TC1070 Datasheet, PDF (11/12 Pages) TelCom Semiconductor, Inc – 50mA ADJUSTABLE CMOS LDO WITH SHUTDOWN

100mA ADJUSTABLE CMOS
LDO WITH SHUTDOWN
Equation 2 can be used in conjunction with Equation 3
to ensure regulator thermal operation is within limits. For
example:
Given:
V_INMAX = 3.0V ±10%
V_OUTMIN = 2.7V ±0.5V
I_LOAD = 98mA
T_AMAX = 55°C
Find: 1. Actual power dissipation
2. Maximum allowable dissipation
Actual power dissipation:
P_{D ≈} (V_{INMAX –} V_{OUTMIN)ILOADMAX}
= [(3.0 x 1.1) – (2.7 x .995)]40 x 10^–3
= 60mW
Maximum allowable power dissipation:
P_DMAX = (T_JMAX – T_AMAX)
θ_JA
= (125 – 55)
220
= 318mW
In this example, the TC1071 dissipates a maximum of
only 60mW; far below the allowable limit of 318mW. In a
similar manner, Equation 1 and Equation 2 can be used to
calculate maximum current and/or input voltage limits. For
example, the maximum allowable V_IN is found by substitut-
ing the maximum allowable power dissipation of 318mW
into Equation 1, from which V_INMAX = 5.9V.
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 θ_JA and therefore increase the
maximum allowable power dissipation limit.
PRELIMINARY INFORMATION
TC1071
TC1071-01 6/13/97
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