Low-Output-Voltage, 800mA, Step-Down DC-DC Converters MAX1927/MAX

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Low-Output-Voltage, 800mA, Step-Down DC-DC Converters MAX1927/MAX

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19-2527; 7/02
Low-Output-Voltage, 800mA, Step-Down DC-DC Converters
MAX1927/MAX1928 800mA step-down converters power low-voltage microprocessors compact equipment requiring highest possible efficiency. MAX1927/MAX1928 optimized generating output voltages (down 750mV) high efficiency using small external components. supply voltage range from 2.6V 5.5V guaranteed minimum output current 800mA. 1MHz pulse-width modulation (PWM) switching allows small external components. unique control scheme minimizes ripple light loads, while maintaining 140µA quiescent current. MAX1927/MAX1928 include on-resistance internal MOSFET switch synchronous rectifier maximize efficiency minimize external component count. external diode needed. 100% duty-cycle operation allows dropout voltage only 340mV 800mA. Other features include internal soft-start, power-OK (POK) output, selectable forced operation lower noise load currents. MAX1928 available with several preset output voltages: 1.5V (MAX1928-15), 1.8V (MAX1928-18), 2.5V (MAX1928-25). MAX1927R adjustable output range down 0.75V. MAX1927/MAX1928 available tiny 10-pin µMAX package. 800mA Output Current Output Voltages from 0.75V 2.6V 5.5V Input Voltage Range Power-OK Output Schottky Diode Required Selectable Forced Operation 1MHz Fixed-Frequency Operation 140µA Quiescent Current Soft-Start 10-Pin µMAX Package
Features
MAX1927/MAX1928
Ordering Information
PART MAX1927REUB PRESET TEMP PINOUTPUT PACKAGE RANGE VOLTAGE Adj. 0.75V -40°C +85°C µMAX 1.5V 1.8V 2.5V -40°C +85°C µMAX -40°C +85°C µMAX -40°C +85°C µMAX
Applications
WCDMA Handsets PDAs Palmtops Core Power Battery-Powered Equipment
MAX1928EUB15 MAX1928EUB18 MAX1928EUB25
Configuration
VIEW
COMP BATT
2.6V 5.5V
Typical Operating Circuit
SHDN COMP VOUT 0.75V 800mA
BATT
MAX1927R MAX1928
PGND SHDN
MAX1927R
µMAX
PGND
Maxim Integrated Products
pricing, delivery, ordering information, please contact Maxim/Dallas Direct! 1-888-629-4642, visit Maxim's website www.maxim-ic.com.
Low-Output-Voltage, 800mA, Step-Down DC-DC Converters MAX1927/MAX1928
ABSOLUTE MAXIMUM RATINGS
BATT, PWM, POK, COMP, SHDN .-0.3V PGND .-0.3V +0.3V REF, .-0.3V (VBATT 0.3V) Continuous Power Dissipation +70°C) 10-Pin µMAX (derate 5.6mW/°C above +70°C) .444mW Operating Temperature Range .-40°C +85°C Junction Temperature .+150°C Storage Temperature Range .-65°C +150°C Lead Temperature (soldering, 10s) .+300°C
Stresses beyond those listed under "Absolute Maximum Ratings" cause permanent damage device. These stress ratings only, functional operation device these other conditions beyond those indicated operational sections specifications implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
ELECTRICAL CHARACTERISTICS
(VBATT 3.6V, SHDN BATT, CREF 0.1µF, +85°C, unless otherwise noted. Typical values +25°C.)
PARAMETER BATT Input Voltage Undervoltage Lockout Threshold Quiescent Current Quiescent Current Dropout Shutdown Supply Current REFERENCE ERROR MAX1927R Voltage Accuracy MAX1928-15 MAX1928-18 MAX1928-25 Input Current MAX1928 MAX1927R MAX1927R MAX1928-15 MAX1928-18 MAX1928-25 1.231 2.6V VBATT 5.5V VBATT 3.6V VBATT 2.6V VBATT 3.6V VBATT 2.6V 0.11 0.738 1.477 1.773 2.462 0.75 1.25 0.25 0.17 0.48 0.13 -0.55 0.15 0.762 1.523 1.827 2.538 SHDN VBATT rising falling (35mV hysteresis) load, pulse skipping, 1MHz switching CONDITIONS 2.15 2.35 2.55 UNITS
Transconductance (gm)
Reference Voltage Accuracy Reference Supply Rejection CONTROLLER P-Channel On-Resistance N-Channel On-Resistance Current-Sense Transresistance (RCS P-Channel Current-Limit Threshold P-Channel Pulse-Skipping Current Threshold N-Channel Negative Current-Limit Threshold
1.269 0.35
Low-Output-Voltage, 800mA, Step-Down DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)
(VBATT 3.6V, SHDN BATT, CREF 0.1µF, +85°C, unless otherwise noted. Typical values +25°C.)
