LP38690_15 Datasheet, PDF (16/31 Pages) Texas Instruments – LP38690, LP38692 1-A Low Dropout CMOS Linear Regulators Stable with Ceramic Output Capacitors

LP38690, LP38692
SNVS322L – DECEMBER 2004 – REVISED MARCH 2015
www.ti.com
P_D-MAX = ((T_J-MAX – T_A) / R_θJA)
(1)
The actual power being dissipated in the device can be represented by Equation 2:
P_D = (V_IN – V_OUT) × I_OUT
(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 (P_D) and/or excellent package thermal resistance (R_θJA) is present,
the maximum ambient temperature (T_A-MAX) may be increased.
In applications where high power dissipation and/or poor package thermal resistance is present, the maximum
ambient temperature (T_A-MAX) may have to be derated. T_A-MAX is dependent on the maximum operating junction
temperature (T_J-MAX-OP = 125°C), the maximum allowable power dissipation in the device package in the
application (P_D-MAX), and the junction-to ambient thermal resistance of the part/package in the application (R_θJA),
as given by Equation 3:
T_A-MAX = (T_J-MAX-OP – (R_θJA × P_D-MAX))
(3)
Alternately, if T_A-MAX can not be derated, the P_D value must be reduced. This can be accomplished by reducing
V_IN in the V_IN – V_OUT term as long as the minimum V_IN is met, or by reducing the I_OUT term, or by some
combination of the two.
8.2.2.2 External Capacitors
In common with most regulators, the LP38690 and LP38692 require external capacitors for regulator stability.
The LP38690 and LP38692 are specifically designed for portable applications requiring minimum board space
and smallest components. These capacitors must be correctly selected for good performance.
8.2.2.2.1 Input Capacitor
An input capacitor is required for stability. It is recommended that a 1-μF capacitor be connected between the
LP38690 or LP38692 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.
Important: To ensure stable operation it is essential that good PCB design practices are employed to minimize
ground impedance and keep input inductance low. If these conditions cannot be met, or if long leads are used to
connect the battery or other power source to the LP38690 or LP38692, then it is recommended that the input
capacitor is increased. Also, tantalum capacitors can suffer catastrophic failures due to surge current when
connected to a low-impedance source of power (like a battery or a very large capacitor). If a tantalum capacitor is
used at the input, it must be ensured by the manufacturer to have a surge current rating sufficient for the
application.
There are no requirements for the equivalent series resistance (ESR) on the input capacitor, but tolerance and
temperature coefficient must be considered when selecting the capacitor to ensure the capacitance remains
approximately 1 μF over the entire operating temperature range.
8.2.2.2.2 Output Capacitor
The LP38690 and LP38692 are designed specifically to work with very small ceramic output capacitors. A 1-μF
ceramic capacitor (temperature types Z5U, Y5V or X7R/X5R) with ESR between 5 mΩ to 500 mΩ, is suitable in
the LP38690 or LP38692 application circuit.
For this device the output capacitor should be connected between the OUT pin and GND pin. It is also possible
to use tantalum or film capacitors at the device output, but these are not as attractive for reasons of size and cost
(see Capacitor Characteristics). The output capacitor must meet the requirement for the minimum value of
capacitance and also have an ESR value that is within the range 5 mΩ to 500 mΩ for stability.
8.2.2.2.3 No Load Stability
The LP38690 and LP38692 remain stable and in regulation with no external load. This is an important
consideration in some circuits, for example CMOS RAM keep-alive applications.
16
Submit Documentation Feedback
Copyright © 2004–2015, Texas Instruments Incorporated
Product Folder Links: LP38690 LP38692