TLE 4275 V33
Block Description and Electrical Characteristics
Datasheet 7 Rev. 1.0, 2006-09-22
3.3 Reset Function
The reset function contains serveal features:
Output Undervoltage Reset:
An output undervoltage condition is indicated setting the Reset Output “RO” to low. This signal might be used to
reset a microcontroller during low supply voltage.
In case the battery voltage is already lower than the buffered output voltage VQ of the voltage regulator, the reset
circuit is supplied from the output “Q”, ensuring a defined reset switching threshold also at VI = 0 V. The Reset
Output “RO” is held “low” down to an output voltage of VQ = 1 V, even if the input voltage VI is 0 V.
Power-On Reset Delay Time:
The power-on reset delay time td,PWR-ON allows a microcontoller and oscillator to start up. This delay time is the
time period from exceeding the reset switching threshold VRT until the reset is released by switching the reset
output “RO” from “low” to “high”. The power-on reset delay time td,PWR-ON is defined by an external delay
capacitor CD connected to pin “D” which is charged up by the delay capacitor charge current ID,ch starting from
VD= 0 V.
For easy calculating the power-on reset delay time, a multiplier factor Fd,PWR-ON =td,PWR-ON /CD is specified.
Hence, td,PWR-ON becomes:
td,PWR-ON = Fd,PWR-ON / CD . (1)
For a precise calculation consider also the delay capacitor’s tolerance.
Undervoltage Reset Delay Time:
Unlike the power-on reset delay time, the undervoltage reset delay td time considers a short output undervoltage
event where the delay capacitor CD is assumed to be discharged to VD=VDST,lo only before the charging sequence
restarts. Therefore, the undervoltage reset delay time td is defined by the delay capacitor charge current ID,ch
starting from VD=VDST,lo and the external delay capacitor CD.
For easy calculating the undervoltage reset delay time, a multiplier factor Fd=td/CD is specified. Hence, td
becomes:
td = Fd / CD . (2)
For a precise calculation consider also the delay capacitor’s tolerance.
Reset Reaction Time:
The total reset reaction rime trr,total considers the internal reaction time trr,int and the discharge time trr,d defined by
the external delay capacitor CD (see typical performance graph for details). Hence, the total reset reaction rime
becomes:
trr,total = trr,int + trr,d . (3)
Reset Output “RO” Low for VQ
≥
1V:
In case of an undervoltage reset condition reset output “RO” is held “low” for VQ≥1 V, even if the input voltage VI
is 0 V. This is achieved by supplying the reset circuit from the output capacitor.