FMS3810/3815

PRODUCT SPECIFICATION

2

REV. 1.08 12/21/00

Functional Description

Within the FMS3810/3815 are three identical 10-bit D/A

converters, each with a current source output. External loads

are required to convert the current to voltage outputs. Data

signals.

Digital Inputs

All digital inputs are TTL-compatible. Data is registered on

the rising edge of the CLK signal. Following one stage of

edge of CLK.

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 = L turns off a current source that is

connected to the green D/A converter. SYNC = H adds a 40

IRE sync pulse to the green output, SYNC = L sets the green

output to 0.0 Volts during the sync tip. SYNC and BLANK

are registered on the rising edge of CLK.

Figure 1. Nominal Output Levels

BLANK gates the D/A inputs and sets the pedestal voltage.

If BLANK = H, the D/A inputs are added to a pedestal which

offsets the current output. If BLANK = L, data inputs and the

pedestal are disabled.

D/A Outputs

Each D/A output is a current source. To obtain a voltage

output, a resistor must be connected to ground. Output

voltage depends upon this external resistor, the reference

voltage, and the value of the gain-setting resistor connected

Normally, a source termination resistor of 75 Ohms is

connected between the D/A current output pin and GND

near the D/A converter. A 75 Ohm line may then be

connected 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 FMS3810/3815 may also be operated with a single 75

Ohm terminating resistor. To lower the output voltage swing

to the desired range, the nominal value of the resistor on

Voltage Reference

All three D/A converters are supplied with a common

voltage reference. Internal bandgap voltage reference voltage

is +1.235 Volts with a 3K

Ω source resistance. An external

overriding the internal voltage reference.

A 0.1µF capacitor must be connected between the COMP

low-noise operation.

Power and Ground

Required power is a single +5.0 Volt supply. To minimize

power supply induced noise, analog +5V should be

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 distortion or

reduced signal-to-noise performance. All ground pins should

be connected to a common solid ground plane for best

performance.

data: 660 mV max.

pedestal: 54 mV

sync: 286 mV