much as possible and must never exceed 100nA. 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 10nF capacitor for CBYPASS. Ceramic and film capacitors are good choices for this purpose.

7.1.4 Power Dissipation (PD)

Circuit reliability requires consideration of the device power dissipation, location of the circuit on the printed

circuit board (PCB), and correct sizing of the thermal plane. The PCB area around the regulator must have few

or no other heat-generating devices that cause added thermal stress.

To first-order approximation, power dissipation in the regulator depends on the input-to-output voltage difference

and load conditions. The following equation calculates power dissipation (PD).

PD = (VIN – VOUT) × IOUT

(4)

Note

Power dissipation can be minimized, and therefore greater efficiency can be achieved, by correct

selection of the system voltage rails. For the lowest power dissipation use the minimum input voltage

required for correct output regulation.

For devices with a thermal pad, the primary heat conduction path for the device package is through the thermal

pad to the PCB. Solder the thermal pad to a copper pad area under the device. This pad area must contain an

array of plated vias that conduct heat to additional copper planes for increased heat dissipation.

The maximum power dissipation determines the maximum allowable ambient temperature (TA) for the device.

According to the following equation, power dissipation and junction temperature are most often related by the

junction-to-ambient thermal resistance (RθJA) of the combined PCB and device package and the temperature of

the ambient air (TA).

TJ = TA + (RθJA × PD)

(5)

Thermal resistance (RθJA) is highly dependent on the heat-spreading capability built into the particular PCB

design, and therefore varies according to the total copper area, copper weight, and location of the planes.

The junction-to-ambient thermal resistance listed in the Thermal Information table is determined by the JEDEC

standard PCB and copper-spreading area, and is used as a relative measure of package thermal performance.

7.1.5 Recommended Capacitor Types

This section describes the recommended capacitors for both the new chip and the legacy chip.

7.1.5.1 Recommended Capacitors (Legacy Chip)

The LP2992 is designed specifically to work with ceramic output capacitors, using circuitry that allows the

regulator to be stable across the entire range of output current with an output capacitor whose ESR is as low as

5mΩ. Tantalum or film capacitors are available for use at the output, but these capacitors are not as attractive for

size and cost reasons.

Make sure the output capacitor meets the requirement for minimum amount of capacitance and also have an

ESR value within the stable range. Curves are provided that show the stable ESR range as a function of load

current (see Figure 5-59).

Make sure the output capacitor maintains the ESR within the stable region over the full operating temperature

range of the application to provide stability.

The legacy chip version of the LP2992 requires a minimum of 4.7µF on the output (increase output capacitor

size without limit). Remember to take capacitor tolerance and variation with temperature into consideration when

selecting an output capacitor so that the minimum required amount of output capacitance is provided over

the full operating temperature range. Ceramic capacitors potentially exhibit large changes in capacitance with

temperature.

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LP2992

SNVS171L – NOVEMBER 2001 – REVISED FEBRUARY 2025

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