LM26LVCISD-080SLASHNOPB datasheet(18/33 Pages) TI1

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Rpull-up = VDD (Max) ± VOL

iT = iL + isink

OVERTEMP

VDD

RPull-Up

VOUT

isink

Digital Input

LM26LV

SNIS144F – JULY 2007 – REVISED FEBRUARY 2013

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OVERTEMP and OVERTEMP Digital Outputs

The OVERTEMP Active High, Push-Pull Output and the OVERTEMP Active Low, Open-Drain Output both assert

at the same time whenever the Die Temperature reaches the factory preset Temperature Trip Point. They also

assert simultaneously whenever the TRIP TEST pin is set high. Both outputs de-assert when the die temperature

goes below the Temperature Trip Point - Hysteresis. These two types of digital outputs enable the user the

flexibility to choose the type of output that is most suitable for his design.

Either the OVERTEMP or the OVERTEMP Digital Output pins can be left open if not used.

OVERTEMP OPEN-DRAIN DIGITAL OUTPUT

The OVERTEMP Active Low, Open-Drain Digital Output, if used, requires a pull-up resistor between this pin and

VDD. The following section shows how to determine the pull-up resistor value.

Determining the Pull-up Resistor Value

The Pull-up resistor value is calculated at the condition of maximum total current, iT, through the resistor. The

total current is:

(7)

where,

iT is the maximum total current through the Pull-up Resistor at VOL.

iL is the load current, which is very low for typical digital inputs.

VOUT VOUT is the Voltage at the OVERTEMP pin. Use VOL for calculating the Pull-up resistor.

VDD(Max) VDD(Max) is the maximum power supply voltage to be used in the customer's system.

The pull-up resistor maximum value can be found by using the following formula:

(8)

EXAMPLE CALCULATION

Suppose we have, for our example, a VDD of 3.3 V ± 0.3V, a CMOS digital input as a load, a VOL of 0.2 V.

1. We see that for VOL of 0.2 V the electrical specification for OVERTEMP shows a maximim isink of 385 µA.

2. Let iL= 1 µA, then iT is about 386 µA max. If we select 35 µA as the current limit then iT for the calculation

becomes 35 µA

3. We notice that VDD(Max) is 3.3V + 0.3V = 3.6V and then calculate the pull-up resistor as RPull-up = (3.6 −

0.2)/35 µA = 97k

4. Based on this calculated value, we select the closest resistor value in the tolerance family we are using.

In our example, if we are using 5% resistor values, then the next closest value is 100 k

Ω.

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