Datasheet

LM4132-4.1
DAC121C081/5
SDA
SCL
V
OUT
= 0V to 4.092V
C1
0.1 PF
C2
2.2 PF
Input
Voltage
V
REF
C3
0.1 PF
V
A
t
outz
SCL
SDA
DAC121C081, DAC121C085
SNAS395D –DECEMBER 2007–REVISED MARCH 2013 www.ti.com
ADDITIONAL TIMING INFORMATION: t
outz
The t
outz
specification is provided to aid the design of the I
2
C bus. After the SCL bus is driven low by the I
2
C
master, the SDA bus will be held for a short time by the DAC121C081. This time is referred to as t
outz
. The
following figure illustrates the relationship between the fall of SCL, at the 30% threshold, to the time when the
DAC begins to transition the SDA bus. The t
outz
specification only applies when the DAC is in control of the SDA
bus. The DAC is only in control of the bus during an ACK by the DAC121C081 or a data byte read from the DAC
(see Figure 24).
Figure 26. Data Output Timing
The t
outz
specification is typically 87nsec in Standard-Fast Mode and 38nsec in Hs-Mode.
Applications Information
USING REFERENCES AS POWER SUPPLIES
While the simplicity of the DAC121C081 implies ease of use, it is important to recognize that the path from the
reference input (V
A
for the DAC121C081 & V
REF
for the DAC121C085) to V
OUT
will have essentially zero Power
Supply Rejection Ratio (PSRR). Therefore, it is necessary to provide a noise-free supply voltage to the
reference. In order to use the full dynamic range of the DAC121C085, the supply pin (V
A
) and V
REF
can be
connected together and share the same supply voltage. Since the DAC121C081 consumes very little power, a
reference source may be used as the supply voltage. The advantages of using a reference source over a voltage
regulator are accuracy and stability. Some low noise regulators can also be used. Listed below are a few
reference and power supply options for the DAC121C081. When using the DAC121C081, it is important to treat
the analog supply (V
A
) as the reference.
LM4132
The LM4132, with its 0.05% accuracy over temperature, is a good choice as a reference source for the
DAC121C081. The 4.096V version is useful if a 0 to 4.095V output range is desirable or acceptable. Bypassing
the LM4132 V
IN
pin with a 0.1µF capacitor and the V
OUT
pin with a 2.2µF capacitor will improve stability and
reduce output noise. The LM4132 comes in a space-saving 5-pin SOT-23.
Figure 27. The LM4132 as a power supply
LM4050
Available with accuracy of 0.44%, the LM4050 shunt reference is also a good choice as a reference for the
DAC121C081. It is available in 4.096V and 5V versions and comes in a space-saving 3-pin SOT-23.
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