Datasheet

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General Description

The MAX8505 step-down regulator operates from a 2.6V

to 5.5V input and generates an adjustable output voltage

from 0.8V to 0.85



VIN at up to 3A. With a 2.6V to 5.5V

bias supply, the input voltage can be as low as 2.25V.

The MAX8505 integrates power MOSFETs and

operates at 1MHz/500kHz switching frequency to

provide a compact design. Current-mode pulse-width-

modulated (PWM) control simplifies compensation with

ceramic or polymer output capacitors and provides

excellent transient response.

The MAX8505 features 1% accurate output over load,

line, and temperature variations. Adjustable soft-start is

achieved with an external capacitor. During the

soft-start period, the voltage-regulation loop is active.

This limits the voltage dip when the active devices,

such as microprocessors or ASICs connected to the

MAX8505’s output, apply a sudden load current step

upon passing their undervoltage thresholds.

The MAX8505 features current-limit, short-circuit, and

thermal-overload protection and enables a rugged

design. Open-drain power-OK (POK) monitors the

output voltage.

Applications

µP/ASIC/DSP/FPGA Core and I/O Supplies

Chipset Supplies

Server, RAID, and Storage Systems

Network and Telecom Equipment

Features

o Saves Space—4.9mm x 6mm Footprint, 1µH

Inductor, 47µF Ceramic Output Capacitor

o Input Voltage Range

2.6V to 5.5V

Down to 2.25V with Bias Supply

o 0.8V to 0.85

 V

, 3A Output

o Ceramic or Polymer Capacitors

o ±1% Output Accuracy Over Load, Line, and

Temperature

o Fast Transient Response

o Adjustable Soft-Start

o In-Regulation Soft-Start Limits Output-Voltage

Dips at Power-On

o POK Monitors Output Voltage

MAX8505

3A, 1MHz, 1% Accurate, Internal Switch

Step-Down Regulator with Power-OK

________________________________________________________________

Maxim Integrated Products

Ordering Information

19-2992; Rev 1; 9/10

PART TEMP RANGE PIN-PACKAGE

MAX8505EEE+ -40°C to +85°C 16 QSOP

PGND

GND

REF

COMP

TOP VIEW

MAX8505

QSOP

BST

POK

CTL

Pin Configuration

MAX8505

INPUT

2.6V TO 5.5V

ENABLE

POWER-OK

OUTPUT

0.8V TO

0.85 x V

BST

CTL

POK

GND

REF

COMP

PGND

Typical Operating Circuit

Functional Diagram appears at end of data sheet.

EVALUATION KIT

AVAILABLE

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.

Summary of content (15 pages)

