Datasheet

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_______________General Description

The MAX1649/MAX1651 BiCMOS, step-down, DC-DC

switching controllers provide high efficiency over loads

ranging from 1mA to more than 2.5A. A unique, current-

limited pulse-frequency-modulated (PFM) control scheme

gives these devices the benefits of pulse-width-modula-

tion (PWM) converters (high efficiency at heavy loads),

while using only 100µA of supply current (vs. 2mA to

10mA for PWM converters). Dropout performance down

to 300mV is provided by a high switch duty cycle (96.5%)

and a low current-sense threshold (110mV).

A high switching frequency (up to 300kHz) allows these

devices to use miniature external components.

The MAX1649/MAX1651 have dropout voltages less

than 0.3V at 500mA and accept input voltages up to

16V. Output voltages are preset at 5V (MAX1649), or

3.3V (MAX1651). They can also be adjusted to any

voltage from 1.5V to the input voltage by using two

resistors.

These step-down controllers drive external P-channel

MOSFETs at loads greater than 12.5W. If less power is

required, use the MAX639/MAX640/MAX653 step-down

converters with on-chip FETs, which allow up to a

225mA load current.

________________________Applications

PDAs

High-Efficiency Step-Down Regulation

5V-to-3.3V Green PC Applications

Battery-Powered Applications

____________________________Features

♦ More than 90% Efficiency (10mA to 1.5A Loads)

♦ More than 12.5W Output Power

♦ Less than 0.3V Dropout Voltage at 500mA

♦ 100µA Max Quiescent Supply Current

♦ 5µA Max Shutdown Supply Current

♦ 16V Max Input Voltage

♦ 5V (MAX1649), 3.3V (MAX1651), or Adjustable

Output Voltage

♦ Current-Limited Control Scheme

♦ Up to 300kHz Switching Frequency

♦ Up to 96.5% Duty Cycle

______________Ordering Information

*Dice are tested at T

= +25°C.

MAX1649/MAX1651

5V/3.3V or Adjustable, High-Efficiency,

Low-Dropout, Step-Down DC-DC Controllers

________________________________________________________________ Maxim Integrated Products 1

GND

EXT

V+

REF

SHDN

OUT

DIP/SO

TOP VIEW

MAX1649

MAX1651

__________________Pin Configuration

__________Typical Operating Circuit

19-0305; Rev 3; 3/09

PART TEMP RANGE PIN-PACKAGE

MAX1649CPA

0°C to +70°C 8 Plastic DIP

MAX1649CSA 0°C to +70°C 8 SO

MAX1649C/D 0°C to +70°C Dice*

MAX1649EPA -40°C to +85°C 8 Plastic DIP

MAX1649ESA -40°C to +85°C 8 SO

MAX1651

V+

CSSHDN

FB GND

ON/OFF

EXT

REF

OUT

OUTPUT

3.3V

INPUT

3.6V TO 16V

MAX1651CPA

0°C to +70°C 8 Plastic DIP

MAX1651CSA 0°C to +70°C 8 SO

MAX1651C/D 0°C to +70°C Dice*

MAX1651EPA -40°C to +85°C 8 Plastic DIP

MAX1651ESA -40°C to +85°C 8 SO

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.maxim-ic.com.

Summary of content (12 pages)

