Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - DC/DC voltage regulator Holder TSSOP 28 EP

General Description

The MAX1945R/MAX1945S high-efficiency pulse-width

modulation (PWM) switching regulators deliver up to 6A

of output current. The devices operate from an input

supply range of 2.6V to 5.5V and provide selectable

output voltages of 1.8V, 2.5V, and adjustable output

voltages from 0.8V to 85% of the supply voltage. With

at 3.3V/5V, the input voltage can be as low as

2.25V. The MAX1945R/MAX1945S are ideal for on-

board post-regulation applications. Total output voltage

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

The MAX1945R/MAX1945S operate at a selectable

fixed frequency (500kHz or 1MHz) or can be synchro-

nized to an external clock (400kHz to 1.2MHz). The

high operating frequency minimizes the size of external

components. The high bandwidth of the internal error

amplifier provides excellent transient response. The

MAX1945R/MAX1945S have internal dual N-channel

MOSFETs to lower heat dissipation at heavy loads. Two

MAX1945R/MAX1945Ss can operate 180 degrees out-

of-phase of each other to minimize input capacitance.

The devices provide output voltage margining for

board-level testing. The MAX1945R provides a ±4%

voltage margining. The MAX1945S provides a ±9%

voltage margining.

The MAX1945R/MAX1945S are available in 28-pin

TSSOP-EP packages and are specified over the -40°C

to +85°C industrial temperature range. An evaluation kit

is available to speed designs.

Applications

Low-Voltage, High-Density Distributed Power

Supplies

ASIC, CPU, and DSP Core Voltages

RAM Power Supply

Base Station, Telecom, and Networking

Equipment Power Supplies

Server and Notebook Power Supplies

Features

♦ 6A PWM Step-Down Regulator with 95%

Efficiency

♦ 1MHz/500kHz Switching for Small External

Components

♦ 0.76in

Complete 6A Regulator Footprint

♦ External Components’ Height <3mm

♦ ±1% Output Accuracy over Load, Line, and

Temperature

♦ Operate from 2.6V to 5.5V Supply

♦ Operate from 2.5V Input with V

at 3.3V/5V

♦ Preset Output Voltage of 1.8V or 2.5V

♦ Adjustable Output from 0.8V to 85% of Input

♦ Voltage Margining: ±4% (MAX1945R) or ±9%

(MAX1945S)

♦ Synchronize to External Clock

♦ SYNCOUT Provides 180-Degree Out-of-Phase

Clock Output

♦ All-Ceramic or Electrolytic Capacitor Designs

MAX1945R/MAX1945S

1MHz, 1% Accurate, 6A Internal Switch

Step-Down Regulators

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

REF

COMP

BST

GND

PGND

INPUT

2.6V TO 5.5V

FBSEL

CTL1

CTL2

SYNC

SYNCOUT

OUTPUT

0.8V TO

0.85 x V

VOLTAGE

MARGINING

ON/OFF

SYNCHRONIZATION

CLOCK

MAX1945R

MAX1945S

180° OUT-OF-PHASE

Typical Operating Circuit

19-2640; Rev 1; 7/04

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.

*EP = Exposed pad.

Pin Configuration appears at end of data sheet.

EVALUATION KIT

AVAILABLE

PART TEMP RANGE PIN-PACKAGE

MAX1945REUI -40°C to +85°C 28 TSSOP-EP*

MAX1945SEUI -40°C to +85°C 28 TSSOP-EP*

Summary of content (19 pages)

