MAX7462 데이터 시트보기 (PDF) - Maxim Integrated

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MAX7462

Single-Channel Video Reconstruction Filters and Buffers

Maxim Integrated 

Single-Channel Video Reconstruction Filters

and Buffers

Pin Description

PIN

MAX7462 MAX7463

1

1

NAME

IN

FUNCTION

Video Input. AC-couple IN with a series 0.1µF capacitor.

2

—

GAIN Gain Control Input. Connect GAIN to GND for a gain of +6dB (+2V/V). Connect GAIN to VCC

for a gain of +9.5dB (+3V/V).

3, 4, 5

—

3

2, 4, 5, 6

GND

N.C.

Ground

No Connection. Not internally connected. Connect to GND for better performance.

6

—

DISABLE Disable Input. Connect to VCC to enable the output buffer (normal operation). Connect to GND

to put the output buffer in a high-impedance state.

7

7

VCC +5V Supply Input

8

8

OUT

Buffer Output. This output can be either AC- or DC-coupled. Use at minimum a 220µF

capacitor for AC-coupled loads.

Detailed Description

The MAX7462/MAX7463 filters and buffers the analog

CVBS video outputs of DAC video-encoders in applica-

tions such as set-top boxes, hard-disk recorders, DVD

players, and digital VCRs. The MAX7462/MAX7463 con-

sist of a lowpass filter and an output video buffer that can

drive two standard 150Ω video loads. These devices

operate from a single +5V supply and have a bandwidth

optimized for interlaced NTSC, PAL, and SDTV.

Filter

The reconstruction filter is a 4th-order Butterworth-type

response that features a maximally flat passband for

NTSC and PAL bandwidths. The stopband attenuation

is optimized for a video-encoder DAC sampling fre-

quency of 27MHz (see the Typical Operating

Characteristics).

Output Buffer

The output buffer can drive two 150Ω video loads with

a 2VP-P signal. For the MAX7462, the output buffer gain

is selectable between +6dB and +9.5dB by using GAIN

(see Table 1). The MAX7463 has a fixed gain of +6dB.

The MAX7462/MAX7463 can drive an AC load or drive

the video load directly without using a large output

Table 1. Gain Setting Control (MAX7462)

GAIN

GND

VCC

BUFFER GAIN (dB)

+6

+9.5

capacitor. The output buffer can drive DC loads while

maintaining an output blanking level of less than 1V. The

blanking level allows the MAX7462/MAX7463 to meet the

digital TV interface specifications for DC coupling.

Applications Information

Input Considerations

Use a 0.1µF ceramic capacitor to AC-couple the input.

The input capacitor stores a DC voltage so that the out-

put is clamped to the appropriate DC voltage level.

Output Considerations

The outputs are typically connected to a 75Ω series

back-match resistor followed by the video cable.

Because of the inherent divide-by-two of this configura-

tion, the blanking level on the video cable is always

less than 1V, complying with industry-standard video

requirements such as the digital TV standard (which

allows up to 1VDC on the video cable) and the

European SCART standard (which allows up to 2VDC

on the video cable). The video buffer can also drive an

AC-coupled video load. Good video performance is

achieved with an output capacitor as low as 220µF.

Power-Supply Bypassing and Layout

The MAX7462/MAX7463 operate from a single +5V

supply. Bypass VCC to GND with a 0.1µF capacitor. In

addition, it is sometimes advantageous to connect a

10µF capacitor within the general vicinity of the video

circuitry. Place all other external components as close

to the device as possible.

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