by the high input impedance op amp of a MAX951

(Figure 6). The comparator and resistor voltage divider

set an alarm threshold to indicate a fire.

Design and fabrication of the connection from the inter-

mediate plate of the ionization chamber to the nonin-

verting input of the op amp is critical, since the

impedance of this node must be well above 50M

Ω. This

connection must be as short and direct as possible to

prevent charge leakage and 60Hz interference. Where

possible, the grounded outer electrode or chassis of

the ionization chamber should shield this connection to

reduce 60Hz interference. Pay special attention to

board cleaning, to prevent leakage due to ionic com-

pounds such as chlorides, flux, and other contaminants

from the manufacturing process. Where applicable, a

coating of high-purity wax may be used to insulate this

connection and prevent leakage due to surface mois-

ture or an accumulation of dirt.

0.084"

(2.134mm)

0.058"

(1.473mm)

COMPOUT

REF(COMPIN-)

COMPIN+

AMPIN+

( ) ARE FOR MAX953/MAX954

AMPIN-

AMPOUT

Ultra-Low-Power, Single-Supply

Op Amp + Comparator + Reference

______________Ordering Information

___________________Chip Topography

PART

MAX951C/D

0°C to +70°C

TEMP. RANGE

PIN-PACKAGE

Dice*

** Contact factory for availability and processing to MIL-STD-883.

TRANSISTOR COUNT: 163

3

AMPIN+

INPUT

2

5

6

1

8

4

REF

0.1

µF

1.20V

R1

R2

1M

COMPOUT

7

MAX951

MAX952

__________Typical Operating Circuit

MAX951EPA

-40°C to +85°C

8 Plastic DIP

MAX951MJA

-55°C to +125°C

8 CERDIP**

MAX951ESA

-40°C to +85°C

8 SO

MAX952C/D

0°C to +70°C

Dice*

MAX952EPA

-40°C to +85°C

8 Plastic DIP

MAX952MJA

-55°C to +125°C

8 CERDIP**

MAX952ESA

-40°C to +85°C

8 SO

MAX953C/D

0°C to +70°C

MAX954C/D

0°C to +70°C

Dice*

MAX953EPA

-40°C to +85°C

8 Plastic DIP

MAX953MJA

-55°C to +125°C

8 CERDIP**

Dice*

MAX954EPA

-40°C to +85°C

8 Plastic DIP

MAX954MJA

-55°C to +125°C

8 CERDIP**

MAX954ESA

-40°C to +85°C

8 SO

MAX953ESA

-40°C to +85°C

8 SO

MAX951EUA

-40°C to +85°C

8 µMAX

MAX952EUA

-40°C to +85°C

8 µMAX

MAX953EUA

-40°C to +85°C

8 µMAX

MAX954EUA

-40°C to +85°C

8 µMAX

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.

12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 1997 Maxim Integrated Products

Printed USA

is a registered trademark of Maxim Integrated Products.