Features: Three selectable 6th order 8/32MHz (SD/HD) filters Three fixed sixth order 8MHz (SD) filters Transparent input clamp Single video loading driver (2VPP, 150Ω , AV=6dB) AC or DC Coupled Input AC or DC Coupled Output DC Coupled Output Eliminates AC Coupling Capacitors Low Power Only 5V Reliable (12KV HBM) Output ESD Protection Lead Free Package - TSSOP-20

Application: Cable and Satellite Set-Top Box DVD Player HDTV Personal Video Recorder Video on Demand (VOD)

Description: Intended to use the FMS6346 Low Cost Video Filter (LCVF) to replace passive lc filter and driver integration devices at low cost. Sixth-order Butterworth filters have better image quality resolution than typical passive filters. The combination of low-power standard definition (SD) and high definition (HD) filters greatly simplifies DVD video output circuitry. Three channels offer fixed SDfi lters, while the other three can choose between SD and HD filters. The FMS6346 provides a fixed gain of 6dB. The FMS6346 can output directly from a DC-coupled DAC or an AC-coupled signal. Internal Diode Clamping and Biasing Circuits are available if AC-coupled inputs are desired (see the Applications section for details). The output can drive AC or DC coupled single (150Ω) video loading. The DC-coupled output eliminates the need for output coupling capacitors. The input DC level is the output with an offset approximately equal to +280MV.

Application Information Functionality: The FMS6346 Low Cost Video Filter (LCVF) provides 6dB of gain from input to output. Also, the input is slightly offset to optimize output driver performance. The offset reaches the minimum required to reduce the continuous DC current into the load. typical voltage levels.

The FMS6346 provides an internal diode clamp to support AC-coupled input signals. If the input signal is not below ground, the input clamp does not work. This allows the DAC output to directly drive the FMS6346 AC coupling capacitor. Worst case due to clamp sync tip compression does not exceed 7 mV. The input level set by the clamp, combined with the internal DC offset, keeps the output within an acceptable range. when? The input is AC coupled, and the diode clamp sets the sync terminal (or lowest voltage) just 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 plus a pull-up resistor DC input voltage. The DAC output can also drive these same signals without AC coupling capacitors. The concept of input clamp circuit.

For a DC-coupled DAC driver with a DC-coupled output, use the configuration as shown

If the average DC output level of the DAC causes the signal to exceed the 0V to 1.4V range, it can act as shown.

When switched by an unknown external source or scart with its own clamping circuit, the inputs should be AC coupled as shown.

The same method can be used with the addition of a pull-up resistor to ensure that the clamp does not operate. The internal pull-down resistor is 800kΩ 0%, so the external resistor should be 7.5MΩ for a DC level of 500mV. If the pull-up resistance is less than the required 7.5MΩ, an external pull-down can be added to set the DC input level to 500mV.

NOTE: Video skew or line time distortion is primarily caused by AC coupling capacitors. This value may need to be increased above 220µF in some applications. Power consumption When calculating the total power consumption, the FMS6346 output driver configuration must be considered. 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 FMS6346: tj=ta+pdθja where PD=pch1+pch2+pchx and pchx=vsICH-(VO2)/right rear) VO=2vin+0.280vch=( icc/6) + (vo/rl)vin = rms value of input signal CC = 60 mA vs = 5 volts = channel load resistors Board layout affects thermal characteristics. For more information, see the "Layout Considerations" section. Layout Considerations General layout and power supply bypass performance and thermal characteristics at high frequency. Fairchild provides a demo board, a FMS6346 demo, to guide the layout and to aid in device testing and characterization. The FMS6346DEMO is a four-layer board with a complete power and ground plane. Following this layout configuration provides the best performance and thermal characteristics. For best results, follow these steps High Frequency Layout Basis: Include 10µf and 0.1µf ceramic bypass capacitors Place 10µF capacitors on power pins Place 0.1µf capacitors on power pins For multilayer boards, use a large ground plane to help dissent For double-layer boards, use a ground plane that extends at least 0.5 inches 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 offer slightly lower power consumption.