TC562502ECT Ver la hoja de datos (PDF) - Microchip Technology
Número de pieza
componentes Descripción
Fabricante
TC562502ECT Datasheet PDF : 16 Pages
| |||
TC56
4.0 THERMAL CONSIDERATIONS
4.1 Power Dissipation
The amount of power the regulator dissipates is
primarily a function of input and output voltage, and
output current. The following equation is used to
calculate worst case actual power dissipation.
EQUATION 4-1:
PD ≈ (VINMAX – VOUTMIN)ILOADMAX
Where:
PD = Worst case actual power dissipation
VINMAX = Maximum voltage on VIN
VOUTMIN = Minimum regulator output voltage
ILOADMAX = Maximum output (load) current
The maximum allowable power dissipation
(Equation 4-2) is a function of the maximum ambient
temperature (TAMAX), the maximum allowable die
temperature (TJMAX) and the thermal resistance from
junction-to-air (θJA). The 5-Pin SOT-23A package has
a θJA of approximately 220°C/Watt.
EQUATION 4-2:
PDMAX = (TJMAX – TAMAX)
θJA
Where all terms are previously defined.
Equation 4-1 can be used in conjunction with
Equation 4-2 to ensure regulator thermal operation is
within limits. For example:
Given:
VINMAX = 3.0V ±10%
VOUTMIN = 2.7V – 2%
ILOADMAX = 98mA
TJMAX = 125°C
TAMAX = 55°C
Find: 1. Actual power dissipation
2. Maximum allowable dissipation
Actual power dissipation:
PD ≈ (VINMAX – VOUTMIN)ILOADMAX
= [(3.0 x 1.1) – (2.7 x .98)]98 x 10-3
= 64mW
Maximum allowable power dissipation:
PDMAX = (TJMAX – TAMAX)
θJA
= (125 – 55)
220
= 318mW
In this example, the TC56 dissipates a maximum of
64mW; below the allowable limit of 318mW. In a similar
manner, Equation 4-1 and Equation 4-2 can be used to
calculate maximum current and/or input voltage limits.
4.2 Layout Considerations
The primary path of heat conduction out of the package
is via the package leads. Therefore, layouts having a
ground plane, wide traces at the pads, and wide power
supply bus lines combine to lower θJA and therefore,
increase the maximum allowable power dissipation
limit.
DS21436B-page 4
2002 Microchip Technology Inc.
Share Link: 