Datasheet

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General Description

The MAX1795/MAX1796/MAX1797 are high efficiency

step-up DC-DC converters intended for small portable

hand-held devices. These devices feature Maxim’s

True-Shutdown™ circuitry, which fully disconnects the

output from the input in shutdown, improves efficiency,

and eliminates costly external components. All three

devices also feature Maxim’s proprietary LX-damping

circuitry for reduced EMI in noise-sensitive applica-

tions. For additional in-system flexibility, a battery moni-

toring comparator (LBI/LBO) remains active even when

the DC-DC converter is in shutdown.

The input voltage range is +0.7V to V

OUT

, where V

OUT

can be set from +2V to +5.5V. Startup is guaranteed

from +0.85V. The MAX1795/MAX1796/MAX1797 have a

preset, pin-selectable 5V or 3.3V output. The output

can also be adjusted to other voltages, using two exter-

nal resistors. The three devices differ only in their cur-

rent limits, allowing optimization of external components

for different loads: The MAX1795, MAX1796, and

MAX1797 have current limits of 0.25A, 0.5A, and 1A,

respectively. All devices are packaged in a compact 8-

pin µMAX package that is only 1.09mm tall and half the

size of an 8-pin SO.

________________________Applications

Portable Digital Audio Players

PDAs/Palmtops

Wireless Handsets

Portable Terminals

Features

♦ >95% Efficiency

♦ True-Shutdown Circuitry

Output Disconnects from Input in Shutdown

No External Schottky Diode Needed

♦ 25µA Quiescent Supply Current

♦ Low-Noise Antiringing Feature

♦ LBI/LBO Comparator Enabled in Shutdown

♦ 2µA Shutdown Current

♦ 8-Pin µMAX Package

MAX1795/MAX1796/MAX1797

Low Supply Current, Step-Up DC-DC Converters

with True-Shutdown

________________________________________________________________ Maxim Integrated Products 1

BATT

OUT

GND

LBO

LBI

MAX1795

MAX1796

MAX1797

µMAX

TOP VIEW

SHDN

Pin Configuration

GND

LBI

LBO

BATT

OUT

MAX1795

MAX1796

MAX1797

SHDN

OUT

0.7V TO

5.5V

OFF

Typical Operating Circuit

19-1798; Rev 0; 12/00

Ordering Information

PART TEMP. RANGE PIN-PACKAGE

MAX1795

EUA -40°C to +85°C 8 µMAX

MAX1796 EUA -40°C to +85°C 8 µMAX

MAX1797 EUA -40°C to +85°C 8 µMAX

True-Shutdown is a trademark of Maxim Integrated Products.

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 (13 pages)

