Device

IN

OUT

GND

COUT

CIN

Schottky Diode

Internal Body Diode

19

TLV751

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SBVS385B – DECEMBER 2019 – REVISED APRIL 2020

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Application Information (continued)

If reverse current flow is expected in the application, external protection must be used to protect the device.

Figure 41 shows one approach of protecting the device.

Figure 41. Example Circuit for Reverse Current Protection Using a Schottky Diode

8.1.6 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. Equation 4 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 Equation 5, 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.

8.1.7 Feed-Forward Capacitor (CFF)

For the adjustable-voltage version device, a feed-forward capacitor (CFF) can be connected from the OUT pin to

the FB pin. CFF improves transient, noise, and PSRR performance, but is not required for regulator stability.

Recommended CFF values are listed in the Recommended Operating Conditions table. A higher capacitance CFF

can be used; however, the startup time increases. For a detailed description of CFF tradeoffs, see the Pros and

Cons of Using a Feedforward Capacitor with a Low-Dropout Regulator application report.