PAGE 1
9-0305; Rev 3; 3/09 KIT ATION EVALU E L B A AVAIL 5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers The MAX1649/MAX1651 BiCMOS, step-down, DC-DC switching controllers provide high efficiency over loads ranging from 1mA to more than 2.5A. A unique, currentlimited pulse-frequency-modulated (PFM) control scheme gives these devices the benefits of pulse-width-modulation (PWM) converters (high efficiency at heavy loads), while using only 100µA of supply current (vs.
PAGE 2
MAX1649/MAX1651 5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers ABSOLUTE MAXIMUM RATINGS Supply Voltage, V+ to GND.......................................-0.3V, +17V REF, SHDN, FB, CS, EXT, OUT .......................-0.3V, (V+ + 0.3V) Continuous Power Dissipation (TA = +70°C) Plastic DIP (derate 9.09mW/°C above +70°C) .............727mW SO (derate 5.88mW/°C above +70°C) ..........................471mW Operating Temperature Ranges MAX1649C_A, MAX1651C_A ....................
PAGE 3
5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers (V+ = 5V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL Current-Limit Trip Level (V+ to CS) VCS CONDITIONS 3V ≤ V+ ≤ 16V MIN TYP MAX UNITS 80 110 140 mV CS Input Current 3V ≤ V+ ≤ 16V ±1 µA Switch Maximum On-Time tON (max) V+ = 12V 24 32 40 µs Switch Minimum Off-Time tOFF (min) V+ = 12V 0.8 1.1 1.8 µs EXT Rise Time CEXT = 0.
PAGE 4
____________________________Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) SWITCH OFF-TIME vs. TEMPERATURE 33.5 1.4 99 1.3 33.0 tOFF (μs) 32.5 32.0 DUTY CYCLE (%) 1.2 1.1 1.0 0.9 31.5 0.8 31.0 98 97 96 95 0.7 30.5 94 0.6 30.0 0.5 93 -60 -40 -20 0 20 40 60 80 100 120 140 -60 -40 -20 0 20 40 60 80 100 120 140 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) 110 105 100 400 VOUT = 4.80V 300 VOUT = 3.
PAGE 5
V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers MAX1649 LOAD-TRANSIENT RESPONSE MAX1649 LINE-TRANSIENT RESPONSE A A 16V 1.6A B B 6V 0A 200μs/div CIRCUIT OF FIGURE 1, V+ = 10V A: VOUT = 5V, 100mV/div, AC-COUPLED B: ILOAD = 30mA TO 1.
PAGE 6
MAX1649/MAX1651 5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers ______________________________________________________________Pin Description PIN NAME FUNCTION 1 OUT Sense Input for fixed 5V or 3.3V output operation. OUT is internally connected to the on-chip voltage divider. Although it is connected to the output of the circuit, OUT does not supply current. Leave OUT unconnected for adjustable-output operation. 2 FB Feedback Input.
PAGE 7
5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers MAX1649/MAX1651 V+ FB DUAL-MODE™ COMPARATOR MAX1649 MAX1651 50mV OUT SHDN ERROR COMPARATOR REF 1.5V REFERENCE N Q MINIMUM OFF-TIME TRIG ONE-SHOT FROM V+ S EXT Q F/F MAXIMUM TRIG ON-TIME Q ONE-SHOT R CURRENT COMPARATOR CS 110mV FROM V+ GND Figure 2. Block Diagram Shutdown Mode Quiescent Current When SHDN is high, the MAX1649/MAX1651 enter shutdown mode.
PAGE 8
MAX1649/MAX1651 5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers VIN V+ MAX1649 MAX1651 CS 1.5A 1A 3 0A 4 SHDN EXT REF OUT GND ( VOUT R2 = R3 –1 VREF ) C1 100μF R1 0.05Ω 6 P1 Si9430 7 L1 47μH OUTPUT @ 1.5A 1 2 R2 8 C3 0.1μF 2μs/div V+ = 10V, ILOAD = 1.3A CIRCUIT OF FIGURE 1, R1 = 75mΩ FB C4 0.1μF 5 C2 330μF D1 1N5820 R3 150k VREF = 1.5V Figure 3.
PAGE 9
5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers 2.5 rs = 0.030 2.0 rs = 0.040 rs = 0.050 1.5 rs = 0.060 1.0 rs = 0.080 0.5 rs = 0.100 0 where ΔI is the inductor-current overshoot factor, ILIM = VCS/RSENSE, and 0.3µs is the time it takes the comparator to switch. Set ΔI = 0.1 for an overshoot of 10%. For highest efficiency, use a coil with low DC resistance; a value smaller than 0.1V/ILIM works best.
PAGE 10
MAX1649/MAX1651 5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers Table 1. Component Selection Guide PRODUCTION METHOD Surface Mount Miniature Through-Hole Low-Cost Through-Hole INDUCTORS CAPACITORS Sumida CDRH125-470 (1.8A) CDRH125-220 (2.2A) Coilcraft DO3316-473 (1.6A) DO3340-473 (3.
PAGE 11
5V/3.
PAGE 12
MAX1649/MAX1651 5V/3.3V or Adjustable, High-Efficiency, Low-Dropout, Step-Down DC-DC Controllers Revision History REVISION NUMBER REVISION DATE 3 3/09 DESCRIPTION Corrected Output Voltage conditions and Figure 1 title PAGES CHANGED 2, 6 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.