TC1188/TC1189
DS21364C-page 8 2002-2012 Microchip Technology Inc.
EXAMPLE 3-1:
The previously defined power dissipation equations
can be used to ensure that the regulator thermal
operation is within limits.
Given:
V
IN(MAX)
= 3.0V +10%
V
OUT(MAX)
= 2.7V - 2.5%
I
LOAD(MAX)
= 40 MA
T
J(MAX)
= 125°C
T
A(MAX)
= 55°C
Find:
1. Actual power dissipation.
2. Maximum allowable dissipation.
Actual power dissipation:
Maximum allowable power dissipation:
In this example, the TC1188/TC1189 dissipates a max-
imum of 26.7 mW below the allowable limit of 318 mW.
In a similar manner, the power dissipation equation, as
a function of V
IN
, V
OUT
and I
LOAD,
along with the power
dissipation equation, as a function of maximum junction
temperature, maximum ambient temperature and junc-
tion to air thermal resistance, can be used to calculate
maximum current and/or maximum input voltage limits.
4.0 APPLICATIONS INFORMATION
4.1 Input Capacitor
A 1 µF (or larger) capacitor is recommended to bypass
the LDO input and lower input impedance for circuit
stability when operating from batteries or high imped-
ance sources. The input capacitor can be ceramic, tan-
talum or aluminum electrolytic. For applications that
require low noise and input power supply rejection, low
effective series resistance (ESR) ceramic capacitors
are recommended over higher ESR electrolytic capac-
itors. Larger value input capacitors can be used to
improve circuit performance.
4.2 Output Capacitor
A 1 µF (minimum) capacitor is required from V
OUT
to
ground to ensure circuit stability. The output capacitor
should have an ESR greater than 0.1 ohms and less
than 2 ohm. Tantalum or aluminum electrolytic capaci-
tors are recommended. Since many aluminum electro-
lytic capacitors freeze at approximately -30°C, solid
tantalums are recommended for applications operating
below 25°C.
P
D
= V
IN(MAX)
- V
OUT(MIN)
x I
LOAD(MAX)
P
D
= ((3.0 * 1.1) - (2.7 * 0.975)) * 40 mA
P
D
= 26.7 mWatts
P
D
= (T
J(MAX)
- T
A(MAX)
)/
JA
P
D(MAX)
= (125 - 55) / 220
P
D(MAX)
= 318 mWatts.
