Maxim MAX8643A, MAX8643AETG+ Datasheet

General Description

The MAX8643A high-efficiency switching regulator
delivers up to 3A load current at output voltages from

0.6V to (0.9 x V

IN

).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.

The MAX8643A 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 induc­tances, 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 MAX8643A comes with a high-bandwidth (>14MHz)
voltage-error amplifier. The voltage-mode control archi­tecture and the voltage-error amplifier permit a type III
compensation scheme to be utilized to achieve maxi­mum loop bandwidth, up to 20% of the switching fre­quency. High loop bandwidth provides fast transient
response, resulting in less required output capacitance
and allowing for all-ceramic capacitor designs.

The MAX8643A provides two tri-state logic inputs to
select one of nine preset output voltages. The preset
output voltages allow customers to achieve ±1% out­put-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 resis­tors at the feedback with 0.6V internal reference or
applying an external reference voltage to the REFIN
input. The MAX8643A offers programmable soft-start
time using one capacitor to reduce input inrush current.
The MAX8643A 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

o Internal 37mΩ R

DS(ON)

MOSFETs

o Continuous 3A Output Current
o ±1% Output Accuracy Over Load, Line,

and Temperature

o Operates from 2.35V to 3.6V Supply
o Adjustable Output from 0.6V to (0.9 x VIN)
o Soft-Start Reduces Inrush Supply Current
o 500kHz to 2MHz Adjustable Switching Frequency
o Compatible with Ceramic, Polymer, and

Electrolytic Output Capacitors

o VID-Selectable Output Voltages

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

o Fully Protected Against Overcurrent

and Overtemperature

o Safe-Start into Prebiased Output
o Lead-Free, 24-Pin, 4mm x 4mm

Thin QFN Package

MAX8643A

3A, 2MHz Step-Down Regulator

with Integrated Switches

________________________________________________________________

Maxim Integrated Products

1

Ordering Information

19-0767; Rev 0; 3/07

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

+

Denotes a lead-free package.

*

EP = Exposed pad.

Pin Configuration appears at end of data sheet.

OUTPUT

1.8V, 3A

INPUT

2.4V, 3.6V
BST

LX

OUT

IN

EN

V

DD

CTL1

CTL2

PGND

FB

V

DD

COMP

PWRGD

FREQ

REFIN

SS

GND

PREBIAS

MAX8643A

Typical Operating Circuit

PART

MAX8643AETG+

TEMP
RANGE

-40°C to
+85°C

PIN-PACKAGE

24 Thin QFN
4mm x 4mm

PACKAGE
CODE

T2444-4

MAX8643A

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

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(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)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

IN, VDD, PWRGD to GND ......................................-0.3V to +4.5V

COMP, FB, REFIN, OUT,

CTL_, EN, SS, FREQ to GND...................-0.3V to (V

DD

+ 0.3V)

LX Current (Note 1) .....................................................-4A to +4A

BST to LX..................................................................-0.3V to +4V

PGND to GND .......................................................-0.3V to +0.3V

Continuous Power Dissipation (T

A

= +70°C)

24-Pin TQFN-EP

(derated 27.8mW/°C above +70°C)........................2222.2mW

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

Note 1: LX has internal clamp diodes to GND and IN. Applications that forward bias these diodes should take care not to exceed

the IC’s package power dissipation limits.

IN/V

IN and V

IN Supply Current

VDD Supply Current fS = 1MHz

Total Shutdown Current from IN
and V

VDD Undervoltage Lockout
Threshold

BST

BST Supply Current

PWM COMPARATOR

PWM Comparator Propagation
Delay

COMP

COMP Clamp Voltage, High V

COMP Slew Rate 1.4 V/µs

PWM Ramp Amplitude 1V

COMP Shutdown Resistance From COMP to GND, V

ERROR AMPLIFIER

Preset Output-Voltage Accuracy REFIN = SS -1

FB Regulation Accuracy Using
External Resistors

FB to OUT Resistor All VID settings except CTL1 = CTL2 = GND 5 8 11 kΩ

PARAMETER CONDITIONS MIN TYP MAX UNITS

DD

Voltage Range 2.35 3.60 V

DD

f

= 1MHz, no load,

DD

S

L = 0.47µH
(includes gate-drive current)

