Datasheet

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________________General Description

The MAX767 is a high-efficiency, synchronous buck

controller IC dedicated to converting a fixed 5V supply

into a tightly regulated 3.3V output. Two key features set

this device apart from similar, low-voltage step-down

switching regulators: high operating frequency and all

N-channel construction in the application circuit. The

300kHz operating frequency results in very small, low-

cost external surface-mount components.

The inductor, at 3.3µH for 5A, is physically at least five

times smaller than inductors found in competing solu-

tions. All N-channel construction and synchronous rectifi-

cation result in reduced cost and highest efficiency.

Efficiency exceeds 90% over a wide range of loading,

eliminating the need for heatsinking. Output capacitance

requirements are low, reducing board space and cost.

The MAX767 is a monolithic BiCMOS IC available in

20-pin SSOP packages. For other fixed output voltages

and package options, please consult the factory.

________________________Applications

Local 5V-to-3.3V DC-DC Conversion

Microprocessor Daughterboards

Power Supplies up to 10A or More

____________________________Features

♦ >90% Efficiency

♦ 700µA Quiescent Supply Current

♦ 120µA Standby Supply Current

♦ 4.5V-to-5.5V Input Range

♦ Low-Cost Application Circuit

♦ All N-Channel Switches

♦ Small External Components

♦ Tiny Shrink-Small-Outline Package (SSOP)

♦ Predesigned Applications:

Standard 5V to 3.3V DC-DC Converters up to 10A

High-Accuracy Pentium P54C VR-Spec Supply

♦ Fixed Output Voltages Available:

3.3V (Standard)

3.45V (High-Speed Pentium™)

3.6V (PowerPC™)

_______________Ordering Information

MAX767

5V-to-3.3V, Synchronous, Step-Down

Power-Supply Controller

________________________________________________________________ Maxim Integrated Products 1

BST

GND

TOP VIEW

MAX767

PGND

REF

GND

N.C.

GND

SYNC

SSOP

__________________Pin Configuration

OUTPUT

3.3V

AT 5A

INPUT

4.5V TO 5.5V

GND

MAX767

REF

3.3

BST

PGND

_________Typical Application Circuit

19-0224; Rev 3; 7/00

PART TEMP. RANGE

PIN-

PACKAGE

MAX767CAP 0°C to +70°C 20 SSOP

MAX767RCAP 0°C to +70°C 20 SSOP

MAX767SCAP 0°C to +70°C 20 SSOP

Pentium is a trademark of Intel. PowerPC is a trademark of IBM.

MAX767C/D 0°C to +70°C Dice*

REF

TOL

±1.8%

—

Ordering Information continued at end of data sheet.

* Contact factory for dice specifications.

OUT

(V)

3.3

3.45

3.6

—

MAX767TCAP 0°C to +70°C 20 SSOP ±1.2% 3.3

EVALUATION KIT MANUAL

FOLLOWS DATA SHEET

For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

Summary of content (19 pages)

