Detailed Description

Principles of Operation

MOSFET Gate Drivers (DH_, DL_)

DH_ is driven high when the PWM_ is high; DL_ is dri-

ven high when PWM_ is low. PWM pulsewidths under

20ns (typ) are rejected, and no switching occurs.

The low-side drivers (DL_) have typical 0.9

Ω sourcing

resistance and 0.4

Ω sinking resistance, and are capable

of driving 3000pF capacitive loads with 11ns typical rise

and 8ns typical fall times. The high-side drivers (DH_)

have typical 1.0

Ω sourcing resistance and 0.7Ω sinking

resistance, and are capable of driving 3000pF capaci-

tive loads with 14ns typical rise and 9ns typical fall times.

This facilitates fast switching, reducing switching losses,

and makes the MAX8811 ideal for both high-frequency

and high-output current applications.

Shoot-Through Protection

Adaptive shoot-through protection is incorporated for

the switching transition after the high-side MOSFET is

turned off and before the low-side MOSFET is turned

on. The low-side driver is turned on when the LX volt-

age falls below 2.5V, or after 135ns typical delay,

whichever occurs first. Furthermore, the delay time

between the low-side MOSFET turn-off and high-side

MOSFET turn-on can be adjusted by selecting the

value of R1 (see the Setting the Dead Time section).

Undervoltage Lockout (UVLO)

When the voltage at the VL1/VL2 connection is below

the UVLO threshold, all driver outputs are held low. This

prevents switching when the supply voltage is too low

for proper operation.

Thermal Protection

Thermal-overload protection limits total power dissipa-

tion in the MAX8811. When the junction temperature

exceeds +165°C, all driver outputs are held low. The IC

resumes normal operation after the junction tempera-

ture cools by 15°C (typ).

Boost Capacitor Selection

The MAX8811 uses a bootstrap circuit to generate the

supply voltages for the high-side drivers (DH_). The select-

ed high-side MOSFET determines the appropriate boost

capacitance values, according to the following equation:

MOSFET and

the high-side MOSFET drive. Choose

tors should be used.

VL_ Decoupling

VL1 and VL2 provide the supply voltage for the low-side

drivers. The decoupling capacitors at VL_ also charge the

BST capacitors during the time period when DL_ is high.

Therefore, the decoupling capacitor C3 for VL_ should be

large enough to minimize the ripple voltage during

switching transitions. Choose the VL capacitor approxi-

mately 10 times the value of the BST capacitor value.

C

Q

V

BST

GATE

BST

=

Δ

High-Speed, Dual-Phase Driver

with Integrated Boost Diodes

_______________________________________________________________________________________

7

DESIGNATION

DESCRIPTION

MANUFACTURER

C1

2 x 10µF ±20%, X7R

25V capacitor

12103D106MAT2W

AVX

C2

2 x 10µF ±20%, X7R

25V capacitor

12103D106MAT2W

AVX

C3

2.2µF ±20%, 10V X5R

capacitor

GRM39X5R225K10

Murata

C4, C5

0.22µF ±20%, 10V

X7R capacitors

GRM39X7R224K10

Murata

C6–C9

100µF ±20%, 6.3V

X5R capacitors

C3225X5R0J107M

TDK

L1, L2

0.2µH, 28A inductors

FDV0630-

R20M,1.9m

Ω DCR

TOKO

Q1, Q3

HAT2168, 8m

Ω, 30V

MOSFET

Renesas

Q2

2 x HAT2164H, 3m

Ω,

30V, MOSFET

Renesas

Q4

2 x HAT2164H, 3m

Ω,

30V MOSFET

Renesas

R1

Dead-time delay

programming resistor;

see Programmable

Typical Operating

Characteristics

—

Table 1. Components for Figure 3, 800kHz,

20A/Phase Typical Application Circuit