Datasheet

LM4050-4.1
or
LM4050-5.0
V
OUT
= 0V to 5V
0.47 PF
Input
Voltage
R
V
Z
DAC104S085
DIN
SCLK
SYNC
V
A
V
REFIN
0.1 PF
I
Z
I
DAC
DAC104S085
www.ti.com SNAS362F –MAY 2006–REVISED MARCH 2013
LM4050
Available with accuracy of 0.44%, the LM4050 shunt reference 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.
Figure 32. The LM4050 as a power supply
The minimum resistor value in the circuit of Figure 32 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 DAC104S085 drawing zero current. The maximum
resistor value must allow the LM4050 to draw more than its minimum current for regulation plus the maximum
DAC104S085 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
DAC104S085 draws its maximum current. These conditions can be summarized as
R(min) = ( V
IN
(max) − V
Z
(min) ) /I
Z
(max) (3)
and
R(max) = ( V
IN
(min) − V
Z
(max) ) / ( (I
DAC
(max) + I
Z
(min) )
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
• I
DAC
(max) is the maximum DAC104S085 supply current. (4)
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 DAC104S085. 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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