TLE4678 datasheet(19/37 Pages) INFINEON

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Datasheet

Rev. 1.2, 2014-10-17

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 capacitor’s voltage has reached the lower delay

switching threshold VDST,lo, the reset output “RO” will be set to “low”.

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 “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 RRO,ext must not be lower than specified in

Item 7.2.8.

Reset Output “RO” Low for VQ ≥ 1V

In case of an undervoltage reset condition reset output “RO” is held “low” for VQ ≥ 1 V, even if the input

voltage VIis 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 (RADJ1, RADJ2) 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 VRT,adj is calculated as follows:

VRT,adj = VRADJ,th × (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.

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