TLE 4678EL Infineon Technologies, TLE 4678EL Datasheet - Page 22

• Manufacturer Part Number: TLE 4678EL
• Manufacturer: Infineon Technologies

Specifications of TLE 4678EL

• Packages: PG-SSOP-14
• Regulator Type: single output
• Output Voltage: 5V
• Accuracy: 2.0 %
• Max. Output Current: 200mA
• Dropout Voltage: 250mV

8
8.1
The TLE4678 features a load dependent watchdog function with a programmable activating threshold as well as
a programmable watchdog timing.
The watchdog function monitors a microcontroller, including time base failures. In case of a missing rising edge
within a certain pulse repetition time, the watchdog output is set to ‘low’. The programming of the expected
watchdog pulse repetition time can be easily done by an external reset delay capacitor.
The watchdog output “WO” is separated from the reset output “RO”. Hence, the watchdog output might be used
as an interrupt signal for the microcontroller independent from the reset signal. It is possible to interconnect pin
“WO” and pin “RO” in order to establish a wire-or function with a dominant low signal.
Programmable Watchdog Activation Threshold and Hysteresis
In case a microcontroller is set to sleep mode or to low power mode, its current consumption is very low and the
controller might not be able to send any watchdog pulses to the regulators watchdog input “WI”. In order to avoid
unwanted wake-up signals due to missing edges at pin “WI”, the TLE4678 watchdog function can be activated
dependent on the regulator’s output current. The TLE4678 comprises a default watchdog activating threshold
I
R
The following equation calculates the external resisistor
watchdog at a desired output current
At decreasing output current, the deactivation threshold then would be:
The watchdog activating threshold hysteresis
with:
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Datasheet
Q,WDact,th
WADJ,ext
I
R
R
F
F
F
Q,WDact,th
WADJ,int
WADJ,ext
WDact,th
WDdeact,th
WDact,hy
R
I
I
Q,WDdeact,th
Q,WDact,hy
WADJ,ext
to pin “WADJ”. For using the default watchdog activating threshold, leave pin “WADJ” open.
with a small hysteresis
: Internal Watchdog Adjust Resistor
: Activating Threshold Factor
: External Watchdog Adjust Resistor
: Activating Threshold Factor Hysteresis
Watchdog Function
Description
: Desired “Watchdog Activating Threshold”
: Deactivating Threshold Factor
=
=
=
F
(
R
F
WDact,hy
WADJ,int
WDdeact,th
F
WDact,th
I
R
R
Q,WDact,th
WADJ,int
WADJ,int
R
R
I
WADJ,int
WADJ,int
Q,WDact,hy
R
WADJ,int
I
) -
+
Q,WDact,th
R
R
+
F
WADJ,ext
WADJ,ext
WDact,th
R
R
. The thresholds can be increased by connecting an external resistor
WADJ,ext
WADJ,ext
I
:
Q,WDact,hy
for
I
Q,WDact,th
22
calculates:
R
WADJ,ext
larger than the default value given in
that is needed at pin “WADJ” for activating the
Rev. 1.1, 2009-08-27
Watchdog Function
Item
TLE4678
8.2.1. (5)
(6)
(7)