TLE4678 Datasheet, PDF (17/31 Pages) Infineon Technologies AG – Low Drop Out Linear Voltage Regulator 5 V Fixed Output Voltage

TLE4678
Reset Function
7
Reset Function
7.1
Description Reset Function
The reset function provides several features:
Output Undervoltage Reset:
An output undervoltage condition is indicated by setting the Reset Output “RO” to “low”. This signal might be used
to reset a microcontroller during low supply voltage.
Power-On Reset Delay Time
The power-on reset delay time t_d,PWR-ON allows a microcontroller and oscillator to start up. This delay time is the
time period from exceeding the upper reset switching threshold V_RT,hi 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.
In case a power-on reset delay time t_d,PWR-ON different from the value for C_D = 100nF is required, the delay
capacitor’s value can be derived from the specified value given in Item 7.2.15:
C_D = 100nF × t_d,PWR-ON / t_{d,PWR-ON,100nF}
(1)
with
• t_d,PWR-ON: Desired power-on reset delay time
• t_{d,PWR-ON,100nF}: Power-on reset delay time specified in Item 7.2.15
• C_D: Delay capacitor required.
The formula is valid for C_D ≥ 10nF. For precise timing calculations consider also the delay capacitor’s tolerance.
Undervoltage Reset Delay Time
Unlike the power-on reset delay time, the undervoltage reset delay time t_d 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
starts. 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.
A delay capacitor C_D for a different undervoltage reset delay time as specified in Item 7.2.14 can be calculated
similar as above:
C_D = 100nF × t_d / t_d,100nF
(2)
with
• t_d: Desired undervoltage reset delay time
• t_d,100nF: Power-on reset delay time specified in Item 7.2.14
• C_D: Delay capacitor required
The formula is valid for C_D ≥ 10nF. For precise timing calculations consider also the delay capacitor’s tolerance.
Datasheet
17
Rev. 1.1, 2009-08-27