M16C6S_09 Datasheet, PDF (186/208 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

M16C/6S Group
IT800AFE (Analog Front End)
In the circumference of a DAC circuit, it is cautious of the following point and a constant is set up.
(a)Full-scale output current of DAC
Although the current by which DAC is outputted to a pin (Iout/Ioutc) according to the change width of an
internal bit changes, total is fixed and serves as full-scale output current (IFULL). This IFULL can be set
up by the following formula.
IFULL=2131/Rext(mA)
The unit of Rext is Ω
Since about 1mA of an IFULL value is the optimal value, Rext is 2.1kΩ.
DAC is total and Iout/Ioutc changes between 0 to IFULL at 1024 steps by the full range for a change
width of 10 bits.
The value of Iout/Ioutc is expressed with the following formula if the step value which converted the 10-
bit binary input into decimal is set to d. (d=0 to 1023)
Iout=IFULL/1023*d
Ioutc=IFULL/1023*(1023-d)
(b)About DAC load resistance
Resistance (Rout/Routc) is connected to a DAC output pin.In this resistance, signal voltage occurs by
the current (Iout/Ioutc) which flows, respectively. In order to maintain the linearity of Iout/Ioutc, it is neces-
sary to set up Rout/Routc so that this potential may not exceed maximum 2V. Since Iout/Ioutc is mostly
set to one half of IFULL(s) at the time of a non-signal (balanced state), the signal voltage (Vout/Voutc) of
a DAC output pin is set to below:
Vout=Rout X Iout
Voutc=Routc X Ioutc
Since the recommendation value of Vout/Voutc at the time of a non-signal is about 1V, in Rext=2.1kΩ,
Rout/Routc serves as 2.1kΩ.
The capacitor (Cout/Coutc) for output filters cuts the high frequency ingredient of DAC, and sets it up
on balance with necessary zone frequency.
Rev.5.01 Dec 10, 2009 page 186 of 201
REJ03B0014-0501