REF01/REF02/REF03

Rev. K | Page 14 of 20

THEORY OF OPERATION

REF01, REF02, and REF03 are high precision, low drift 10.0 V,

5.0 V, and 2.5 V voltage references available in a variety of

packages. These devices are standard band gap references (see

Figure 33). The band gap cell contains two NPN transistors

(Q18 and Q19) that differ in emitter area by a factor of 2. The

proportional-to-absolute temperature current (PTAT) through

With an internal op amp and the feedback network created by

laser trimming of various resistors and other proprietary circuit

techniques are used to further enhance the initial accuracy,

temperature curvature, and drift performance of the device.

The PTAT voltage is brought out directly from the band gap,

unbuffered, at the TEMP pin. Since this voltage output has a

stable 1.96 mV/°C temperature coefficient, users can estimate

the temperature change of the device by simply monitoring the

change in voltage at this pin.

R1

R2

R3

R4

Q23

Q1

Q2

Q7

Q8

Q9

Q3

Q10

D1

D2

Q4

D3

C1

R13

Q12

Q13

R5

I1

R12

Q14 Q15

2×

1×

R20

TRIM

Q18

TEMP

R27

Q19

Q16

Q17

Q20

R6

R42

R41

R24

R32

R11

R17

R14

GND

Figure 33. REF0x Simplified Schematic

INPUT AND OUTPUT CAPACITORS

Figure 34 shows the basic input/output capacitor configuration

for the REF0x series of references.

U1

REF01/

REF02/

REF03

C2

0.1µF

C1

0.1µF

TEMP TRIM

GND

Figure 34. Basic REF0x Capacitor Configuration

While the REF0x series of references are designed to function

stably without any external components, connecting a 0.1 μF

ceramic capacitor to the output is highly recommended to

improve stability and filter out low level voltage noise. An

additional 1 μF to 10 μF electrolytic, tantalum, or ceramic

capacitor can be added in parallel to improve transient perfor-

mance in response to sudden changes in load current; however,

the designer should keep in mind that doing so increases the

turn-on time of the device.

A 1 μF to 10 μF electrolytic, tantalum, or ceramic capacitor

can also be connected to the input to improve transient

response in applications where the supply voltage may fluctuate.

An additional 0.1 μF ceramic capacitor should be connected in

parallel to reduce supply noise.

Both input and output capacitors should be mounted as close to

the device pins as possible.

OUTPUT ADJUSTMENT

The REF0x trim terminal can be used to adjust the output

up or down from the internally trimmed, nominal output

voltage. This feature allows the system designer to trim out

system errors due to changes in line and load conditions,

thermal hysteresis, output offset due to solder reflow, or other

error sources. The basic trim circuit configuration is shown

in Figure 35.

Table 7 also lists the range of output voltages obtainable from

each model in this configuration.

U1

REF01/

REF02/

REF03

TEMP TRIM

GND

POT

10k

Ω

R2

1k

Ω

R1

470k

Ω

Figure 35. Optional Trim Adjustment Circuit

Table 7. Adjustment Range Using Trim Circuit

Model

REF01

9.70 V

10.05 V

REF02

4.95 V

5.02 V

REF03

2.3 V

2.8 V

Adjustment of the output does not significantly affect the

temperature performance of the reference itself, provided the

temperature coefficients of the resistors used are low.