MAX8791GTA 查看數據表（PDF） - Maxim Integrated

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MAX8791GTA

Single-Phase, Synchronous MOSFET Drivers

Maxim Integrated 

Single-Phase, Synchronous MOSFET Drivers

VDD

BST

PWM

DRV

DH

DRIVER LOGIC

THERMAL SHUTDOWN

AND

LX

DEAD-TIME

CONTROL

UVLO

DRV#

VDD

SKIP

DL

LX

GND

ZX DETECTION

PAD

Figure 4. Overview Block Diagram

Adaptive Shoot-Through Protection

The DH and DL drivers are optimized for driving mod-

erately sized high-side and larger low-side power

MOSFETs. This is consistent with the low duty factor

seen in the notebook CPU environment, where a large

VIN - VOUT differential exists. Two adaptive dead-time

circuits monitor the DH and DL outputs and prevent the

opposite-side FET from turning on until the other is fully

off. The MAX8791/MAX8791B constantly monitor the

low-side driver output (DL) voltage, and only allow the

high-side driver to turn on when DL drops below the

adaptive threshold. Similarly, the controller monitors the

high-side driver output (DH), and prevents the low side

from turning on until DH falls below the adaptive thresh-

old before allowing DL to turn on.

The adaptive driver dead time allows operation without

shoot-through with a wide range of MOSFETs, minimiz-

ing delays and maintaining efficiency. There must be a

low-resistance, low-inductance path from the DL and

DH drivers to the MOSFET gates for the adaptive dead-

time circuits to work properly; otherwise, the sense cir-

cuitry in the MAX8791/MAX8791B interprets the

MOSFET gates as off while charge actually remains.

Use very short, wide traces (50 mils to 100 mils wide if

the MOSFET is 1in from the driver).

Internal Boost Switch

The MAX8791/MAX8791B use a bootstrap circuit to

generate the necessary drive voltage to fully enhance

the high-side n-channel MOSFET. The internal p-chan-

nel MOSFET creates an ideal diode, providing a low

voltage drop between VDD and BST.

The selected high-side MOSFET determines appropriate

boost capacitance values (CBST in Figure 1), according

to the following equation:

CBST = QGATE ∆VBST

where QGATE is the total gate charge of the high-side

MOSFET and ∆VBST is the voltage variation allowed on

the high-side MOSFET driver. Choose ∆VBST = 0.1V to

0.2V when determining CBST. The boost flying capacitor

should be a low equivalent-series resistance (ESR)

ceramic capacitor.

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