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General Description

The MAX8720 step-down controller is intended for core

CPU DC-DC converters in notebook computers. It fea-

tures a dynamically adjustable output, ultra-fast transient

response, high DC accuracy, and the high efficiency

needed for leading-edge CPU core power supplies.

Maxim’s proprietary Quick-PWM™ quick-response, con-

stant-on-time, PWM control scheme handles wide

input/output voltage ratios with ease and provides

100ns “instant-on” response to load transients while

maintaining a relatively constant switching frequency.

The output voltage can be dynamically adjusted through

the 6-bit digital-to-analog converter (DAC) over a 0.275V

to 1.850V range in 25mV steps. The MAX8720 has inde-

pendent four-level logic inputs for setting the suspend

voltage (S0-S1). Precision slew-rate control provides

“just-in-time” arrival at the new DAC setting, minimizing

surge currents to and from the battery. The internal DAC

of the MAX8720 is synchronized to the slew-rate clock

for improved operation under aggressive power man-

agement of newer chipsets and operating systems that

can make incomplete mode transitions. Remote feed-

back and ground-sense inputs allow easy compensa-

tion for IR drops in PC board traces.

Single-stage buck conversion allows these devices to

directly step down high-voltage batteries for the highest

possible efficiency. Alternatively, two-stage conversion

(stepping down the 5V system supply instead of the

battery) at a higher switching frequency allows the mini-

mum possible physical size.

The MAX8720 is available in a 28-pin QSOP or 36-pin

6mm x 6mm thin QFN package.

Applications

CPU Core Supply Converters

GPU Core Supply Converters

Notebook and Subnotebook Computers

Features

♦ Quick-PWM Architecture

♦ ±1% V

OUT

Accuracy Over Line and Load

♦ 6-Bit On-Board DAC with Input Muxes

♦ Precision-Adjustable V

OUT

Slew Control

♦ 0.275V to 1.850V Output Adjust Range

♦ Remote Feedback and Ground Sense

♦ Supports Voltage-Positioned Applications

♦ 2V to 28V Battery Input Range

♦ 200kHz/300kHz/550kHz/1000kHz Switching

Frequency

♦ Over/Undervoltage Protection

♦ Drives Large Synchronous-Rectifier FETs

♦ 800µA (typ) I

Supply Current

♦ 10µA (typ) Shutdown Supply Current

♦ 2V ±0.75% Reference Output

♦ PGOOD Blanking During Transition

MAX8720

Dynamically Adjustable 6-Bit VID

Step-Down Controller

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

MAX8720

PGOOD

VID0

VID1

VID2

VID3

VID4

VID5

SUS

AGND

OUTPUT (V

OUT

)

0.275V TO 1.850V

INPUT (V

)

7V TO 28V

BST

V+

PGND

SHDN

+5V BIAS

FBS

GNDS

REF

TIME

SKIP

ILIM

Minimal Operating Circuit

19-3319; Rev 2; 9/05

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.

EVALUATION KIT

AVAILABLE

PART

TEMP RANGE

PIN-PACKAGE

MAX8720EEI

-40°C to +85°C

28 QSOP

MAX8720ETX

-40°C to +85°C

36 Thin QFN 6mm x 6mm

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

Pin Configurations appear at end of data sheet.

Summary of content (31 pages)

