The UCC381-3/-5/-ADJ family of positive linear series pass regulators is tailored for low drop out applications where low quiescent power is important. Fabricated with a BiCMOS technology ideally suited for low input to output differential applications, the UCC381 will pass 1A while requiring only 0.5V of input voltage headroom. Dropout voltage decreases linearly with output current, so that dropout at 200mA is less than 100mV. Quiescent current is always less than 650uA. To prevent reverse current conduction, on-chip circuitry limits the minimum forward voltage to typically 50mV. Once the forward voltage limit is reached, the input-output differential voltage is maintained as the input voltage drops until undervoltage lockout disables the regulator.
UCC381-3 and UCC381-5 versions have on-chip resistor networks preset to regulate either 3.3V or 5.0V, respectively. Furthermore, remote sensing of the load voltage is possible by connecting the VOUTS pin directly at the load. The output voltage is then regulated to 1.5% at room temperature and better than 2.5% over temperature. The UCC381-ADJ version has a regulated output voltage programmed by an external user-definable resistor ratio.
Short circuit current is internally limited. The device responds to a sustained overcurrent condition by turning off after a TON delay. The device then stays off for a period, TOFF, that is 32 times the TON delay. The device
then begins pulsing on and off at the TON/(TON +TOFF) duty cycle of 3%. This drastically reduces the power dissipation during short circuit such that heat sinking, if at all required, must only accommodate normal operation. On the fixed output versions of the device TON is fixed at 400us - a guaranteed minimum. On the adjustable version an external capacitor sets the on time. The off time is always 32 times TON.
The UCC381 can be shutdown to 25uA (max) by pulling the CT pin low.
Internal power dissipation is further controlled with thermal overload protection circuitry. Thermal shutdown occurs if the junction temperature exceeds 165°C. The chip
will remain off until the temperature has dropped 20°C.
The UCC281 series is specified for operation over the industrial range of -40°C to +85°C, and the UCC381 series is specified from 0°C to +70°C. These devices are
available in the 8 pin DP surface mount power package. For other packaging options consult the factory.
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