PARAMETER N-Channel Synchronous Rectifier Turn-Off Threshold Leakage Current Maximum Duty Cycle Minimum Duty Cycle Internal Oscillator Frequency Thermal Shutdown Threshold COMPARATOR BATT Operating Voltage Range Output Voltage Output High Leakage Current IPOK 0.5V, IPOK VPOK 5.5V MAX1927R Threshold MAX1928-15 MAX1928-18 MAX1928-25 Output Valid Release Delay LOGIC INPUTS (SHDN, PWM) Logic Input High Logic Input Logic Input Current 2.6V VBATT 2.6V VBATT VBATT 5.5V transitions high impedance 20ms after VPOK 0.650 1.305 1.566 2.175 0.675 1.350 1.620 2.250 0.01 0.700 1.395 1.674 2.325 15°C hysteresis BATT 0.85 1.15 VBATT 5.5V, BATT CONDITIONS UNITS Degrees
MAX1927/MAX1928
ELECTRICAL CHARACTERISTICS
(VBATT 3.6V, SHDN BATT, CREF 0.1µF, -40°C +85°C, unless otherwise noted.)
PARAMETER BATT Input Voltage Undervoltage Lockout Threshold Quiescent Current Quiescent Current Dropout Shutdown Supply Current REFERENCE ERROR MAX1927R Voltage Accuracy MAX1928-15 MAX1928-18 MAX1928-25 Input Current MAX1928 0.732 1.47 1.764 2.45 0.768 1.53 1.836 2.55 SHDN VBATT rising falling (35mV hysteresis) load, pulse skipping, CONDITIONS 2.15 2.55 UNITS
Low-Output-Voltage, 800mA, Step-Down DC-DC Converters MAX1927/MAX1928
ELECTRICAL CHARACTERISTICS (continued)
(VBATT 3.6V, SHDN BATT, CREF 0.1µF, -40°C +85°C, unless otherwise noted. Typical values +25°C.)
PARAMETER Input Current Reference Voltage Accuracy Reference-Supply Rejection CONTROLLER P-Channel On-Resistance N-Channel On-Resistance P-Channel Current-Limit Threshold P-Channel Pulse-Skipping Current Threshold Leakage Current Maximum Duty Cycle Minimum Duty Cycle Internal Oscillator Frequency COMPARATOR BATT Operating Voltage Range Output Voltage Output High Leakage Current IPOK 0.5V, IPOK VPOK 5.5V MAX1927R MAX1928-15 Threshold MAX1928-18 MAX1928-25 Output Valid Release Delay LOGIC INPUTS (SHDN, PWM) Logic Input High Logic Input Logic Input Current 2.6V VBATT 2.6V VBATT VBATT 5.5V transitions high impedance 20ms after VPOK 0.650 1.305 1.566 2.175 VBATT 5.5V, BATT 2.6V VBATT 5.5V VBATT 3.6V VBATT 2.6V VBATT 3.6V VBATT 2.6V 0.10 0.700 1.395 1.674 2.325 0.10 MAX1927R 1.22 CONDITIONS 1.269 0.30 0.35 0.16 UNITS
Low-Output-Voltage, 800mA, Step-Down DC-DC Converters MAX1927/MAX1928
Typical Operating Characteristics
(Circuits Figure +25°C, unless otherwise noted.)
MAX1927R EFFICIENCY LOAD CURRENT
MAX1927 toc01
MAX1928-25 EFFICIENCY LOAD CURRENT
MAX1927 toc02
MAX1928-18 EFFICIENCY LOAD CURRENT
2.7V
MAX1927 toc03
EFFICIENCY 3.6V
EFFICIENCY 3.6V
EFFICIENCY VOUT 1.8V
3.6V
VOUT 3.3V 1000 1000 LOAD CURRENT (mA) LOAD CURRENT (mA)
1000
LOAD CURRENT (mA)
MAX1928-15 EFFICIENCY LOAD CURRENT
2.7V EFFICIENCY VOUT 1.5V 1000 LOAD CURRENT (mA) 3.6V
MAX1927 toc04
MAX1927R EFFICIENCY LOAD CURRENT
MAX1927 toc05
MAX1928-25 DROPOUT VOLTAGE LOAD CURRENT
DROPOUT VOLTAGE (mV)
MAX1927 toc06
EFFICIENCY VOUT 3.6V 2.7V
2.5V LOAD CURRENT
1000
LOAD CURRENT (mA)
MAX1928-18 OUTPUT VOLTAGE LOAD CURRENT
MAX1927 toc07
NO-LOAD INPUT CURRENT INPUT VOLTAGE
MAX1927 toc08
OSCILLATOR FREQUENCY INPUT VOLTAGE
+85°C
MAX1927 toc09
1.90 1.88 1.86 OUTPUT VOLTAGE 1.84 1.82 1.80 1.78 1.76 1.74 1.72 1.70 3.6V
INPUT CURRENT (µA)
1.06 OSCILLATOR FREQUENCY (MHz) 1.04 1.02 1.00 0.98 0.96 0.94 -40°C +25°C
1000 LOAD CURRENT (mA)
INPUT VOLTAGE
INPUT VOLTAGE
Low-Output-Voltage, 800mA, Step-Down DC-DC Converters MAX1927/MAX1928
Typical Operating Characteristics (continued)
(Circuits Figure +25°C, unless otherwise noted.)