PAGE 1
9-3319; Rev 2; 9/05 KIT ATION EVALU E L B A IL AVA Dynamically Adjustable 6-Bit VID Step-Down Controller The MAX8720 step-down controller is intended for core CPU DC-DC converters in notebook computers. It features a dynamically adjustable output, ultra-fast transient response, high DC accuracy, and the high efficiency needed for leading-edge CPU core power supplies.
PAGE 2
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller ABSOLUTE MAXIMUM RATINGS (Note 1) VCC to AGND............................................................-0.3V to +6V VDD to PGND............................................................-0.3V to +6V AGND to PGND .....................................................-0.3V to +0.3V V+ to PGND............................................................-0.3V to +30V SHDN to AGND ......................................................-0.
PAGE 3
Dynamically Adjustable 6-Bit VID Step-Down Controller (Circuit of Figure 1, V+ = 15V, SHDN = SKIP = VDD = VCC = +5V, VOUT = 1.25V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 4
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, V+ = 15V, SHDN = SKIP = VDD = VCC = +5V, VOUT = 1.25V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 5
Dynamically Adjustable 6-Bit VID Step-Down Controller (Circuit of Figure 1, V+ =15V, SHDN = SKIP = VDD = VCC = +5V, VOUT = 1.25V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 4) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS PWM CONTROLLER Battery Voltage, V+ Input Voltage Range 2 28 4.5 5.5 DAC codes from 0.9V to 1.85V -1 +1 DAC codes from 0.45V to 0.875V -15 +15 VCC, VDD V+ = 4.
PAGE 6
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, V+ =15V, SHDN = SKIP = VDD = VCC = +5V, VOUT = 1.25V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 4) PARAMETER SYMBOL CONDITIONS Output Overvoltage Trip Threshold MIN TYP MAX UNITS 2.20 2.
PAGE 7
Dynamically Adjustable 6-Bit VID Step-Down Controller 80 VIN = 12V 70 VIN = 20V PWM MODE SWITCHING FREQUENCY (kHz) OUTPUT VOLTAGE (V) 90 400 MAX8720 toc02 VIN = 7V SKIP MODE 1.250 60 SKIP = GND SKIP = VCC 50 0.01 0.1 1 100 10 SKIP MODE 200 100 0 0 5 LOAD CURRENT (A) 10 20 15 0 5 LOAD CURRENT (A) 20 25 SUPPLY CURRENT (mA) 340 330 320 310 IOUT = 3A MAX8720 toc05 30 MAX8720 toc04 IOUT = 18A 300 15 NO-LOAD SUPPLY CURRENT vs.
PAGE 8
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller Typical Operating Characteristics (continued) (MAX8720 Circuit of Figure 1, VIN = 12V, VDD = VCC = 5V, TON = open, TA = +25°C, unless otherwise noted.) STARTUP WAVEFORMS (NO LOAD) STARTUP WAVEFORMS (HEAVY LOAD) MAX8720 toc08 MAX8720 toc09 1.25V 1.
PAGE 9
Dynamically Adjustable 6-Bit VID Step-Down Controller SUSPEND TRANSITION (SKIP MODE) DYNAMIC OUTPUT VOLTAGE TRANSITION (PWM MODE) MAX8720 toc15 MAX8720 toc14 A 1.65V 1.25V A 0.65V 12V 1.25V 12V B C 0 10A 0 B 0 5V 0 C 0 10A D D 0 -10A -10A 100µs/div SKIP = GND, IOUT = 0.2A A = VOUT, 500mV/div C = D4, 5V/div B = LX, 10V/div D = INDUCTOR CURRENT, 10A/div 50µs/div SKIP = VCC, IOUT = 0.
PAGE 10
Dynamically Adjustable 6-Bit VID Step-Down Controller MAX8720 Pin Description PIN 28 QSOP 36 THIN QFN NAME 1 33 V+ Battery Voltage-Sense Connection. Connect V+ to input power source. V+ is used only for PWM one-shot timing. DH on-time is inversely proportional to input voltage over a 2V to 28V range. SHDN Shutdown Control Input. Connect SHDN to VCC for normal operation. Connect SHDN to GND to put the controller into its shutdown state.
PAGE 11
Dynamically Adjustable 6-Bit VID Step-Down Controller PIN 28 QSOP 13 36 THIN QFN 11 NAME FUNCTION GNDS Ground Remote-Sense Input. For nonvoltage-positioned circuits, connect GNDS to ground directly at the load. GNDS internally connects to the integrator that fine tunes the output voltage. The output voltage rises by an amount of GNDS - AGND. For voltagepositioned circuits, increase the output voltage by biasing GNDS with a resistor-divider from REF to AGND. Open-Drain Power-Good Output.
