MAX786 Просмотр технического описания (PDF) - Maxim Integrated

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MAX786

Dual-Output Power-Supply Controller for Notebook Computers

Maxim Integrated 

Dual-Output Power-Supply

Controller for Notebook Computers

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_

1X

REF, 3.3V

(OR INTERNAL

5V REFERENCE)

60kHz

LPF

MAIN PWM

COMPARATOR

Σ

SLOPE COMP

R

Q

S

OSC

FB_

BST_

LEVEL

DH_

SHIFT

LX_

25mV

4µA

MINIMUM

CURRENT

(IDLE MODE)

VL

CURRENT

LIMIT

0mV TO 100mV

SS_

30R

3.3V 1R

ON_

N

SYNCHRONOUS

RECTIFIER CONTROL

R

Q

S

Figure 3. PWM Controller Block Diagram

SHOOT-

THROUGH

CONTROL

LEVEL

SHIFT

VL

DL_

PGND

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