PAGE 1
9-1798; Rev 0; 12/00 Low Supply Current, Step-Up DC-DC Converters with True-Shutdown Features ♦ >95% Efficiency ________________________Applications True-Shutdown is a trademark of Maxim Integrated Products. ♦ True-Shutdown Circuitry Output Disconnects from Input in Shutdown No External Schottky Diode Needed ♦ 25µA Quiescent Supply Current ♦ Low-Noise Antiringing Feature ♦ LBI/LBO Comparator Enabled in Shutdown ♦ 2µA Shutdown Current ♦ 8-Pin µMAX Package Ordering Information PART TEMP.
PAGE 2
MAX1795/MAX1796/MAX1797 Low Supply Current, Step-Up DC-DC Converters with True-Shutdown ABSOLUTE MAXIMUM RATINGS OUT, LX, SHDN, LBI, LBO, BATT to GND................-0.3V to +6V FB .............................................................-0.3V to (VOUT + 0.3V) ILX, IOUT ..............................................................................±1.5A Output Short-Circuit Duration ...................................................5s Continuous Power Dissipation 8-Pin µMAX (derate 4.
PAGE 3
Low Supply Current, Step-Up DC-DC Converters with True-Shutdown (VBATT = +2V, OUT = FB (VOUT = +3.3V), SHDN = LBI = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are TA = +25°C.) PARAMETER SYMBOL Operating Current into BATT CONDITIONS MIN VFB = +1.
PAGE 4
MAX1795/MAX1796/MAX1797 Low Supply Current, Step-Up DC-DC Converters with True-Shutdown ELECTRICAL CHARACTERISTICS (continued) (VBATT = +2V, OUT = FB (VOUT = +3.3V), SHDN = LBI = GND, TA = -40°C to +85°C, unless otherwise noted.) (Note 3) PARAMETER Internal NFET, PFET OnResistance LX Switch Current Limit (NFET only) LX Leakage Current SYMBOL RDS(ON) ILIM ILEAK CONDITIONS VOUT = +3.3V, ILX = 100mA MIN MAX NFET 0.3 PFET 0.45 MAX1795 0.19 MAX1796 0.35 0.7 MAX1797 0.8 1.32 UNITS 0.
PAGE 5
Low Supply Current, Step-Up DC-DC Converters with True-Shutdown VBATT = +1.2V 60 50 40 VBATT = +1.2V 60 50 40 80 50 40 30 20 10 10 0 0 100 10 L = 10µH 0 1000 0.1 1 10 100 1000 0.1 1 10 100 1000 LOAD CURRENT (mA) LOAD CURRENT (mA) LOAD CURRENT (mA) MAX1796 EFFICIENCY vs. LOAD CURRENT (+3.3V) MAX1797 EFFICIENCY vs. LOAD CURRENT (+5V) MAX1797 EFFICIENCY vs. LOAD CURRENT (+3.3V) 60 50 40 100 70 VBATT = +2.4V 60 VBATT = +1.
PAGE 6
Typical Operating Characteristics (continued) (L = 22µH, CIN = 47µF, COUT = 47µF, TA = +25°C, unless otherwise noted.) INCREASING VLBI 0.875 DECREASING VLBI 0.825 200 INCREASING VLBI 0.900 0.875 0.850 DECREASING VLBI -40 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 -15 10 35 60 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 BATT VOLTAGE (V) 300 VOUT = +3.3V 200 VOUT = +5.0V 1000 800 LOAD CURRENT (mA) LOAD CURRENT (mA) 400 VOUT = +3.3V 600 400 VOUT = +5.0V 200 100 0 0 0 0.5 1.0 1.5 2.0 2.
PAGE 7
Low Supply Current, Step-Up DC-DC Converters with True-Shutdown LINE-TRANSIENT RESPONSE LIGHT-LOAD SWITCHING WAVEFORMS MAX1795/96/97 toc18 MAX1795/96/97 toc17 VLX 5V/div VBATT +2.7V TO +3V IINDUCTOR 500mA/div VOUT (AC-COUPLED) 20mV/div VOUT (AC-COUPLED) 100mV/div 10µs/div VBATT = +2.7V TO +3V VOUT = +5.0V NO LOAD 20µs/div VBATT = +3.6V VOUT = +5.
PAGE 8
MAX1795/MAX1796/MAX1797 Low Supply Current, Step-Up DC-DC Converters with True-Shutdown Pin Description PIN NAME FUNCTION 1 LBI Low-Battery Comparator Input. Internally set to trip at +0.85V. This function remains operational in shutdown. 2 FB Dual-Mode™ Feedback Input. Connect to GND for preset 5.0V output. Connect to OUT for preset 3.3V output. Connect a resistive voltage-divider from OUT to GND to adjust the output voltage from 2V to 5.5V.
PAGE 9
Low Supply Current, Step-Up DC-DC Converters with True-Shutdown MAX1795/MAX1796/MAX1797 BATT R1 1M SHDN ZEROCROSSING AMPLIFIER MAX1795 MAX1796 MAX1797 LBO LBI + _ S Q + OUT OUT R + _ 47µF BODY DIODE CONTROL 0.85V S BATT Q BATT R 22µH TIMER BLOCK 47µF S Q START TON MAX LX R TOFF MAX OUT R2 FB R3 FB SELECT REFERENCE + _ + _ CURRENT-LIMIT AMPLIFIER ERROR AMPLIFIER + _ GND Figure 2.
PAGE 10
MAX1795/MAX1796/MAX1797 Low Supply Current, Step-Up DC-DC Converters with True-Shutdown pate this energy, minimizing the ringing at LX. Damping LX ringing does not reduce VOUT ripple, but does reduce EMI (Figures 3, 4, and 5). VIN Setting the Output Voltage BATT MAX1795 MAX1796 MAX1797 R1 200Ω VOUT can be set to 3.3V or 5.0V by connecting the FB pin to GND (5V) or OUT (3.3V). To adjust the output voltage, connect a resistive voltage-divider from OUT to FB to GND (Figure 6).
PAGE 11
Low Supply Current, Step-Up DC-DC Converters with True-Shutdown Connect a pullup resistor of 100kΩ or greater from LBO to OUT for a logic output. LBO is an open-drain output and can be pulled as high as 6V regardless of the voltage at OUT. When LBI is below the threshold, the LBO output is high impedance. If the low-battery comparator is not used, ground LBI and LBO. Applications Information Inductor Selection An inductor value of 22µH performs well in most applications.
PAGE 12
MAX1795/MAX1796/MAX1797 Low Supply Current, Step-Up DC-DC Converters with True-Shutdown Table 1. Suggested Components for Typical Applications COMPONENT COMPONENT VALUE (MAX1797, 1A CURRENT LIMIT) COMPONENT VALUE (MAX1796, 0.5A CURRENT LIMIT) COMPONENT VALUE (MAX1795, 0.
PAGE 13
Low Supply Current, Step-Up DC-DC Converters with True-Shutdown 8LUMAXD.EPS 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.