MAX4326 Просмотр технического описания (PDF) - Maxim Integrated

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MAX4326

Single/Dual/Quad, Low-Cost, UCSP/SOT23, Low-Power, Rail-to-Rail I/O Op Amps

Maxim Integrated 

Single/Dual/Quad, Low-Cost, UCSP/SOT23,

Low-Power, Rail-to-Rail I/O Op Amps

__________ Applications Information

Rail-to-Rail Input Stage

Devices in the MAX4322/MAX4323/MAX4326/MAX4327/

MAX4329 family of high-speed amplifiers have rail-to-

rail input and output stages designed for low-voltage,

single-supply operation. The input stage consists of

separate NPN and PNP differential stages, which com-

bine to provide an input common-mode range extend-

ing to the supply rails. The PNP stage is active for input

voltages close to the negative rail, and the NPN stage

is active for input voltages near the positive rail. The

input offset voltage is typically below 250µV. The

switchover transition region, which occurs near VCC/2,

has been extended to minimize the slight degradation in

CMRR caused by the mismatch of the input pairs. Their

low offset voltage, high bandwidth, and rail-to-rail

common-mode range make these op amps excellent

choices for precision, low-voltage, data-acquisition

systems.

Since the input stage switches between the NPN and

PNP pairs, the input bias current changes polarity as

the input voltage passes through the transition region.

To reduce the offset error caused by input bias cur-

rents flowing through external source impedances,

match the effective impedance seen by each input

(Figures 1a, 1b). High-source impedances, together

with the input capacitance, can create a parasitic pole

that produces an underdamped signal response.

Reducing the input impedance or placing a small (2pF

to 10pF) capacitor across the feedback resistor

improves the response.

The MAX4322/MAX4323/MAX4326/MAX4327/MAX4329s’

inputs are protected from large differential input voltages

by 1kΩ series resistors and back-to-back triple diodes

across the inputs (Figure 2). For differential input volt-

ages less than 1.8V, the input resistance is typically

500kΩ. For differential input voltages greater than 1.8V,

the input resistance is approximately 2kΩ, and the input

bias current is determined by the following equation:

R3

MAX4322/MAX4323

MAX4326/MAX4327

MAX4329

R1

R2

R3 = R1 R2

Figure 1a. Reducing Offset Error Due to Bias Current

(Noninverting)

1kΩ

R3

MAX4322/MAX4323

MAX4326/MAX4327

MAX4329

R1

R2

R3 = R1 R2

Figure 1b. Reducing Offset Error Due to Bias Current

(Inverting)

1kΩ

Figure 2. Input Protection Circuit

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