Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - voltage regulators - DC DC switch controllers uMAX 10

General Description

The MAX1762/MAX1791 PWM step-down controllers

provide high efficiency, excellent transient response,

and high DC output accuracy needed for stepping

down high-voltage batteries to generate low-voltage

CPU core, I/O, and chipset RAM supplies in notebook

computers and PDAs.

Maxim’s proprietary Quick-PWM™ pulse-width modula-

tor is a free-running constant on-time type with input

feed-forward. Its high operating frequency (300kHz)

allows small external components to be utilized in PC

board area-critical applications such as subnotebook

computers and smart phones. PWM operation occurs

at heavy loads, and automatic switchover to pulse-skip-

ping operation occurs at lighter loads. The external

high-side p-channel and low-side n-channel MOSFETs

require no bootstrap components. The MAX1762/

MAX1791 are simple, easy to compensate, and do not

have the noise sensitivity of conventional fixed-frequen-

cy current-mode PWMs.

These devices achieve high efficiency at a reduced

cost by eliminating the current-sense resistor found in

traditional current-mode PWMs. Efficiency is further

enhanced by their ability to drive synchronous-rectifier

MOSFETs. The MAX1762/MAX1791 come in a 10-pin

µMAX package and offer two fixed voltages (Dual

Mode™) for each device, 1.8V/2.5V/adj (MAX1762) and

3.3V/5.0V/adj (MAX1791).

________________________Applications

Notebooks Handy-Terminals

Subnotebooks PDAs

Digital Cameras Smart Phones

1.8V/2.5V Logic

and I/O Supplies

Features

♦ High Operating Frequency (300kHz)

♦ No Current-Sense Resistor

♦ Accurate Current Limit

♦ ±1% Total DC Error over Line and During

Continuous Conduction

♦ Dual Mode Fixed Output

1.8V/2.5V/adj (MAX1762)

3.3V/5.0V/adj (MAX1791)

♦ 0.5V to 5.5V Output Adjust Range

♦ 5V to 20V Input Range

♦ Automatic Light-Load Pulse Skipping Operation

♦ Free-Running On-Demand PWM

♦ Foldback Mode™ UVLO

♦ PFET/NFET Synchronous Buck

♦ 4.65V at 25mA Linear Regulator Output

♦ 5µA Shutdown Supply Current

♦ 230µA Quiescent Supply Current

♦ 10-Pin µMAX Package

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down

Controllers for Notebooks

________________________________________________________________ Maxim Integrated Products 1

19-1923; Rev 1; 10/05

EVALUATION KIT

AVAILABLE

Ordering Information

PART TEMP RANGE

PIN-PACKAGE

MAX1762EUB -40°C to +85°C 10 µMAX

MAX1791EUB -40°C to +85°C 10 µMAX

GND

OUT

REF

SHDN

BATT

(5V TO 20V)

OUT

1.8V/3.3V

MAX1762

MAX1791

Typical Operating Circuit

DLOUT

REF

MAX1762

MAX1791

µMAX

TOP VIEW

GNDSHDN

Pin Configuration

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.

Quick-PWM, Dual Mode, and Foldback Mode are a trade-

marks of Maxim Integrated Products, Inc.

Summary of content (20 pages)

