DAC104S085EVAL NSC [National Semiconductor], DAC104S085EVAL Datasheet - Page 15

• Manufacturer Part Number: DAC104S085EVAL
• Description: 10-Bit Micro Power QUAD Digital-to-Analog Converter with Rail-to-Rail Output
• Manufacturer: NSC [National Semiconductor]

1.0 Functional Description
1.6 POWER-ON RESET
The power-on reset circuit controls the output voltages of the
four DACs during power-up. Upon application of power, the
DAC registers are filled with zeros and the output voltages
are 0V. The outputs remain at 0V until a valid write sequence
is made to the DAC.
1.7 POWER-DOWN MODES
The DAC104S085 has four power-down modes, two of
which are identical. In power-down mode, the supply current
drops to 20 µA at 3V and 30 µA at 5V. The DAC104S085 is
set in power-down mode by setting OP1 and OP0 to 11.
Since this mode powers down all four DACs, the address
bits, A1 and A0, are used to select different output termina-
tions for the DAC outputs. Setting A1 and A0 to 00 or 11
causes the outputs to be tri-stated (a high impedance state).
While setting A1 and A0 to 01 or 10 causes the outputs to be
terminated by 2.5 kΩ or 100 kΩ to ground respectively (see
Table 1).
The bias generator, output amplifiers, resistor strings, and
other linear circuitry are all shut down in any of the power-
down modes. However, the contents of the DAC registers
are unaffected when in power-down. Each DAC register
maintains its value prior to the DAC104S085 being powered
down unless it is changed during the write sequence which
instructed it to recover from power down. Minimum power
consumption is achieved in the power-down mode with
SYNC and D
power-down (Wake-Up Time) is typically 0.8 µsec at 3V and
0.5 µsec at 5V.
2.0 Applications Information
2.1 USING REFERENCES AS POWER SUPPLIES
While the simplicity of the DAC104S085 implies ease of use,
it is important to recognize that the path from the reference
input (V
Supply Rejection Ratio (PSRR). Therefore, it is necessary to
provide a noise-free supply voltage to V
utilize the full dynamic range of the DAC104S085, the supply
pin (V
the same supply voltage. Since the DAC104S085 consumes
very little power, a reference source may be used as the
reference input and/or the supply voltage. The advantages of
using a reference source over a voltage regulator are accu-
racy and stability. Some low noise regulators can also be
used. Listed below are a few reference and power supply
options for the DAC104S085.
2.1.1 LM4130
The LM4130, with its 0.05% accuracy over temperature, is a
good choice as a reference source for the DAC104S085.
The 4.096V version is useful if a 0 to 4.095V output range is
desirable or acceptable. Bypassing the LM4130 VIN pin with
A1
0
0
1
1
A
) and V
REFIN
A0
0
1
0
1
IN
) to the VOUTs will have essentially zero Power
TABLE 1. Power-Down Modes
idled low and SCLK disabled. The time to exit
REFIN
OP1
1
1
1
1
can be connected together and share
OP0
1
1
1
1
100 kΩ to GND
2.5 kΩ to GND
Operating Mode
High-Z outputs
High-Z outputs
REFIN
(Continued)
. In order to
15
a 0.1µF capacitor and the VOUT pin with a 2.2µF capacitor
will improve stability and reduce output noise. The LM4130
comes in a space-saving 5-pin SOT23.
2.1.2 LM4050
Available with accuracy of 0.44%, the LM4050 shunt refer-
ence is also a good choice as a reference for the
DAC104S085. It is available in 4.096V and 5V versions and
comes in a space-saving 3-pin SOT23.
The minimum resistor value in the circuit of Figure 6 must be
chosen such that the maximum current through the LM4050
does not exceed its 15 mA rating. The conditions for maxi-
mum current include the input voltage at its maximum, the
LM4050 voltage at its minimum, and the DAC104S085 draw-
ing zero current. The maximum resistor value must allow the
LM4050 to draw more than its minimum current for regula-
tion plus the maximum DAC104S085 current in full opera-
tion. The conditions for minimum current include the input
voltage at its minimum, the LM4050 voltage at its maximum,
the resistor value at its maximum due to tolerance, and the
DAC104S085 draws its maximum current. These conditions
can be summarized as
and
where V
voltages
I
Z
R(max) = ( V
(max) is the maximum allowable current through the
FIGURE 5. The LM4130 as a power supply
FIGURE 6. The LM4050 as a power supply
Z
(min) and V
±
R(min) = ( V
the LM4050 output tolerance over temperature,
IN
(min) − V
Z
IN
(max) are the nominal LM4050 output
(max) − V
Z
(max) ) / ( (I
Z
(min) ) /I
DAC
(max) + I
Z
(max)
www.national.com
Z
20195313
(min) )
20195314