Datasheet

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General Description

The MAX15021 is a dual-output, pulse-width-modulated

(PWM), step-down DC-DC regulator with tracking (coin-

cident and ratiometric) and sequencing options. The

device operates from 2.5V to 5.5V and each output can

be adjusted from 0.6V to the input supply (V

AVIN

). The

MAX15021 delivers up to 4A (regulator 1) and 2A (reg-

ulator 2) of output current. This device offers the ability

to adjust the switching frequency from 500kHz to 4MHz

and provides the capability of optimizing the design in

terms of size and performance.

The MAX15021 utilizes a voltage-mode control scheme

with external compensation to provide good noise

immunity and maximum flexibility in selecting inductor

values and capacitor types. The dual switching regula-

tors operate 180° out-of-phase, thereby reducing the

RMS input ripple current and thus the size of the input

bypass capacitor significantly.

The MAX15021 offers the ability to track (coincident or

ratiometric) or sequence during power-up and power-

down operation. When sequencing, it powers up glitch-

free into a prebiased output.

Additional features include an internal undervoltage

lockout with hysteresis and a digital soft-start/soft-stop

for glitch-free power-up and power-down. Protection

features include lossless cycle-by-cycle current limit,

hiccup-mode output short-circuit protection, and ther-

mal shutdown.

The MAX15021 is available in a space-saving, 5mm x

5mm, 28-pin TQFN-EP package and is specified for

operation from -40°C to +125°C temperature range.

Applications

RFID Reader Cards

Power-over-Ethernet (PoE) IP Phones

Automotive Multimedia

Multivoltage Supplies

Networking/Telecom

Features

♦ 2.5V to 5.5V Input-Voltage Range

♦ Dual-Output Synchronous Buck Regulators

♦ Integrated Switches for 4A and 2A Output

Currents

♦ 180° Out-Of-Phase Operation

♦ Output Voltage Adjustable from 0.6V to V

AVIN

♦ Lossless, Cycle-by-Cycle Current Sensing

♦ External Compensation for Maximum Flexibility

♦ Digital Soft-Start and Soft-Stop for Tracking

Applications

♦ Digital Soft-Start into a Prebiased Load for

Sequencing Applications

♦ Sequencing or Coincident/Ratiometric Tracking

♦ Programmable Switching Frequency from 500kHz

to 4MHz

♦ Thermal Shutdown and Hiccup-Mode Short-

Circuit Protection

♦ 20µA Shutdown Current

♦ 100% Maximum Duty Cycle

♦ Space-Saving (5mm x 5mm) 28-Pin TQFN

Package

MAX15021

Dual, 4A/2A, 4MHz, Step-Down DC-DC

Regulator with Tracking/Sequencing Capability

For pricing, delivery, and ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

MAX15021

TOP VIEW

PGND1

PVIN1

LX1

PGND1

SEL

N.C.

LX2

PGND2

N.C.

DVDD2

N.C.

EN2

*EP

*EP = EXPOSED PAD.

567

2021 19 17 16 15

SGND

AVIN

COMP1

FB1

EN1

DVDD1

LX1

PVIN2

PGND1

FB2

N.C.

COMP2

N.C.

Pin Configuration

Ordering Information

19-4106; Rev 1; 8/12

PART

TEMP RANGE

PIN-PACKAGE

MAX15021ATI/V+

-40°C to +125°C

28 TQFN-EP*

Denotes a lead-free package.

EP = Exposed pad.

/V denotes an automotive qualified part.

Summary of content (24 pages)

