Datasheet

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General Description

The MAX8643 high-efficiency switching regulator deliv-

ers up to 3A load current at output voltages from 0.6V

to (0.9 x V

).The IC operates from 2.35V to 3.6V, mak-

ing it ideal for on-board point-of-load and postregula-

tion applications. Total output error is less than ±1%

over load, line, and temperature.

The MAX8643 features fixed-frequency PWM mode

operation with a switching frequency range of 500kHz

to 2MHz set by an external resistor. High-frequency

operation allows for an all-ceramic capacitor design.

The high operating frequency also allows for small-size

external components.

The low-resistance on-chip nMOS switches ensure high

efficiency at heavy loads while minimizing critical induc-

tances, making the layout a much simpler task with

respect to discrete solutions. Following a simple layout

and footprint ensures first-pass success in new designs.

The MAX8643 comes with a high-bandwidth (> 14MHz)

voltage-error amplifier. The voltage-mode control archi-

tecture and the voltage-error amplifier permit a type III

compensation scheme to be utilized to achieve maxi-

mum loop bandwidth, up to 20% of the switching fre-

quency. High loop bandwidth provides fast transient

response, resulting in less required output capacitance

and allowing for all-ceramic capacitor designs.

The MAX8643 provides two tri-state logic inputs to

select one of nine preset output voltages. The preset

output voltages allow customers to achieve ±1% out-

put-voltage accuracy without using expensive 0.1%

resistors. In addition, the output voltage can be set to

any customer value by either using two external resis-

tors at the feedback with 0.6V internal reference or

applying an external reference voltage to the REFIN

input. The MAX8643 offers programmable soft-start

time using one capacitor to reduce input inrush current.

The MAX8643 is available in a lead-free, 24-pin, 4mm x

4mm thin QFN package.

Applications

POLs

ASIC/CPU/DSP Core and I/O Voltages

DDR Power Supplies

Base-Station Power Supplies

Telecom and Networking Power Supplies

RAID Control Power Supplies

Features

♦ Internal 37mΩ R

DSON

MOSFETs

♦ Continuous 3A Output Current

♦ ±1% Output Accuracy Over Load, Line,

and Temperature

♦ Operates from 2.35V to 3.6V Supply

♦ Adjustable Output from 0.6V to (0.9 x V

)

♦ Soft-Start Reduces Inrush Supply Current

♦ 500kHz to 2MHz Adjustable Switching Frequency

♦ Compatible with Ceramic, Polymer, and

Electrolytic Output Capacitors

♦ VID-Selectable Output Voltages

0.6, 0.7, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, and 2.5V

♦ Fully Protected Against Overcurrent

and Overtemperature

♦ Sink/Source Current in DDR Application

♦ Lead-Free, 24-Pin, 4mm x 4mm

Thin QFN Package

MAX8643

3A, 2MHz Step-Down Regulator

with Integrated Switches

________________________________________________________________

Maxim Integrated Products

Ordering Information

19-3970; Rev 3; 9/07

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

PART

TEMP

RANGE

PIN-PACKAGE

PKG

CODE

MAX8643ETG+

-40°C to

+85°C

24 Thin QFN-EP*

4mm x 4mm

T2444-4

Denotes lead-free package.

EP = Exposed pad.

Pin Configuration appears at end of data sheet.

OUTPUT

1.8V, 3A

INPUT

2.4V, 3.6V

BST

OUT

CTL1

CTL2

PGND

COMP

PWRGD

FREQ

REFIN

GND

MAX8643

Typical Operating Circuit

Summary of content (16 pages)

