REV. A

–6–

ADR370

PARAMETER DEFINITIONS

Temperature Coefficient

Temperature coefficient is the change of output voltage with

respect to operating temperature changes, normalized by the

output voltage at 25

°C. This parameter is expressed in ppm/°C

and can be determined with the following equation

TCV

ppm

C

VT

VT

VC

T

T

O

OO

O

°











 =

°

()

×

21

21

6

25

10

(1)

where:

°C) = V

°C.

Line Regulation

Line regulation is the change in output voltage due to a specified

change in input voltage. This parameter accounts for the effects

of self-heating. Line regulation is expressed in either percent per

volt, parts-per-million per volt, or microvolts per volt change in

input voltage.

Load Regulation

Load regulation is the change in output voltage due to a specified

change in load current. This parameter accounts for the effects

of self-heating. Load regulation is expressed in either microvolts

per milliampere, parts-per-million per milliampere, or ohms of

dc output resistance.

Long Term Stability

Long term stability is the typical shift of output voltage at 25

°C

on a sample of parts subjected to a test of 1,000 hours at 25

°C.

∆

∆

VV

t

V

t

V

ppm

Vt

Vt

Vt

OO

O

O

OO

O

=

−

()

()

×

01

01

0

6

10

(2)

where:

°C at time 0.

°C after 1,000 hours operation at 25°C.

Thermal Hysteresis

Thermal hysteresis is defined as the change of output voltage after

the device is cycled through temperature from +25

°C to –40°C

to +125

°C and back to +25°C. This is a typical value from a sample

of parts put through such a cycle.

VV

C

V

V

ppm

VC

V

VC

O

HYS

O

O TC

O

HYS

OO TC

O

__

_

_

=°

°

°

()

×

25

25

25

10

6

(3)

where:

°C after temperature cycle at +25°C to –40°C

to +125

°C and back to +25°C.

THEORY OF OPERATION

The ADR370 uses the band-gap concept to produce a stable,

low temperature coefficient voltage reference suitable for high

accuracy data acquisition components and systems. This device

makes use of underlying temperature characteristics of a silicon

operating region. Under this condition, all such transistors have

a –2 mV/

°C temperature coefficient (TC) and a V

extrapolated to absolute zero, 0 K, (with collector current pro-

portional to absolute temperature) approximates the silicon

band-gap voltage. By summing a voltage that has an equal and

opposite temperature coefficient of 2 mV/

°C with a V

forward biased transistor, an almost zero TC reference can be

developed. The simplified circuit diagram in Figure 1 shows how

a compensating voltage, V1, is achieved by driving two transistors

difference (

∆V

and V1 is then buffered and amplified to produce a stable reference

voltage of 2.048 V at the output.

GND

R5

R6

R4

R3

R2

R1

V1

Figure 1. Simplified Schematic

Applying the ADR370

In order to achieve the specified performance, two external

components should be used in conjunction with the ADR370,

a 4.7

µF capacitor and a 1 µF capacitor should be applied to the

input and output, respectively. Figure 2 shows the ADR370 with

both the input and output capacitors attached.

For further transient response optimization, an additional 0.1

µF

capacitor in parallel with the 4.7

µF input capacitor can be used.

A 1

µF output capacitor will provide stable performance for all

loading conditions. The ADR370 can, however, operate under

low (–100

µA < I

µA) current conditions with just a

0.2

µF output capacitor and a 1 µF input capacitor.

ADR370

GND

4.7 F

1 F

Figure 2. Typical Connection Diagram