TLE 4275 V33
Block Description and Electrical Characteristics
Datasheet 7 Rev. 1.2, 2015-12-18
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
V
Q
of the voltage regulator, the reset
circuit is supplied from the output “Q”, ensuring a defined reset switching threshold also at
V
I
= 0 V. The Reset
Output “RO” is held “low” down to an output voltage of
V
Q
= 1 V, even if the input voltage V
I
is 0 V.
Power-On Reset Delay Time:
The power-on reset delay time
t
d,PWR-ON
allows a microcontoller and oscillator to start up. This delay time is the
time period from exceeding the reset switching threshold
V
RT
until the reset is released by switching the reset
output “RO” from “low” to “high”. The power-on reset delay time
t
d,PWR-ON
is defined by an external delay
capacitor
C
D
connected to pin “D” which is charged up by the delay capacitor charge current I
D,ch
starting from
V
D
= 0 V.
For easy calculating the power-on reset delay time, a multiplier factor
F
d,PWR-ON
= t
d,PWR-ON
/ C
D
is specified.
Hence,
t
d,PWR-ON
becomes:
t
d,PWR-ON
= F
d,PWR-ON
*C
D
. (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
t
d
time considers a short output undervoltage
event where the delay capacitor
C
D
is assumed to be discharged to V
D
= V
DST,lo
only before the charging sequence
restarts. Therefore, the undervoltage reset delay time
t
d
is defined by the delay capacitor charge current I
D,ch
starting from V
D
= V
DST,lo
and the external delay capacitor C
D
.
For easy calculating the undervoltage reset delay time, a multiplier factor
F
d
= t
d
/ C
D
is specified. Hence, t
d
becomes:
t
d
= F
d
*C
D
. (2)
For a precise calculation consider also the delay capacitor’s tolerance.
Reset Reaction Time:
The total reset reaction rime
t
rr,total
considers the internal reaction time t
rr,int
and the discharge time t
rr,d
defined by
the external delay capacitor
C
D
(see typical performance graph for details). Hence, the total reset reaction rime
becomes:
t
rr,total
= t
rr,int
+ t
rr,d
. (3)
Reset Output “RO” Low for
V
Q
≥
1V:
In case of an undervoltage reset condition reset output “RO” is held “low” for
V
Q
≥ 1 V, even if the input voltage V
I
is 0 V. This is achieved by supplying the reset circuit from the output capacitor.
