AD8517 데이터 시트보기 (PDF) - Analog Devices

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AD8517

7 MHz Rail-to-Rail Low Voltage Operational Amplifiers

Analog Devices 

AD8517/AD8527

D1

؊IN

D2

R7

R8

ESD

I1

D3

ESD

R3

R4

R1 Q3 Q1 Q2 Q4 R2

D7

R5

R6

D8

D4

ESD

ESD

R9

I2

R10

VCC

Q5

؉IN

C1

Q8

Q6

I3

Q11

Q10

Q9

I4

I7

Q7

Q14

Q13

R14

I8

Q19

Q20

C4

C3

C2

Q18

R11

Q17

Q15

D16

I5

I6 R12

R13

VEE

Figure 19. Simplified Schematic

VCC

D9

VOUT

D6

VEE

Table I. Typical Battery Life Voltage Range

Battery

Lead-Acid

Lithium

NiMH

NiCd

Carbon-Zinc

Nominal

Voltage (V)

2

2.6-3.6

1.2

1.2

1.5

End of Voltage

Discharge (V)

1.8

1.7-2.4

1

1

1.1

RAIL-TO-RAIL INPUT AND OUTPUT

The AD8517 features an extraordinary rail-to-rail input and

output with supply voltages as low as 1.8 V. With the amplifier’s

supply range set to 1.8 V, the input can be set to 1.8 V p-p,

allowing the output to swing to both rails without clipping. Figure

20 shows a scope picture of both input and output taken at unity

gain, with a frequency of 1 kHz, at VS = 1.8 V and VIN = 1.8 V p-p.

VS = ؎0.9V

VIN = 1.8 V p-p

VIN

INPUT BIAS CONSIDERATION

The input bias current (IB) is a nonideal, real-life parameter that

affects all op amps. IB can generate a somewhat significant offset

voltage. This offset voltage is created by IB when flowing through

the negative feedback resistor RF. If IB is 500 nA (worst case),

and RF is 100 kΩ, the corresponding generated offset voltage is

50 mV (VOS = IB ϫ RF).

Obviously the lower RF the lower the generated voltage offset.

Using a compensation resistor, RB, as shown in Figure 21, can

significantly minimize this effect. With the input bias current mini-

mized, we still need to be aware of the input offset current (IOS)

which will generate a slight offset error. Figure 21 shows three

different configurations to minimize IB-induced offset errors.

RF

RI

VI

RB = RIԽԽRF

AD8517

VOUT

INVERTING CONFIGURATION

RF

RI

RB = RIԽԽRF AD8517

VOUT

VI

NONINVERTING CONFIGURATION

RF = RS

VOUT

TIME – 200␮s/Div

Figure 20. Rail-to-Rail Input Output

The rail-to-rail feature of the AD8517 can be observed over the

supply voltage range, 1.8 V to 5 V. Traces are shown offset for

clarity.

RS

AD8517

VOUT

VI

UNITY GAIN BUFFER

Figure 21. Input Bias Cancellation Circuits

REV. B

–9–

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