MAXIMUM LOAD CURRENT INPUT VOLTAGE
VOUT MAXIMUM LOAD CURRENT VOUT VOUT 1.8V VOUT 2.5V
MAX1927 toc10
STARTUP WAVEFORM
MAX1927 toc11
WAVEFORM
MAX1927 toc12
SHDN
5V/div
SHDN
5V/div
1V/div 2V/div
200mA/div
VOUT 20ms/div
2V/div
1ms/div
INPUT VOLTAGE
HEAVY-LOAD SWITCHING WAVEFORMS
MAX1927 toc13
LIGHT-LOAD SWITCHING WAVEFORMS
MAX1927 toc14
VOUT (AC-COUPLED)
10mV/div
VOUT (AC-COUPLED)
10mV/div
200mA/div
5V/div
400ns/div
5V/div
2ms/div
200mA/div
LOAD TRANSIENT
MAX1927 toc15
LINE TRANSIENT
MAX1927 toc16
VOUT (AC-COUPLED)
100mV/div
VOUT (AC-COUPLED)
10mV/div
900mA ILOAD 500mA/div 250mA
4.2V 2V/div
100µs/div
1ms/div
Low-Output-Voltage, 800mA, Step-Down DC-DC Converters
Description
NAME FUNCTION Forced-PWM Input. Drive medium heavy loads pulse-skipping light loads. Drive BATT force operation loads. Ground Internal 1.25V Reference. Bypass with 0.1µF capacitor. Output Feedback Sense Input. output voltage preset voltage (MAX1928), connect directly output. adjust output voltage (MAX1927R), connect center external resistordivider between output GND. regulation voltage 0.75V. Compensation Input. Compensation, Stability, Output Capacitor section compensation component selection. Shutdown Control Input. Drive shut down converter. Drive high normal operation. Power Ground Inductor Connection drains internal power MOSFETs. Supply Voltage Input. Connect 2.6V 5.5V source. Bypass with low-ESR 10µF capacitor. Power-OK Open-Drain Output. Once soft-start routine completed, goes high impedance 20ms after exceeds expected final value.
BATT COMP SLOPE COMPENSATION COMPARATOR BIAS
MAX1927/MAX1928
COMP SHDN PGND BATT
MAX1927 MAX1928
1MHz
CURRENT COMPARATOR
ILIM COMPARATOR CONTROL
SHDN N-CHANNEL CURRENT COMPARATOR COMP 1.25V REFERENCE POWER-OK CONTROL
PGND
MAX1927R ONLY MAX1928 ONLY
Figure Simplified Functional Diagram
Low-Output-Voltage, 800mA, Step-Down DC-DC Converters MAX1927/MAX1928
Detailed Description
MAX1927/MAX1928 step-down DC-DC converters accept inputs 2.6V, while delivering 800mA output voltages 0.75V. These devices operate modes optimize noise quiescent current. Under heavy loads, MAX1927/ MAX1928 operate pulse-width modulation (PWM) mode switch fixed 1MHz frequency. Under light loads, they operate mode reduce power consumption. addition, both devices provide selectable forced operation minimum noise load currents. small, low-valued, output filter capacitor. resulting load regulation 0.3% (typ) from 800mA.
Forced Operation
force PWM-only operation, connect BATT. Forced operation desirable sensitive data-acquisition applications ensure that switching noise does interfere with sensitive data sampling frequencies. minimum load required during forced operation because synchronous rectifier passes reverse inductor current needed allow constant frequency operation with load. Forced operation higher quiescent current than (2mA compared 140µA) continuous switching.
