feature

Three selectable sixth-order 8/15MHz (SD/PS) filters

Three fixed sixth-order 8MHz (SD) filters

Transparent input clamping

Single video loading driver (2Vpp, 150Ω, AV=6dB)

AC or DC coupled input

AC or DC coupled output

DC-coupled output eliminates AC-coupling capacitance

low power

5V only

Robust (12kV HBM) output ESD protection

Lead Free Packaging - TSSOP-20

application

Cable and Satellite Set-Top Boxes, DVD Players, HDTVs, Personal Video Recorders (PVR), Video on Demand (VOD)

illustrate

The FMS6246 Low Cost Video Filter (LCVF) is designed to replace passive LC filter and driver devices with low cost integrated circuits. Six 6th order Butterworth filters provide improved image quality compared to typical passive solutions. Combining low-power standard definition (SD) and progressive scan (PS) filters greatly simplifies DVD video output circuitry. Three channels offer fixed SD filters, while the other three are selectable between SD and PS filters. The FMS6246 provides a fixed gain of 6dB. There is a metal option that provides fixed gain for more flexibility. The FMS6246 can be driven directly by a DC-coupled DAC output or an AC-coupled signal. If an AC-coupled input is required, an internal diode clip and bias circuit can be used (see the Applications section for details). The outputs can drive AC or DC coupled single (150Ω) video loads. The DC-coupled output eliminates the need for output coupling capacitors. The input DC level will be offset by about +280MV at the output.

DC characteristics

Tc=25 degrees Celsius, Vcc=5V, Rsource=37.5 ohms, input AC coupling 0.1 microF, all outputs AC coupling 220 microF

150Ω load, referenced to 400kHz; unless otherwise noted.

Standard Defines Electrical Characteristics

Tc=25 degrees Celsius, Vin=1Vpp, Vcc=5V, Rsource=37.5 ohms, all inputs AC coupling 0.1 microF, all outputs AC coupling

Convert 220µF into a 150Ω load, referenced to 400kHz; unless otherwise noted.

Progressive Scan Electrical Characteristics

Tc=25 degrees Celsius, Vin=1Vpp, Vcc=5V, Rsource=37.5 ohms, FcSEL=0, all inputs AC coupling 0.1 microF, all outputs AC

Coupled to 220µF into a 150Ω load, referenced to 400kHz; unless otherwise noted.

notes:

1. 100% test at 25℃

2. Signal-to-noise ratio = 20*log (714mV/rms noise)

Typical performance characteristics

Tc=25 degrees Celsius, Vin=1Vpp, VCC=5V, Rsource=37.5 ohms, input AC coupling 0.1 microF, all outputs AC coupling

220µF into 150Ω load; unless otherwise noted

Application Information Function Description

The FMS6246 Low Cost Video Filter (LCVF) provides 6dB gain (9dB optional, contact factory for more information) from input and output. Also, the input will be offset slightly to optimize output driver performance. Keeping the offset at a minimum reduces the continuous DC current to load. Typical voltage levels are shown in the figure below.

The FMS6246 provides an internal diode clamp to support coupled input signals. If the input signal is not below ground, the input clamp will not work. This allows the DAC output to drive the FMS6246 directly without the need for AC coupling capacitors. Since the clamp must not exceed 7mV. The input level set by the clamp combined with the internal DC offset will keep the output within its acceptable range. When the input is AC coupled, the diode clamp sets the sync tip (or lowest voltage) below ground. For symmetrical signals such as C, U, V, Cb, Cr, Pb, and Pr, the average DC bias is fairly constant, and the input can be AC coupled plus a pull-up resistor to set the DC input voltage. The DAC output can also drive these same signals without the need for AC coupling capacitors. The conceptual diagram circuit of the input clamp is shown in the following figure:

The same method can also be used to bias the signal with a pull-up resistor to ensure that the clamp never works. The internal pull-down resistor is 800kΩ±20%, so the external resistor should be 7.5MΩ to set the DC level to 500mV. If a pull-up resistor smaller than 7.5MΩ is required, a pull-down menu can be added externally to set the DC input level to 500mV.

NOTE: Video skew or line time distortion will be caused by AC coupling capacitors. The value may need to be increased by more than 220µF for satisfactory operation in some applications.

Power consumption

The FMS6246 output driver configuration must be considered when calculating the total power consumption. Care must be taken not to exceed the maximum die junction temperature. The following example can be used to calculate the power dissipation and internal temperature rise of the FMS6246.

Tj Company

=Tantalum+Palladium•ΘJA where Pd=PCH1+PCH2+PCHx and PCHx=Vs•ICH-(VO2/RL)VO=2Vin+0.280VICH=(ICC/6)+(VO/RL)Vin=input signal rms value ICC = 60 mA Vs = 5 volts RL = channel load resistance Board layout also affects thermal characteristics.

Layout Considerations

The general floor plan and supply bypass play an important role in high-rise building frequency performance and thermal characteristics. Fairchild provides a demo board, the FMS6246DEMO, for use as a guide for device testing and characterization. The FMS6246DEMO is a 4-layer full power board and ground. Following this layout configuration will provide the best performance and thermal characteristics. For best results, follow these steps as the basis for a high frequency layout:

10µF and 0.1µF ceramic bypass capacitors included

Place 10µF capacitors within 0.75" of the power pins

Place 0.1µF capacitors within 0.1" of the power pins

For multi-layer boards, use a large ground plane to help dissipate heat

For 2-layer boards, use at least 0.5" beyond the device

Minimize all trace lengths to reduce series inductance

Typical application diagram

The following circuit can be used to drive a DAC directly DC-coupled with an output voltage range of 0V to 1.4V. AC-coupled or DC-coupled outputs can be used with AC-coupled outputs that provide slightly lower power consumption.