TLE42794_14 Datasheet, PDF (17/32 Pages) Infineon Technologies AG – Very low Current Consumption

TLE42794
5.6
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 trd 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 Power On Reset Delay
Time, the delay capacitor’s value can be derived from the specified values in Power On Reset Delay Time and
the desired power-on delay time:
(1)
C_D
=
t--_{r--d---,--n---e--w-- × 47nF}
t_rd
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:
(2)
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. In Table 6 “Electrical
Characteristics Reset Function” on Page 19 a minimum value for the external resistor R_RO is given. Keep in
mind to stay within the values specified for the Reset Output RO in Table 1 “Absolute Maximum Ratings” on
Page 8
Data Sheet
17
Rev. 1.2, 2014-07-03