LP38691-ADJ_16 Datasheet, PDF (12/27 Pages) Texas Instruments – 500-mA Low-Dropout CMOS Linear Regulators Stable

LP38691-ADJ, LP38693-ADJ, LP38691-ADJ-Q1, LP38693-ADJ-Q1
SNVS324K – JANUARY 2005 – REVISED JANUARY 2016
www.ti.com
7.3 Feature Description
7.3.1 Enable (EN)
The LP38693-ADJ has an enable pin (EN) which allows an external control signal to turn the regulator output to
either an ON or OFF state. The Enable on/off threshold has no hysteresis. The voltage signal must rise and fall
cleanly, and promptly, through the on and off voltage thresholds. The EN pin voltage must be higher than the
V_EN(MIN) threshold to ensure that the device is fully enabled under all operating conditions. The EN pin voltage
must be lower than the V_EN(MAX) threshold to ensure that the device is fully disabled. The EN pin has no internal
pullup or pulldown to establish a default condition and, as a result, this pin must be terminated either actively or
passively. If the EN pin is driven from a source that actively pulls high and low, the drive voltage should not be
allowed to go below ground potential or higher than V_IN. If the application does not require the enable function,
the EN pin should be connected directly to the IN pin.
7.3.2 Thermal Overload Protection (T_SD)
Thermal shutdown disables the output when the junction temperature rises to approximately 160°C which allows
the device to cool. When the junction temperature cools to approximately 150°C, the output circuitry enables.
Based on power dissipation, thermal resistance, and ambient temperature, the thermal protection circuit may
cycle on and off. This thermal cycling limits the dissipation of the regulator and protects it from damage as a
result of overheating. The T_SD circuitry of the LP38693 has been designed to protect against temporary thermal
overload conditions.
The T_SD circuitry was not intended to replace proper heat-sinking. Continuously running the LP38693 device into
thermal shutdown degrades device reliability.
7.3.3 Foldback Current Limiting
Foldback current limiting is built into the LP3869x-ADJ devices which reduces the amount of output current the
part can deliver as the output voltage is reduced. The amount of load current is dependent on the differential
voltage between the V_IN and V_OUT. Typically, when this differential voltage exceeds 5 V, the load current will limit
at about 350 mA. When the V_IN – V_OUT differential is reduced below 4 V, load current is limited to about 850 mA.
CAUTION
When toggling the LP38693 Enable (EN) after the input voltage (V_IN) is applied, the
foldback current limit circuitry is functional the first time that the EN pin is taken high.
The foldback current limit circuitry is non-functional the second, and subsequent, times
that the EN pin is taken high. Depending on the input and output capacitance values
the input inrush current may be higher than expected which can cause the input
voltage to droop.
If the EN pin is connected to the IN pin, the foldback current limit circuitry is functional
when V_IN is applied if V_IN starts from less than 0.4 V.
7.4 Device Functional Modes
7.4.1 Enable (EN)
The LP38693-ADJ may be switched to the ON or OFF state by logic input at the EN pin. A logic-high voltage on
the EN pin turns the device to the ON state. A logic-low voltage on the EN pin turns the device to the OFF state.
If the application does not require the shutdown feature, the EN pin must be tied to V_IN to keep the regulator
output permanently in the ON state when power is applied.
To ensure proper operation, the signal source used to drive the EN input must be able to swing above and below
the specified turnon or turnoff voltage thresholds listed in the Electrical Characteristics section under V_EN.
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