ADM1021

–5–

REV. 0

FREQUENCY – Hz

10

0

50

50M

500

5k

50k

500k

5M

6

5

4

2

1

3

10mV SQ. WAVE

9

8

7

100k

25M

Figure 8. Temperature Error vs. Differential-Mode Noise

Frequency

CONVERSION RATE – Hz

200

0

0.0625

8

0.125

0.25

0.5

1

2

4

180

80

60

40

20

140

100

160

120

Figure 9. Operating Supply Current vs. Conversion

Rate

SUPPLY VOLTAGE – Volts

100

40

–20

0

1.1 1.3

1.5 1.7 1.9 2.1

2.3 2.5 2.7

2.9 3.5

4.5

80

60

20

0

ADDX = HI-Z

ADDX = GND

Figure 10. Standby Supply Current vs. Supply Voltage

TIME – Sec

125

100

0

T = 0

T = 10

T = 2

T = 4

T = 6

T = 8

75

50

25

IMMERSED

IN +115 C

FLUORINERT BATH

Figure 11. Response to Thermal Shock

FUNCTIONAL DESCRIPTION

The ADM1021 contains a two-channel A-to-D converter with

special input-signal conditioning to enable operation with remote

and on-chip diode temperature sensors. When the ADM1021 is

operating normally, the A-to-D converter operates in a free-

running mode. The analog input multiplexer alternately selects

either the on-chip temperature sensor to measure its local tem-

perature, or the remote temperature sensor. These signals are

digitized by the ADC and the results stored in the Local and

Remote Temperature Value Registers as 8-bit, twos complement

words.

The measurement results are compared with Local and Remote,

High and Low Temperature Limits, stored in four on-chip regis-

ters. Out-of-limit comparisons generate flags that are stored in

the status register, and one or more out-of-limit results will

cause the

ALERT output to pull low.

The limit registers can be programmed, and the device con-

trolled and configured, via the serial System Management Bus.

The contents of any register can also be read back via the SMBus.

Control and configuration functions consist of:

• Switching the device between normal operation and standby

mode.

• Masking or enabling the

ALERT output.

• Selecting the conversion rate.

MEASUREMENT METHOD

A simple method of measuring temperature is to exploit the

negative temperature coefficient of a diode, or the base-emitter

voltage of a transistor, operated at constant current. Unfortu-

nately, this technique requires calibration to null out the effect

The technique used in the ADM1021 is to measure the change

This is given by:

∆V

where:

K is Boltzmann’s constant

q is charge on the electron (1.6 x 10

T is absolute temperature in Kelvins

N is ratio of the two currents