Pam3131, Application information – Diodes PAM3131 User Manual
Page 10
PAM3131
Document number: DSxxxxx Rev. 1 - 1
10 of 14
October 2012
© Diodes Incorporated
PAM3131
A Product Line of
Diodes Incorporated
Application Information
The PAM3116 family of low-dropout (LDO) regulators have several features that allow them to apply to a wide range of applications. The family
operates with very low input voltage and low dropout voltage (typically 300mV at full load), making it an efficient stand-alone power supply or
post regulator for battery or switch mode power supplies. The 1.5A output current make the PAM3116 family suitable for powering many
microprocessors and FPGA suppl ies. The PAM3116 family also has low output noise (typically 50
μVRMS with 4.7μF output capacitor), making it
ideal for use in telecom equipment.
External Capacitor Requirements
A 4.7
μF or larger ceramic input bypass capacitor, connected between V
IN
and GND and located close to the PAM3116, is required for stability. A
4.7µF minimum value capacitor from V
O
to GND is also required. To improve transient response, noise rejection, and ripple rejection, an
additional 1 0
μF or larger, low ESR capacitor is recommended at the output. A higher-value, low ESR output capacitor may be necessary if large,
fast-rise-time load transients are anticipated and the device is located several inches from the power source, especially if the minimum input
voltage of 2.5V is used.
Regulator Protection
The PAM3116 features internal current limiting, thermal protection and short circuit protection. During normal operation, the PAM3116 limits
output current to about 2.5A. When current limiting engages, the output voltage scales back linearly until the over current condition ends. While
current limiting is designed to prevent gross device failure, care should be taken not to exceed the power dissipation ratings of the package. If the
temperature of the device exceeds +150°C, thermal-protection circuitry will shut down. Once the device has cooled down to approximately +40°C
below the high temp trip point, regulator operation resumes. The short circuit current of the PAM3116 is about 0.7A when its output pin is shorted
to ground.
Thermal Information
The amount of heat that an LDO linear regulator generates is:
(
)
I
V
V
P
O
O
IN
D
−
=
All integrated circuits have a maximum allowable junction temperature (T
J(MAX)
) above which normal operation is not assured. A system designer
must design the operating environment so that the operating junction temperature (T
J
) does not exceed the maximum junction temperature
(T
J(MAX)
). The two main environmental variables that a designer can use to improve thermal performance are air flow and external heat sinks.
The purpose of thi s information is to aid the designer in determining the proper operating environment for a linear regulator that is operating at a
specific power level.
In general, the maximum expected power (P
D(MAX)
) consumed by a linear regulator is computed as:
Where:
•
V
I(AVG)
is the average input voltage.
•
V
O(AVG)
is the average output voltage.
•
I
O(AVG)
is the average output current.
•
I
(Q)
is the quiescent current.
For most LDO regulators, the quiescent current is insignificant compared to the average output current; therefore, the term V
I(AVG)
xI
Q
can be
neglected. The operating junction temperature is computed by adding the ambient temperature (T
A
) and the increase in temperature due to the
regulator's power dissipation. The temperature rise is computed by multiplying the maximum expected power dissipation by the sum of the
thermal resistances between the junction and the case R
θJC
), the case to heatsink (R
θCS
), and the heatsink to ambient (R
θSA
). Thermal
resistances are measures of how effectively an object dissipates heat. Typically, the larger the device, the more surface area available for power
dissipation so that the object’s thermal resistance will be lowers.