TC2117 Datasheet, PDF (5/12 Pages) Microchip Technology – 800mA Fixed Low Dropout Positive Regulator

TABLE 3-2:
THERMAL RESISTANCE
GUIDELINES FOR TC2117 IN
3-PIN DDPAK PACKAGE
Copper
Area
(Topside)*
Copper
Area
(Backside)
Board Area
2500 sq mm 2500 sq mm 2500 sq mm
1000 sq mm 2500 sq mm 2500 sq mm
125 sq mm 2500 sq mm 2500 sq mm
*Tab of device attached to topside copper.
Thermal
Resistance
(θ_JA)
25°C/W
27°C/W
35°C/W
Equation 3-1 can be used in conjunction with
Equation 3-2 to ensure regulator thermal operation is
within limits. For example:
Given:
V_INMAX = 5.0V ± 5%
V_OUTMIN = 3.3V ± 0.5%
I_LOADMAX = 400mA
T_JMAX = 125°C
T_AMAX = 55°C
θ_JA = 59°C/W (SOT-223)
Find: 1. Actual power dissipation
2. Maximum allowable dissipation
TC2117
Actual power dissipation:
P_D ≈ (V_INMAX – V_OUTMIN)I_LOADMAX
= [(5.0 x 1.05) – (3.3 x .995)] 400 x 10^-3
= 786mW
Maximum allowable power dissipation:
P_DMAX = (T_JMAX – T_AMAX)
θ_JA
= (125 – 55)
59
= 1.186mW
In this example, the TC2117 dissipates a maximum of
only 786mW; below the allowable limit of 1.186mW. In
a similar manner, Equation 3-1 and Equation 3-2 can
be used to calculate maximum current and/or input
voltage limits.
© 2002 Microchip Technology Inc.
DS21665B-page 5