®

REF200

5

FIGURE 1. Simplified Circuit Diagram.

(Substrate)

Current

Source

(1 of 2)

4k

Ω

8X

8,7

5k

Ω

1k

Ω

1,2

6

3

54

1k

Ω

12k

Ω

Current

Mirror

APPLICATIONS INFORMATION

The three circuit sections of the REF200 are electrically

isolated from one another using a dielectrically isolated

fabrication process. A substrate connection is provided (pin

6), which is isolated from all circuitry. This pin should be

connected to a defined circuit potential to assure rated DC

performance. The preferred connection is to the most nega-

tive constant potential in your system. In most analog

systems this would be –V

S

. For best AC performance, leave

pin 6 open and leave unused sections unconnected.

Drift performance is specified by the “box method,” as

illustrated in the Current vs Temperature plot of the typical

performance curves. The upper and lower current extremes

measured over temperature define the top and bottom of the

box. The sides are determined by the specified temperature

range of the device. The drift of the unit is the slope of the

diagonal—typically 25ppm/

°C from –25°C to +85°C.

If the current sources are subjected to reverse voltage, a

protection diode may be required. A reverse voltage circuit

model of the REF200 is shown in the Reverse Current vs

Reverse Voltage curve. If reverse voltage is limited to less

than 6V or reverse current is limited to less than 350

µA, no

protection circuitry is required. A parallel diode (Figure 2a)

will protect the device by limiting the reverse voltage across

the current source to approximately 0.7V. In some applica-

tions, a series diode may be preferable (Figure 2b) because

it allows no reverse current. This will, however, reduce the

compliance voltage range by one diode drop.

Applications for the REF200 are limitless. Application Bul-

letin AB-165 shows additional REF200 circuits as well as

other related current source techniques. A collection of

circuits is shown to illustrate some techniques. Also, see

AB-165A.

FIGURE 2. Reverse Voltage Protection.

100µA

Bidirectional

Current Source

D

4

D

2

DD

3

1

D

2

D

1

100µA

100µA

NOTE: All diodes = 1N4148.

Bidirectional

Current Source

(a)

(b)

(c)

(d)