PAGE 1
9-0224; Rev 3; 7/00 ANUAL N KIT M EET IO T A U EVAL TA SH WS DA FOLLO 5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller ____________________________Features The MAX767 is a high-efficiency, synchronous buck controller IC dedicated to converting a fixed 5V supply into a tightly regulated 3.3V output. Two key features set this device apart from similar, low-voltage step-down switching regulators: high operating frequency and all N-channel construction in the application circuit.
PAGE 2
MAX767 5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller ABSOLUTE MAXIMUM RATINGS VCC to GND .................................................................-0.3V, +7V PGND to GND ........................................................................±2V BST to GND ...............................................................-0.3V, +15V LX to BST.....................................................................-7V, +0.3V Inputs/Outputs to GND (ON, REF, SYNC, CS, FB, SS) ....................
PAGE 3
5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller 70 80 70 60 50 0.001 0.01 0.1 1 10 0.01 0.1 1 OUTPUT CURRENT (A) EFFICIENCY vs. OUTPUT CURRENT (7A CIRCUIT) EFFICIENCY vs. OUTPUT CURRENT (10A CIRCUIT) 10 EFFICIENCY (%) 70 80 70 0.001 0.01 0.1 1 10 OUTPUT CURRENT (A) 0.001 0.01 0.1 1 SYNC = REF (300kHz) 100 10 1 0.1 10 0.001 0.01 0.1 1 10 100 LOAD CURRENT (% FULL LOAD) OUTPUT CURRENT (A) IDLE-MODE WAVEFORMS PWM-MODE WAVEFORMS 3.
PAGE 4
MAX767 5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller _____________________________Typical Operating Characteristics (continued) (Circuit of Figure 1 (5A configuration), VIN = 5V, oscillator frequency = 300kHz, TA = +25°C, unless otherwise noted.) 1.5A CIRCUIT LOAD-TRANSIENT RESPONSE 3A CIRCUIT LOAD-TRANSIENT RESPONSE 1.5A 3A LOAD CURRENT LOAD CURRENT 0A 0A 3.3V OUTPUT 50mV/div AC-COUPLED 3.
PAGE 5
V-to-3.3V, Synchronous, Step-Down Power-Supply Controller PIN NAME FUNCTION 1 CS Current-sense input: +100mV = nominal current-limit level referred to FB. 2 SS 3 ON Soft-start input. Ramp time to full current limit is 1ms/nF of capacitance to GND. ——– ON/OFF control input to disable the PWM. Tie directly to VCC for automatic start-up. 4–7, 11 GND Low-current analog ground. Feedback reference point for the output. 8 REF 3.3V internal reference output. Bypass to GND with 0.
PAGE 6
MAX767 5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller _____Standard Application Circuits This data sheet shows five predesigned circuits with output current capabilities from 1.5A to 10A. Many users will find one of these standard circuits appropriate for their needs. If a standard circuit is used, the remainder of this data sheet (Detailed Description and Applications Information and Design Procedure) can be bypassed. Figure 1 shows the Standard Application Circuit.
PAGE 7
5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller MAX767 Table 1. Component Values Part 1.5A Circuit L1 10µH Sumida CDR74B-100 R1 N1, N2 3A Circuit 5A Circuit 5µH Sumida CDR125 DRG# 4722-JPS-001 3.3µH Coilcraft DO3316-332 0.012Ω 0.04Ω 0.02Ω DD WSL-2512-R012 IRC LR2010-01-R040 IRC LR2010-01-R020 or 2 x 0.
PAGE 8
MAX767 5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller FAT, HIGH-CURRENT TRACES because the minimum-current comparator immediately resets the high-side latch at the beginning of each cycle, unless the FB signal falls below the reference voltage level. MAIN CURRENT PATH Soft-Start SENSE RESISTOR MAX767 Connecting a capacitor from the soft-start pin (SS) to ground allows a gradual build-up of the 3.3V output after power is applied or ON is driven high.
PAGE 9
5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller MAX767 CS 1X VCC 60kHz LPF REF FB MAIN PWM COMPARATOR +3.3V REFERENCE BST R LEVEL SHIFT Q S DH LX SLOPE COMP 4V MINIMUM CURRENT (IDLE-MODE) 25mV VCC CURRENT LIMIT 4µA FAULT SHOOTTHROUGH CONTROL 2.8V 0mV TO 100mV 30R SS 3.3V N 200kHz/300kHz OSCILLATOR ON 1R ON SYNCHRONOUS RECTIFIER CONTROL R VCC Q LEVEL SHIFT S MAX767 DL PGND SYNC Figure 3.
PAGE 10