V

= V

= V

- V

= 3.6V,

IN

LX

EN

= 3.6V, V

= 0V

EN

IN

DD

BST

LX starts/stops switching

V

= V

DD

= V

BST

V

= 3.6V or 0V, V

LX

10mV overdrive 20 ns

= 2.35V to 3.6V 2 V

IN

CTL1 = CTL2 = GND 0.594 0.600 0.606 V

V

= 2.5V 4 4.6

IN

V

= 3.3V 5.5

IN

V

= 2.5V 1.4 2.3

IN

= 3.3V 2

V

IN

= 0V 13 µA

EN

VDD rising 2 2.1

VDD falling 1.8 1.9

Deglitching 2 µs

TA = +25°C 5

T

= +85°C 10

A

= V

= 0V 8 Ω

SS

Select

from

Table 1

+1 %

mA

mA

V

µA

MAX8643A

3A, 2MHz Step-Down Regulator

with Integrated Switches

_______________________________________________________________________________________ 3

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

Open-Loop Voltage Gain 1kΩ from COMP to GND 115 dB

Error-Amplifier Unity-Gain
Bandwidth

Error-Amplifier Common-Mode
Input Range

Error-Amplifier Minimum Output
Current

FB Input Bias Current

Parallel 10kΩ, 40pF from COMP to GND (Note 3) 14 26 MHz

V

= 2.35V to 2.6V 0 V

DD

= 2.6V to 3.6V 0 V

V

DD

= 1V

V

COMP

V

= 0.7V, CTL1 = CTL2 =

FB

Sourcing 1000

Sinking -500

= +25°C -200 -40 nA

T

A

DD

DD

- 1.65

- 1.7

V

µA

CTL_

V

= 0V -7

CTL_ Input Bias Current

CTL_

V

CTL_

= V

DD

+7

µA

Rising 0.75

High-Impedance Threshold

Falling

V

DD

- 1.2V

V

Hysteresis All VID transitions 50 mV

REFIN

REFIN Input Bias Current V

REFIN Common-Mode Range

= 0.6V TA = +25°C -500 -100 nA

REFIN

V

= 2.3V to 2.6V 0 V

DD

= 2.6V to 3.6V 0 V

V

DD

DD

DD

- 1.65

- 1.7

V

REFIN Offset Voltage CTL1 = CTL2 = GND, TA = +25°C -3 +3 mV

LX (ALL PINS COMBINED)

V

= V

- V

LX On-Resistance, High Side ILX = -2A

LX On-Resistance, Low Side ILX = 2A

LX Current-Limit Threshold V

LX Leakage Current V

LX Switching Frequency V

= 2.5V, high-side sourcing 4 5.5 A

IN

= 3.6V, V

IN

= 2.5V to 3.3V

IN

EN

= V

SS

= 0V

IN

BST

= V

V

IN

BST

V

= 2.5V 36

IN

= 3.3V 34 55

V

IN

TA = +25°C

T

= +85°C

A

R

= 50kΩ 0.9 1 1.1

FREQ

= 23.2kΩ 1.8 2.0 2.2

R

FREQ

= 2.5V 39

LX

- V

= 3.3V 37 58

LX

V

= 0V -2

LX

V

= 3.6V +2

LX

V

= 0V 1

LX

= 3.6V 1

V

LX

mΩ

mΩ

µA

MHz

Frequency Range 500 2000 kHz

LX Minimum Off-Time V

LX Maximum Duty Cycle R

= 2.5V to 3.3V 40 75 ns

IN

FREQ

= 50kΩ, V

= 2.5V to 3.3V 93 96 %

IN

LX Minimum On-Time 80 ns

RMS LX Output Current 3A

MAX8643A

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

4 _______________________________________________________________________________________

Note 2: Specifications are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by

design and characterization.

Note 3: Guaranteed by design.

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)

Typical Operating Characteristics

(Typical values are at VIN= VDD= 3.3V, V

OUT

= 1.8V, R

FREQ

= 50kΩ, I

OUT

= 3A, and TA = +25°C, unless otherwise noted.)

