Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - DC/DC voltage regulator Holder TQFN 32 EP

General Description

The MAX8855/MAX8855A high-efficiency, dual step-down

regulators are capable of delivering up to 5A at each out-

put. The devices operate from a 2.25V to 3.6V supply, and

provide output voltages from 0.6V to 0.9 x V

, making them

ideal for on-board point-of-load applications. Total output

error is less than ±1% over load, line, and temperature.

The MAX8855/MAX8855A operate in PWM mode with a

switching frequency ranging from 0.5MHz to 2MHz, set

by an external resistor. It can also be synchronized to

an external clock in the same frequency range. Two

internal switching regulators operate 180° out-of-phase

to reduce the input ripple current, and consequently

reduce the required input capacitance. The high

operating frequency minimizes the size of external

components. High efficiency, internal dual-nMOS

design keeps the board cool under heavy loads. The

voltage-mode control architecture and the high-band-

width (> 15MHz typ) voltage-error amplifier allow a type

III compensation scheme to be utilized to achieve fast

response under both line and load transients, and also

allow for ceramic output capacitors.

Programmable soft-start reduces input inrush current.

Two enable inputs allow the turning on/off of each out-

put individually, resulting in great flexibility for system-

level designs. A reference input is provided to facilitate

output-voltage tracking applications. The MAX8855/

MAX8855A are available in a 32-pin TQFN (5mm x 5mm)

package with 0.8mm max height.

Applications

ASIC/CPU/DSP Power Supplies

DDR Power Supplies

Set-Top Box Power Supplies

Printer Power Supplies

Network Power Supplies

Features

o 27mΩ On-Resistance Internal MOSFETs

o Dual, 5A, PWM Step-Down Regulators

o Fully Protected Against Overcurrent,

Short Circuit, and Overtemperature

o ±1% Output Accuracy Over Load, Line,

and Temperature

o Operates from 2.25V to 3.6V Supply

o REFIN on One Channel for Tracking or

External Reference

o Integrated Boost Diodes

o Adjustable Output from 0.6V to 0.9 x V

o Soft-Start Reduces Inrush Supply Current

o 0.5MHz to 2MHz Adjustable Switching,

or FSYNC Input

o All-Ceramic-Capacitor Design

o 180° Out-of-Phase Operation Reduces Input

Ripple Current

o Individual Enable Inputs and PWRGD Outputs

o Safe-Start into Prebiased Output

o Available in 5mm x 5mm Thin QFN Package

o Sink/Source Current in DDR Applications

MAX8855/MAX8855A

Dual, 5A, 2MHz Step-Down Regulators

________________________________________________________________

Maxim Integrated Products

Ordering Information

19-0726; Rev 4; 10/11

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.

Denotes a lead(Pb)-free/RoHS-compliant package.

EP = Exposed pad.

EVALUATION KIT

AVAILABLE

PART TEMP RANGE PIN-PACKAGE

MAX8855ETJ+ -40°C to +85°C 32 TQFN-EP*

MAX8855AETJ+

-40°C to +85°C 32 TQFN-EP*

Pin Configuration appears at end of data sheet.

FB2

EN2

COMP2

LX2

BST2

GND

PGND2

INPUT1

2.25V TO 3.6V

EN1

BST1

COMP1

FB1

PGND1

LX1

IN1 IN2

TYPE III

COMPENSATION

OUTPUT1

1.2V / 5A

INPUT2

2.25V TO 3.6V

PWRGD1 PWRGD2

OFF

MAX8855/

MAX8855A

TYPE III

COMPENSATION

OUTPUT2

1.5V / 5A

OFF

Typical Operating Circuit

Summary of content (20 pages)

PAGE 1
9-0726; Rev 4; 10/11 KIT ATION EVALU E L B AVAILA Dual, 5A, 2MHz Step-Down Regulators The MAX8855/MAX8855A high-efficiency, dual step-down regulators are capable of delivering up to 5A at each output. The devices operate from a 2.25V to 3.6V supply, and provide output voltages from 0.6V to 0.9 x VIN, making them ideal for on-board point-of-load applications. Total output error is less than ±1% over load, line, and temperature.
PAGE 2
MAX8855/MAX8855A Dual, 5A, 2MHz Step-Down Regulators ABSOLUTE MAXIMUM RATINGS IN_, LX_, VDD, VDL, PWRGD_ to GND..................-0.3V to +4.5V VDD, VDL to IN_.....................................................-0.3V to +4.5V EN_, SS_, COMP_, FB_, REFIN, FSYNC to GND ......-0.3V to the lower of (VVDD + 0.3V) and (VVDL + 0.3V) Continuous LX_ Current (Note 1) ...................................5.5ARMS BST_ to LX_ ...........................................................-0.3V to +4.5V PGND_ to GND.........
PAGE 3
Dual, 5A, 2MHz Step-Down Regulators (VIN_ = VVDD = VVDL = 3.3V, VFB_ = 0.5V, VSS_ = VREFIN = 600mV, PGND_ = GND, RFSYNC = 10kΩ, L = 0.47μH, CBST_ = 0.1μF, CSS_ = 0.022μF, PWRGD_ not connected; TA = -40°C to +85°C, typical values are at TA = +25°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS 0.594 0.600 0.606 V 0.594 0.600 0.606 V VVDD 1.
PAGE 4
ELECTRICAL CHARACTERISTICS (continued) (VIN_ = VVDD = VVDL = 3.3V, VFB_ = 0.5V, VSS_ = VREFIN = 600mV, PGND_ = GND, RFSYNC = 10kΩ, L = 0.47μH, CBST_ = 0.1μF, CSS_ = 0.022μF, PWRGD_ not connected; TA = -40°C to +85°C, typical values are at TA = +25°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN TYP MAX UNITS EN1, EN2 EN_ Logic-Low 0.7 EN_ Logic-High V 1.7 TA = +25°C VEN_ = 0 or 3.6V, VVDD = 3.6V EN_ Input Current V -1 +1 TA = +85°C μA 0.
PAGE 5
Dual, 5A, 2MHz Step-Down Regulators SWITCHING FREQUENCY vs. TEMPERATURE FEEDBACK VOLTAGE vs. TEMPERATURE 1060 1040 1020 1000 980 960 608 606 604 602 600 598 596 940 594 920 592 590 900 -40 -15 10 35 60 -40 85 -15 10 60 35 AMBIENT TEMPERATURE (°C) AMBIENT TEMPERATURE (°C) SHUTDOWN SUPPLY CURRENT vs.
PAGE 6
Typical Operating Characteristics (continued) (VIN1 = VIN2 = 3.3V, MAX8855/MAX8855A, circuit of Figure 6, TA = +25°C, unless otherwise noted.) OUTPUT PEAK CURRENT LIMIT vs.
PAGE 7
Dual, 5A, 2MHz Step-Down Regulators PIN 1 NAME FUNCTION Power-Good Open-Drain Output for Regulator 1. PWRGD1 is high impedance when VREFIN ≥ 0.54V and PWRGD1 VFB1 ≥ 0.9 x VREFIN. PWRGD1 is low when VREFIN < 0.54V, EN1 is low, VDD or IN1 is below UVLO, the thermal shutdown is activated, or when VFB1 < 0.9 x VREFIN. External Reference Input for Regulator 1. Connect an external reference to REFIN, or connect REFIN to SS1 to use the internal reference.
PAGE 8
Dual, 5A, 2MHz Step-Down Regulators MAX8855/MAX8855A Pin Description (continued) PIN NAME FUNCTION 27, 28 IN1 Power-Supply Input for Regulator 1. The voltage range is 2.35V to 3.6V for the MAX8855. The voltage range is 2.30V to 3.6V for the MAX8855A. Connect two 10μF and one 0.1μF ceramic capacitors from IN1 to PGND1. 29 EN1 Enable Input for Regulator 1. Drive EN1 high to enable regulator 1, or low for shutdown. For always-on operation, connect EN1 to VDD. 30 COMP1 Compensation for Regulator 1.
PAGE 9
Dual, 5A, 2MHz Step-Down Regulators MAX8855/MAX8855A CURRENT-LIMIT COMPARATOR VDD VDL BST CAP CHARGING SWITCH IN1 SHUTDOWN CONTROL UVLO CIRCUITRY DC EN1 EN2 VDD - + IN2 BIAS GENERATOR - LX1 CONTROL LOGIC LX1 EN1 REF CLOCK SOFT-START 1 PGND1 THERMAL SHUTDOWN1 SS2 IN1 ILIM THRESHOLD IN1 VOLTAGE REFERENCE SS1 BST1 + BST CAP CHARGING SWITCH VDL SOFT-START 2 REFIN + FB1 - CURRENT-LIMIT COMPARATOR PWM COMPARATOR - IN2 DC + COMP1 COMP LOW DETECTOR FROM SS2 (0.
PAGE 10
MAX8855/MAX8855A Dual, 5A, 2MHz Step-Down Regulators The power-good, open-drain output for regulator 2 (PWRGD2) is high impedance when VSS2 ≥ 0.54V and VFB2 ≥ 0.9 x VSS2. PWRGD2 is low when VSS2 < 0.54V, EN2 is low, VVDD or VIN2 is below VUVLO, the thermal-overload protection is activated, or when VFB2 < 0.9 x VSS2. Startup and Sequencing The MAX8855/MAX8855A feature separate enable inputs (EN1 and EN2) for the two regulators.
PAGE 11