Operation Control Scheme
mode improves efficiency reduces quiescent current 140µA light loads. MAX1927/ MAX1928 initiate pulse-skipping operation when peak inductor current drops below 130mA. During operation, MAX1927/MAX1928 switch only necessary service load, reducing switching frequency associated losses internal switch, synchronous rectifier, inductor. During mode, switching cycle initiates when error amplifier senses that output voltage dropped below regulation point. output voltage low, P-channel MOSFET switch turns conducts current output filter capacitor load. PMOS switch turns when comparator satisfied. MAX1927/MAX1928 then wait until error amplifier senses output voltage start again. Some jitter normal during transition from with loads around 100mA. This adverse impact regulation. loads greater than 130mA, MAX1927/MAX1928 fixed-frequency, current-mode, controller capable achieving 100% duty cycle. Current-mode feedback provides cycle-by-cycle current limiting, superior load line response, well overcurrent protection internal MOSFET synchronous rectifier. comparator P-channel MOSFET switch detects overcurrent conditions exceeding 1.1A. During operation, MAX1927/MAX1928 regulate output voltage switching constant frequency then modulating power transferred load using comparator (Figure error-amp output, main switch current-sense signal, slope compensation ramp summed comparator. comparator modulates output power adjusting peak inductor current during first half each cycle based output-error voltage. MAX1927/MAX1928 have relatively ACloop gain coupled with high-gain integrator enable
100% Duty-Cycle Operation
maximum on-time exceed internal oscillator cycle, which permits operation 100% duty cycle. input voltage drops, duty cycle increases until internal P-channel MOSFET stays continuously. Dropout voltage 100% duty cycle output current multiplied internal PMOS onresistance (typically 0.25) inductor resistance. Near dropout, switching cycles skipped, reducing switching frequency. However, voltage ripple remains small because current ripple still low.
Synchronous Rectification
N-channel synchronous rectifier eliminates need external Schottky diode improves efficiency. synchronous rectifier turns during second half each cycle (off-time). During this time, voltage across inductor reversed, inductor current falls. normal mode, synchronous rectifier turned when either output falls regulation (and another on-time begins) when inductor current approaches zero. forced mode, synchronous rectifier remains active until beginning cycle.
Shutdown Mode
Driving SHDN places MAX1927/MAX1928 shutdown mode. shutdown, reference, control circuitry, internal switching MOSFET, synchronous rectifier turn output becomes high impedance. Drive SHDN high normal operation. Input current falls 0.1µA (typ) during shutdown mode.
Output
open-drain output that goes high impedance 20ms after soft-start ramp concluded within threshold. impedance when shutdown.
Low-Output-Voltage, 800mA, Step-Down DC-DC Converters MAX1927/MAX1928
Table Regulation Voltages
PART
PRESET OUTPUT VOLTAGE 0.75V, Adjustable
MAX1927R MAX1928-15
MAX1927R
MAX1928-18 MAX1928-25
following equation calculate maximum input current: IRMS VOUT (VIN VOUT
Figure Setting Adjustable Output Voltage
Applications Information
Output Voltage Selection
MAX1927/MAX1928 have preset output voltages. addition, MAX1927R adjustable output. output voltage preset voltage, connect output. Table list preset voltages their corresponding part numbers. output voltage MAX1927R adjustable from 0.75V input voltage connecting resistor-divider between output (Figure determine values resistor-divider, first select value feedback resistor between 50k. then given where 0.75V.
Compensation, Stability, Output Capacitor
MAX1927/MAX1928 externally compensated with resistor capacitor (see Figure series from COMP GND. additional capacitor (Cf) required from COMP highESR output capacitors used. capacitor integrates current from transimpedance amplifier, averaging output capacitor ripple. This sets device speed transient response allows small ceramic output capacitors because phaseshifted capacitor ripple does disturb current regulation loop. resistor sets proportional gain output error voltage factor Increasing this resistor also increases sensitivity control loop output ripple. resistor capacitor compensation zero that defines system's transient response. load creates dynamic pole, shifting frequency with changes load. load decreases, pole frequency decreases. System stability requires that compensation zero must placed ensure adequate phase margin least unity gain). following design procedure compensation network: Select appropriate converter bandwidth (fC) stabilize system while maximizing transient response. This bandwidth should exceed 1/10 switching frequency. Calculate compensation capacitor, based this bandwidth: MAX1927: IOUT(MAX)
Input Capacitor Selection
Capacitor equivalent series resistance (ESR) major contributor input ripple high-frequency DC-DC converters. Ordinary aluminum-electrolytic capacitors have high should avoided. Low-ESR aluminum electrolytic capacitors acceptable relatively inexpensive. Low-ESR tantalum capacitors polymer capacitors better provide compact solution space-constrained surface-mount designs. Ceramic capacitors have lowest overall. input filter capacitor reduces peak currents noise input voltage source. Connect low-ESR bulk capacitor (10µF typ) input. Select this bulk capacitor meet input ripple requirements voltage rating rather than capacitance value.
