UM1556 datasheet(53/87 Pages) STMICROELECTRONICS

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UM1556

Switching inductive loads

Doc ID 023520 Rev 2

53/87

Figure 43.

Transil – V/A characteristic

Considering the worst case values (VBAT = 16 V, VHSDClampMin = 41 V) the demagnetization

voltage should be limited at least to 16 – 41 = -25 V. Assuming 1 V voltage drop on the

protection diode (D) we need a transil with VCL < 24 V at the given current level (load current

at switch-off event). The clamping voltage is usually specified only at the maximum peak

power limit of the device. To determine the voltage at a given current level, apply a linear

approximation using VBR/IR and VCL/IPP data or estimate the value using VCL/IPP diagram in

the datasheet.

The transil must not conduct during a reverse battery condition. Assuming VBAT = -16 V, a

0.5 V drop on the HSD channel and a 0.5 V drop on the protection diode, we have -15 V

across the transil. We can find the parameter VRM (Stand-off voltage) in the transil

specification. VRM is the maximum operation voltage with low leakage current (valid in the

whole temperature range).

●

Single pulse energy capability

The maximum nonrepetitive transient power and current capability of transils is specified

mostly for 10/1000 µs exponential pulse at 25 °C. A real application condition is usually

different. In our case, the pulse length is given by the demagnetization time, while the

current waveform is close to the sawtooth shape (depending on L/R ratio of the load). To

check if the transil can safely operate under the desired conditions we can use the

translation diagrams in Figure 44, Figure 45 and Figure 46.

GAPGMS00119

VRM>15 V

VCL<24 V (at given I0)

UM1556 Datasheet(PDF) 53 Page - STMicroelectronics