn-off of either MOSFET and the turn-on of the other

one, where both MOSFETs are off. This deadtime is essential in order for the converter to

work correctly: it enables soft-switching and, then, the high frequency operation with high

efficiency and low EMI emissions.

STCMB1 数据表(PDF) 28 Page - STMicroelectronics