TLE4678-2_15 Datasheet, PDF (17/33 Pages) Infineon Technologies AG – Low Drop Out Linear Voltage Regulator

TLE4678-2
Reset Function
Reset Reaction Time
In case the output voltage of the regulator drops below the output undervoltage lower reset threshold V_RT,lo, the
delay capacitor C_D is discharged rapidly. Once the delay capacitor’s voltage has reached the lower delay switching
threshold V_DST,lo, the reset output “RO” will be set to “low”. In case of a very short drop of output voltage, may the
delay capacitor voltage doesn‘t reach the lower delay switching threshold and therefore no “RO” = “low will be set.
This prevents a microcontroller reset because of a very short distortion on output voltage. Typically the time of this
fiter effect is about 550 ns (t_rr,blank). See also timing diagram on Page 18
Additionally to the delay capacitor discharge time t_rr,d, an internal reaction time t_rr,int applies. Hence, the total reset
reaction rime t_rr,total becomes:
t_rr,total = t_rr,int + t_rr,d
(3)
with
• t_rr,total: Total reset reaction time
• t_rr,int: Internal reset reaction time; see Table “Internal Reset Reaction Time” on Page 20.
• t_rr,d: Delay capacitor discharge time. For a capacitor C_D different from the value specified in Table “Delay
Capacitor Discharge Time” on Page 20, see typical performance graphs.
Reset Ouput “RO”
The reset output “RO” is an open collector output with an integrated pull-up resistor. In case a lower-ohmic “RO”
signal is desired, an external pull-up resistor to the output “Q” can be connected. Since the maximum “RO” sink
current is limited, the optional external resistor R_RO,ext must not below as specified in Table “Reset Output” on
Page 19.
Reset Output “RO” Low for V_Q ≥ 1 V
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.
Reset Adjust Function
The undervoltage reset switching threshold can be adjusted according to the application’s needs by connecting
an external voltage divider (R_ADJ1, R_ADJ2) at pin “RADJ”. For selecting the default threshold connect pin “RADJ” to
GND. The reset adjustment range is given in Table “Reset Adjustment Range” on Page 19.
When dimensioning the voltage divider, take into consideration that there will be an additional current constantly
flowing through the resistors.
With a voltage divider connected, the reset switching threshold V_RT,new is calculated as follows (neglecting the
Reset Adjust Pin Current I_RADJ):
V_RT,new = V_RADJ,th × (R_ADJ,1 + R_ADJ,2) / R_ADJ,2
(4)
with
• V_RT,new: Desired reset switching threshold.
• R_ADJ,1, R_ADJ,2: Resistors of the external voltage divider, see Figure 6.
• V_RADJ,th: Reset adjust switching threshold given in Table “Reset Adjust” on Page 19.
Data Sheet
17
Rev. 1.0, 2014-03-03