PAGE 12
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller R1 10Ω +5V BIAS C2 1µF R2 TO R7 (6) 100kΩ VCC VDD AGND* C1 1µF DBST V+ CIN (2) 10µF BST VID0 D0 VID1 D1 VID2 D2 VID3 D3 VID4 D4 VID5 D5 +5V BIAS R8 100kΩ DH NH L1 0.8µH CBST 0.1µF MAX8720 DL DL NL FB S1 FBS VCPU_SENSE OPEN (300kHz) TON GNDS VGND_SENSE PGOOD PWM SKIP ON SKIP CC CREF 0.22µF RILIM1 100kΩ RTIME 100kΩ RILIM2 33.
PAGE 13
Dynamically Adjustable 6-Bit VID Step-Down Controller COMPONENT 15A/300kHz Table 2. Component Suppliers SUPPLIER WEBSITE AVX www.avx.com Input Voltage VIN = 7V to 24V Central Semiconductor www.centralsemi.com Output Voltage VOUT = 1.25V Coiltronics www.coiltronics.com Fairchild Semiconductor www.fairchildsemi.com CIN Input Capacitor (2) 10µF, 25V TDK C3225X7R1E106M AVX 12103D106M Taiyo Yuden TMK325BJ106MM Panasonic www.panasonic.com/industrial Sanyo www.secc.co.
PAGE 14
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller VBATT 2V TO 28V REF V+ ILIM MAX8720 TOFF TON FROM D/A ON-TIME COMPUTE TON S Q TRIG +5V ONE-SHOT TRIG Q 9 BST 1 Q R DH CURRENT LIMIT ONE-SHOT Σ LX ERROR AMP SHDN REF ZERO CROSSING VDD 10kΩ 70kΩ CC GNDS FBS REF -15% Gm +5V DL REF Gm VOUT S Q PGND R Gm FB FB REF +15% PGOOD OVP/UVP DETECT CHIP SUPPLY VCC 2V REF REF R-2R D/A CONVERTER +5V AGND MUX AND SLEW CONTROL SKIP SUS S0, S1 D0–D5 TIME Figure
PAGE 15
Dynamically Adjustable 6-Bit VID Step-Down Controller fSW = VOUT + VDIS t ON (VIN + VDIS − VCHG ) where VDIS is the sum of the parasitic voltage drops in the inductor discharge path, including synchronous rectifier, inductor, and PC board resistances; VCHG is the sum of the parasitic voltage drops in the inductor charge path, including high-side switch, inductor, and PC board resistances; and tON is the on-time calculated by the MAX8720.
PAGE 16
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller threshold between pulse-skipping PFM and nonskipping PWM operation to coincide with the boundary between continuous and discontinuous inductor-current operation. The load-current level at which PFM/PWM crossover occurs, ILOAD(SKIP), is equal to half the peak-to-peak ripple current, which is a function of the inductor value (Figure 3).
PAGE 17
Dynamically Adjustable 6-Bit VID Step-Down Controller MAX8720 ∆I = ∆t IPEAK VIN - VOUT L IPEAK ILOAD = IPEAK / 2 INDUCTOR CURRENT INDUCTOR CURRENT ILOAD ILIMIT ( LIR2 ) ILIM(VAL) = ILOAD(MAX) 1- 0 ON-TIME TIME 0 Figure 3. Pulse-Skipping/Discontinuous Crossover Point Figure 4. Valley Current-Limit Threshold C  VGS(TH) > VIN  RSS   CISS  Lot-to-lot variation of the threshold voltage can cause problems in marginal designs.
PAGE 18
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller VCC(UVLO) VCC VCC DL DL MODE FORCED-PWM MODE FORCED-PWM MODE PWM SHDN SHDN PGOOD PGOOD SOFT-STARTUP AND SHUTDOWN 1/4TH SLEW RATE SET BY RTIME VCPU VCPU 8x RTIME CLOCKS Figure 6. Soft-Startup and Soft-Shutdown Soft-Startup and Soft-Shutdown (SHDN) When SHDN goes low, the MAX8720 enters low-power shutdown mode. PGOOD goes low immediately. The output voltage ramps down to 0V in 25mV steps at 1/4th the clock rate set by RTIME.
PAGE 19
Dynamically Adjustable 6-Bit VID Step-Down Controller MAX8720 Table 4. Output Voltage vs. DAC Codes D5 D4 D3 D2 D1 D0 VOUT D5 D4 D3 D2 D1 D0 VOUT 0 0 0 0 0 0 1.850 1 0 0 0 0 0 1.050 0 0 0 0 0 1 1.825 1 0 0 0 0 1 1.025 0 0 0 0 1 0 1.800 1 0 0 0 1 0 1.000 0 0 0 0 1 1 1.775 1 0 0 0 1 1 0.975 0 0 0 1 0 0 1.750 1 0 0 1 0 0 0.950 0 0 0 1 0 1 1.725 1 0 0 1 0 1 0.925 0 0 0 1 1 0 1.700 1 0 0 1 1 0 0.
PAGE 20
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller Table 5. Suspend-Mode DAC Codes S1 S0 VOUT S1 S0 VOUT GND GND GND 0.650 OPEN GND 0.450 REF 0.625 OPEN REF 0.425 GND OPEN GND VCC 0.600 OPEN OPEN 0.400 0.575 OPEN VCC 0.375 REF GND REF REF 0.550 VCC GND 0.350 0.525 VCC REF 0.325 REF OPEN 0.500 VCC OPEN 0.300 REF VCC 0.475 VCC VCC 0.
PAGE 21
