SPT02-236DDB datasheet(6/12 Pages) STMICROELECTRONICS

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Application considerations

SPT02-236DDB

6/12

DocID024333 Rev2

Application considerations

5.1

Demagnetization of an inductive load driven by the switch

protection diode.

The turn off energy EOFF that could be dissipated in the D1 diode is calculated as shown in

AN587 and AN1351 application notes:

EOFF = VBR x L / / (RS)² x [VCC + (VCC - VBR) x ln (VBR / (VBR - VCC))]

tOFF = L x ln (VBR / (VBR - VCC)) / RS

POFF = EOFF / tOFF

With L = 1 H; I = 0.3 A; VBR = 39 V; VCC = 30 V, RS = 100 Ω the stress withstood by D1

becomes:

EOFF = 65 mJ; tOFF = 15 ms; POFF = 4.3 W

In a single pulse mode operation, the junction temperature can be fairly estimated:

TJ = Tamb + [ZTH (tOFF) x POFF]

In a repetitive operation with an F repetitive rate,

PAV = EOFF x F

TJ_AV = Tamb + PAV x RTH_JA

And during the demagnetization tOFF, TJ_PK < TJ_AV + POFF x ZTH (tOFF)

ZTH is the transient thermal impedance of each diode for a pulse having a duration

tOFF.

Figure 7. Electrical diagram for inductive load demagnetization

5.2

Life time considerations

Life time of the product is calculated to exceed 10 years. The key parameters to

consider are the ambient temperature (Tamb < 100 °C), the power supply voltage

(VCC < 30 V), and the current in the reverse blocking diode (IF = 0.1 A switching at

0.5 Hz with 50% duty cycle, the stand-by current being less than 1.5 mA).

For higher current or higher switching frequency operation, the life time should be

calculated considering the peak and average junction temperature.

Load

Switch

Load

Switch

Load

Switch

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