PAGE 1
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability General Description ♦ Programmable Switching Frequency from 500kHz to 4MHz ♦ Thermal Shutdown and Hiccup-Mode ShortCircuit Protection ♦ 20µA Shutdown Current ♦ 100% Maximum Duty Cycle ♦ Space-Saving (5mm x 5mm) 28-Pin TQFN Package RFID Reader Cards Power-over-Ethernet (PoE) IP Phones N.C. 18 17 16 15 N.C. 22 14 N.C. COMP2 23 13 N.C.
PAGE 2
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability ABSOLUTE MAXIMUM RATINGS AVIN, PVIN_, DVDD_, EN_, FB_, RT, SEL to SGND .........................................................-0.3V to +6V COMP_ to SGND .....................................-0.3V to (VAVIN + 0.3V) PGND_ to SGND ...................................................-0.3V to +0.3V LX_ Current (Note 1) Regulator 1...............................................................................6A Regulator 2.
PAGE 3
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability ELECTRICAL CHARACTERISTICS (continued) (VAVIN = VPVIN_ = VDVDD_ = 3.3V, VPGND_ = VSGND_ = 0V, RT = 25kΩ, and TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 3) PARAMETER SYMBOL CONDITIONS MIN TYP MAX VAVIN = 3.3V 4.5 4.9 5.3 VAVIN = 2.5V 3.4 3.65 3.
PAGE 4
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Typical Operating Characteristics (VAVIN = VDVDD1 = VDVDD2 = VPVIN1 = VPVIN2 = 5V, VOUT1 = 3.3V, VOUT2 = 1.5V, VPGND_ = 0V, RT = 16.5kΩ. TA = +25°C, unless otherwise noted.) VPVIN1 = 5V 50 40 30 60 VOUT1 = 1.8V 50 VOUT1 = 3.3V 40 5000 1000 VOUT2 = 1.5V fSW = 2MHz EN1 = 0V 0 100 100 5000 1000 LOAD CURRENT (mA) CHANNEL 2 EFFICIENCY vs. LOAD CURRENT CHANNEL 1 LOAD REGULATION CHANNEL 2 LOAD REGULATION 3.
PAGE 5
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Typical Operating Characteristics (continued) (VAVIN = VDVDD1 = VDVDD2 = VPVIN1 = VPVIN2 = 5V, VOUT1 = 3.3V, VOUT2 = 1.5V, VPGND_ = 0V, RT = 16.5kΩ. TA = +25°C, unless otherwise noted.) QUIESCENT CURRENT vs. TEMPERATURE 4.50 4.25 4.00 3.75 3.50 3.25 3.00 2.75 NO SWITCHING REGULATOR 1 ENABLED VOUT1 = 3.3V REGULATOR 2 ENABLED VOUT2 = 1.
PAGE 6
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Typical Operating Characteristics (continued) (VAVIN = VDVDD1 = VDVDD2 = VPVIN1 = VPVIN2 = 5V, VOUT1 = 3.3V, VOUT2 = 1.5V, VPGND_ = 0V, RT = 16.5kΩ. TA = +25°C, unless otherwise noted.) CHANNEL 1 LOAD STEP RESPONSE CHANNEL 1 LOAD STEP RESPONSE MAX15021 toc15 MAX15021 toc16 EN2 = 0V EN2 = 0V VPVIN1 5V/div 0V VPVIN1 5V/div 0V VOUT1 3.3V, AC-COUPLED 100mV/div VOUT1 3.
PAGE 7
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Pin Description PIN NAME FUNCTION 1 SEL Track/Sequence Select Input. Connect SEL to ground to configure the device as a sequencer. Connect SEL to AVIN for tracking with output 1 as the master. Leave SEL unconnected for tracking with output 2 as the master. Use the output with the higher voltage as the master and the output with the lower voltage as the slave.
PAGE 8
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Functional Diagrams AVIN SEL SGND ON1 ON2 SHDN MAX15021 SEQ1 1.225V 1.1V EN CONFIG PWM CONTROLLER 1 SEQ2 SEL DECODE SEQ1 VREF CLK1 VREF VR1 EN1 ON1 SEQ1 SEQ2 DOWN1 DIGITAL SOFT-START AND SOFT-STOP EN1 SHDN THERMAL SHDN 0.6V REF OVL CONFIG SEQ1 1.225V 1.
PAGE 9
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Functional Diagrams (continued) SEQ2 SHDN EN2 MAX15021 ON1 ON2 ON2 1.225V 1.
PAGE 10
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Detailed Description The MAX15021 incorporates dual-output, PWM, stepdown, DC-DC regulators with tracking and sequencing options. The device operates over the input-voltage range of 2.5V to 5.5V. Each PWM regulator provides an adjustable output down to 0.6V and delivers up to 4A (regulator 1) and 2A (regulator 2) of load current.
PAGE 11
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Coincident/Ratiometric Tracking The enable inputs in conjunction with digital soft-start and soft-stop provide coincident/ratiometric tracking. Track an output voltage by connecting a resistive divider from the output being tracked to its enable input. For example, for VOUT2 to coincidentally track V OUT1, connect the same resistive divider used for FB2, from VOUT1 to EN2 to SGND (see Figure 2).
PAGE 12
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Error Amplifier The output of the internal voltage-mode error amplifier (COMP_) is provided for frequency compensation (see the Compensation-Design Guidelines section). FB_ is the inverting input of the error amplifier. The error amplifier has an 80dB open-loop gain and a 12MHz gain bandwidth (GBW) product.
PAGE 13
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Effective Input-Voltage Range Although the MAX15021’s regulators can operate from input supplies ranging from 2.5V to 5.5V, the input-voltage range can be effectively limited by the MAX15021’s duty-cycle limitations for a given output voltage (V OUT_ ).
PAGE 14
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Use the following equation to calculate the input ripple when only one regulator is enabled: ICIN(RMS)[A] = ILOAD(MAX)[A] × ( ) VOUT_ [V] × VPVIN_ − VOUT_ [V] VPVIN_ [V] The MAX15021 includes UVLO hysteresis to avoid possible unintentional chattering during turn-on. Use additional bulk capacitance if the input source impedance is high.
PAGE 15
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability VAVIN V = AVIN = 4V/V VRAMP VAVIN 4 1 1 fLC = ≈ 2 π L × × COUT ⎛R + ESR ⎞ 2π × L × COUT × ⎜ OUT ⎟ ⎝ ROUT + DCR ⎠ GainMOD(DC) = fESR = 1 2π × ESR × COUT ROUT is the load resistance of the regulator, fLC is the resonant break frequency of the filter, and fESR is the ESR zero of the output capacitor. See the Closed-Loop Response and Compensation of Voltage-Mode Regulators section for more information on fLC and fESR.
PAGE 16
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability MAX15021 fig04c 40 |GMOD| 20 gentler response of the previous example. This is due to the filter components’ lower parasitic (DCR and ESR) and corresponding higher frequency of the inherent ESR zero. In this example, the desired crossover frequency occurs below the ESR zero frequency.
PAGE 17
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Type II: Compensation when fCO > fZERO,ESR When the fCO is greater than fESR, a Type II compensation network provides the necessary closed-loop compensated response. The Type II compensation network provides a midband compensating zero and a high-frequency pole (see Figures 5a and 5b). R F C F provides the midband zero f MID,ZERO , and RFCCF provides the high-frequency pole, fHIGH,POLE.
PAGE 18
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Solving for R1: R1 [kΩ] = VOUT_ RF [kΩ] × 4 × ESR[mΩ] × VFB [V] 2π × fCO [kHz] × L[μH] × VOUT_ [V] where VFB is the 0.6V (typ) FB_ input-voltage set-point, L is the value of the regulator inductor, ESR is the series resistance of the output capacitor, and VOUT_ is the desired output voltage.
PAGE 19
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability The locations of the zeros and poles should be such that the phase margin peaks around fCO. Solving for CI: Set the ratios of fCO-to-fZ and fP-to-fCO equal to one another, e.g., fCO = fP = 5 is a good number to get approximately fZ fCO 60° of phase margin at fCO. Whichever technique, it is important to place the two zeros at or below the double pole to avoid the conditional stability issue.
PAGE 20
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Applications Information PCB Layout Guidelines Careful PCB layout is critical to achieve clean and stable operation. Follow these guidelines for good PCB layout: 1) Place decoupling capacitors as close as possible to the IC pins. 2) Keep SGND and PGND isolated and connect them at one single point close to the negative terminal of the input filter capacitor.
PAGE 21
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Typical Operating Circuits VIN CI2 R1FB2 RI2 C1 R1 CF2 RF2 R2FB2 C2 CIN2 AVIN EN2 PVIN2 DVDD2 CDD2 CCF2 FB2 COMP2 LX2 L2 VOUT2 RS2 COUT2 CS2 PGND2 VIN CDD1 DVDD1 EN1 MAX15021 VIN VAVIN CIN1 PVIN1 VOUT1 L1 LX1 RS1 COUT1 CS1 PGND1 CI1 RI1 R1FB1 R1EN2 R2FB1 R2EN2 FB1 RT PGND SGND SGND SEL COMP1 VAVIN RT CT CF1 RF1 CCF1 Figure 7.
PAGE 22
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Typical Operating Circuits (continued) VOUT1 VIN CI2 R1OUT2 RI2 C1 R1 CF2 RF2 R2OUT2 C2 CIN2 AVIN EN2 PVIN2 CDD2 DVDD2 CCF2 FB2 COMP2 LX2 L2 VOUT2 RS2 COUT2 CS2 PGND2 VIN CDD1 DVDD1 EN1 VIN MAX15021 VAVIN CIN1 PVIN1 VOUT1 L1 LX1 RS1 COUT1 CS1 PGND1 CI1 RI1 R1OUT1 FB1 RT PGND SGND SEL COMP1 R2OUT1 SGND CF1 RT CT RF1 CCF1 Figure 8.
PAGE 23
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Package Information Chip Information PROCESS: BiCMOS Maxim Integrated For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
PAGE 24
MAX15021 Dual, 4A/2A, 4MHz, Step-Down DC-DC Regulator with Tracking/Sequencing Capability Revision History REVISION NUMBER REVISION DATE 0 5/08 Initial release — 1 8/12 Added automotive qualified part to Ordering Information 1 DESCRIPTION PAGES CHANGED Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.