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General Description

The MAX1684/MAX1685 are high-efficiency, internal-

switch, pulse-width modulation (PWM) step-down switch-

ing regulators intended to power cellular phones,

communicating PDAs, and handy-terminals. These

devices deliver a guaranteed 1A output current from two

lithium-ion (Li+) batteries. Their wide-input voltage range

of 2.7V to 14V gives design flexibility and allows batteries

to charge from a wall cube, since the ICs operate at the

higher voltages that occur when the battery is removed.

The output voltage is preset to 3.3V or can be externally

adjusted from 1.25V to V

The low on-resistance power switch and built-in synchro-

nous rectifier provide high efficiencies of up to 96%.

There are four modes of operation: fixed-frequency, nor-

mal, low-power, and shutdown. The fixed-frequency

PWM mode of operation offers excellent noise character-

istics. The normal mode maintains high efficiency at all

loads. The low-power mode is used to conserve power in

standby or when full load is not required. The shutdown

mode is used to power down the device for minimal cur-

rent draw.

The MAX1684 runs at 300kHz for applications that

require highest efficiency. The MAX1685 runs at

600kHz to allow the use of smaller external compo-

nents. These devices can also be synchronized to an

external clock. Other features include a 100% duty

cycle for low-dropout applications, an auxiliary 3V/5mA

output, and a 1% accurate reference.

Both devices are available in a space-saving 16-QSOP

package. An evaluation kit is also available to help

speed designs. For a similar device in a 10-pin µMAX

package with lower input voltage requirements (5.5V

max), refer to the MAX1692 data sheet.

Applications

Cellular Phones

Two-Way Radios and Walkie-Talkies

Computer Peripherals

Personal Communicators

PDAs and Handy-Terminals

Features

♦ Up to 96% Efficiency

♦ 1A Guaranteed Output Current

♦ 100% Duty Cycle in Dropout

♦ 2.7V to 14V Input Range (15V Absolute Max)

♦ ±1% Accurate Reference Output

♦ 0.24Ω P-Channel On-Resistance

♦ Synchronizable Switching Frequency

♦ Fixed-Frequency PWM Operation

300kHz (MAX1684)

600kHz (MAX1685)

♦ 150µA Normal-Mode Quiescent Current

♦ 25µA Low-Power Mode Quiescent Current

♦ 2µA Shutdown Current

♦ Dual Mode™ Fixed 3.3V (±1%) Output or

Adjustable Output (1.25V to V

)

♦ Small 16-QSOP Package

♦ Auxiliary Output (CVL): 3V/5mA

MAX1684/MAX1685

Low-Noise, 14V Input, 1A, PWM

Step-Down Converters

MAX1684

MAX1685

LXIN

AIN

GND

OUTPUT

3.3V AT 1A

INPUT

2.7V TO 14V

BOOT

SHDN

CVH

CVL

STBY

SYNC/PWM

FB CC REF

19-1454; Rev 2; 7/01

PART

MAX1684EEE

MAX1685EEE

-40°C to +85°C

TEMP RANGE PIN-PACKAGE

16 QSOP

EVALUATION KIT

AVAILABLE

Typical Operating Circuit

Ordering Information

Pin Configuration appears at end of data sheet.

Dual Mode is a trademark of Maxim Integrated Products, Inc.

________________________________________________________________ Maxim Integrated Products 1

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.

Summary of content (14 pages)

