AD8609ARZ(RevC) View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

AD8609ARZ
(Rev.:RevC)

Precision Micropower, Low Noise CMOS, Rail-to-Rail Input/Output Operational Amplifiers

Analog Devices 

AD8603/AD8607/AD8609

APPLICATIONS

NO PHASE REVERSAL

The AD8603/AD8607/AD8609 do not exhibit phase inversion

even when the input voltage exceeds the maximum input

common-mode voltage. Phase reversal can cause permanent

damage to the amplifier, resulting in system lockups. The

AD8603/AD8607/AD8609 can handle voltages of up to 1 V

over the supply.

VS = ±2.5V

VIN

VIN = 6V p-p

AV = 1

RL = 10kΩ

VOUT

The use of the snubber circuit is usually recommended for unity

gain configurations. Higher gain configurations help improve

the stability of the circuit. Figure 44 shows the same output

response with the snubber in place.

VS = ±0.9V

VIN = 100mV

CL = 2nF

RL = 10kΩ

TIME (4µs/DIV)

Figure 41. No Phase Response

INPUT OVERVOLTAGE PROTECTION

If a voltage 1 V higher than the supplies is applied at either

input, the use of a limiting series resistor is recommended. If

both inputs are used, each one should be protected with a

series resistor.

To ensure good protection, the current should be limited to a

maximum of 5 mA. The value of the limiting resistor can be

determined from the following equation:

(VIN − VS)/(RS + 200 Ω) ≤ 5 mA

DRIVING CAPACITIVE LOADS

The AD8603/AD8607/AD8609 are capable of driving large

capacitive loads without oscillating. Figure 42 shows the output

of the AD8603/AD8607/AD8609 in response to a 100 mV input

signal, with a 2 nF capacitive load.

Although it is configured in positive unity gain (the worst case),

the AD8603 shows less than 20% overshoot. Simple additional

circuitry can eliminate ringing and overshoot.

One technique is the snubber network, which consists of a

series RC and a resistive load (see Figure 43). With the snubber

in place, the AD8603/AD8607/AD8609 are capable of driving

capacitive loads of 2 nF with no ringing and less than 3%

overshoot.

Figure 42. Output Response to a 2 nF Capacitive Load, Without Snubber

VEE

V–

V+

RS

+

150Ω

CL

200mV –

VCC

CS

47pF

Figure 43. Snubber Network

VSY = ±0.9V

VIN = 100mV

CL = 2nF

RL = 10kΩ

RS = 150Ω

CS = 470pF

Figure 44. Output Response to a 2 nF Capacitive Load with Snubber

Optimum values for RS and CS are determined empirically;

Table 5 lists a few starting values.

Table 5. Optimum Values for the Snubber Network

CL (pF)

RS (Ω)

CS (pF)

100 to ~500

500

680

1500

100

330

1600 to ~2000

400

100

Rev. C | Page 12 of 16

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