FAQ - Digital to Analog Converters (DAC)

Q: I would like to use the RDA012M4 die in our project, what are its dimensions?

A: The RDA012M4 die size is 182x199 mils or aprox 5000x4600 µm. Worthy of note is the pad distribution; it has staggered pads in a two row configuration.

Q: What interface should I use when connecting the RDA012M4 (RDA012M4MS) to a FPGA?

A: Although the RDA012M4’s input buffers can accept signals with 3.3V swing, at high clock frequencies (300MHz when operating at 1.2GHz) a smaller swing is preferred. With 1.5V swing and 0.75V termination voltage, the HSTLI standard is a perfect match for the RDA012M4 data input signals.

Q: How much current does the RDA012M4 use?

A: The typical values will be:

ICC = 0.15A @ 3.3V = 0.50W
IEEA = 0.10A @ -5.2V = 0.52W
IEED = 0.45A @ -5.2V = 2.34W

Q: What code should I use to get a differential output of 0V?

A: With a differential output, the 0V crossing lies between code 7FFh and 800h, which means that it will be a difference of 1/2 LSB from the DAC output and 0V. With both single end outputs having a 600mV swing, 1/2 LSB will be 0.147mV.

Q: Does the RDA012M4/MS need a heatsink?

A: The RDA012M4 dissipates the heat through the metal pad at the bottom of the package, which is also electrically connected to the device GND. The suggested way to dissipate the heat is to use the PCB’s ground plane as a heatsink. The PCB should have a metal pad where the RDA012M4 body will sit. This pad is connected to the ground plane through metal vias that also conduct the heat.

If you feel that a heatsink is needed, it should be mounted on the opposite side of the PCB, directly bellow where the MUXDAC will be located. It will attach to a metal pad, soldered if possible, that will be connected to the metal pad where the MUXDAC is seated through metal vias. Since the back of the package is used as ground connection, the heatsink will be grounded. Care should be taken to avoid contact between the heatsink and other circuitry that might be close to it.

Via configuration for MUXDAC ground connection / heat dissipation:

10 mil diameter vias spaced 50 mils apart, evenly distributed in an array covering the metal pad where the MUXDAC will be mounted. Those vias should connect the metal pad to the PCB ground plane.

Q: What is the minimum set-up and hold time between the data and clock in the RDA012?

A: The minimum setup is 100ps and the hold time is 100ps

Q: What is the minimum set-up and hold time between the data and clock in the RDA012M4/MS?

A: The minimum setup at the RDA012M4 is 300ps and the hold time is -50ps. One should consider the full path from the RDA012M4 clock out to the data input (PCB trace delay for the clock, propagation delay from clock to data generation, and PCB trace delay for the data) when computing the system timing budget.

Q: Are there ECL terminations (50 Ohm) on the data and clock inputs inside the RDA012?

A: There is no ECL termination on the data lines, so external termination is required. The CLK and CLKB signals, however, have internal 50 Ohm terminations to VTT.

Q: I need to demetallize the RDA012M4/MS pins, what is the thickness of the plating?

A: The plating is 50 microinches Au on 100-350 microinches Ni on KOVAR.

Q: Will I see clipping in the single-ended output if I increase V_REF to say, -2.1V from the nominal -2.0V?

A: No. If V_REF = -2.1V, the single-ended output swing does increase (from 600mV to 630mV) but the mid-point of the swing is automatically shifted down (from -0.3V to -0.315V in this case), preventing any clipping at 0V.

Q: How much current can I expect to be drawn from the VREFA supply? Is this just 2X the analog output current (i.e. 2X(12mA) = 24mA)?

A: VREFA pin is provided for added control over the full-scale of the DAC. The internal reference circuit is designed to provide -2.0V, which can change up to +/- 0.5% as the supply voltage and /or operating temperature changes. If the user prefers more stable absolute full-scale, one can use external voltage reference with low output impedance to override the internal reference. The output resistance of the reference node is 560 Ohm +/- 10%. The expected current, as a result, can be calculated from the equation I_REF = (V_REF +2.0) / 560.

For example, if the external reference voltage is set to -2.5V for larger output swing, the external reference circuit needs to be able to drive -893 µA. Please note that the DAC is optimized for best performance using -2V reference. However, as long as the reference voltage is confined to a -1 ~ -2.5V range, the degradation in DAC performance is minor.

Q: Does the clock duty cycle in the RDA012 have to be 50%?

A: A 50% duty cycle is recommended. It has not been tested otherwise, but the chip should operate within a within +/- 10% margin.