STCMB1 datasheet(42/59 Pages) STMICROELECTRONICS

42 / 59 page

Application information

STCMB1

42/59

DocID028958 Rev 4

The HSP and ACP functions in the STCMB1 help to prevent the severe drawbacks of the

capacitive mode operation, while enabling a design that needs to ensure the inductive mode

operation only in the specified operating range, neglecting abnormal operating conditions.



If the phase shift of the tank current approaches zero, which is indicative of the

impending capacitive mode operation, at some point the tank current will cross the zero

current band within the deadtime. Therefore, the ACP circuit will find an anomalous

condition and will extend the deadtime until the tank current changes the sign.

Additionally, the soft-start capacitor is discharged, so that the resulting frequency rise

pushes the operation away from that dangerous condition.



If the phase relationship reverses abruptly (which may happen in case of dead short at

the converter's output), the HSP will find it has the wrong sign and extend the duration

of that conduction cycle until the tank current changes the sign.

The HSP control method helps to avoid hard switching condition at MOSFET’s turning-on,

confirming the ISEN_HB sign is coherent with the driver is going to be turned-on. It checks

the sign of the ISEN_HB before the driver is turned-off. When the ramp of the oscillator

reaches the peak value VCFp, if the sign of the ISEN_HB signal is correct (positive with HS

on and LS off, negative with LS on and HS off), the driver currently active is turned off and

the deadtime starts. Otherwise, if the sign of the ISEN_HB is not correct the HSP acts

resetting the oscillator and letting the driver currently active on until the ISEN_HB sign

becomes correct.

The ACP (anti-capacitive mode protection) works monitoring the sign of the ISEN_HB

voltage signal at the end of the deadtime. If the sign on the ISEN_HB pin has not correct

polarity with respect to the driver is going to be turned-on (positive after LVG turn-off or

negative after HVG turn-off), a capacitive mode (CM) condition is asserted. Hence the

oscillator is reset and the drivers are kept off until the ISEN_HB sign returns to be consistent

with the proper HB operation, preventing the hard switching condition. During CM condition

the CSS capacitor is discharged, in this way increasing frequency as long as CM conditions

end.

The half-bridge current sign definition is resulting from the use of two comparators

monitoring the ISEN_HB signal. The sign of the current is considered positive when the

voltage on that pin exceeds -VISEN_Z, negative when it falls below VISEN_Z

(|VISEN_Z| = 20 mV typ.)

During the start-up, the CSS discharge is disabled as long as the CSS pin voltage reaches

1.85 V to prevent deadlock conditions. For the same reason, the CSS discharge is disabled

for about 50

s after that the HB exits from the idle state of the burst mode operation.

STCMB1 数据表(PDF) 42 Page - STMicroelectronics

STCMB1 数据表(HTML) 42 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59

数据表下载