Datasheet

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19-3173; Rev 3; 4/13

MAX8550/MAX8551

Integrated DDR Power-Supply Solutions for

Desktops, Notebooks, and Graphic Cards

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.maximintegrated.com.

General Description

The MAX8550/MAX8551 integrate a synchronous-buck

PWM controller to generate V

DDQ

, a sourcing and sinking

LDO linear regulator to generate V

, and a 10mA refer-

ence output buffer to generate V

TTR

. The buck controller

drives two external N-channel MOSFETs to generate out-

put voltages down to 0.7V from a 2V to 28V input with out-

put currents up to 15A. The LDO can sink or source up to

1.5A continuous and 3A peak current. Both the LDO out-

put and the 10mA reference buffer output can be made

to track the REFIN voltage. These features make the

MAX8550/MAX8551 ideally suited for DDR memory appli-

cations in desktops, notebooks, and graphic cards.

The PWM controller in the MAX8550/MAX8551 utilizes

Maxim’s proprietary Quick-PWM™ architecture with pro-

grammable switching frequencies of up to 600kHz. This

control scheme handles wide input/output voltage ratios

with ease and provides 100ns response to load tran-

sients while maintaining high efficiency and a relatively

constant switching frequency. The MAX8550 offers fully

programmable UVP/OVP and skip-mode options ideal in

portable applications. Skip mode allows for improved

efficiency at lighter loads. The MAX8551, which is tar-

geted towards desktop and graphic-card applications,

does not offer the pulse-skip feature.

The VTT and VTTR outputs track to within 1% of V

REFIN

/ 2.

The high bandwidth of this LDO regulator allows excel-

lent transient response without the need for bulk capac-

itors, thus reducing cost and size.

The buck controller and LDO regulators are provided with

independent current limits. Adjustable lossless foldback

current limit for the buck regulator is achieved by monitor-

ing the drain-to-source voltage drop of the low-side MOS-

FET. Additionally, overvoltage and undervoltage

protection mechanisms are built in. Once the overcurrent

condition is removed, the regulator is allowed to enter

soft-start again. This helps minimize power dissipation

during a short-circuit condition. The MAX8550/MAX8551

allow flexible sequencing and standby power manage-

ment using the SHDNA, SHDNB, and STBY inputs.

Both the MAX8550 and MAX8551 are available in a

small 5mm × 5mm, 28-pin thin QFN package.

Applications

DDR I and DDR II Memory Power Supplies

Desktop Computers

Notebooks and Desknotes

Graphic Cards

Game Consoles

RAID

Networking

Features

Buck Controller

o Quick-PWM with 100ns Load-Step Response

o Up to 95% Efficiency

o 2V to 28V Input Voltage Range

o 1.8V/2.5V Fixed or 0.7V to 5.5V Adjustable Output

o Up to 600kHz Selectable Switching Frequency

o Programmable Current Limit with Foldback

Capability

o 1.7ms Digital Soft-Start and Independent

Shutdown

o Overvoltage/Undervoltage-Protection Option

o Power-Good Window Comparator

LDO Section

o Fully Integrated VTT and VTTR Capability

o VTT has ±3A Sourcing/Sinking Capability

o VTT and VTTR Outputs Track V

REFIN

/ 2

o All-Ceramic Output-Capacitor Designs

o 1.0V to 2.8V Input Voltage Range

o Power-Good Window Comparator

PART TEMP RANGE PIN-PACKAGE

MAX8550ETI -40°C to +85°C 28 5mm × 5mm TQFN

MAX8550ETI+ -40°C to +85°C 28 5mm × 5mm TQFN

MAX8551ETI -40°C to +85°C 28 5mm × 5mm TQFN

MAX8551ETI+ -40°C to +85°C 28 5mm × 5mm TQFN

Ordering Information

MAX8550

MAX8551

5mm x 5mm Thin QFN

TOP VIEW

OVP/UVP

(N.C. FOR

MAX8551)

TON

REF

ILIM

POK1

POK2

STBY

SHDNB

SHDNA

SKIP

(TP1 FOR

MAX8551)

GND

PGND1

BST

OUT

REFIN

VTTI

VTT

PGND2

VTTR

VTTS

Pin Configuration

Typical Operating Circuit appears at end of data sheet.

