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TLE4678_15 Datasheet, PDF (19/37 Pages) Infineon Technologies AG – Low Drop Out Linear Voltage Regulator | |||
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TLE4678
Reset Function
Reset Reaction Time
In case the output voltage of the regulator drops below the output undervoltage lower reset threshold VRT,lo,
the delay capacitor CD is discharged rapidly. Once the delay capacitorâs voltage has reached the lower delay
switching threshold VDST,lo, the reset output âROâ will be set to âlowâ.
Additionally to the delay capacitor discharge time trr,d, an internal reaction time trr,int applies. Hence, the total
reset reaction rime trr,total becomes:
trr,total = trr,int + trr,d
(7.3)
with
⢠trr,total: Total reset reaction time
⢠trr,int: Internal reset reaction time; see Item 7.2.16.
⢠trr,d: Delay capacitor discharge time. For a capacitor CD different from the value specified in Item 7.2.17,
see typical performance graphs.
Reset Output âROâ
The reset output âROâ is an open collector output with an integrated pull-up resistor. In case a lower-ohmic
âROâ signal is desired, an external pull-up resistor to the output âQâ can be connected. Since the maximum
âROâ sink current is limited, the optional external resistor RRO,ext must not be lower than specified in
Item 7.2.8.
Reset Output âROâ Low for VQ ⥠1 V
In case of an undervoltage reset condition reset output âROâ is held âlowâ for VQ ⥠1 V, even if the input
voltage VI 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 applicationâs needs by
connecting an external voltage divider (RADJ1, RADJ2) at pin âRADJâ. For selecting the default threshold connect
pin âRADJâ 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 VRT,adj is calculated as follows:
VRT,adj = VRADJ,th à (RADJ,1 + RADJ,2) / RADJ,2
(7.4)
with
⢠VRT,adj: Desired reset switching threshold.
⢠RADJ,1, RADJ,2: Resistors of the external voltage divider, see Figure 7.
⢠VRADJ,th: Reset adjust switching threshold given in Item 7.2.5.
Datasheet
19
Rev. 1.2, 2014-10-17
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