TLE4278G Datasheet, PDF (2/18 Pages) Siemens Semiconductor Group – 5-V Low-Drop Fixed Voltage Regulator

TLE 4278 G
Two additional features of the TLE 4278 are a load dependent watchdog function as well
as a power on reset and under voltage reset function with an adjustable reset delay time
and adjustable reset switching threshold.
The watchdog function monitors whether the microcontroller is functioning appropriately,
including time base failures. In the case that there is no positive-going edge within a
certain pulse repetition-time the watchdog output is set to LOW. Programming of the
max. repetition time is done by the reset delay capacitor so that no additional external
components are necessary. To prevent the microcontroller from a automatic reset in
case of missing pulses, the watchdog output WO is separated from the reset output RO
for the TLE 4278. The watchdog output can be used as an interrupt signal for the
microcontroller. Pin WO can be externally connected to pin RO.
When the controller is set to sleep mode or low power mode its current consumption
drops and no watchdog pulses are created. In order to prevent the microcontroller from
unnecessary wake ups due to missing pulses at pin WI the watchdog feature can be
disabled as a function of the load. The switch off threshold is set by an external resistor
to pin WADJ. This function can also be used as a timer, which periodically wakes up the
controller. Therefore the pin WADJ has to be connected to the output Q.
The power on reset feature is necessary for a defined start of the microprocessor when
switching on the application. For a certain delay time after the output voltage of the
regulator has surpassed the reset threshold, a reset signal is generated. The delay time
is set by an external delay capacitor. The under voltage reset circuit supervises the
output voltage. In case VQ falls below the reset threshold the reset output is set LOW
after a short reaction time. The reset LOW signal is generated down to an output voltage
VQ of 1 V. In addition the reset switching threshold can be adjusted by an external
voltage divider. This feature is useful with microprocessors which guarantee a safe
operation down to voltages below the internally set reset threshold of 4.65 V typical.
Semiconductor Group
2
1998-11-01