TLE 4268
Reset Timing
The power-on reset delay time is defined by the charging time of an external capacitor
CD which can be calculated as follows:
CD = (∆trd × ID,c)/∆V
Definitions: CD = delay capacitor
∆trd = delay time
ID,c = charge current, typical 12 µA
∆V = VDU, typical 1.8 V
VDU = upper delay switching threshold at CD for reset delay time
The reset reaction time trr is the time it takes the voltage regulator to set the reset out
LOW after the output voltage has dropped below the reset threshold. It is typically 1 µs
for delay capacitor of 47 nF. For other values for CD the reaction time can be estimated
using the following equation:
trr ≈ 20 s/F × CD
VΙ
VQ
VD
t rd
t rr
VRO
t
< t rr
V Q, rt
dV
dt
=
Ι D,c
CD
t
V DU
V DRL
t
Power-on-Reset
Thermal
Shutdown
Voltage Dip
at Input
Undervoltage Secondary Overload
Spike at Output
t
AED03010
Figure 5 Timing (Watchdog Disabled)
Data Sheet Rev. 1.3
10
2001-07-18