PAGE 1
9-2640; Rev 1; 7/04 KIT ATION EVALU E L B AVAILA 1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators The MAX1945R/MAX1945S high-efficiency pulse-width modulation (PWM) switching regulators deliver up to 6A of output current. The devices operate from an input supply range of 2.6V to 5.5V and provide selectable output voltages of 1.8V, 2.5V, and adjustable output voltages from 0.8V to 85% of the supply voltage. With VCC at 3.3V/5V, the input voltage can be as low as 2.25V.
PAGE 2
MAX1945R/MAX1945S 1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators ABSOLUTE MAXIMUM RATINGS Continuous Power Dissipation (TA = +85°C) (derate 23.8mW/°C above +70°C) .............................1191mW Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C CTL1, CTL2, IN, SYNC, VCC, VDD to GND ...............-0.
PAGE 3
1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators (VIN = VCC = VCTL1 = VCTL2 = VDD = 3.3V, SYNC = GND, FBSEL = High-Z, VFB = 0.7V, CREF = 0.22µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX FBSEL = GND 1.782 1.800 1.818 FBSEL = VCC 2.475 2.500 2.525 FBSEL = High-Z 0.792 0.800 0.808 UNITS FB FB Regulation Voltage (Error Amp Only) Maximum Output Current VFB IFB_OUT VCOMP = 1V to 2V, VIN = 2.6V to 5.5V VIN = 3.
PAGE 4
MAX1945R/MAX1945S 1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators ELECTRICAL CHARACTERISTICS (continued) (VIN = VCC = VCTL1 = VCTL2 = VDD = 3.3V, SYNC = GND, FBSEL = High-Z, VFB = 0.7V, CREF = 0.22µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at +25°C.) PARAMETER SYMBOL LX Minimum Duty Cycle CONDITIONS VIN = 2.6V/3.3V MIN TYP MAX SYNC = GND 8.8 10.5 SYNC = VCC 17.6 RMS LX Output Current 6 UNITS % A FBSEL FBSEL Input Threshold 1.8V FBSEL Input Threshold 2.
PAGE 5
1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators (VIN = VCC = VCTL1 = VCTL2 = VDD = 3.3V, SYNC = GND, FBSEL = High-Z, VFB = 0.7V, CREF = 0.22µF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS THERMAL SHUTDOWN Thermal-Shutdown Hysteresis °C °C 20 Thermal-Shutdown Threshold When LX stops switching 165 ELECTRICAL CHARACTERISTICS (VIN = VCC = VCTL1 = VCTL2 = VDD = 3.3V, SYNC = GND, FBSEL = High-Z, VFB = 0.
PAGE 6
MAX1945R/MAX1945S 1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators ELECTRICAL CHARACTERISTICS (continued) (VIN = VCC = VCTL1 = VCTL2 = VDD = 3.3V, SYNC = GND, FBSEL = High-Z, VFB = 0.7V, CREF = 0.22µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS FB FB Regulation Voltage (Error Amp Only) Maximum Output Current VFB IFB_OUT VCOMP = 1V to 2V, VIN = 2.6V to 5.5V FBSEL = GND 1.773 1.827 FBSEL = VCC 2.462 2.538 FBSEL = High-Z 0.
PAGE 7
1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators (VIN = VCC = VCTL1 = VCTL2 = VDD = 3.3V, SYNC = GND, FBSEL = High-Z, VFB = 0.7V, CREF = 0.22µF, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN SYNC = GND, VIN = 2.6V/3.3V LX Minimum Duty Cycle TYP MAX UNITS 10.5 % FBSEL FBSEL Input Threshold 1.8V FBSEL Input Threshold 2.5V FBSEL Input Current Low ILOW_ Where 1.8V feedback switches in and out, VCC = 2.6V/3.3V/5.5V FBSEL rising Where 2.
PAGE 8
Typical Operating Characteristics (VIN = VCC = 5V, VOUT = 1.8V, IOUT = 6A, fSW = 500kHz, VDD = VCC, and TA = +25°C, unless otherwise noted.) EFFICIENCY vs. OUTPUT CURRENT VIN = VCC = 5V EFFICIENCY vs. OUTPUT CURRENT VIN = VCC = 3.3V D E 50 40 A: VOUT = 0.8V B: VOUT = 1.5V C: VOUT = 1.8V D: VOUT = 2.5V E: VOUT = 3.3V 30 20 10 0 0 1 2 50 40 10 4 5 6 7 MAX1945 toc03 A B 60 40 A: VOUT = 0.8V B: VOUT = 1.5V C: VOUT = 1.8V 10 1 2 3 4 5 6 7 1 0 2 IOUT (A) FREQUENCY vs.
PAGE 9
1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators PGND-MEASURED TEMPERATURE vs. OUTPUT CURRENT VREF (V) 60 2.015 2.010 40 20 2.005 VCC = VIN = 5V VOUT = 1.8V 0 6.0 6.5 AMBIENT TEMP: 0°C 7.0 7.5 VIN = VCC = 5V fSW = 500kHz 2.000 8.0 -40 -15 10 35 60 85 110 MAX1945 toc11 OUTPUT SHORT-CIRCUIT CURRENT (A) 2.025 2.020 AMBIENT TEMP: +25°C 80 12 MAX1945 toc10 AMBIENT TEMP: +85°C 100 2.
