MAX3509 데이터 시트보기 (PDF) - Maxim Integrated

부품명

상세내역

제조사

MAX3509

Upstream CATV Amplifier

Maxim Integrated 

Upstream CATV Amplifier

Applications Information

Transformer

To maintain rated performance into a 75Ω load, a 1:1

impedance ratio output transformer with adequate

bandwidth is required. A step-up transformer with a

1:1.5 impedance ratio will increase gain and output

voltage swing nominally by 1.7dB, but output noise per-

formance will increase by the same amount.

Input Circuit

To achieve rated performance, the input of the

MAX3509 must be driven differentially with 34dBmV or

lower input level. The MAX3509 can be driven from a

single-ended source. A slight degradation in even-

order distortion at a 10W output level will result. The dif-

ferential input impedance is approximately 1.2kΩ.

Most applications require a differential lowpass filter

preceding the MAX3509. The filter design dictates a

terminating resistance of a specified value. Place this

resistance across the AC-coupled inputs (see Typical

Operating Circuit).

The MAX3509 has sufficient gain to produce an output

level of 66dBmV when driven with a 34dBmV input sig-

nal. Rated performance is achieved with this input

level. When a lower input level is present, the maximum

output level will be reduced proportionally and output

linearity will improve. If an input level greater than

34dBmV is used, distortion performance degrades.

If a single-ended source drives the MAX3509, one of the

input terminals must be capacitively coupled to ground

(IN+ or IN-). The value of this capacitor must be large

enough to look like a short circuit at the lowest frequen-

cy of interest. For operation at 5MHz with a 50Ω source

impedance, a value of 0.1µF will suffice.

A typical model for the MAX3509 input impedance is

shown in Figure 3.

Layout Issues

A well-designed PC board is an essential part of an RF

circuit. For best performance, pay attention to power-

supply layout issues, as well as the output circuit layout.

Exposed Paddle Thermal Considerations

The exposed paddle (EP) of the MAX3509’s 20-pin

TSSOP-EP package provides a low thermal resistance

path to the die. It is important that the PC board on

which the MAX3509 is mounted be designed to con-

duct heat from this contact. In addition, the EP should

be provided with a low inductance path to electrical

ground.

It is recommended that the EP be soldered to a ground

plane on the PC board, either directly or through an

array of plated via holes.

Output Circuit Layout

The differential implementation of the MAX3509’s out-

put has the benefit of reducing even-order distortion,

the most significant of which is second-harmonic distor-

tion. The degree of distortion cancellation depends on

the amplitude and phase balance of the overall circuit.

It is important that the traces that lead from the output

pins be the same length.

Power-Supply Layout

To achieve minimal coupling between different sections

of the IC, the ideal power-supply layout is a star config-

uration. This configuration has a large-value decoupling

capacitor at the central power-supply node. The power-

supply traces branch out from this node, each going to

a separate power-supply node in the MAX3509 circuit.

At the end of each of these traces is a decoupling

capacitor that provides a very low impedance at the

frequency of interest. This arrangement provides local

power-supply decoupling at each power-supply pin.

The power-supply traces must be made as thick as

practical to keep resistance well below 1Ω.

Ground inductance degrades distortion performance.

Therefore, ground plane connections to GND, GND1,

and GND2 should be made with multiple vias if possi-

ble.

IN+

2.5kΩ

1.9pF

IN-

Figure 3. Typical Equivalent Input Circuit

Chip Information

TRANSISTOR COUNT: 1085

_______________________________________________________________________________________________________ 9

Share Link: