Rainbow-electronics MAX786 Uživatelský manuál stáhnout pdf (Strana 11)

MAX786

Dual-Output Power-Supply

Controller for Notebook Computers

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second half-cycle, the PWM turns on the high-side

MOSFET by connecting the capacitor to the MOSFET

gate by closing an internal switch between BST_ and

DH_. This provides the necessary enhancement voltage

to turn on the high-side switch, an action that “boosts”

the 5V gate-drive signal above the battery voltage.

Ringing seen at the high-side MOSFET gates (DH3 and

DH5) in discontinuous-conduction mode (light loads) is

a natural operating condition caused by the residual

energy in the tank circuit formed by the inductor and

stray capacitance at the LX_ nodes. The gate driver

negative rail is referred to LX_, so any ringing there is

directly coupled to the gate-drive supply.

CS_

FB_

BST_

DH_

LX_

LEVEL

SHIFT

SHOOT-

THROUGH

CONTROL

DL_

PGND

LEVEL

SHIFT

SYNCHRONOUS

RECTIFIER CONTROL

3.3V

30R

4µA

0mV TO 100mV

CURRENT

LIMIT

MINIMUM

CURRENT

(IDLE MODE)

25mV

SLOPE COMP

REF, 3.3V

(OR INTERNAL

5V REFERENCE)

MAIN PWM

COMPARATOR

60kHz

LPF

OSC

SS_

ON_

Figure 3. PWM Controller Block Diagram

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 19 20

Dual-Output Power-Supply 1

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Rainbow-electronics MAX786 Uživatelský manuál Strana 11

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