Datasheet

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General Description

The ultra-small MAX870/MAX871 monolithic, CMOS

charge-pump inverters accept input voltages ranging

from +1.4V to +5.5V. The MAX870 operates at 125kHz,

and the MAX871 operates at 500kHz. Their high efficien-

cy (90%) and low operating current (0.7mA for the

MAX870) make these devices ideal for both battery-pow-

ered and board-level voltage-conversion applications.

Oscillator control circuitry and four power MOSFET

switches are included on-chip. A typical MAX870/

MAX871 application is generating a -5V supply from a

+5V logic supply to power analog circuitry. Both parts

come in a 5-pin SOT23-5 package and can deliver 25mA

with a voltage drop of 500mV.

For a similar device with logic-controlled shutdown,

refer to the MAX1720/MAX1721. For applications

requiring more power, the MAX860 delivers up to 50mA

with a voltage drop of 600mV, in a space-saving µMAX

package.

________________________Applications

Local -5V Supply from 5V Logic Supply

Small LCD Panels

Cell Phones

Medical Instruments

Handy-Terminals, PDAs

Battery-Operated Equipment

Features

♦ 5-Pin SOT23-5 Package

♦ 99% Voltage Conversion Efficiency

♦ Invert Input Supply Voltage

♦ 0.7mA Quiescent Current (MAX870)

♦ +1.4V to +5.5V Input Voltage Range

♦ Require Only Two Capacitors

♦ 25mA Output Current

♦ Shutdown Control

MAX870/MAX871

Switched-Capacitor Voltage Inverters

________________________________________________________________ Maxim Integrated Products 1

TOP VIEW

GND

C1-

C1+

OUT

SOT23-5

MAX870

MAX871

Pin Configuration

NEGATIVE VOLTAGE CONVERTER

C1+

C1-

OUT

GND

INPUT

SUPPLY

VOLTAGE

NEGATIVE

OUTPUT

VOLTAGE

MAX870

MAX871

Typical Operating Circuit

19-1240; Rev 1; 2/04

PART

MAX870EUK

-40°C to +85°C

TEMP RANGE

PIN-

PACKAGE

5 SOT23-5

Ordering Information

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.

MAX871EUK

-40°C to +85°C 5 SOT23-5

SOT

TOP MARK

ABZN

ABZO

Summary of content (8 pages)

PAGE 1
9-1240; Rev 1; 2/04 Switched-Capacitor Voltage Inverters Features The ultra-small MAX870/MAX871 monolithic, CMOS charge-pump inverters accept input voltages ranging from +1.4V to +5.5V. The MAX870 operates at 125kHz, and the MAX871 operates at 500kHz. Their high efficiency (90%) and low operating current (0.7mA for the MAX870) make these devices ideal for both battery-powered and board-level voltage-conversion applications.
PAGE 2
Switched-Capacitor Voltage Inverters MAX870/MAX871 ABSOLUTE MAXIMUM RATINGS Continuous Power Dissipation (TA = +70°C) SOT23-5 (derate 7.1mW/°C above +70°C)...................571mW Operating Temperature Range MAX870EUK/MAX871EUK ...............................-40°C to +85°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10s) .................................+300°C IN to GND ..............................................................+6.0V to -0.
PAGE 3
Switched-Capacitor Voltage Inverters MAX871 1.0 MAX870 50 40 MAX871 30 MAX870 0.5 20 0 10 45 OUTPUT RESISTANCE (Ω) 2.0 50 MAX828/829-02 MAX870/71-TOC01 SUPPLY CURRENT (mA) 2.5 60 OUTPUT RESISTANCE (Ω) 3.0 1.5 MAX870 OUTPUT RESISTANCE vs. TEMPERATURE OUTPUT RESISTANCE vs. SUPPLY VOLTAGE MAX870/71 ROC3 SUPPLY CURRENT vs. SUPPLY VOLTAGE 40 VIN = 1.5V 35 30 VIN = 3.3V 25 20 15 VIN = 5.0V 10 5 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 2.0 2.5 3.5 4.0 4.5 5.0 -40 5.
PAGE 4
____________________________Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = +5V, C1 = C2 = C3, TA = +25°C, unless otherwise noted.) VIN = 5.0V VIN = 2.0V 60 70 EFFICIENCY (%) VIN = 3.3V 70 50 40 500 60 VIN = 3.3V VIN = 2.0V 50 40 450 350 300 30 20 20 200 10 10 150 0 0 5 10 15 20 25 30 35 40 45 50 VIN = 1.5V, MAX871 400 30 0 VIN = 3.3V OR 5.0V, MAX871 550 PUMP FREQUENCY (kHz) 80 VIN = 5.0V 80 PUMP FREQUENCY vs.
PAGE 5
Switched-Capacitor Voltage Inverters The MAX870/MAX871 capacitive charge pumps invert the voltage applied to their input. For highest performance, use low equivalent series resistance (ESR) capacitors (e.g., ceramic). During the first half-cycle, switches S2 and S4 open, switches S1 and S3 close, and capacitor C1 charges to the voltage at IN (Figure 2). During the second halfcycle, S1 and S3 open, S2 and S4 close, and C1 is level shifted downward by VIN volts.
PAGE 6
MAX870/MAX871 Switched-Capacitor Voltage Inverters Flying Capacitor (C1) Increasing the flying capacitor’s size reduces the output resistance. Small C1 values increase the output resistance. Above a certain point, increasing C1’s capacitance has a negligible effect, because the output resistance becomes dominated by the internal switch resistance and capacitor ESR. Output Capacitor (C2) Increasing the output capacitor’s size reduces the output ripple voltage.
PAGE 7
Switched-Capacitor Voltage Inverters MAX870/MAX871 … … 2 4 5 2 2 3 C1 +VIN +VIN 3 MAX870 MAX871 “1” 4 C1 1 5 2 3 3 MAX870 MAX871 “n” C1 1 … 4 5 VOUT MAX870 MAX871 “1” 1 5 C2 1 VOUT … C2 ROUT OF SINGLE DEVICE ROUT = NUMBER OF DEVICES VOUT = -nVIN Figure 4. Cascading MAX870s or MAX871s to Increase Output Voltage MAX870 MAX871 “n” 4 C1 VOUT = -VIN C2 Figure 5.
PAGE 8
Shutdown Control For a similar device with logic-controlled shutdown, please refer to the MAX1720/MAX1721. To add manual shutdown control to the MAX870/MAX871, use the circuit in Figure 8. The output resistance of the MAX870/ MAX871 will typically be 20Ω plus two times the output resistance of the buffer driving IN. The 0.1µF capacitor at the IN pin absorbs the transient input currents of the MAX870/MAX871.