Texas Instruments Evaluation Board for the LP38502 LP38502TS-ADJEV LP38502TS-ADJEV Datenbogen
Produktcode
LP38502TS-ADJEV
Power Dissipation
However, if the value of R2 is increased above 10 k
Ω
, the effect of the internal zero gradually diminishes
and the phase margin is reduced. At an R2 value of approximately 50 k
Ω
, the phase margin will be low
enough that instability may occur. In such cases, some of the lost phase margin can be regained by
placing a capacitor at C2. Although it is sometimes possible to regain adequate phase margin this way, it
is recommended that the data sheet guidelines be followed and R2 not exceed 10 k
placing a capacitor at C2. Although it is sometimes possible to regain adequate phase margin this way, it
is recommended that the data sheet guidelines be followed and R2 not exceed 10 k
Ω
(so C2 is never
required).
5
Power Dissipation
The power dissipated within the regulator IC is given by:
P
D
= I
L
(V
IN
- V
OUT
)
(2)
Where:
P
D
is the power dissipated in the IC regulator U1.
I
L
is the load current.
V
IN
is the value of V
IN
measured at TP2 (not at J1).
V
OUT
is the value of V
OUT
measured at TP5 (not at J4).
The thermal resistance of U1 from junction to ambient can be assumed to be approximately 30°C/W for
this assembly. That means that the junction temperature will rise about 30°C above ambient for each Watt
of power dissipated within the IC.
this assembly. That means that the junction temperature will rise about 30°C above ambient for each Watt
of power dissipated within the IC.
The parametric specifications of the IC are for a maximum junction temperature of 125°C, and the
maximum allowable junction temperature is 150°C. This limits maximum usable power dissipation for
this package to approximately 4W. If power dissipation exceeds this (and the junction temperature
approaches 150°C) the part may go into thermal shutdown.
maximum allowable junction temperature is 150°C. This limits maximum usable power dissipation for
this package to approximately 4W. If power dissipation exceeds this (and the junction temperature
approaches 150°C) the part may go into thermal shutdown.
6
PCB Component Layout
The components listed in the basic application circuit can be identified using the silkscreen on the top
layer of the PCB (see
layer of the PCB (see
Figure 2. Top View of the PCB Assembly
2
AN-1759 LP38502TS-ADJ Evaluation Board
SNVA307B – November 2007 – Revised April 2013
Copyright © 2007–2013, Texas Instruments Incorporated