AN2025 datasheet(5/11 Pages) STMICROELECTRONICS

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AN2025 - APPLICATION NOTE

5/11

The real peak current in avalanche (IAR) is less than I1 and I1 is less than IPEAK. We first approximate an

avalanche current value by taking IPEAK for all further calculations.

Moreover, STMicroelectronics guarantees that the maximum clamping voltage of Schottky diodes is al-

ways less than 2×VRRM (VRRM: Maximum repetitive reverse voltage).

Consequently from these 2 conditions, a conservative estimation of the maximum avalanche peak power

can be done:

PAVALANCHE = IAR.VClamp < PPEAK_AV = IPEAK.(2×VRRM)

Finally, to determine if a given Schottky diode can work in the avalanche area in a given SMPS, the fol-

lowing condition must be respected:

2.IPEAK.VRRM < PARM(1µs,Tj)

III.3. Methodology

Here below are the three steps to follow in order to define PPEAK_AV and to then compare it with

PARM(1µs,Tj).

■ Step1: Total current measurement iT (with snubber)

⇒ I

PEAK

■ Step2: Maximum avalanche peak power estimation

⇒ P

PEAK_AV = 2.IPEAK.VRRM

■ Step3: Check that:

⇒ P

PEAK_AV < PARM(1µs, Tj) using the specification tool (see § II)

[As tp < 1µs

⇒ P

ARM(tp, Tj) = cst = PARM(1µs, Tj)]

Example:

In this example, a 16A-100V Schottky diode (STPS16H100CT) working in the avalanche area is

considered.

■ Step1:

The figure 9 shows the total current through both

the snubber circuit and the STPS16H100CT.

■ Step2:

PPEAK_AV is given by:

⇒ P

PEAK_AV = 4.4 x (2 x 100)

⇒ P

PEAK_AV = 880W

■ Step3:

The data sheet of the STPS16H100CT gives:

PARM(1µs, 25°C)(STPS16H100CT) = 8700W

With the derating curve figure 2, we get:

PARM(1µs, 130°C)(STPS16H100CT) = 3045W

As PPEAK_AV is lower than PARM(1µs, Tj), the

STPS16H100CT can be used safely in this appli-

cation.

Figure 9: Total current iT (diode + snubber)

= 4.4A

PEAK

2A/div

0.1µs/div

T = 130°C

t < 1µs

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