PAGE 1
9-3970; Rev 3; 9/07 KIT ATION EVALU E L B A AVAIL 3A, 2MHz Step-Down Regulator with Integrated Switches The MAX8643 high-efficiency switching regulator delivers up to 3A load current at output voltages from 0.6V to (0.9 x VIN).The IC operates from 2.35V to 3.6V, making it ideal for on-board point-of-load and postregulation applications. Total output error is less than ±1% over load, line, and temperature.
PAGE 2
MAX8643 3A, 2MHz Step-Down Regulator with Integrated Switches ABSOLUTE MAXIMUM RATINGS IN, VDD, PWRGD to GND ......................................-0.3V to +4.5V COMP, FB, REFIN, OUT, CTL_, EN, SS, FREQ to GND...................-0.3V to (VDD + 0.3V) LX Current (Note 1) .....................................................-4A to +4A BST to LX..................................................................-0.3V to +4V PGND to GND .......................................................-0.3V to +0.
PAGE 3
A, 2MHz Step-Down Regulator with Integrated Switches (VIN = VDD = 3.3V, VFB = 0.5V, TA = -40°C to +85°C. Typical values are at TA = +25°C, circuit of Figure 1, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX Open-Loop Voltage Gain 1kΩ from COMP to GND Error-Amplifier Unity-Gain Bandwidth Parallel 10kΩ, 40pF from COMP to GND (Note 3) 14 VDD = 2.35V to 2.6V 0 VDD - 1.65 VDD = 2.6V to 3.6V 0 VDD - 1.
PAGE 4
ELECTRICAL CHARACTERISTICS (continued) (VIN = VDD = 3.3V, VFB = 0.5V, TA = -40°C to +85°C. Typical values are at TA = +25°C, circuit of Figure 1, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS 1.2 0.7 V ENABLE EN Input Logic-Low, Falling EN Input Logic-High, Rising 1.7 EN Hysteresis VEN = 0V or 3.6V, VDD = 3.6V EN, Input Current 1.4 V 200 mV TA = +25°C 1 TA = +85°C 0.01 µA SS SS Charging Current VSS = 0.
PAGE 5
3A, 2MHz Step-Down Regulator with Integrated Switches 1800 FREQUENCY (kHz) EFFICIENCY (%) 90 85 VOUT = 1.8V 80 VOUT = 1.5V 75 VOUT = 1.2V 70 -40°C 1500 1350 -40°C 65 60 0.1 1 OUTPUT CURRENT (A) +85°C 1650 1200 VIN = 2.5V VDD = 3.3V +25°C +25°C +85°C -0.04 -0.10 -0.12 900 3.0 3.4 INPUT VOLTAGE (V) VOUT = 1.8V -0.08 -0.16 2.6 VOUT = 2.5V -0.06 -0.14 2.2 VIN = VDD = 3.3V -0.
PAGE 6
Typical Operating Characteristics (continued) (Typical values are at VIN = VDD = 3.3V, VOUT = 1.8V, RFREQ = 50kΩ, IOUT = 3A, and TA = +25°C, unless otherwise noted.) 6 CURRENT LIMIT (A) 7 6 5 4 3 MAX8643 toc11 8 MAX8643 toc12 7 MAX8643 toc10 VEN = 0V 9 HICCUP CURRENT LIMIT CURRENT LIMIT vs. OUTPUT VOLTAGE INPUT CURRENT vs. INPUT VOLTAGE 10 VOUT 0V 5 4 IOUT 5A/div 3 0A 2 2 IIN 1 1 1V/div 1A/div 0A 0 0 2.2 2.4 2.6 2.8 3.0 3.2 INPUT VOLTAGE (V) 3.4 3.6 0.5 1.0 1.5 2.
PAGE 7
3A, 2MHz Step-Down Regulator with Integrated Switches PIN NAME 1, 7 GND Analog Circuit Ground FUNCTION 2 VDD Supply Voltage and Bypass Input. Connect VDD to IN with a 10Ω resistor. Connect a 1µF ceramic capacitor from VDD to GND. 3, 4 CTL1, CTL2 Preset Output Voltage Selection Input. CTL1 and CTL2 set the output voltage to one of nine preset voltages. See Table 1 for preset voltages. 5 REFIN External Reference Input. Connect REFIN to SS to use the internal 0.6V reference.
PAGE 8
