ML6427CS datasheet(6/16 Pages) MICRO-LINEAR

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ML6427

FUNCTIONAL DESCRIPTION

The ML6427 is a quad monolithic continuous time analog

video filter designed for reconstructing signals from four

video D/A sources. The ML6427 is intended for use in AC

coupled input and output applications.

The filters approximate a 4th-order Butterworth

characteristic with an optimization toward low overshoot

and flat group delay. All outputs are capable of driving

2VP-P into AC coupled 150W video loads with up to 35pF

of load capacitance at the output pin. They are also

capable of driving a 75

W load at 1VP-P.

All channels are clamped during sync to establish the

appropriate output voltage swing range. Consequently the

input coupling capacitors do not behave according to the

conventional RC time constant. Clamping for all channels

settles within 10ms of a change in video sources.

Input coupling capacitors of 0.1µF are recommended for

all channels. During sync a feedback error amplifier

sources/sinks current to restore the DC level. The net result

is that the average input current is zero. Any change in the

value of the input coupling capacitors will linearly affect

the clamp response times.

The RGB channels have no pulldown current sources and

are essentially tilt-free. The inputs of the CV channels sink

less than 1µA during active video, resulting in a tilt of less

than 1mV for 220µF output capacitors. A 1000µF

capacitor is recommended for TV applications to minimize

tilt in the CV channels.

SWAP MULTIPLEXER CONTROL

Output pins CVOUT1/YOUTA and CVOUT2/YOUTB are each

independently selectable among three input sources

(CVINU/Y1, CVINFA/Y2, or CVINFB/Y3) depending on the

state of digital inputs SWAP CVF, SWAP CVU, and A/B

MUX. This allows the two outputs to remain independent

and pass straight through, or to remain independent but

swapped, or for both outputs to have the same signal

sourcing from either CVINU/Y1, CVINFA/Y2, or CVINFB/Y3

(See Table 1). If SWAP CVF is forced to logic low then

CVOUT2/YOUTB is sourced from either the CVINFA/Y2 OR

THE CVINFB/Y3 input. If SWAP CVU is logic low then

CVOUT1/YOUTA provides video from either the CVINFA/Y2

OR THE CVINFB/Y3 input. If SWAP CVF is logic high then

CVOUT2/YOUTB provides video from the CVINU/Y1 input.

If SWAP CVU is high then CVOUT1/YOUTA provides video

from either the CVINFA/Y2 or the CVINFB/Y3 input. Both

SWAP CVF and SWAP CVU will pull low if they are not

driven.

The ML6427 is robust and stable under all stated load and

input conditions. Bypassing both VCC pins directly to

ground ensures this performance. Two ML6427s can be

connected in a master-slave sync configuration. When

using this configuration (See Figure 6) only the “master”

ML6427 is required to have a signal with embedded sync

present on the CVINFA/Y2 and CVINFB/Y3 inputs. In the

absence of sync on the CVINFA/Y2 and CVINFB/Y3 inputs

of the “slave” ML6427 it will have its SYNCIN input

connected to the SYNCOUT output of the “master”

ML6427.

SYNCIN AND SYNCOUT PINS

Each ML6427 has two sync detectors which control the

DC restore functions. The unfiltered channel has its own

detector, which controls the DC restore function during

the horizontal sync period of the CVINU/Y1 input. The

other sync detector controls the DC restore functions for

the filtered channels based upon the composite or luma

silgnal at the CVINFA/Y2 or CVINFB/Y3 input.

Required Setup: A composite or luma or green signal

must be present on CVINFA/Y2 or CVINFB/Y3 inputs to

provide necessary sync signals to other channels (R, G, B,

Y, C). Otherwise, sync must be provided at the SYNCIN

pin. For RGB applications the green channel with sync can

be used as an input to CVINFA/Y2 or CVINFB/Y3.

The SYNCOUT pin provides a logic high when it detects

the horizontal sync of either the CVINFA/Y2 or CVINFB/Y3

input (note that one input is selected by the A/B MUX pin).

The SYNCIN pin is an input for an external H-sync logic

signal to enable or disable the internal DC restore loop for

the filtered channels. When SYNCIN is logic high the DC

restore function is enabled.

For normal operation the SYNCOUT pin is connected to

the SYNCIN pin (see Figure 4). If neither the CVINFA/Y2

nor the CVINFB/Y3 has an embedded sync an external

sync can be applied on the SYNCIN pin. In master-slave

configurations the SYNCOUT of a ML6427 master can be

used as the SYNCIN of a ML6427 slave (see Figure 6).

VIDEO I/O DESCRIPTION

Each input is driven by either a low impedance source or

the output of a 75

W terminated line. The input is required

to be AC coupled via a 0.1µF coupling capacitor which

gives a nominal clamping time of 10ms. All outputs are

capable of driving an AC coupled 150

W load at 2VP-P or

1VP-P into a 75W load. At the output pin, up to 35pF of

load capacitance can be driven without stability or slew

issues. A 220µF AC coupling capacitor is recommended at

the output to reduce power consumption. For DC coupled

outputs see the Typical Applications section.

ANALOG MULTIPLEXER CONTROL

The four filter channels each have two input multiplexers

which are paired to select between two four-channel

video sources (

i.e., composite video plus RGB component

video). If A/B MUX is forced to logic high, it will select

Bank<A> of the video inputs (CVINFA/Y2, RINA/Y4, GINA/

Y6, BINA/C1) to be enabled. If A/B MUX is logic low then

Bank<B> of video inputs (CVINFB/Y3, RINB/Y5,GINB/Y7,

BINFB/C2) will be selected. If the A/B MUX is open it will

pull to logic high.

ML6427CS Datasheet(PDF) 6 Page - Micro Linear Corporation

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