PAGE 1
9-2992; Rev 1; 9/10 KIT ATION EVALU E L B AVAILA 3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK 6m m -QSOP 16 General Description The MAX8505 step-down regulator operates from a 2.6V to 5.5V input and generates an adjustable output voltage from 0.8V to 0.85 VIN at up to 3A. With a 2.6V to 5.5V bias supply, the input voltage can be as low as 2.25V. The MAX8505 integrates power MOSFETs and operates at 1MHz/500kHz switching frequency to provide a compact design.
PAGE 2
MAX8505 3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK ABSOLUTE MAXIMUM RATINGS Operating Temperature Range MAX8505EEE...................................................-40°C to +85°C Storage Temperature Range .............................-65°C to +150°C Junction Temperature ......................................................+150°C Lead Temperature (soldering, 10s) .................................+300°C Soldering Temperature (reflow) .......................................
PAGE 3
A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK (VIN = VCC = VCTL = +3.3V, VFB = 0.8V, VCOMP = 1.25V, CREF = 0.01µF, TA = 0°C to +85°C, unless otherwise noted.) MIN TYP MAX UNITS COMP Clamp Voltage, Low PARAMETER SYMBOL VIN = VCC = 2.6V, 3.3V, 5.5V, VFB = 0.9V CONDITIONS 0.45 0.75 1.00 V COMP Clamp Voltage, High VIN = VCC = 2.6V, 3.3V, 5.5V, VFB = 0.7V 1.7 1.9 2.1 V COMP Shutdown Resistance From COMP to GND, VCTL = 0V 13 100 Ω VIN = VBST - VLX = 3.
PAGE 4
MAX8505 3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK ELECTRICAL CHARACTERISTICS (VIN = VCC = VCTL = +3.3V, VFB = 0.8V, VCOMP = 1.25V, CREF = 0.01µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 2.25 VCC V 2.6 IN AND VCC IN Voltage Range VIN VCC Voltage Range 5.5 V IN Supply Current IIN Switching with no load VIN = 3.3V 10 mA VCC Supply Current ICC Switching with no load VCC = 3.
PAGE 5
3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK (VIN = VCC = VCTL = +3.3V, VFB = 0.8V, VCOMP = 1.25V, CREF = 0.01µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN 90 1MHz 84 TYP MAX LX Maximum Duty Cycle VIN = VCC = 2.6V, 3.3V, 5.5V 500kHz LX Minimum Duty Cycle VIN = VCC = 2.6V, 3.3V, 5.
PAGE 6
Typical Operating Characteristics (Typical values are at VIN = VCC = VCTL = 5V, VOUT = 1.2V, IOUT = 3A, and TA = +25°C, unless otherwise noted.) 90 A 90 B A 90 B D 70 A: VOUT = 3.3V B: VOUT = 2.5V C: VOUT = 1.2V D: VOUT = 0.8V D C EFFICIENCY (%) EFFICIENCY (%) B C 80 70 A: VOUT = 2.5V B: VOUT = 1.8V C: VOUT = 1.2V D: VOUT = 0.8V 60 0 1 2 1 2 1 3 1.03 FREQUENCY (MHz) B C 70 MAX8505 toc05 1.05 MAX8505 toc04 A 90 80 2 OUTPUT CURRENT (A) FREQUENCY vs.
PAGE 7
3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK SHUTDOWN SUPPLY CURRENT vs. INPUT VOLTAGE MAX8505 toc09 5.3 CURRENT LIMIT (A) 0.2 fSW = 1MHz 5.4 0.3 0.1 5.2 5.1 5.0 4.9 4.8 4.7 4.6 fSW = 1MHz 3.5 4.0 4.5 4.5 5.5 5.0 0.8 1.3 1.8 2.3 OUTPUT VOLTAGE (V) OUTPUT SHORT-CIRCUIT CURRENT vs. INPUT VOLTAGE GND-MEASURED TEMPERATURE vs. OUTPUT CURRENT fSW = 1MHz 4.5 3.5 3.3 2.8 INPUT VOLTAGE (V) 120 GND-MEASURED TEMPERATURE (°C) 5.5 3.0 MAX8505 toc10 2.
PAGE 8
MAX8505 3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK Typical Operating Characteristics (continued) (Typical values are at VIN = VCC = VCTL = 5V, VOUT = 1.2V, IOUT = 3A, and TA = +25°C, unless otherwise noted.) SWITCHING WAVEFORM (VIN = 5V, VOUT = 1.2V, IOUT = 2.5A) TRANSIENT RESPONSE (VIN = 3.3V, VOUT = 1.2V) MAX8505 toc15 MAX8505 toc14 VLX 2V/div OUTPUT VOLTAGE AC-COUPLED 100mV/div INDUCTOR CURRENT AC-COUPLED 2A/div 2.25A OUTPUT 0.
PAGE 9
3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK PIN NAME FUNCTION 1, 3, 14, 16 LX Inductor Connection. Connect an inductor between these pins and the regulator output. All LX pins must be connected together externally. Connect a 3300pF ceramic capacitor from LX to PGND. 2, 4 IN Power-Supply Inputs. Ranges from 2.6V to 5.5V. Bypass with two ceramic 22µF capacitors to GND. All IN pins must be connected together externally. 5 BST Bootstrapped Voltage Input.
PAGE 10
MAX8505 3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK Current Limit Soft-Start The MAX8505 offers both high-side and low-side current limits. The high-side current limit monitors the inductor peak current and the low-side current limit monitors the inductor valley current. Current-limit thresholds are 6A (typ) for high side and 3.8A (typ) for low side.
PAGE 11
3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK ⎛V ⎞ R2 = R3 × ⎜ OUT − 1⎟ ⎝ VREF ⎠ VRIPPLE = VRIPPLE(C)2 + VRIPPLE(ESR)2 + VRIPPLE(ESL)2 where the output ripples due to output capacitance, ESR, and ESL are: VRIPPLE(C) = IP − P 8 × COUT × fS VRIPPLE(ESR) = IP−P × ESR where VREF = 0.8V. Inductor Design When choosing the inductor, the key parameters are inductor value (L) and peak current (I PEAK ).
PAGE 12
MAX8505 3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK Input Capacitor Design The input capacitor reduces the current peaks drawn from the input power supply and reduces switching noise in the IC. The impedance of the input capacitor at the switching frequency should be less than that of the input source so high-frequency switching currents do not pass through the input source but instead are shunted through the input capacitor.
PAGE 13
3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK 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 the high-side MOSFET, the low-side MOSFET, and the input capacitors. Avoid vias in the switching paths. PC Board Layout Considerations Careful PC board layout is critical to achieve clean and stable operation. The switching power stage requires particular attention.
PAGE 14
3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK MAX8505 Functional Diagram REFERENCE 1.25V POK MAX8505 N 50µs VCC FB UVLO BST GND IN 25µA REF LX PWM 25µA FB PGND GND COMP CTL Package Information Chip Information PROCESS: BiCMOS 14 For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only.
PAGE 15
3A, 1MHz, 1% Accurate, Internal Switch Step-Down Regulator with Power-OK REVISION NUMBER REVISION DATE 0 10/03 Initial release 9/10 Added lead-free notation to Ordering Information and corrected equations in the Compensation Design section 1 DESCRIPTION PAGES CHANGED — 1, 12 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.