PAGE 1
9-1454; Rev 2; 7/01 KIT ATION EVALU E L B AVAILA Low-Noise, 14V Input, 1A, PWM Step-Down Converters Both devices are available in a space-saving 16-QSOP package. An evaluation kit is also available to help speed designs. For a similar device in a 10-pin µMAX package with lower input voltage requirements (5.5V max), refer to the MAX1692 data sheet.
PAGE 2
MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters ABSOLUTE MAXIMUM RATINGS AIN to AGND ............................................................-0.3 to +15V IN to PGND ................................................-0.3V to (VAIN + 0.3V) LX to PGND .................................................-0.5V to (VIN + 0.3V) PGND to AGND ..................................................................±0.3V SHDN to AGND .........................................-0.3V to (VAIN + 0.
PAGE 3
Low-Noise, 14V Input, 1A, PWM Step-Down Converters (VIN = V SHDN = 6V, STBY = SYNC/PWM = CVL, VBOOT = VOUT, FB = AGND, circuit of Figure 1, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 4
MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters ELECTRICAL CHARACTERISTICS (VIN = V SHDN = 6V, STBY = SYNC/PWM = CVL, VBOOT = VOUT, FB = AGND, circuit of Figure 1, TA = -40°C to +85°C, unless otherwise noted.) (Note 5) PARAMETER SYMBOL CONDITIONS Input Voltage Range Output Feedback Voltage Output Voltage (3.3V Mode) MAX UNITS 2.7 14 V V VFB VFB = VOUT, ILOAD = 0 to 1A 1.233 1.269 VOUT FB = AGND, ILOAD = 0 to 1A 3.280 3.
PAGE 5
Low-Noise, 14V Input, 1A, PWM Step-Down Converters MAX1684 EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V) 60 C B A: VOUT = 2.5V LP MODE B: VOUT = 1.8V LP MODE C: VOUT = 2.5V NORM MODE D: VOUT = 1.8V NORM MODE E: VOUT = 2.5V PWM MODE F: VOUT = 1.8V PWM MODE F 30 20 10 0 0.1 1 10 100 1000 A: VIN = 4V B: VIN = 5V C: VIN = 9V D: VIN = 12V MAX1684/85 toc02 10 0 0.1 1 10 100 1000 10,000 1 10 100 1000 10,000 MAX1684 EFFICIENCY vs. LOAD CURRENT (VOUT = 5V) MAX1684 EFFICIENCY vs.
PAGE 6
Typical Operating Characteristics (continued) (Circuit of Figure 1, TA = +25°C, unless otherwise noted.) MAXIMUM LOAD CURRENT vs. INPUT VOLTAGE SAFE OPERATING AREA 1.4 1.3 1000 1.2 800 600 400 MAX1684/85 toc12 400 DROPOUT VOLTAGE (mV) 1.5 VOUT = 3.3V 1200 LOAD CURRENT (mA) 300 VOUT = 3.3V 200 VOUT = 5V 100 200 1.1 INDUCTOR RESISTANCE INCLUDED PWM OR NORMAL MODE 0 1.0 2 4 6 8 10 12 0 14 2 6 8 10 12 INPUT VOLTAGE (V) INPUT VOLTAGE (V) NO-LOAD SUPPLY CURRENT vs.
PAGE 7
Low-Noise, 14V Input, 1A, PWM Step-Down Converters STARTUP CURRENT LINE-TRANSIENT RESPONSE MAX1684/85 toc20 MAX1684/85 toc19 VSHDN 5V/div VIN 5V/div 0V VOUT 100mV/div IIN 50mA/div 10ms/div 2ms/div MAX1684, ILOAD = 100mA, VOUT = 3.3V, VIN = 5V, CILIM/SS = 0.1µF, SYNC/PWM = 3.3V MAX1684, ILOAD = 100mA, VIN = 5V TO 10V, SYNC/PWM = 3.3V Pin Description PIN NAME FUNCTION 1 CVH High-Side MOSFET Gate Bias. Bias voltage for P-channel switch. Bypass to IN with a 0.1µF capacitor.
PAGE 8
MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters 0.1µF INPUT 14V MAX 3 22µF 2 1 CVH IN LX MAX1685 PGND 15 1µF 11 OUTPUT 3.3V AT 1A COUT 100µF MBRS 130LT3 AIN 0.1µF ON/OFF L 10µH* 13, 14 AGND SHDN 4 CVL BOOT STBY 9 SYNC/PWM 16 5 12 7 synchronization to an external clock. The MAX1684/MAX1685 can operate in five modes. Setting the devices to operate in the appropriate mode for the intended application (Table 1) achieves highest efficiency.
PAGE 9
Low-Noise, 14V Input, 1A, PWM Step-Down Converters CVL IN MAX1684 MAX1685 4µA AIN SHDN CVH VH VL THERMAL SHUTDOWN MAX1684/MAX1685 ILIM/SS ILIM THRESHOLD ON CVL REF PFM CURRENT COMPARATOR REF ILIM COMPARATOR LX CONTROL AND DRIVER UNDERVOLTAGE COMPARATOR 2.5V SYNC/PWM STBY LOGIC PWM COMPARATOR OSC SYNC SLOPE COMPENSATION AND STANDBY PWM MODE CONTROL NORMAL MODE LOW-POWER MODE PGND ZERO-CROSSING COMPARATOR CVL 2.5V CC PFM COMPARATOR BOOT GM INTEGRATOR FB 0.125V AGND Figure 2.
PAGE 10
MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters inductor peak current during the first half of each cycle, based on the output error voltage. The MAX1684/ MAX1685s’ loop gain is relatively low to enable the use of a small, low-value output filter capacitor. The 1.4% transient load regulation from 0 to 1A is compensated by an integrator circuit that lowers DC load regulation to 0.01% typical.
PAGE 11
Low-Noise, 14V Input, 1A, PWM Step-Down Converters Internal Low-Voltage Regulators and Bootstrap (BOOT) The MAX1684/MAX1685 have two internal regulators (VH and VL) that generate low-voltage supplies for internal circuitry (see the Functional Diagram). The VH regulator generates -4.6V with respect to IN to supply the P-channel switch and driver. Bypass CVH to IN with a 0.1µF capacitor.
PAGE 12
MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters capacitors have the lowest ESR of the high-value electrolytic types. Use ceramic and OS-CON capacitors for very compact, high-reliability, or wide-temperature applications, where expense is justified. When using very low ESR capacitors, such as ceramic or OS-CON, check for stability while examining load-transient response, and increase the output compensation capacitor if needed.
PAGE 13
Low-Noise, 14V Input, 1A, PWM Step-Down Converters PC Board Layout High switching frequencies and large peak currents make PC board layout a very important part of design. Poor design can result in excessive EMI on the feedback paths and voltage gradients in the ground plane, both of which result in instability or regulation errors.
PAGE 14
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 MAX1684/MAX1685 Low-Noise, 14V Input, 1A, PWM Step-Down Converters Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.