MAX17491 データシートの表示（PDF） - Maxim Integrated

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MAX17491

Single-Phase Synchronous MOSFET Driver

Maxim Integrated 

Single-Phase Synchronous MOSFET Driver

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 moder-

ately 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 MAX17491 constantly monitors the low-side dri-

ver output (DL) voltage, and only allows the high-side

driver to turn on only when DL drops below the adap-

tive 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 MAX17491 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 MAX17491 uses a bootstrap circuit to generate the

necessary drive voltage to fully enhance the high-side

n-channel MOSFET. The internal p-channel 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 ΔVBST

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

MOSFET and ΔVBST is the voltage variation allowed on

the high-side MOSFET driver. Choose ΔVBST = 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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