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LP2980

DAC081S101

DIN

SCLK

SYNC

VOUT = 0V to 5V

1 PF

Input

Voltage

ON / OFF

VIN

VOUT

LP3985

DAC081S101

DIN

SCLK

SYNC

VOUT = 0V to 5V

1 PF

0.1 PF

Input

Voltage

0.01 PF

DAC081S101

SNAS323C – JUNE 2005 – REVISED FEBRUARY 2013

www.ti.com

The minimum resistor value in the circuit of Figure 42 should 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, the resistor value at its minimum due to tolerance, and the

DAC081S101 draws zero current. The maximum resistor value must allow the LM4050 to draw more than its

minimum current for regulation plus the maximum DAC081S101 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 DAC081S101 draws its maximum current. These conditions can be

summarized as

R(min) = ( VIN(max) − VZ(min) / (IA(min) + IZ(max))

(3)

and

R(max) = ( VIN(min) − VZ(max) / (IA(max) + IZ(min) )

(4)

where VZ(min) and VZ(max) are the nominal LM4050 output voltages ± the LM4050 output tolerance over

temperature, IZ(max) is the maximum allowable current through the LM4050, IZ(min) is the minimum current

required by the LM4050 for proper regulation, IA(max) is the maximum DAC081S101 supply current, and IA(min)

is the minimum DAC081S101 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 DAC081S101. 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.

Figure 43. 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 5m

Ω 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 44. Using the LP2980 regulator

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LM8261 Datasheet(PDF) 18 Page - Texas Instruments

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