TLE4678 datasheet(18/37 Pages) INFINEON

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Datasheet

Rev. 1.2, 2014-10-17

TLE4678

Reset Function

7.1

Description Reset Function

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 td,PWR-ON allows a microcontroller and oscillator to start up. This delay time is

the time period from exceeding the upper reset switching threshold VRT,hi until the reset is released by

switching the reset output “RO” from “low” to “high”. The power-on reset delay time td,PWR-ON is defined by an

external delay capacitor CD connected to pin “D” which is charged up by the delay capacitor charge

current ID,ch starting from VD = 0 V.

In case a power-on reset delay time td,PWR-ON different from the value for CD = 100nF is required, the delay

capacitor’s value can be derived from the specified value given in Item 7.2.15:

CD = 100nF × td,PWR-ON / td,PWR-ON,100nF

(7.1)

with

• td,PWR-ON: Desired power-on reset delay time

• td,PWR-ON,100nF: Power-on reset delay time specified in Item 7.2.15

• CD: Delay capacitor required.

The formula is valid for CD ≥ 10nF. For precise timing calculations consider also the delay capacitor’s

tolerance.

Undervoltage Reset Delay Time

Unlike the power-on reset delay time, the undervoltage reset delay time td considers a short output

undervoltage event where the delay capacitor CD is assumed to be discharged to VD = VDST,lo only before the

charging sequence starts. Therefore, the undervoltage reset delay time td is defined by the delay capacitor

charge current ID,ch starting from VD = VDST,lo and the external delay capacitor CD.

A delay capacitor CD for a different undervoltage reset delay time as specified in Item 7.2.14 can be calculated

similar as above:

CD = 100nF × td / td,100nF

(7.2)

with

• td: Desired undervoltage reset delay time

• td,100nF: Power-on reset delay time specified in Item 7.2.14

• CD: Delay capacitor required

The formula is valid for CD ≥ 10nF. For precise timing calculations consider also the delay capacitor’s

tolerance.

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