SPT01-335DEE datasheet(8/16 Pages) STMICROELECTRONICS

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Evaluation of the clamping voltage

SPT01-335DEE

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DocID15200 Rev3

Evaluation of the clamping voltage

VBR (TJ) = VBR (25) x (1+ αT (TJ – 25))

VCL MAX (8/20 µs) = VBR MAX + RD x IPP

5.1

Application considerations

5.1.1

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

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

T(J_AV) = Tamb + PAV x Rth(j-a)

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 12. Electrical diagram for inductive load demagnetization

Load

Switch

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