Quick-PWM is a trademark of Maxim Integrated Products, Inc.

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

Summary of content (29 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards General Description Features The MAX8550/MAX8551 integrate a synchronous-buck PWM controller to generate VDDQ, a sourcing and sinking LDO linear regulator to generate VTT, and a 10mA reference output buffer to generate VTTR. The buck controller drives two external N-channel MOSFETs to generate output voltages down to 0.7V from a 2V to 28V input with output currents up to 15A.
PAGE 2
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards ABSOLUTE MAXIMUM RATINGS VTTS to GND............................................-0.3V to (AVDD + 0.3V) PGND1, PGND2 to GND .......................................-0.3V to +0.3V REF Short Circuit to GND ...........................................Continuous Continuous Power Dissipation (TA = +70°C) 28-Pin 5mm x 5mm TQFN (derate 35.7mW/°C above +70°C).................................................................
PAGE 3
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards ELECTRICAL CHARACTERISTICS (continued) (VIN = +15V, VDD = AVDD = V SHDNA = V SHDNB = VBST = VILIM = 5V, VOUT = VREFIN = VVTTI = 2.5V, UVP/OVP = STBY = FB = SKIP = GND, PGND1 = PGND2 = LX = GND, TON = OPEN, VVTTS = VVTT, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS AVDD = 4.5V to 5.5V; IREF = 0 1.98 2 2.02 V 0.
PAGE 4
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards ELECTRICAL CHARACTERISTICS (continued) (VIN = +15V, VDD = AVDD = V SHDNA = V SHDNB = VBST = VILIM = 5V, VOUT = VREFIN = VVTTI = 2.5V, UVP/OVP = STBY = FB = SKIP = GND, PGND1 = PGND2 = LX = GND, TON = OPEN, VVTTS = VVTT, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 5
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards ELECTRICAL CHARACTERISTICS (continued) (VIN = +15V, VDD = AVDD = V SHDNA = V SHDNB = VBST = VILIM = 5V, VOUT = VREFIN = VVTTI = 2.5V, UVP/OVP = STBY = FB = SKIP = GND, PGND1 = PGND2 = LX = GND, TON = OPEN, VVTTS = VVTT, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 6
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards Typical Operating Characteristics (VIN = 12V, VOUT = 2.5V, TON = GND, SKIP = AVDD, circuit of Figure 8, TA = +25°C, unless otherwise noted.) VOUT = 1.8V 60 50 VOUT = 1.5V 40 30 60 VOUT = 1.8V 50 VOUT = 1.5V 40 30 20 20 SKIP = GND 10 0.01 0.1 1 SKIP = AVDD 0 100 10 SKIP = GND 10 SKIP = AVDD 0 0.01 0.
PAGE 7
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards Typical Operating Characteristics (continued) (VIN = 12V, VOUT = 2.5V, TON = GND, SKIP = AVDD, circuit of Figure 8, TA = +25°C, unless otherwise noted.) LOAD TRANSIENT (BUCK) LOAD TRANSIENT VTT (-1.5A TO +1.5A) MAX8550/51 toc10 LOAD TRANSIENT VTT (-3A TO +3A) MAX8550/51 toc11 MAX8550/51 toc12 ILOAD = 12A, IVTTR = 15mA IVTT = 1.
PAGE 8
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards Typical Operating Characteristics (continued) (VIN = 12V, VOUT = 2.5V, TON = GND, SKIP = AVDD, circuit of Figure 8, TA = +25°C, unless otherwise noted.
PAGE 9
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards Pin Description PIN NAME 1 2 TON FUNCTION On-Time Selection-Control Input. This four-level logic input sets the nominal DH on-time. Connect to GND, REF, AVDD, or leave TON unconnected to select the following nominal switching frequencies: TON = AVDD (200kHz) TON = OPEN (300kHz) TON = REF (450kHz) TON = GND (600kHz) OVP/ UVP (MAX8550) Overvoltage/Undervoltage-Protection Control Input.
PAGE 10
