Preliminary
EUP7522
Power Dissipation and Junction Temperature
Application Information
Input Capacitor
Specified regulator operation is assured to a junction
temperature of 125°C; the maximum junction
temperature should be restricted to 125°C under normal
operating conditions. This restriction limits the power
dissipation the regulator can handle in any given
application. To ensure the junction temperature is within
acceptable limits, calculate the maximum allowable
dissipation, PD(max), and the actual dissipation, PD, which
must be less than or equal to PD(max)
A minimum input capacitance of 2.2µF is required
between the EUP7522 input pin and ground (the amount
of the capacitance may be increased without limit).This
capacitor must be located a distance of not more than
1cm from the input pin and returned to a clean analog
ground.
Any good quality ceramic, tantalum, or film capacitor
may be used at the input. If a tantalum capacitor is used
at the input, it must be guaranteed by the manufacturer to
have asurge current rating sufficient for the application.
The maximum-power-dissipation limit is determined
using the following equation:
T max − T
J
=
A
P
D(max)
No-Load Stability
R
θJA
The EUP7522 will remain stable and in regulation with
no external load. This is specially important in CMOS
RAM keep-alive applications.
Where:
JMAX is the maximum allowable junction temperature.
T
R
θJA is the thermal resistance junction-to-ambient for the
Output Capacitance
package
TA is the ambient temperature.
The EUP7522 is specifically designed to employ ceramic
output capacitors as low as 2.2µF. Ceramic capacitors
below 10µF offer significant cost and space savings,
along with high frequency noise filtering. Higher values
and other types and of capacitor may be used, but their
equivalent series resistance (ESR) should be maintained
below 0.5Ω. Ceramic capacitor of the value required by
the EUP7522 are available in the following dielectric
types: Z5U, Y5V, X5R, and X7R. The Z5U and Y5V
types exhibit a 50% or more drop in capacitance value as
their temperature increase from 25°C, an important
consideration. The X5R generally maintain their
capacitance value within ± 20%. The X7R type are
desirable for their tighter tolerance of 10% over
temperature.
The regulator dissipation is calculated using:
PD=(VI-VO) × IO
Power dissipation resulting from quiescent current is
negligible. Excessive power dissipation triggers the
thermal protection circuit.
DS7522 Ver 0.5 March. 2006
8
EUTECH [ EUTECH MICROELECTRONICS INC ]
