LP38691_15 Datasheet, PDF (13/34 Pages) Texas Instruments – LP3869x/-Q1 500-mA Low-Dropout CMOS Linear Regulators Stable With Ceramic Output Capacitors

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LP38691, LP38693, LP38691-Q1, LP38693-Q1
SNVS321N – JANUARY 2005 – REVISED MARCH 2015
8.3 Feature Description
8.3.1 Enable (EN)
The LP38693 has an Enable pin (EN) which allows an external control signal to turn the regulator output On and
Off. 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 pin should be
connected directly to the IN pin.
8.3.2 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 Thermal Shutdown circuitry of the LP38693 has been designed to protect against
temporary thermal overload conditions.
The Thermal Shutdown circuitry was not intended to replace proper heat-sinking. Continuously running the
LP38693 device into thermal shutdown degrades device reliability.
8.3.3 Foldback Current Limiting
Foldback current limiting is built into the LP38691 and LP38693 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 IN and OUT pins. 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.
8.4 Device Functional Modes
8.4.1 Enable (EN)
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.
8.4.2 Minimum Operating Input Voltage (V_IN)
The LP38691 and LP38693 do not include any dedicated UVLO circuitry. Neither device internal circuitry is fully
functional until V_IN is at least 2.7 V. The output voltage is not regulated until V_IN ≥ (V_OUT + V_DO), or 2.7 V,
whichever is higher.
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Product Folder Links: LP38691 LP38693 LP38691-Q1 LP38693-Q1