PAGE 1
9-1923; Rev 1; 10/05 KIT ATION EVALU E L B AVAILA High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks The MAX1762/MAX1791 PWM step-down controllers provide high efficiency, excellent transient response, and high DC output accuracy needed for stepping down high-voltage batteries to generate low-voltage CPU core, I/O, and chipset RAM supplies in notebook computers and PDAs. Maxim’s proprietary Quick-PWM™ pulse-width modulator is a free-running constant on-time type with input feed-forward.
PAGE 2
MAX1762/MAX1791 High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks ABSOLUTE MAXIMUM RATINGS VP, SHDN to GND ..................................................-0.3V to +22V VP to VL ..................................................................-0.3V to +22V OUT, VL to GND .......................................................-0.3V to +6V DL, FB, REF to GND ....................................-0.3V to (VL + 0.3V) DH to GND....................................................-0.
PAGE 3
High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks (VVP = 15V, VL enabled, CVL = 1µF, CREF = 0.1µF, TA = 0 to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) CONDITIONS MIN TYP MAX UNITS Reference Voltage PARAMETER VVL = 4.75V to 5.25V, no load 1.98 2 2.02 V Reference Load Regulation IREF = 0 to 50µA 0.
PAGE 4
MAX1762/MAX1791 High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks ELECTRICAL CHARACTERISTICS (VVP = 15V, VL enabled, CVL = 1µF, CREF = 0.1µF, TA = -40 to +85°C, unless otherwise noted.) (Note 1) PARAMETER VVP VL Input Voltage Range VVL OUT Output Voltage (MAX1762, 1.8V Fixed) CONDITIONS MIN TYP MAX UNITS 5 20 V VL (overdriven) 4.75 5.25 V VOUT VVP = 5V to 20V, VVL = 4.75V to 5.25V, FB = GND, continuous conduction mode 1.773 1.827 V OUT Output Voltage (MAX1762, 2.
PAGE 5
High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks (VVP = 15V, VL enabled, CVL = 1µF, CREF = 0.1µF, TA = -40 to +85°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL VL Undervoltage Lockout Threshold CONDITIONS Rising edge, hysteresis = 20mV, PWM disabled below this level SHDN Logic Input High Threshold Voltage VIH SHDN Logic Input Low Threshold Voltage VIL MIN 4.1 TYP MAX UNITS 4.4 V 1.6 MAX1762 VOUT = 1.8V fixed MAX1791 VOUT = 3.
PAGE 6
Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) MAX1762 EFFICIENCY vs. LOAD (1.8V) EFFICIENCY (%) VVP = 18V 60 VVP = 12V 50 40 VVP = 7V VVP = 12V 60 VVP = 18V 50 90 40 70 50 30 30 20 20 10 10 10 0 0 10 100 1000 1 10 100 1000 10,000 0.1 10 100 MAX1791 EFFICIENCY vs. LOAD (5V) MAX1791 EFFICIENCY vs. LOAD (3.3V) MAX1791 EFFICIENCY vs. LOAD (3.
PAGE 7
High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks SUPPLY CURRENT vs. INPUT VOLTAGE (SHUTDOWN) SUPPLY CURRENT vs. INPUT VOLTAGE 200 MAX1762/91 toc10 5.8 5.6 SUPPLY CURRENT (µA) 250 SUPPLY CURRENT (µA) 6.0 MAX1762/91 toc09 300 VOUT = 3.3V NO LOAD 150 100 5.4 5.2 5.0 NO LOAD 4.8 4.6 4.4 50 4.2 4.0 0 5 8 11 14 5 17 8 MAX1762/91 toc13 MAX1762/91 toc12 MAX1762/91 toc11 7V VOUT AC-COUPLED 20mV/div 100µs/div VVP = 12V, ILOAD = 0 TO 2A, VOUT = 1.
PAGE 8
High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks MAX1762/MAX1791 Pin Description PIN NAME FUNCTION 1 VL +4.65V Linear Regulator Output. Serves as the supply input for the DL gate driver and supplies up to 25mA to external loads. VL can be overdriven using an external 5V supply. Bypass VL to GND with at least a 1µF ceramic capacitor. 2 REF 3 FB 4 OUT 5 SHDN Shutdown Input. Connect to a voltage less than VIL (<0.6V) to shut down the device.
PAGE 9
High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks MAX1762/MAX1791 VVP C2 1µF C1 10µF 10Ω VL VP 1µF MAX1762 MAX1791 C3 0.1µF REF DH FB CS OUT DL Q1 L1 7µH Q2 VOUT C4 220µF GND SHDN Figure 1. Typical Application Circuit for Fixed Voltage VVP C2 1µF C1 10µF 10Ω VL VP 1µF MAX1762 MAX1791 C3 0.1µF REF DH FB CS OUT DL Q1 L1 7µH Q2 VOUT C4 220µF R1 GND SHDN R2 Figure 2. Typical Application Circuit for Adjustable Output VOUT > 1.
PAGE 10
MAX1762/MAX1791 High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks VVP C1 10µF C2 1µF 10Ω VL VP 1µF MAX1762 MAX1791 C3 0.1µF REF DH FB CS OUT DL Q1 L1 10µH Q2 VOUT C4 150µF RS GND SHDN Figure 4. Operation with External Current-Sense Resistor Table 1. Component Selection for Standard Applications 10 COMPONENT 1.8V/2.5V/3.3V/5.0V AT 2A 1V AT 2A Input Voltage Range 5V to 20V 5V to 20V Inductor (µH) 7 5.
PAGE 11