3A, 2MHz Step-Down Regulator with Integrated Switches MAX8643 Block Diagram VDD MAX8643 UVLO CIRCUITRY SHUTDOWN CONTROL EN CURRENT-LIMIT COMPARATOR BIAS GENERATOR LX ILIM THRESHOLD BST IN VOLTAGE REFERENCE SS BST CAPACITOR CHARGING SWITCH SOFT-START CONTROL LOGIC LX IN THERMAL SHUTDOWN REFIN PGND OUT ERROR AMPLIFIER 8kΩ PWM COMPARATOR FB CTL1 CTL2 VID VOLTAGECONTROL CIRCUITRY FREQ 1VP-P OSCILLATOR COMP SHDN COMP LOW DETECTOR FB 0.
PAGE 9
3A, 2MHz Step-Down Regulator with Integrated Switches INPUT 2.4V TO 3.6V IN C6 22μF C7 0.01μF VDD R5 10Ω BST C10 0.1μF L1 0.47μH MAX8643 OUTPUT 1.8V, 3A LX VDD C5 1μF OUT C8 22μF C3 560pF CTL2 C9 0.01μF R3 158Ω CTL1 PGND EN FB FREQ C2 1500pF R2 2.67kΩ REFIN R4 50kΩ C1 33pF SS C4 0.022μF COMP GND VDD R1 20kΩ PWRGD Figure 1. 1MHz, All-Ceramic Capacitor Design with VOUT = 1.
PAGE 10
MAX8643 3A, 2MHz Step-Down Regulator with Integrated Switches Current Limit Undervoltage Lockout (UVLO) The internal, high-side MOSFET has a typical 5.5A peak current-limit threshold. When current flowing out of LX exceeds this limit, the high-side MOSFET turns off and the synchronous rectifier turns on. The synchronous rectifier remains on until the inductor current falls below the low-side current limit.
PAGE 11
3A, 2MHz Step-Down Regulator with Integrated Switches Shutdown Mode Drive EN to GND to shut down the IC and reduce quiescent current to less than 12µA. During shutdown, the LX is high impedance. Drive EN high to enable the MAX8643. Thermal Protection Thermal-overload protection limits total power dissipation in the device. When the junction temperature exceeds TJ = +165°C, a thermal sensor forces the device into shutdown, allowing the die to cool.
PAGE 12
MAX8643 3A, 2MHz Step-Down Regulator with Integrated Switches Input-Capacitor Selection The input capacitor reduces the current peaks drawn from the input power supply and reduces switching noise in the IC.
PAGE 13
3A, 2MHz Step-Down Regulator with Integrated Switches OPEN-LOOP GAIN THIRD POLE DOUBLE POLE C1 = GAIN (dB) SECOND POLE POWER-STAGE TRANSFER FUNCTION FIRST AND SECOND ZEROS Figure 4. Type III Compensation Illustration Due to the underdamped nature of the output LC double pole, set the two zero frequencies of the type III compensation less than the LC double-pole frequency to provide adequate phase boost. Set the two zero frequencies to 80% of the LC double-pole frequency.
PAGE 14
Pin Configuration PCB Layout Considerations and Thermal Performance 14 PGND LX LX LX BST 18 17 16 15 14 13 PGND 19 12 PWRGD PGND 20 11 FREQ IN 21 10 OUT MAX8643 IN 22 IN 23 3 4 5 6 SS 2 REFIN 1 CTL2 + CTL1 EN 24 VDD 3) Keep the high-current paths as short and wide as possible. Keep the path of switching current short and minimize the loop area formed by LX, the output capacitors, and the input capacitors.
PAGE 15
3A, 2MHz Step-Down Regulator with Integrated Switches 24L QFN THIN.EPS ______________________________________________________________________________________ 15 MAX8643 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.
PAGE 16
MAX8643 3A, 2MHz Step-Down Regulator with Integrated Switches Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.) Revision History Pages changed at Rev 2: 1, 4, 5, 6, 13–16 Pages changed at Rev 3: 1, 2, 4, 8, 13, 15, 16 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product.