MAX4451 查看數據表（PDF） - Maxim Integrated

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MAX4451

Ultra-Small, Low-Cost, 210MHz, Single-Supply Op Amps with Rail-to-Rail Outputs

Maxim Integrated 

Ultra-Small, Low-Cost, 210MHz, Single-Supply

Op Amps with Rail-to-Rail Outputs

Table 1. Recommended Component Values

COMPONENT

GAIN (V/V)

+1

-1

+2

-2

+5

-5

+10 -10 +25 -25

RF (Ω)

RG (Ω)

RS (Ω)

RTIN (Ω)

RTO (Ω)

Small-Signal -3dB Bandwidth (MHz)

24

500 500 500 500 500 500 500 500 1200

∞

500 500 250 124 100

56

50

20

50

—

0

—

0

—

0

—

0

—

0

49.9

56 49.9

62

49.9 100 49.9

∞

49.9

∞

49.9 49.9 49.9 49.9 49.9 49.9 49.9 49.9 49.9 49.9

210 100

95

50

25

25

11

15

5

10

Note:

RL = RO + RTO; RTIN and RTO are calculated for 50Ω applications. For 75Ω systems, RTO = 75Ω; calculate RTIN from the

following equation:

R TIN =

75 Ω

1- 75

RG

0.1µF capacitor as close to the pin as possible. If operat-

ing with dual supplies, bypass each supply with a 0.1µF

capacitor.

Maxim recommends using microstrip and stripline tech-

niques to obtain full bandwidth. To ensure that the PC

board does not degrade the amplifier’s performance,

design it for a frequency greater than 1GHz. Pay care-

ful attention to inputs and outputs to avoid large para-

sitic capacitance. Whether or not you use a constant-

impedance board, observe the following design guide-

lines:

• Don’t use wire-wrap boards; they are too inductive.

• Don’t use IC sockets; they increase parasitic capaci-

tance and inductance.

• Use surface-mount instead of through-hole compo-

nents for better high-frequency performance.

• Use a PC board with at least two layers; it should be

as free from voids as possible.

• Keep signal lines as short and as straight as possi-

ble. Do not make 90° turns; round all corners.

Rail-to-Rail Outputs,

Ground-Sensing Input

The input common-mode range extends from

(VEE - 200mV) to (VCC - 2.25V) with excellent common-

mode rejection. Beyond this range, the amplifier output

is a nonlinear function of the input, but does not under-

go phase reversal or latchup.

The output swings to within 55mV of either power-

supply rail with a 2kΩ load. The input ground sensing

and the rail-to-rail output substantially increase the

dynamic range. With a symmetric input in a single +5V

application, the input can swing 2.95VP-P and the out-

put can swing 4.9VP-P with minimal distortion.

Output Capacitive Loading and Stability

The MAX4450/MAX4451 are optimized for AC perfor-

mance. They are not designed to drive highly reactive

loads, which decrease phase margin and may produce

excessive ringing and oscillation. Figure 2 shows a cir-

cuit that eliminates this problem. Figure 3 is a graph of

the optimal isolation resistor (RS) vs. capacitive load.

Figure 4 shows how a capacitive load causes exces-

sive peaking of the amplifier’s frequency response if

the capacitor is not isolated from the amplifier by a

resistor. A small isolation resistor (usually 20Ω to 30Ω)

placed before the reactive load prevents ringing and

oscillation. At higher capacitive loads, AC performance

is controlled by the interaction of the load capacitance

and the isolation resistor. Figure 5 shows the effect of a

27Ω isolation resistor on closed-loop response.

Coaxial cable and other transmission lines are easily

driven when properly terminated at both ends with their

characteristic impedance. Driving back-terminated

transmission lines essentially eliminates the line’s

capacitance.

8 _______________________________________________________________________________________

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