LP5907 datasheet(15/47 Pages) TI

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LP5907

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SNVS798O – APRIL 2012 – REVISED JUNE 2020

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8.2.2 Detailed Design Procedure

8.2.2.1 Custom Design With WEBENCH® Tools

Click here to create a custom design using the LP5907 device with the WEBENCH® Power Designer.

1. Start by entering the input voltage (VIN), output voltage (VOUT), and output current (IOUT) requirements.

2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.

3. Compare the generated design with other possible solutions from Texas Instruments.

The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time

pricing and component availability.

In most cases, these actions are available:

•

Run electrical simulations to see important waveforms and circuit performance

•

Run thermal simulations to understand board thermal performance

•

Export customized schematic and layout into popular CAD formats

•

Print PDF reports for the design, and share the design with colleagues

Get more information about WEBENCH tools at www.ti.com/WEBENCH.

8.2.2.2 Power Dissipation and Device Operation

The permissible power dissipation for any package is a measure of the capability of the device to pass heat from

the power source, the junctions of the IC, to the ultimate heat sink, the ambient environment. Thus, the power

dissipation is dependent on the ambient temperature and the thermal resistance across the various interfaces

between the die junction and ambient air.

The maximum allowable power dissipation for the device in a given package can be calculated using Equation 1:

PD-MAX = ((TJ-MAX – TA) / RθJA)

(1)

The actual power being dissipated in the device can be represented by Equation 2:

PD = (VIN – VOUT) × IOUT

(2)

These two equations establish the relationship between the maximum power dissipation allowed due to thermal

consideration, the voltage drop across the device, and the continuous current capability of the device. These two

equations should be used to determine the optimum operating conditions for the device in the application.

In applications where lower power dissipation (PD) and/or excellent package thermal resistance (RθJA) is present,

the maximum ambient temperature (TA-MAX) may be increased.

In applications where high power dissipation and/or poor package thermal resistance is present, the maximum

ambient temperature (TA-MAX) may have to be derated. TA-MAX is dependent on the maximum operating junction

temperature (TJ-MAX-OP = 125°C), the maximum allowable power dissipation in the device package in the

application (PD-MAX), and the junction-to ambient thermal resistance of the part/package in the application (RθJA),

as given by Equation 3:

TA-MAX = (TJ-MAX-OP – (RθJA × PD-MAX))

(3)

Alternately, if TA-MAX can not be derated, the PD value must be reduced. This can be accomplished by reducing

VIN in the VIN–VOUT term as long as the minimum VIN is met, or by reducing the IOUT term, or by some

combination of the two.

8.2.2.3 External Capacitors

Like most low-dropout regulators, the LP5907 requires external capacitors for regulator stability. The device is

specifically designed for portable applications requiring minimum board space and smallest components. These

capacitors must be correctly selected for good performance.

8.2.2.4 Input Capacitor

An input capacitor is required for stability. The input capacitor should be at least equal to, or greater than, the

output capacitor for good load transient performance. At least a 1 µF capacitor has to be connected between the

LP5907 input pin and ground for stable operation over full load current range. Basically, it is ok to have more

output capacitance than input, as long as the input is at least 1 µF.

LP5907 Datasheet(PDF) 15 Page - Texas Instruments

LP5907 Datasheet(HTML) 15 Page - Texas Instruments

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