SM74501_15 Datasheet, PDF (7/10 Pages) Texas Instruments – SM74501 Ultra-Low Quiescent Current LDO Voltage Regulator

SM74501
www.ti.com
SNVS721B – JUNE 2011 – REVISED APRIL 2013
APPLICATIONS INFORMATION
Unlike other PNP low dropout regulators, the SM74501 remains fully operational to 40V. Owing to power
dissipation characteristics of the available packages, full output current cannot be ensured for all combinations of
ambient temperature and input voltage. As an example, consider an SM74501–5.0 operating at 25°C ambient.
Using the formula for maximum allowable power dissipation given in ⁽¹⁾ , we find that P_Dmax = 839mW at 25°C.
Including the small contribution of the quiescent current to total power dissipation the maximum input voltage
(while still delivering 50 mA output current) is 20.9V. The SM74501–5.0 will go into thermal shutdown if it
attempts to deliver full output current with an input voltage of more than 20.9V. Similarly, at 40V input and 25°C
ambient the SM74501–5.0 can deliver 21.4 mA maximum.
Under conditions of higher ambient temperatures, the voltage and current calculated in the previous examples
will drop. For instance, at the maximum ambient of 125°C the SM74501–5.0 can only dissipate 167 mW, limiting
the input voltage to 8.2V for a 50 mA load, or 2.3 mA output current for a 40V input.
The junction to ambient thermal resistance θ_JA rating has two distinct components: the junction to case thermal
resistance rating θ_JC; and the case to ambient thermal resistance rating θ_CA. The relationship is defined as: θ_JA =
θ_JC + θ_CA.
While the SM74501 has an internally set thermal shutdown point of typically 160°C, this is intended as a safety
feature only. Continuous operation near the thermal shutdown temperature should be avoided as it may have a
negative affect on the life of the device.
While the SM74501 maintains regulation to 60V, it will not withstand a short circuit above 40V because of safe
operating area limitations in the internal PNP pass device. Above 60V the SM74501 will break down with
catastrophic effects on the regulator and possibly the load as well. Do not use this device in a design where the
input operating voltage may exceed 40V, or where transients are likely to exceed 60V.
(1) The maximum power dissipation is a function of T_Jmax, θ_JA, and T_A. The maximum allowable power dissipation at any ambient
temperature is P_D = (T_Jmax − T_A)/θ_JA. If this dissipation is exceeded, the die temperature will rise above 150°C and the SM74501 will go
into thermal shutdown.
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