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards Pin Description (continued) PIN NAME FUNCTION 11 PGND2 12 VTT Termination Power-Supply Output. Connect VTT to VTTS to regulate to VREFIN / 2. 13 VTTI Power-Supply Input Voltage for VTT and VTTR. Normally connected to the output of the buck regulator for DDR application. 14 REFIN 15 FB Feedback Input for Buck Output. Connect to AVDD for a +1.8V fixed output or to GND for a +2.5V fixed output.
PAGE 11
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards IN tOFF TRIG Q ON-TIME COMPUTE TON MAX8550/ MAX8551 ONE-SHOT OUT BST tON S TRIG DH Q ONE-SHOT Q R LX VDD DL S INTREF Q 1.16 x INTREF PGND R QUAD LEVEL DECODE OVP/UVP (N.C. IN MAX8551) ILIM OVP/UVP LATCH BUCK ON/OFF SHDNA VDD - 1V 1.0V SHDNB SHUTDOWN DECODER SKIP (TP1 IN MAX8551 MUST BE CONNECTED TO GND) LX BIAS ON/OFF 20ms TIMER ZERO CROSSING LX STBY OUT 0.
PAGE 12
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards Detailed Description The MAX8550/MAX8551 combine a synchronous-buck PWM controller, an LDO linear regulator, and a 10mA reference output buffer. The buck controller drives two external N-channel MOSFETs to deliver load currents up to 12A and generate voltages down to 0.7V from a +2V to +28V input. The LDO linear regulator can sink and source up to 1.
PAGE 13
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards 2) The inductor ripple-current operating point remains relatively constant, resulting in an easy design methodology and predictable output voltage ripple. The on-time one-shot has good accuracy at the operating points specified in the Electrical Characteristics table (approximately ±12.5% at 600kHz and 450kHz, and ±10% at 200kHz and 300kHz).
PAGE 14
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards Forced-PWM Mode (SKIP = AVDD in MAX8550 Only) The low-noise forced-PWM mode (SKIP = AVDD) disables the zero-crossing comparator, which controls the low-side switch on-time. This forces the low-side gatedrive waveform to constantly be the complement of the high-side gate-drive waveform, so the inductor current reverses at light loads while DH maintains a duty factor of VOUT / VIN.
PAGE 15
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards MAX8550/ MAX8551 TO PWM CONTROLLER (SEE FIGURE 1) CREF REF RA ILIM CILIM RB 1.0V VDD - 1V LX Figure 3. Adjustable Current-Limit Threshold INDUCTOR CURRENT IPEAK ILOAD ILOAD(MAX) ( ILIM(VAL) = 1 - LIR 2 0 ILIMIT )xI LOAD TIME Figure 4.
PAGE 16
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards attained when SS reaches approximately 1.6V. This lowering of the current limit during startup limits the initial inrush current peaks, particularly when driving capacitors. Choose the value of the SS cap appropriately to set the soft-start time window. Leave SS floating to disable the soft-start feature. Power-OK (POK1) POK1 is an open-drain output for a window comparator that continuously monitors VOUT.
PAGE 17
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards Current Limit (LDO for VTT and VTTR Buffer) The VTT output is a linear regulator that regulates the input (VTTI) to half the VREFIN voltage. The feedback point for VTT is at the VTTS input (Figure 1). VTT is capable of sinking and sourcing at least 1.5A of continuous current and 3A peak current. The current limit for VTT and VTTR is typically ±5A and ±40mA, respectively.
PAGE 18
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards shut off, go high impedance, and restart after the die portion of the IC cools by 15°C. Both thermal faults are independent. For example, if the VTT output is overloaded to the point that it triggers its thermal fault, the buck regulator continues to function.
PAGE 19
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards L VOUT LX MAX8550/ MAX8551 DL COUT Q2 Also look for nonstandard values, which can provide a better compromise in LIR across the input voltage range. If using a swinging inductor (where the no-load inductance decreases linearly with increasing current), evaluate the LIR with properly scaled inductance values.