EFFICIENCY vs. OUTPUT CURRENT

OUTPUT CURRENT (A)

EFFICIENCY (%)

MAX8643A toc02

60

65

75

70

80

85

90

95

100

0.1 1 10

V

OUT

= 1.5V

V

OUT

= 1.88V

VIN = VDD = 2.5V

V

OUT

= 1.2V

ENABLE

EN Input Logic-Low 0.7 V

EN Input Logic-High 1.7 V

EN, Input Current

SS

SS Charging Current V

SS Discharge Resistance 500 Ω

THERMAL SHUTDOWN

Thermal-Shutdown Threshold +165 °C

Thermal-Shutdown Hysteresis 20 °C

POWER-GOOD (PWRGD)

Power-Good Threshold Voltage VFB falling, 3mV hysteresis 87 90 93 %

Power-Good Falling-Edge Deglitch 48

PWRGD Output-Voltage Low I

PWRGD Leakage Current V

OVERCURRENT LIMIT

Current-Limit Startup Blanking 128

Restart Time 1024

PARAMETER CONDITIONS MIN TYP MAX UNITS

V

= 0V or 3.6V,

EN

= 3.6V

V

DD

= 0.45V 7 8 9 µA

SS

= 4mA 0.03 0.15 V

PWRGD

DD

= V

PWRGD

= 3.6V, V

TA = +25°C 1

= +85°C 0.01

T

A

= 0.9V 0.01 µA

FB

µA

Clock

cycles

Clock

cycles

Clock

cycles

EFFICIENCY vs. OUTPUT CURRENT

100

90

80

V

70

EFFICIENCY (%)

60

50

VIN = VDD = 3.3V

40

0.1 1

OUT

V

= 1.2V

OUT

OUTPUT CURRENT (A)

= 1.8V

V

= 2.5V

OUT

MAX8643A toc01

10

Typical Operating Characteristics (continued)

(Typical values are at VIN= VDD= 3.3V, V

OUT

= 1.8V, R

FREQ

= 50kΩ, I

OUT

= 3A, and TA = +25°C, unless otherwise noted.)

MAX8643A

3A, 2MHz Step-Down Regulator

with Integrated Switches

_______________________________________________________________________________________

5

EFFICIENCY vs. OUTPUT CURRENT

100

95

90

85

80

75

EFFICIENCY (%)

V

VIN = 2.5V

= 3.3V

V

DD

OUT

OUTPUT CURRENT (A)

70

65

60

0.1 1 10

V

= 1.2V

OUT

= 1.5V

V

= 1.8V

OUT

LOAD TRANSIENT

V

OUT

I

OUT

40μs/div

MAX8643A toc03

MAX8643A toc06

VIN = VDD = 3.3V

FREQUENCY vs. INPUT VOLTAGE

1950

1800

1650

1500

1350

FREQUENCY (kHz)

1200

1050

900

2.2 2.6 3.0 3.4 3.8

AC-COUPLED
50mV/div

1A/div

0A

-40°C

+25°C

-40°C

+25°C

INPUT VOLTAGE (V)

V

OUT

V

I

LX

LX

+85°C

+85°C

-0.02

MAX8643A toc04

-0.04

-0.06

-0.08

-0.10

-0.12

OUTPUT VOLTAGE CHARGE (%)

-0.14

-0.16

SWITCHING WAVEFORMS

100ns/div

0

V

= 1.8V

OUT

V

012345

LOAD CURRENT (A)

MAX8643A toc07

= 1.2V

OUT

AC-COUPLED
20mV/div

2A/div

0A

2V/div
0V

VIN = VDD = 3.3V

V

= 2.5V

OUT

LOAD REGULATION

MAX8643A toc05

SOFT-START WAVEFORMS

V

EN

V

OUT

R

400μs/div

LOAD

= 1Ω

MAX8643A toc08

2V/div

0V

1V/div

0V

V

EN

V

OUT

SHUTDOWN WAVEFORMS

R

= 1Ω

LOAD

10μs/div

MAX8643A toc09

2V/div
0V

1V/div

0V