DIO2399A/B

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DIO2399A/B• Rev. 1.7

voltage, the REF pin should be buffered by an op amp.

In systems where the DIO2399X output can be sensed differentially, such as by a differential input

analog-to-digital converter (ADC) or by using two separate ADC inputs, the effects of external impedance on

the REF input can be canceled. Figure 10 depicts a method of taking the output from the DIO2399X by using the

REF pin as a reference.

Figure 10. Sensing DIO2399X to cancel effects of impedance on the REF input

Using the DIO2399X with common-mode transients above 26 V

With a small amount of additional circuitry, the DIO2399X series can be used in circuits subject to transients

higher than 26 V, such as automotive applications. Use only zener diode or zener-type transient absorbers

(sometimes referred to as Transzorbs); any other type of transient absorber has an unacceptable time delay.

Start by adding a pair of resistors as shown in Figure 11 as a working impedance for the zener. It is desirable

to keep these resistors as small as possible, most often around 10 Ω. Larger values can be used with an effect

on gain that is discussed in the section on input filtering. Because this circuit limits only short-term transients,

many applications are satisfied with a 10 Ω resistor along with conventional zener diodes of the lowest power

rating that can be found. This combination uses the least amount of board space.

Figure 11. DIO2399X transient protection using dual zener diodes

In the event that low-power zeners do not have sufficient transient absorption capability and a higher power

transzorb must be used, the most package-efficient solution then involves using a single transzorb and back-to-

back diodes between the device inputs. This method is shown in Figure 12.