PAGE 20
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards The actual capacitance value required relates to the physical size needed to achieve low ESR, as well as to the chemistry of the capacitor technology. Thus, the capacitor is usually selected by ESR and voltage rating rather than by capacitance value (this is true of tantalums, OSCONs, polymers, and other electrolytics).
PAGE 21
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards VTTR Output Capacitor Selection (LDO) The VTTR buffer is a scaled-down version of the VTT regulator, with much smaller output transconductance. Its compensation cap can therefore be smaller, and its ESR larger, than what is required for its larger counterpart. For typical applications requiring load current up to ±20mA, a ceramic cap with a minimum value of 1µF is recommended (R ESR < 0.3Ω).
PAGE 22
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards QGS + QGD PHSSW = VIN × ILOAD × fSW × IGATE where IGATE is the average DH-driver output current determined by: IGATE(ON) = 2.5V RDH + RGATE where RDH is the high-side MOSFET driver’s on-resistance (1Ω typ) and RGATE is the internal gate resistance of the MOSFET (≈2Ω): PHSDR = QG × VGS × fSW × RGATE RGATE + RDH where VGS = VDD = 5V.
PAGE 23
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards a divider current of approximately 10µA to prevent significant inaccuracy in the valley current-limit tolerance. Foldback Current Limit Alternately, foldback current limit can be implemented if the UVP latch option is not available.
PAGE 24
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards C1 0.01µF VTTI C2 10µF VTT 1.25V / ±1.5A REFIN AVDD VTT C4 60µF VTTS MAX8550 PGND2 VTTR 1.25V / 10mA R1 10Ω VDD C6 1µF VIN (4.5V TO 28V) VIN R3 100kΩ BST C7 0.22µF POK POK1 C8 2 x 10µF SKIP DH Q1 IRF7821 N-CHANNEL 30V, 9mW L1 TOKO FDA1254-1R0M 1.0µH, 21A, 1.6mΩ TON GND C9 3.9nF C14 470µF (OPTIONAL) LX POK2 2.5V / 12A SS C10 0.22µF DL REF R5 20kΩ 5V BIAS SUPPLY C5 4.
PAGE 25
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards The output sag is also a function of the maximum duty factor, which can be calculated from the on-time and minimum off-time: ⎡V ⎤ × K L × ∆ILOAD(MAX)2 ⎢ OUT + t OFF(MIN) ⎥ VIN ⎣ ⎦ VSAG = ⎡ ( VIN - VOUT ) × K ⎤ 2COUT × VOUT ⎢ + t OFF(MIN) ⎥ VIN ⎢⎣ ⎥⎦ where t OFF(MIN) is the minimum off-time (see the Electrical Characteristics) and K is from Table 1.
PAGE 26
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards +5V BIAS SUPPLY AVDD VDD IN VIN BST MAX8550/ MAX8551 DH RPOS VOLTAGEPOSITIONED OUTPUT LX DL PGND1 GND FB OUT Figure 9. Voltage-Positioned Output PC Board Layout Guidelines Careful PC board layout is critical to achieve low switching losses and clean, stable operation. The switching power stage requires particular attention.
PAGE 27
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards Typical Operating Circuit C1 0.01µF REFIN VTTI C3 1µF C2 VTT 0.9V - 1.25V / 1.5A AVDD VTT R1 10Ω VTTS C4 VTTR 0.9V - 1.25V / 10mA VTTR C5 MAX8550/ MAX8551 VIN (4.5V TO 28V) VIN C6 OVP/UVP R2 5V BIAS SUPPLY VDD PGND2 BST R3 C8 C7 POK POK1 LX Q1 POK2 SKIP DH TON GND L1 Q2 C9 SS 1.8V - 2.
PAGE 28
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards Package Information Chip Information PROCESS: BiCMOS 28 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. PACKAGE TYPE PACKAGE CODE OUTLINE NO.
PAGE 29
MAX8550/MAX8551 Integrated DDR Power-Supply Solutions for Desktops, Notebooks, and Graphic Cards Revision History REVISION NUMBER REVISION DATE 3 4/13 DESCRIPTION Added MAX8551ETI+ to Ordering Information PAGES CHANGED 1 Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied.