Datasheet

LM4050-4.1
or
LM4050-5.0
V
OUT
= 0V
to 5V
1 PF
Input
Voltage
R
V
Z
DAC128S085
DIN
SCLK
SYNC
V
A
V
REF1,2
0.1 PF
I
Z
I
DAC
LM4132-4.1
DAC128S085
DIN
SCLK
SYNC
V
OUT
= 0V
to 4.095V
C1
4.7 PF
C2
4.7 PF
Input
Voltage
V
A
V
REF1,2
C3
0.1 PF
+
+
DAC128S085
www.ti.com SNAS407F –AUGUST 2007–REVISED MARCH 2013
Figure 32. The LM4132 as a power supply
LM4050
Available with accuracy of ±0.1%, the LM4050 shunt reference is also a good choice as a reference for the
DAC128S085. It is available in 4.096V and 5V versions and comes in a space-saving 3-pin SOT-23.
Figure 33. The LM4050 as a power supply
The minimum resistor value in the circuit of Figure 33 must be chosen such that the maximum current through
the LM4050 does not exceed its 15 mA rating. The conditions for maximum current include the input voltage at
its maximum, the LM4050 voltage at its minimum, and the DAC128S085 drawing zero current. The maximum
resistor value must allow the LM4050 to draw more than its minimum current for regulation plus the maximum
DAC128S085 current in full operation. 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
DAC128S085 draws its maximum current. These conditions can be summarized as
R(min) = ( V
IN
(max) − V
Z
(min) ) /I
Z
(max) (4)
and
R(max) = ( V
IN
(min) − V
Z
(max) ) / ( (I
DAC
(max) + I
Z
(min) ) (5)
where V
Z
(min) and V
Z
(max) are the nominal LM4050 output voltages ± the LM4050 output tolerance over
temperature, I
Z
(max) is the maximum allowable current through the LM4050, I
Z
(min) is the minimum current
required by the LM4050 for proper regulation, and I
DAC
(max) is the maximum DAC128S085 supply current.
LP3985
The LP3985 is a low noise, ultra low dropout voltage regulator with a ±3% accuracy over temperature. It is a
good choice for applications that do not require a precision reference for the DAC128S085. It comes in 3.0V,
3.3V and 5V versions, among others, and sports a low 30 µV noise specification at low frequencies. Since low
frequency noise is relatively difficult to filter, this specification could be important for some applications. The
LP3985 comes in a space-saving 5-pin SOT-23 and 5-bump DSBGA packages.
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