ADR280ART-REEL(RevA) Просмотр технического описания (PDF) - Analog Devices

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ADR280ART-REEL
(Rev.:RevA)

1.2 V Ultralow Power High PSRR Voltage Reference

Analog Devices 

ADR280

The ADR280 provides the core 1.2 V band gap voltage and is

able to drive a maximum load of only 100 µA. Users can simply

buffer the output for high current or sink/source current applica-

tions, such as ADC or LCD driver references (see Figure 5).

0.1F

U1

V+

ADR280

V–

U2

VOUT

VOUT

0.1F

U2 = AD8541, SC70

AD8601, SOT-23-5

Figure 5. Buffered Output

Users can also tailor any specific need for voltage and dynamics

with an external op amp and discrete components (see Figure 5).

Depending on the specific op amp and PCB layout, it may be

necessary to add a compensation capacitor, C2, to prevent gain

peaking and oscillation. The exact value of C2 needed requires

some trial and error but usually falls in the range of a few pF.

U1

5V

V+

ADR280

5V

V–

VO

1.8V

R2

60k 0.1%

U2 V+

AD8541

V–

C2

2.2pF

1.2V

VOUT

C1

0.1F

R1

120k 0.1%

Figure 6. 1.8 V Reference

LOW COST, LOW POWER CURRENT SOURCE

Because of its low power characteristics, the ADR280 can be

converted to a current source with just a setting resistor. In addi-

tion to the ADR280 current capability, the supply voltage and the

load limit the maximum current. The circuit in Figure 7 produces

100 µA with 2 V compliance at 5 V supply. The load current is

the sum of ISET and IGND. IGND will increase slightly with load; an

RSET of 13.6 k yields 100 µA of load current.

U1

5V

V+

ADR280

V–

ISET

+

RSET

1.2V

–

C1

13.6k

VOUT

0.1F

RL 1k IL

100A

IGND

IL = ISET + IGND

Precision Low Power Current Source

By adding a buffer to redirect the IGND in Figure 8, a current can

be precisely set by RSET with the equation IL = 1.2 V/RSET.

U1

5V

V+

ADR280

V–

VOUT

C2 0.1F

RSET 12k

5V

V+ U2

AD8541

V–

RL 1k IL

100A

IL = 1.2V/RSET

Figure 8. Precision Low Power Current Source

Boosted Current Source

Adding one more buffer to the previous circuit boosts the current

to the level that is limited only by the buffer U2 current handling

capability (see Figure 9).

RSET

230

RL

500

U1

5V

V+

ADR280

V–

5V

U2

V+

VOUT

V–

C1 0.1F

+

1.2V

–

IL

5mA

5V

U3

V+

V–

IL = 1.2V/RSET

U2 = U3 = AD8542, AD822

Figure 9. Precision Current Source

Figure 7. Low Cost Current Source

REV. A

–5–

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