Datasheet 16 Rev. 1.1, 2007-10-17
TLE 4299
Early Warning
The early warning function compares a voltage defined by the user to an internal
reference voltage. Therefore the supervised voltage has to be scaled down by an
external voltage divider in order to compare it to the internal sense threshold of typical
1.36 V. The sense output pin is set low, when the voltage at SI falls below this threshold.
A typical example where the circuit can be used is to supervise the input voltage
V
I
to
give the microcontroller a prewarning of low battery condition.
Calculation to the voltage divider can be easily done since the sense input current can
be neglected.
Figure 9 Sense Timing Diagram
V
thHL
= (R
SI1
+ R
SI2
)/R
SI2
× V
SI low
[4]
V
thLH
= (R
SI1
+ R
SI2
)/R
SI2
× V
SI high
[5]
The sense in comparator uses a hysteresis of typical 90 mV. This hysteresis of the
supervised threshold is multiplied by the resistor dividers amplification (
R
SI1
+ R
SI2
)/R
SI1
.
The sense in comparator can also be used for receiving data with a threshold of typical
1.36 V and a hysteresis of 90 mV. Of course also the data signal can be scaled down
with a resistive divider as shown above. With a typical delay time of 2.5 µs for positive
transitions and 2.4 µs for negative transitions receiving data of up to 100 kBaud are
possible. The sense output is an open collector output.
t
Sense
t
SI, High
V
SI, Low
V
Input
Voltage
High
Low
Output
Sense
t
PD SO LH PD SO HL
t
