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AN1596 - APPLICATION NOTE

50°C/W to 15°C/W by holes linking different copper layers.

In the VIPower HSDs datasheets there are two sections concerning the thermal management. The first

one shows the thermal calculation in order to find out the junction temperature in static conditions together

with a plot of thermal resistance junction to ambient versus PCB heatsink area. The second one shows a

plot of thermal impedance junction ambient in single pulse and the thermal model is shown with relevant

thermal resistances and capacitors values (easy simulations can be performed both in static conditions

and during transients as, for example, switching on a load with high in rush currents or PWM operation).

In figure 6 an example of a double channel HSD thermal model is shown.

Figure 6: VND830 (SO16L package) thermal model

THE CONTROL AND PROTECTION CIRCUIT

Protection against low energy spikes and load dump

The voltage transients are very dangerous hazards to the automotive electronics. The transients tend to

be either low energy- high voltage spikes or high energy-high voltage, up to 125V levels. The low energy

spikes are generated by fast turnoff of high-current inductive loads, such as air-conditioning compressor

clutches. This effect, combined with inductive behavior of wires, causes an overshoot voltage on the

MOSFET T2 that is turned on through an internal clamp circuit (see figure 7).

M0-3 High Side Drivers are designed to successfully pass the 1, 2, 3a, 3b and 4 ISO-7637 standard

pulses test (see table 1 carried in HSDs datasheets as well) - simulating the low energy voltage spikes.

These values must be added to the voltage battery (for cars about 13.5V) to obtain the actual voltage. The

N.5 ISO7637 pulse simulates the alternator load dump in the case of a Generator with an internal

impedance of 2

Ω and different values of magnetic field of the excitation circuit (see figure 8 for the level

IV pulse); this occurs when the battery is disconnected whilst being charged by the alternator. The voltage

spike can reach duration of approximately ½ second and it is of high-energy nature because of the

alternator's low source impedance. Where a centralized clamp circuit is not provided or ISO7637 rated

figure 7). This is done because an internal protection against load dump would require a larger die size

and - therefore - higher cost than putting on a module level protection.

T_amb

Pd1

C1

R4

C3

C4

R3

R1

R6

R5

R2

C5

C6

C2

Pd2

R2

C1

C2

R1

Tj_1

Tj_2

Footprint

6

R1 (°C/W)

0.15

R2 (°C/W)

0.8

R3 (°C/W)

2.2

R4 (°C/W)

12

R5 (°C/W)

15

R6 (°C/W)

37

22

C1 (W.s/°C)

0.0006

C2 (W.s/°C)

2.10E-03

C3 (W.s/°C)

1.50E-02

C4 (W.s/°C)

0.14

C5 (W.s/°C)

1

C6 (W.s/°C)

3

5