LP2985IM5-3.3 datasheet(20/43 Pages) TI

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8.1.4 Reverse Current

Excessive reverse current can damage this device. Reverse current flows through the intrinsic body diode of the

pass transistor instead of the normal conducting channel. At high magnitudes, this current flow degrades the

long-term reliability of the device.

Conditions where reverse current can occur are outlined in this section, all of which can exceed the absolute

maximum rating of VOUT ≤ VIN + 0.3 V.

• If the device has a large COUT and the input supply collapses with little or no load current

• The output is biased when the input supply is not established

• The output is biased above the input supply

If reverse current flow is expected in the application, use external protection to protect the device. Reverse

current is not limited in the device, so external limiting is required if extended reverse voltage operation is

anticipated.

Figure 8-1 shows one approach for protecting the device.

OUT

GND

CIN

GND

COUT

GND

Internal Body Diode

Schottky Diode

Figure 8-1. Example Circuit for Reverse Current Protection Using a Schottky Diode

8.1.5 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

(2)

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)

(3)

LP2985-N

SNVS018Z – MARCH 2000 – REVISED MAY 2023

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