TLE4678 Datasheet, PDF (18/31 Pages) Infineon Technologies AG – Low Drop Out Linear Voltage Regulator 5 V Fixed Output Voltage

TLE4678
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”.
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 Item 7.2.16.
• t_rr,d: Delay capacitor discharge time. For a capacitor C_D different from the value specified in Item 7.2.17, 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 Item 7.2.8.
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 Item 7.2.6.
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,adj is calculated as follows:
V_RT,adj = V_RADJ,th × (R_ADJ,1 + R_ADJ,2) / R_ADJ,2
(4)
with
• V_RT,adj: Desired reset switching threshold.
• R_ADJ,1, R_ADJ,2: Resistors of the external voltage divider, see Figure 7.
• V_RADJ,th: Reset adjust switching threshold given in Item 7.2.5.
Datasheet
18
Rev. 1.1, 2009-08-27