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TMC3033 Datasheet(PDF) 2 Page - Fairchild Semiconductor |
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TMC3033 Datasheet(HTML) 2 Page - Fairchild Semiconductor |
2 / 12 page TMC3033 PRODUCT SPECIFICATION 2 Functional Description The TMC3033 is a low-cost triple 10-bit CMOS D/A converter designed to directly drive computer CRT displays and video transmission lines at pixel rates of up to 80 Msps. It comprises three identical 10-bit D/A converters with registered data inputs, common clock, and internal voltage reference. An independent current source allows sync to be added to the green D/A converter output. Digital Inputs All digital inputs are TTL-compatible. Data are registered on the rising edge of the CLK signal. The analog output changes tDO after the rising edge of CLK. There is one stage of pipeline delay on the chip. The guaranteed clock rates of the TMC3033 are 80, 50, and 30 MHz. SYNC and BLANK SYNC and BLANK inputs control the output level (Figure 1 and Table 1) of the D/A converters during CRT retrace intervals. BLANK forces the D/A outputs to the blanking level while SYNC turns off a separate current source which is connected to the green D/A converter. This connection adds a 40 IRE sync pulse to the D/A output and brings that D/A output to 0.0 Volts during the sync tip. SYNC and BLANK are registered on the rising edge of CLK. BLANK gates the D/A inputs and sets the pedestal voltage. If BLANK = HIGH, the D/A inputs are added to a pedestal which offsets the current output. If BLANK = LOW, data inputs and the pedestal are disabled. Figure 1. Nominal Output Levels data: 660 mV max. 65-3003-02 pedestal: 54 mV sync: 286 mV D/A Outputs Each D/A output is a current source. To obtain a voltage out- put a resistor must be connected to ground. Output voltage of the D/A converters depends upon this resistor, the reference voltage, and the value of the gain-setting resistor connected between RREF and GND. Normally, a source termination resistor of 75 Ohms is con- nected between the D/A current output pin and GND near the D/A converter. A 75 Ohm coaxial cable may then be con- nected with another 75 Ohm termination resistor at the far end of the cable. This “double termination” presents the D/A converter with a net resistive load of 37.5 Ohms. The TMC3033 may also be operated with a single 75 Ohm terminating resistor. To lower the output voltage swing to the desired range, the value of the resistor on RREF should be increased. Voltage Reference The TMC3033 has an internal bandgap voltage reference of +1.235 Volts. An external voltage reference may be connected to the VREF pin, overriding the internal voltage reference. All three D/A converters are driven from the same reference. A 0.1 µF capacitor must be connected between the COMP pin and VDD to stabilize internal bias circuitry and ensure low-noise operation. Power and Ground The TMC3033 D/A converter requires a single +3.3 Volt power supply. The analog (VDD) power supply voltage should be decoupled to GND to reduce power supply induced noise. 0.1 µF decoupling capacitors should be placed as close as possible to the power pins. The high slew-rate of digital data makes capacitive coupling to the outputs of any D/A converter a potential problem. Since the digital signals contain high-frequency components of the CLK signal, as well as the video output signal, the resulting data feedthrough often looks like harmonic distor- tion or reduced signal-to-noise performance. All ground pins should be connected to a common solid ground plane for best performance. |
Número de pieza similar - TMC3033 |
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Descripción similar - TMC3033 |
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