PAGE 10
MAX1945R/MAX1945S 1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators Typical Operating Characteristics (continued) (VIN = VCC = 5V, VOUT = 1.8V, IOUT = 6A, fSW = 500kHz, VDD = VCC, and TA = +25°C, unless otherwise noted.
PAGE 11
1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators PIN NAME 19, 21, 23, 25 PGND 27 CTL1 28 CTL2 EP FUNCTION Power Ground. Connect all PGND together close to the device. Star connect GND to PGND (see the PC Board Layout Considerations section). Output Margining Control Inputs. When CTL1 = CTL2 = GND, the regulator is off. When CTL1 = CTL2 = VCC, the regulator runs at nominal output voltage. When CTL1 = VCC and CTL2 = GND, the output is set to the margin-low output (-4% or -9%).
PAGE 12
MAX1945R/MAX1945S 1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators Soft-Start Shutdown Mode The MAX1945R/MAX1945S employs digital soft-start to reduce supply in-rush current during startup conditions. When the device exits undervoltage lockout (UVLO), shutdown mode, or restarts following a thermal-overload event, the digital soft-start circuitry slowly ramps up the voltages at REF and FB (see the Typical Operating Characteristics). An internal oscillator sets the soft-start time to 3.7ms (typ).
PAGE 13
1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators  LIR  IPEAK = 1+  IOUT(MAX)  2  Example: VIN = 3.3V VOUT = 1.8V fOSC = 500kHz IOUT(MAX) = 6A LIR = 30% IOUT(MAX) = 6A LIR = 30% L = 1µH COUT = 180µF ESR(OUTPUT CAPACITOR) = 30mΩ ESL(OUTPUT CAPACITOR) = 2.5nH VRIPPLE(C) = 2mV VRIPPLE(ESR) = 45mV VRIPPLE(ESL) = 4mV VRIPPLE = 51mV L = 1µH and IPEAK = 6.
PAGE 14
MAX1945R/MAX1945S 1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators Compensation Design The double pole formed by the inductor and the output capacitor of most voltage-mode controllers introduces a large phase shift, which requires an elaborate compensation network to stabilize the control loop.
PAGE 15
1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators CC = (COUT ✕ ROUT)/RC 500kHz Switching The following design example is for the application circuit shown in Figures 1 and 2: VOUT = 1.8V IOUT(MAX) = 6A COUT = 180µF RESR = 0.04Ω gmEA = 50µs gmc = 18.2s fSWITCH = 500kHz ROUT = VOUT/IOUT(MAX) = 1.8V/6 A = 0.3Ω fpDC = 1/(2π ✕ COUT ✕ (ROUT + RESR) = 1/(2 π ✕ 180 ✕ 10-6 ✕ (0.3 + 0.04) = 2.6kHz. fzESR = 1/(2π ✕ COUT RESR) = 1/(2 π ✕ 180 ✕10-6 ✕ 0.04) = 22.1kHz.
PAGE 16
MAX1945R/MAX1945S 1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators Table 3. Compensation Values for Output Voltages (1MHz) VOUT (V) 0.8 1.2 1.8 2.2 3.3 RC (1%) 100kΩ 100kΩ 178kΩ 178kΩ 249kΩ CC (10%) 330pF 330pF 100pF 100pF 100pF mum zero-crossing frequency should be less than onethird of the load-impedance zero frequency, fzESR. The previous requirement on the ESR zero frequency applies to ceramic output capacitors.
PAGE 17
1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators GDC = gmc ✕ ROUT = 18.2 ✕ 0.3 = 5.46 then: RC = (VOUT ✕ fC)/(gmEA ✕ VFB ✕ GDC ✕ fpLOAD) = (1.8 ✕ 120kHz)/(50 ✕ 10-6 ✕ 0.8 ✕ 5.46 ✕ 5.554kHz) ≈ 178kΩ (1%) CC = (COUT ✕ ROUT)/RC =(94µF ✕ 0.3)/178kΩ ≈ 156pF, choose CC = 100pF, 10% Output Inductor: 0.
PAGE 18
1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators MAX1945R/MAX1945S Functional Diagram IN BST N SYNCOUT AC DETECT OSCILLATOR SYNC LX PWM CONTROL LOGIC VDD CTL1 COUNT (8 BIT) CONTROL N CTL2 PGND 8 VCC 8 BIT DAC REFERENCE 2X REF GND 3R COMP FB 2R EAMP FB MAX1945R MAX1945S FBSEL Pin Configuration TOP VIEW BST 1 28 CTL2 VDD 2 27 CTL1 LX 3 26 LX IN 4 25 PGND 24 LX LX 5 IN 6 MAX1945R MAX1945S 23 PGND LX 7 22 LX IN 8 21 PGND LX 9 20 LX IN 10 19 PGND VCC 11 18 SYN
PAGE 19
1MHz, 1% Accurate, 6A Internal Switch Step-Down Regulators TSSOP 4.4mm BODY.EPS XX XX PACKAGE OUTLINE, TSSOP, 4.40 MM BODY, EXPOSED PAD 21-0108 E 1 1 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.