Dual, 5A, 2MHz Step-Down Regulators For ratiometric tracking applications, connect REFIN to the center of a voltage-divider from the output of regulator 2 to GND (see Figure 3b). In this application, the EN_ inputs are connected to each other and driven as a single enable input. Regulator 2 starts up with a normal softstart (C SS2 sets the time), and regulator 1 output ratiometrically tracks the regulator 2 output voltage.
PAGE 12
MAX8855/MAX8855A Dual, 5A, 2MHz Step-Down Regulators EN PWRGD1 EN1 EN 10kΩ OUT1 VDD OUT2 EN2 10kΩ SS2 PWRGD1 PWRGD2 PWRGD2 SS1 REFIN Figure 3d. Startup and Sequencing Options—Matching Startup Slopes of Output Voltages with Internal Reference Sequencing is achieved by connecting EN2 to PWRGD1. In this mode, regulator 2 starts once regulator 1 reaches regulation. In Figure 3d, EN1 and EN2 are connected together and driven as a single input.
PAGE 13
Dual, 5A, 2MHz Step-Down Regulators VOUT1 R19 = VOUT2 R1 + R19 Setting the Switching Frequency The MAX8855/MAX8855A have an adjustable internal oscillator that can be set to any frequency from 500kHz to 2MHz. To set the switching frequency, connect a resistor from FSYNC to GND.
PAGE 14
MAX8855/MAX8855A Dual, 5A, 2MHz Step-Down Regulators Output-Capacitor Selection The key selection parameters for the output capacitor are capacitance, ESR, ESL, and voltage-rating requirements. These affect the overall stability, output ripple voltage, and transient response of the DC-DC converter. The output ripple occurs due to variations in the charge stored in the output capacitor, the voltage drop due to the capacitor’s ESR, and the voltage drop due to the capacitor’s ESL.
PAGE 15
Dual, 5A, 2MHz Step-Down Regulators 1 2π × R4 × C11 fP2 _ EA = 1 2π × R7 × C10 fP3 _ EA = 1 2π × R8 × C11 C9 = These equations are based on the assumptions that C9 >> C10, and R4 >> R8, which are true in most applications. Placement of these poles and zeros is determined by the frequencies of the double pole and ESR zero of the power stage transfer function. It is also a function of the desired closed-loop bandwidth. Figure 5 shows the pole zero cancellations in the type III compensation design.
PAGE 16
MAX8855/MAX8855A Dual, 5A, 2MHz Step-Down Regulators Set the second compensation pole at 1/2 the switching frequency. Calculate C10 as follows: • A multilayer PCB is recommended. Use inner-layer ground (and power) planes to minimize noise coupling. • Place the input ceramic decoupling capacitor directly across and as close as possible to IN_ and PGND_. This is to help contain the high switching currents within a small loop. The recommended range for R4 is 2kΩ to 10kΩ.
PAGE 17
Dual, 5A, 2MHz Step-Down Regulators MAX8855/MAX8855A INPUT 2.35V TO 3.6V (MAX8855) 2.25V to 3.6V (MAX8855A) C16 0.1μF IN1 VDD R11 10Ω VDL VDD C2 0.1μF R4 10kΩ L1 0.56μH BST1 BST2 C6 0.1μF C17 0.1μF LX1 C19 22μF L2 0.56μH R9 1kΩ GND R7 10kΩ C11 1000pF C9 330pF COMP1 R6 10kΩ C10 OPEN VDD C5 0.022μF PWRGD1 MAX8855/ MAX8855A REFIN SS2 SS1 ON R10 27kΩ R12 20kΩ C14 OPEN C12 0.022μF VDD R10 20kΩ FSYNC PWRGD2 R13 40.
PAGE 18
MAX8855/MAX8855A Dual, 5A, 2MHz Step-Down Regulators INPUT 2.35V TO 3.6V FOR MAX8855 2.25V TO 3.6V FOR MAX8855A C16 0.1μF IN1 VDD R11 10Ω VDL VDD C2 0.1μF PGND1 C18 47μF L1 1μH C23 10μF PGND2 BST1 BST2 C6 0.1μF C17 0.1μF LX1 C19 22μF L2 1μH R9 1kΩ GND R7 10kΩ C11 1000pF C9 330pF COMP1 C20 0.1μF OUT2 1.8V/5A LX2 R8 200Ω R4 10kΩ IN2 C3 0.1μF C1 10μF C4 OUT1 0.1μF 0.9V/5A C8 0.22μF MAX8855/ MAX8855A C15 220pF R10 27kΩ R13 40.
PAGE 19
Dual, 5A, 2MHz Step-Down Regulators Chip Information PGND1 LX1 LX1 BST1 BST2 LX2 LX2 PGND2 PROCESS: BiCMOS TOP VIEW 24 23 22 21 20 19 18 17 PGND1 25 16 PGND1 26 15 PGND2 IN1 27 14 IN2 13 IN2 Package Information 12 EN2 11 COMP2 10 FB2 9 SS2 For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only.
PAGE 20
MAX8855/MAX8855A Dual, 5A, 2MHz Step-Down Regulators Revision History PAGES CHANGED REVISION NUMBER REVISION DATE 0 8/07 Initial release 1 6/08 Revised Features section and corrected Figure 6. 2 4/09 Revised Features, Typical Operating Characteristics, and Output-Capacitor Selection sections. Added the Safe-Starting into a Prebiased Output section. 1, 6, 14, 16 3 7/11 Added the MAX8855A to the data sheet.