5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller MAX767 Modes of Operation VIN C1 VCC MAX767 D1 BST VOUT %ON = ________ VIN C3 DH LEVEL TRANSLATOR N1 LX PWM L1 VCC DL N2 Figure 4. Boost Supply for High-Side Gate Driver Gate-Driver Boost Supply Gate-drive voltage for the high-side N-channel switch is generated with the flying-capacitor boost circuit shown in Figure 4.
PAGE 11
5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller Internal Reference The internal 3.3V bandgap reference (REF) remains active, even when the switching regulator is turned off. It can furnish up to 5mA, and can be used to supply memory keep-alive power or for other purposes. Bypass REF to GND with 0.22µF, plus 1µF/mA of load current.
PAGE 12
MAX767 5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller Place R1 as close as possible to the MAX767, preferably less than 10mm. Run the traces at minimum spacing from one another. If they are longer than 20mm, bypass CS to FB with a 1nF capacitor placed as close as possible to these pins. The wiring layout for these traces is critical for stable, low-ripple outputs (see Layout and Grounding section). In idle-mode, the ripple has a capacitive and a resistive component: . 0.
PAGE 13
5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller Rectifier, D2 Use a 1N5817 or similar Schottky diode for applications up to 3A, or a 1N5820 for up to 10A. Surface-mount equivalents are available from N.I.E.C. with part numbers EC10QS02 and NSQ03A02, or from Motorola with part numbers MBRS120T3 and MBRS320T3. D2 must be a Schottky diode to prevent the lossy MOSFET body diode from turning on.
PAGE 14
MAX767 5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller Proper circuit operation requires that the short-circuit current be at least ILOAD x (1 + LIR / 2). However, the standard application circuits are designed for a shortcircuit current slightly in excess of this amount. This excess design current guarantees proper start-up under constant full-load conditions and proper full-load transient response, and is particularly necessary with low input voltages.
PAGE 15
5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller IC Supply-Current Losses PDIC is the quiescent power dissipation of the IC and is 5V times the quiescent supply current (a data sheet parameter), or about 5mW. Light-Load Efficiency Under light loads, the PWM will operate in discontinuous-conduction mode, where the inductor current discharges to zero at some point during each switching cycle. New loss mechanisms, insignificant at heavy loads, begin to become important.
PAGE 16
MAX767 5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller INPUT 4.75V TO 5.5V VOUT = VREF C1 D1 + 1) ( R10 R9 R2 10Ω N1 DH VCC BST C4 4.7µF R1 L1 C2 MAX767T N2 C5 0.01µF D2 C8 620pF REF R8 10k C10 0.01µF (OPTIONAL) R4 1k, 1% SYNC GND C6 0.01µF R7 330k CS SS R3 1k, 1% PGND ON FB TO MAX767 VCC R5 10k, 1% R11 C7 5.1k 10µF CERAMIC (LOCATE AT MIN µP PINS) LOAD R6 10k, 1% C9 0.22µF MAX495 R9 332k, 1% R10 8.06k, 1% REMOTE SENSE LINE Figure 5.
PAGE 17
5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller MAX767 INPUT 4.75V TO 5.5V C1 D1 VOUT = VREF ( R10 +1 R9 ) R2 20Ω N1 DH VCC BST C4 22µF C3 0.1µF MAX767 ON 3.38V OUTPUT 3.408V MAX 3.369V MIN N2 D2 C5 0.01µF R3 1k, 1% R4 1k, 1% PGND REF CS SYNC FB SS C9 0.22µF C2 LX DL SHUTDOWN ON/OFF R1 L1 TO MAX767 VCC GND C6 0.01µF R7 330k C8 1000pF R5 10k, 1% R11 C7 5.1k 10µF CERAMIC (LOCATE AT MIN µP PINS) LOAD R6 10k, 1% C10 0.
PAGE 18
MAX767 5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller Ordering Information (continued) PART TEMP. RANGE PINPACKAGE REF TOL MAX767EAP -40°C to +85°C 20 SSOP ±1.8% 3.3 MAX767REAP -40°C to +85°C 20 SSOP ±1.8% 3.45 ___________________Chip Topography VOUT (V) SS CS ON FB DH LX MAX767SEAP -40°C to +85°C 20 SSOP ±1.8% 3.6 GND MAX767TEAP -40°C to +85°C 20 SSOP ±1.2% 3.3 GND BST DL 0.181" V CC (4.597mm) GND V CC GND V CC GND PGND REF SYNC V CC GND 0.109" (2.
PAGE 19
5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller DIM A A1 B C D E e H L α e E H INCHES MAX MIN 0.078 0.068 0.008 0.002 0.015 0.010 0.009 0.005 0.289 0.278 0.212 0.205 0.0256 BSC 0.311 0.301 0.037 0.022 8˚ 0˚ MILLIMETERS MIN MAX 1.73 1.99 0.05 0.21 0.25 0.38 0.13 0.22 7.07 7.33 5.20 5.38 0.65 BSC 7.65 7.90 0.55 0.95 0˚ 8˚ 21-0003A D α A 0.127mm 0.004in.