MAX8643 查看數據表（PDF） - Maxim Integrated

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MAX8643

3A, 2MHz Step-Down Regulator with Integrated Switches

Maxim Integrated 

3A, 2MHz Step-Down Regulator

with Integrated Switches

Typical Application Circuit

INPUT

2.4V TO 3.6V

C6

C7

22μF

0.01μF

R5

VDD

10Ω

C5

1μF

IN

BST

MAX8643

LX

VDD

OUT

CTL2

R4

50kΩ

CTL1

EN

FREQ

REFIN

SS

C4

0.022μF

PGND

FB

COMP

PWRGD

GND

C10

0.1μF

L1

0.47μH

OUTPUT

1.8V, 3A

C3

560pF

R3

158Ω

C8

C9

22μF

0.01μF

C2

1500pF

R2

2.67kΩ

C1

33pF

VDD

R1

20kΩ

Figure 1. 1MHz, All-Ceramic Capacitor Design with VOUT = 1.8V

Detailed Description

The MAX8643 high-efficiency, voltage-mode switching

regulator is capable of delivering up to 3A of output

current. The MAX8643 provides output voltages from

0.6V to (0.9 x VIN) from 2.35V to 3.6V input supplies,

making it ideal for on-board point-of-load applications.

The output voltage accuracy is better than ±1% over

load, line, and temperature.

The MAX8643 features a wide switching frequency

range, allowing the user to achieve all-ceramic capaci-

tor designs and fast transient responses. The high oper-

ating frequency minimizes the size of external

components. The MAX8643 is available in a small (4mm

x 4mm), lead-free, 24-pin thin QFN package. The REFIN

function makes the MAX8643 an ideal candidate for

DDR and tracking power supplies. Using internal low-

RDSON (37mΩ) n-channel MOSFETs for both high- and

low-side switches maintains high efficiency at both

heavy-load and high-switching frequencies.

The MAX8643 employs voltage-mode control architec-

ture with a high-bandwidth (> 14MHz) error amplifier.

The voltage-mode control architecture allows up to

2MHz switching frequency, reducing board area. The

op-amp voltage-error amplifier works with type 3 com-

pensation to fully utilize the bandwidth of the high-fre-

quency switching to obtain fast transient response.

Adjustable soft-start time provides flexibilities to mini-

mize input startup inrush current. An open-drain,

power-good (PWRGD) output goes high when VFB

reaches 90% of VREFIN or 0.54V.

Controller Function

The controller logic block is the central processor that

determines the duty cycle of the high-side MOSFET

under different line, load, and temperature conditions.

Under normal operation, where the current-limit and

temperature protection are not triggered, the controller

logic block takes the output from the PWM comparator

and generates the driver signals for both high-side and

low-side MOSFETs. The break-before-make logic and

the timing for charging the bootstrap capacitors are

calculated by the controller logic block. The error signal

from the voltage-error amplifier is compared with the

ramp signal generated by the oscillator at the PWM

comparator and, thus, the required PWM signal is pro-

duced. The high-side switch is turned on at the begin-

ning of the oscillator cycle and turns off when the ramp

voltage exceeds the VCOMP signal or the current-limit

threshold is exceeded. The low-side switch is then

turned on for the remainder of the oscillator cycle.

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