Dynamically Adjustable 6-Bit VID Step-Down Controller MAX8720 VOUT HIGH VID VOLTAGE SLEW RATE SET BY RTIME LOW VID VOLTAGE SKIP SUS PGOOD HIGH IMPEDANCE D0-D5 HIGH VID MODE PWM MODE HIGH IMPEDANCE LOW VID FORCED-PWM HIGH VID PWM MODE FORCED-PWM PWM MODE 8x RTIME CLOCKS 8x RTIME CLOCKS Figure 8.
PAGE 22
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller VOUT D0–D5 VOLTAGE SLEW RATE SET BY RTIME S0, S1 VOLTAGE SKIP SUS PGOOD HIGH IMPEDANCE TARGET D0–D5 MODE PWM MODE LOW THRESHOLD ONLY S0, S1 FORCED-PWM HIGH IMPEDANCE D0–D5 AUTOSKIP MODE FORCED-PWM PWM MODE 8x RTIME CLOCKS 8x RTIME CLOCKS Figure 10.
PAGE 23
Dynamically Adjustable 6-Bit VID Step-Down Controller Output Overvoltage Protection The overvoltage-protection (OVP) circuit is designed to protect the CPU against a shorted high-side MOSFET by drawing high current and blowing the battery fuse. The output voltage is continuously monitored for overvoltage. If the output is more than 2.25V, OVP is triggered and the circuit shuts down. The DL low-side gate-driver output is then latched high until SHDN is toggled or VCC power is cycled below 1V.
PAGE 24
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller value also determines the load-current value at which PFM/PWM switchover occurs. Inductor Selection The switching frequency and inductor operating point determine the inductor value as follows: L= VOUT (VIN − VOUT ) VIN fSW ILOAD(MAX) LIR For example: ILOAD(MAX) = 15A, VIN = 12V, VOUT = 1.25V, fSW = 300kHz, 30% ripple current or LIR = 0.3 L= 1.2 5V × (1 2V −1.2 5V) 1 2V × 3 0 0k H z×1 5A × 0.3 = 0.
PAGE 25
Dynamically Adjustable 6-Bit VID Step-Down Controller RESR ≤ VSTEP / ILOAD(MAX) 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, OS-CONs, polymers, and other electrolytics).
PAGE 26
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller significantly higher, consider increasing the size of NH. Conversely, if the losses at VIN(MAX) are significantly higher, consider reducing the size of NH. If VIN does not vary over a wide range, maximum efficiency is achieved by selecting a high-side MOSFET (N H) that has conduction losses equal to the switching losses. Choose a low-side MOSFET (NL) that has the lowest possible on-resistance (RDS(ON)), comes in a moderate-sized package (i.e.
PAGE 27
Dynamically Adjustable 6-Bit VID Step-Down Controller CBST = 1× 14nC = 0.07µF 200mV Select the closest standard value. This example requires a 0.1µF ceramic capacitor. Applications Information Dropout Performance The output-voltage adjust range for continuous-conduction operation is restricted by the nonadjustable 500ns (max) minimum off-time one-shot (375ns max at 1000kHz). For best dropout performance, use the slower (200kHz) on-time settings.
PAGE 28
MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller QSOP LAYOUT EXAMPLE QFN LAYOUT EXAMPLE CC VCC REF VDD ANALOG GROUND POWER GROUND CONNECT AGND AND PGND TO THE CONTROLLER AT ONE POINT ONLY AS SHOWN CONNECT AGND AND PGND TO THE CONTROLLER AT ONE POINT ONLY AS SHOWN CIN COUT COUT INPUT COUT OUTPUT INDUCTOR ANALOG GROUND POWER GROUND GROUND CIN POWER STAGE LAYOUT EXAMPLE Figure 12.
PAGE 29
Dynamically Adjustable 6-Bit VID Step-Down Controller 4) Make the DC-DC controller ground connections as shown in Figures 1 and 12. This diagram can be viewed as having two separate ground planes: power ground, where all the high-power components go, and an analog ground plane for sensitive analog components. The analog ground plane and power ground plane must meet only at a single point directly at the IC.
PAGE 30
Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) QSOP.EPS MAX8720 Dynamically Adjustable 6-Bit VID Step-Down Controller PACKAGE OUTLINE, QSOP .150", .
PAGE 31
Dynamically Adjustable 6-Bit VID Step-Down Controller QFN THIN.EPS (NE-1) X e E E/2 k D/2 CL (ND-1) X e D D2 D2/2 e b E2/2 L CL k E2 e L CL CL L1 L L e A1 A2 e A PACKAGE OUTLINE 36, 40, 48L THIN QFN, 6x6x0.8mm 21-0141 F 1 2 NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4.