Datasheet

TPS7201Q, TPS7225Q, TPS7230Q
TPS7233Q, TPS7248Q, TPS7250Q, TPS72xxY
MICROPOWER LOW-DROPOUT (LDO) VOLTAGE REGULATORS
SLVS102G – MARCH 1995 – REVISED JUNE 2000
30
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
power dissipation and junction temperature
Specified regulator operation is assured to a junction temperature of 125°C; the maximum junction temperature
allowable to avoid damaging the device is 150°C. These restrictions limit the power dissipation that the regulator
can handle in any given application. To ensure the junction temperature is within acceptable limits, calculate
the maximum allowable dissipation, P
D(max)
, and the actual dissipation, P
D
, which must be less than or equal
to P
D(max)
.
The maximum-power-dissipation limit is determined using the following equation:
P
D(max)
T
J
max T
A
R
JA
Where:
T
J
max is the maximum allowable junction temperature, i.e.,150°C absolute maximum and 125°C
recommended operating temperature.
R
θJA
is the thermal resistance junction-to-ambient for the package, i.e., 172°C/W for the 8-terminal
SOIC and 238°C/W for the 8-terminal TSSOP.
T
A
is the ambient temperature.
The regulator dissipation is calculated using:
P
D
V
I
V
O
I
O
Power dissipation resulting from quiescent current is negligible.
regulator protection
The TPS72xx PMOS-pass transistor has a built-in back diode that safely conducts reverse currents when the
input voltage drops below the output voltage (e.g., during power down). Current is conducted from the output
to the input and is not internally limited. If extended reverse voltage is anticipated, external limiting might be
appropriate.
The TPS72xx also features internal current limiting and thermal protection. During normal operation, the
TPS72xx limits output current to approximately 1 A. When current limiting engages, the output voltage scales
back linearly until the overcurrent condition ends. While current limiting is designed to prevent gross device
failure, care should be taken not to exceed the power dissipation ratings of the package. If the temperature of
the device exceeds 165°C, thermal-protection circuitry shuts it down. Once the device has cooled, regulator
operation resumes.