8 Application and Implementation

Note

Information in the following applications sections is not part of the TI component specification,

and TI does not warrant its accuracy or completeness. TI’s customers are responsible for

determining suitability of components for their purposes, as well as validating and testing their design

implementation to confirm system functionality.

8.1 Application Information

The LP2985-N is a linear voltage regulator operating from 2.5 V to 16 V on the input and regulates voltages

between 1.2 V to 5 V (for the new chip) with 1% accuracy across line, load and temperature (for the new

chip) and 150-mA maximum output current. The LP2985-N low output noise of 30 µVRMS (with 10-nF bypass

capacitors) and wide bandwidth PSRR performance of greater than 70 dB at 1 kHz and 40 dB at 1 MHz help

attenuate the switching frequency of an upstream DC/DC converter and minimize post regulator filtering.

8.1.1 Recommended Capacitor Types

The device is designed to be stable using low equivalent series resistance (ESR) ceramic capacitors at the input

and output. Multilayer ceramic capacitors have become the industry standard for these types of applications and

are recommended, but must be used with good judgment. Ceramic capacitors that employ X7R-, X5R-, and

C0G-rated dielectric materials provide relatively good capacitive stability across temperature, whereas the use of

Y5V-rated capacitors is discouraged because of large variations in capacitance.

Regardless of the ceramic capacitor type selected, the effective capacitance varies with operating voltage

and temperature. Generally, expect the effective capacitance to decrease by as much as 50%. The input and

output capacitors listed in the Recommended Operating Conditions table account for an effective capacitance of

approximately 50% of the nominal value.

8.1.2 Input and Output Capacitor Requirements

Although an input capacitor is not required for stability, good analog design practice is to connect a capacitor

from IN to GND. This capacitor counteracts reactive input sources and improves transient response, input ripple,

and PSRR. Use an input capacitor if the source impedance is more than 0.5 Ω. A higher value capacitor can be

necessary if large, fast rise-time load or line transients are anticipated or if the device is located several inches

from the input power source.

Dynamic performance of the device is improved with the use of an output capacitor. Use an output capacitor

within the range specified in the Recommended Operating Conditions table for stability.

8.1.3 Noise Bypass Capacitor (CBYPASS)

The LP2985-N allows for low-noise performance with the use of a bypass capacitor that is connected to the

internal band-gap reference with the BYPASS pin. This high-impedance band-gap circuitry is biased in the

microampere range and, thus, cannot be loaded significantly, otherwise, the output (and, correspondingly, the

output of the regulator) changes. Thus, for best output accuracy, dc leakage current through CBYPASS must be

minimized as much as possible and must never exceed 100 nA. The CBYPASS capacitor also impacts the start-up

behavior of the regulator. Inrush current and start-up time increase with larger bypass capacitor values.

Use a 10-nF capacitor for CBYPASS. Ceramic and film capacitors are good choices for this purpose.

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LP2985-N

SNVS018Z – MARCH 2000 – REVISED MAY 2023

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Product Folder Links: LP2985-N