High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks MAX1762/MAX1791 Table 2. Component Manufacturers MANUFACTURER USA PHONE WEBSITE INFO Coiltronics 561-241-7876 www.coiltronics.com Fairchild Semiconductor 408-822-2181 www.fairchildsemi.com Sanyo 619-661-6835 www.secc.co.jp USA 847-956-0666 Japan 81-3-3607-5111 Sumida www.sumida.com Taiyo Yuden 408-573-4150 www.t-yuden.
PAGE 12
MAX1762/MAX1791 High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks Overdriving the VL regulator with an external 5V supply also increases the MAX1762/MAX1791s’ efficiency. The MAX1762/MAX1791 include an input undervoltage lockout (UVLO) circuit that prevents the device from switching until VL > 4.4V (max). UVLO ensures there is a sufficient drive for the external MOSFETs, prevents the high-side MOSFET from being turned on for near 100% duty cycle, and keeps the output in regulation.
PAGE 13
High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks IPEAK ILOAD = IPEAK/2 0 ON-TIME TIME INDUCTOR CURRENT INDUCTOR CURRENT ILOAD ILIMIT 0 TIME Figure 6. Pulse-Skipping/Discontinuous Crossover Point Figure 7. “Valley” Current-Limit Threshold Point rated for +0.5A, -0.9A source/sink capability and swings from VL to GND. The internal pulldown transistor that drives DL low is robust, with a 1Ω typical on-resistance.
PAGE 14
MAX1762/MAX1791 High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks then the PWM is latched off and does not restart until VP power is cycled, or SHDN is toggled low then high. Design Procedure Begin by establishing the input voltage range and maximum load current before choosing an inductor and its associated ripple-current ratio (LIR). The following four factors dictate the rest of the design: 1) Input voltage range.
PAGE 15
High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks IVALLEY = 90mV / 52mΩ = 1.73A Checking the corresponding ILOAD(MAX) reveals: once enough capacitance is added to meet the overshoot requirement, undershoot at the rising load edge is no longer a problem (see the VSAG equation in the Design Procedure section). The amount of overshoot due to stored inductor energy can be calculated as: 1.73A I ILOAD(MAX) = VALLEY = = 2.1A 1 - 0.5 LIR 1 - 0.5 × 0.
PAGE 16
MAX1762/MAX1791 High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks “fools” the error comparator into triggering a new cycle immediately after the 500ns minimum off-time period has expired. Double pulsing is more annoying than harmful, resulting in nothing worse than increased output ripple. However, it can indicate the possible presence of loop instability, which is caused by insufficient ESR.
PAGE 17
High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks Switching losses in the high-side MOSFET can become an insidious heat problem when maximum battery voltage is applied, due to the squared term in the CV2f switching loss equation. If the high-side MOSFET chosen for adequate R DS(ON) at low battery voltages becomes extraordinarily hot when subjected to VVP(MAX), reconsider your choice of high-side MOSFET.
PAGE 18
MAX1762/MAX1791 High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks OUT FIXED 1.8V TO ERROR AMP FIXED 3.3V (Figure 10). Refer to the MAX1791 EV kit manual for a specific layout example. If possible, mount all of the power components on the top side of the board, with their ground terminals flush against one another. Follow these guidelines for good PC board layout: • Isolate the power components on the top side from the sensitive analog components on the bottom side with a ground shield.
PAGE 19
High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks MAX1762/MAX1791 USE AGND PLANE TO: USE PGND PLANE TO: - BYPASS VCC AND REF - BYPASS VVP - TERMINATE EXTERNAL FB - CONNECT PGND TO THE TOPSIDE STAR GROUND DIVIDER (IF USED) - PIN-STRAP CONTROL INPUTS AGND VOUT L1 PGND C2 D1 P1 VL N1 VIA TO GROUND GND VBATT C1 CONNECT PGND TO AGND BENEATH THE MAX1762/MAX1791 AT ONE POINT ONLY AS SHOWN. NOTE: EXAMPLE SHOWN IS FOR DUAL n-CHANNEL MOSFET. Figure 10.
PAGE 20
Package Information e 10LUMAX.EPS MAX1762/MAX1791 High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks 4X S 10 10 INCHES H Ø0.50±0.1 0.6±0.1 1 1 0.6±0.1 BOTTOM VIEW TOP VIEW D2 MILLIMETERS MAX DIM MIN 0.043 A 0.006 A1 0.002 A2 0.030 0.037 0.120 D1 0.116 0.118 0.114 D2 0.116 0.120 E1 0.118 E2 0.114 0.199 H 0.187 L 0.0157 0.0275 L1 0.037 REF b 0.007 0.0106 e 0.0197 BSC c 0.0035 0.0078 0.0196 REF S α 0° 6° MAX MIN 1.10 0.15 0.05 0.75 0.95 3.05 2.95 3.00 2.89 3.05 2.95 2.89 3.