TC1188 Datasheet, PDF (8/16 Pages) Microchip Technology – MAX8863/64 Pin Compatible, Low Dropout, 120 mA Linear Regulators

TC1188/TC1189
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:
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
Maximum allowable power dissipation:
P_D = (T_J(MAX) - T_A(MAX))/θ_JA
P_D(MAX) = (125 - 55) / 220
P_D(MAX) = 318 mWatts.
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.
DS21364B-page 8
 2002 Microchip Technology Inc.