PM6670 datasheet(22/53 Pages) STMICROELECTRONICS

22 / 53 page

Device description

PM6670

22/53

7.1.1

Constant-On-Time architecture

Figure 30

shows the simplified block diagram of the Constant-On-Time controller.

The switching regulator of the PM6670 owns a one-shot generator that ignites the high-side

MOSFET when the following conditions are simultaneously satisfied: the PWM comparator

is high (i.e. output voltage is lower than Vr = 0.9V), the synchronous rectifier current is below

the current limit threshold and the minimum off-time has expired.

A minimum Off-Time constraint (300ns typ.) is introduced to assure the boot capacitor

charge and allow inductor valley current sensing on low-side MOSFET. A minimum On-Time

is also introduced to assure the start-up switching sequence.

Once the On-Time has timed out, the high side switch is turned off, while the synchronous

rectifier is ignited according to the anti-cross conduction management circuitry.

When the output voltage reaches the valley limit (determined by internal reference

Vr = 0.9V), the low-side MOSFET is turned off according to the anti-cross conduction logic

once again, and a new cycle begins.

Figure 30. Switching section simplified block diagram

driver

Level

shifter

driver

Ton

Ton--min

min

Anti cross-

conduction

circuitry

Toff

Toff--min

min

PWM Comparator

Positive Current Limit comparator

0.9V

Min

Min fsw

fsw

counter

Zero

Zero--crossing

crossing

Comparator

bandgap

1.236V

PHASE

PGND

LGATE

BOOT

CSNS

COMP

Integrator

VSNS

VBG

PULSE

PULSE -- SKIP

SKIP

MODE

MODE<4V

1-Shot generator

Ton

VSNS

VOSC

DDRSEL

0.9V

100uA

500mV

2.5V

HGATE

VREF

SGND

VOSC

VCC

PM6670 数据表(PDF) 22 Page - STMicroelectronics

PM6670 数据表(HTML) 22 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

数据表下载