TLE42754 Datasheet, PDF (15/24 Pages) Infineon Technologies AG – Low Dropout Linear Fixed Voltage Regulator

TLE42754
5.3
Reset Function
Block Description and Electrical Characteristics
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_rd allows a microcontoller and oscillator to start up. This delay time is the time frame
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_rd is defined by an external delay capacitor C_D connected to pin D
charged by the delay capacitor charge current I_D,ch starting from V_D = 0 V.
If the application needs a power-on reset delay time t_rd different from the value given in Item 5.3.6, the delay
capacitor’s value can be derived from the specified values in Item 5.3.6 and the desired power-on delay time:
C_D = ^t--r--^d--t-^,-_r-ⁿ-_d--^e--^w-- × 47nF
with
• C_D: capacitance of the delay capacitor to be chosen
• t_rd,new: desired power-on reset delay time
• t_rd: power-on reset delay time specified in this datasheet
For a precise calculation also take the delay capacitor’s tolerance into consideration.
Reset Reaction Time:
The reset reaction time avoids that short undervoltage spikes trigger an unwanted reset “low” signal. The reset
reaction rime t_rr 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 time becomes:
t_rr = t_{rd, int} + t_{rr, d}
with
• t_rr: reset reaction time
• t_rr,int: internal reset reaction time
• t_rr,d: reset discharge
Reset Output Pull-Up Resistor R_RO:
The Reset Output RO is an open collector output requiring an external pull-up resistor to a voltage V_IO, e.g. V_Q. In
Table “Electrical Characteristics Reset Function” on Page 18 a minimum value for the external resistor R_RO
is given for the case it is connected to V_Q or to a voltage V_IO < V_Q. If the pull-up resistor shall be connected to a
voltage V_IO > V_Q, use the following formula:
R_RO = ^5--V--k---_Q^Ω--- × V_IO
Data Sheet
15
Rev. 1.0, 2008-05-29