Low-Output-Voltage, 800mA, Step-Down DC-DC Converters MAX1927/MAX1928
MAX1928: IOUT(MAX) Resistors external MAX1927 (see Setting Output Voltage section). IOUT(MAX) maximum output current, 0.48V/A, 250µS MAX1927. Electrical Characteristics table MAX1928 values. Select closest standard value that gives acceptable bandwidth. Calculate equivalent load impedance, VOUT IOUT(MAX) dominant pole created output load output capacitance: COUT Solving gives: COUT Calculate high-frequency compensation pole cancel zero created output capacitor's ESR: RESR COUT
Calculate compensation resistance (RC) can-
2.6V 5.5V BATT 10µF
CDRH4D18 4.7µH SHDN VOUT 1.8V 800mA 10µF
MAX1928-18
1200pF COMP 22pF
PGND
0.1µF
Figure Applications Circuit MAX1928
2.6V 5.5V BATT 10µF SHDN PGND 0.1µF 49.9k 16.5k
CDRH4D18 4.7µH
VOUT 800mA 10µF
MAX1927R
COMP 680pF 22pF
Figure Applications Circuit MAX1927
Low-Output-Voltage, 800mA, Step-Down DC-DC Converters
Solving gives: COUT 22pF, whichever greater. ground pins single common node star ground configuration. external voltage feedback network should very close pin, within 0.2in (5mm). Keep noisy traces, such those from pin, away from voltage feedback network. Position bypass capacitors close possible their respective pins minimize noise coupling. optimum performance, place input output capacitors close device possible. Connect PGND highest quality system ground. MAX1928 evaluation illustrates example board layout routing scheme.
MAX1927/MAX1928
Standard Application Circuits
Figures standard applications circuits MAX1927/MAX1928. Figure illustrates preset output voltages (MAX1928), while Figure shows adjustable configuration (MAX1927). Table lists part numbers suppliers components used these circuits.
Chip Information
TRANSISTORS: 3282 PROCESS: BiCMOS
Board Layout Routing
High switching frequencies large peak currents make board layout very important part design. Good design minimizes EMI, noise feedback paths, voltage gradients ground plane, which result instability regulation errors. Connect inductor, input filter capacitor, output filter capacitor close together possible keep their traces short, direct, wide. Connect their
Table Suggested Parts/Suppliers
PART Inductor Input/Output Capacitors COMP Capacitor Capacitor PART NUMBER CDRH3D16-4R7 JMK212BJ106MG GRM1881X1H561J EMK107BJ104KA MANUFACTURER Sumida Taiyo Yuden Murata Taiyo Yuden PHONE 847-956-0666 Japan 81-3-3607-5111 408-573-4150 770-436-1300 408-573-4150 WEBSITE www.sumida.com www.t-yuden.com www.murata.com www.t-yuden.com
Low-Output-Voltage, 800mA, Step-Down DC-DC Converters MAX1927/MAX1928
Package Information
(The package drawing(s) this data sheet reflect most current specifications. latest package outline information, www.maxim-ic.com/packages.)
INCHES 0.043 0.006 0.002 0.030 0.037 0.120 0.116 0.118 0.114 0.116 0.120 0.114 0.118 0.187 0.199 0.0157 0.0275 0.037 0.007 0.0106 0.0197 0.0035 0.0078 0.0196
MILLIMETERS 1.10 0.15 0.05 0.75 0.95 3.05 2.95 3.00 2.89 3.05 2.95 2.89 3.00 4.75 5.05 0.40 0.70 0.940 0.177 0.270 0.500 0.090 0.200 0.498
0.50±0.1 0.6±0.1
0.6±0.1
VIEW
BOTTOM VIEW
GAGE PLANE
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, uMAX/uSOP
APPROVAL DOCUMENT CONTROL REV.
21-0061
Maxim cannot assume responsibility circuitry other than circuitry entirely embodied Maxim product. circuit patent licenses implied. Maxim reserves right change circuitry specifications without notice time.
_Maxim Integrated Products, Gabriel Drive, Sunnyvale, 94086 408-737-7600 2002 Maxim Integrated Products Printed registered trademark Maxim Integrated Products.
10LUMAX.EPS

Low-Output-Voltage, 800mA, Step-Down DC-DC Converters MAX1927/MAX

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