Datasheet

LP2980
4.7 PF
Input
Voltage
ON /
OFF
V
IN
V
OUT
V
OUT
= 0V
to 5V
DAC128S085
DIN
SCLK
SYNC
V
A
V
REF1,2
0.1 PF
+
LP3985-5.0
1 PF
1 PF
Input
Voltage
0.01 PF
V
OUT
= 0V
to 5V
DAC128S085
DIN
SCLK
SYNC
V
A
V
REF1,2
0.1 PF
DAC128S085
SNAS407F –AUGUST 2007–REVISED MARCH 2013 www.ti.com
Figure 34. Using the LP3985 regulator
An input capacitance of 1.0µF without any ESR requirement is required at the LP3985 input, while a 1.0µF
ceramic capacitor with an ESR requirement of 5mΩ to 500mΩ is required at the output. Careful interpretation
and understanding of the capacitor specification is required to ensure correct device operation.
LP2980
The LP2980 is an ultra low dropout regulator with a ±0.5% or ±1.0% accuracy over temperature, depending upon
grade. It is available in 3.0V, 3.3V and 5V versions, among others.
Figure 35. Using the LP2980 regulator
Like any low dropout regulator, the LP2980 requires an output capacitor for loop stability. This output capacitor
must be at least 1.0µF over temperature, but values of 2.2µF or more will provide even better performance. The
ESR of this capacitor should be within the range specified in the LP2980 data sheet. Surface-mount solid
tantalum capacitors offer a good combination of small size and low ESR. Ceramic capacitors are attractive due to
their small size but generally have ESR values that are too low for use with the LP2980. Aluminum electrolytic
capacitors are typically not a good choice due to their large size and high ESR values at low temperatures.
BIPOLAR OPERATION
The DAC128S085 is designed for single supply operation and thus has a unipolar output. However, a bipolar
output may be achieved with the circuit in Figure 36. This circuit will provide an output voltage range of ±5 Volts.
A rail-to-rail amplifier should be used if the amplifier supplies are limited to ±5V.
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