LP38691, LP38693, LP38691-Q1, LP38693-Q1

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SNVS321N – JANUARY 2005 – REVISED MARCH 2015

9.2.1 Design Requirements

Table 1. Design Parameters

DESIGN PARAMETERS

EXAMPLE VALUE

Input voltage range

2.7 V to 10 V

Output range

1.8 V

Output current

1 A

Output capacitor range

1 µF

Input and output capacitor ESR range

5 m

Ω to 500 mΩ

9.2.2 Detailed Design Procedure

9.2.2.1 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:

(1)

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

(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 high power dissipation and/or poor package thermal resistance is present, the maximum

as given by Equation 3:

(3)

combination of the two.

9.2.2.2 External Capacitors

In common with most regulators, the LP38691 and LP38693 require an external capacitors for regulator stability.

The devices are specifically designed for portable applications requiring minimum board space and smallest

components. These capacitors must be correctly selected for good performance.

9.2.2.3 Input Capacitor

An input capacitor is required for stability. It is recommended that a 1-µF capacitor be connected between the

devices' IN pin and GND pin (this capacitance value may be increased without limit).

This capacitor must be located a distance of not more than 1 cm from the IN pin and returned to a clean

analogue ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input.

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Product Folder Links: LP38691 LP38693 LP38691-Q1 LP38693-Q1