SH7205 Datasheet, PDF (1500/1904 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7200 Series

Section 26 2D Graphics Engine (2DG)
26.5 Appendix. VIDEO OUT (D/A Converter)
VIDEO OUT contains a built-in D/A converter (DAC) of the current output method using a
current cell matrix D/A converter; it outputs a current corresponding to 6-bit digital input signals
to analog output pins R, G, and B.
26.5.1 Analog Output Current
(1) Determination of the DAC Output Resistor (RL)
Since this DAC is a current output type unit, in order to convert a current into voltage, it requires a
resistor (RL) external to the LSI. The RL can be set between 75 and 180 Ω based on an allowable
current level, the external load capacity (CL), and a desired settling time (tset). The formula for
calculating RL is given below:
Here, we define the time required from the beginning of a change in output to the time it
converges to the level within ±1.0% of the final attainable level as settling time.
tset = 4.6 × RL × C tset: ±1% settling time [ns], C: total load capacity [pF]
C = Cin + CL Cin: internal capacity of module (approximately 5 pF) [pF],
CL: I/O + PKG + on-board capacity [pF]
The condition that must be satisfied by RL in order to obtain the desired settling time will be:
RL < tset / {4.6 × (Cin + CL)}
Example: (if tset = 18 [ns], CL = 15 [pF])
RL < 18ns / {4.6 × (5 pF + 15 pF)} = 195.6 Ω
Therefore, to settle it at 18 ns, set RL to 195.6 Ω or less (for example, 180 Ω).
Rev. 1.00 Mar. 25, 2008 Page 1468 of 1868
REJ09B0372-0100