ST AN453 APPLICATION NOTE

AN453

Application note

TDE1897C, TDE1897R, TDE1898C and TDE1898R

in extreme overload conditions

Introduction

The purpose of this document is to provide the circuit designer with some insight into how the TDE1897C, TDE1897R, TDE1898C and TDE1898R devices behave in extreme overload conditions. Although the conditions may range outside the limits of the guaranteed performances described in the device datasheet, erroneous connections during the installation phase may occur and momentarily create such conditions. The performed tests confirm the extreme ruggedness of this device and its ability to overcome the accidental overload.

The TDE1897C, TDE1897R, TDE1898C and TDE1898R are monolithic intelligent power switch (IPS) in high-side configuration made in BCD technology (see Figure 1). They can drive resistive and inductive loads such as lamps, relays, electrovalves and so on. An internal voltage clamping diode to +VS creates, in inductive loads, a fast demagnetization path with no external components. Suitable for industrial applications, the device operates in the 18to 35 V supply range, delivering output currents up to 500 mA. In typical applications, it can drive up to 1 or 1.5 H load coils (48 to 60 Ω typical associated resistance).

Figure 1. Block diagram

December 2008

Rev 3

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Contents	AN453

Contents

1	Overload conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	3
2	Overload operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	4
3	Measurements and calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	5
4	Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	6
5	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	7

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AN453	Overload conditions

1 Overload conditions

To investigate how the TDE1897C, TDE1897R, TDE1898C and TDE1898R behave in extreme inductive overload conditions, which can occur when too big a load is connected to the device output, tests have been performed in bias conditions that lead the device to function out of the operatives and rated limits specified in the datasheet.

The test conditions (depicted in Figure 2) are the following: VS = +24 V,

IO = internal limited, Tamb = 25 °C, L = 1.4 H (non saturating), RL = 12 Ω, Vi = 2 V (Vih)(a), Tj = from Θ Lim-TH to Θ Lim and above(b).

Figure 2. Inductive load equivalent circuit and demagnetization cycle waveforms

a.The input signal asks for a permanent "on" state.

b.Θ Lim and TH = thresholds of intervention and hysteresis of the internal thermal protection circuit.

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