Datasheet

A5972D Functional description
Doc ID 13956 Rev 5 11/37
diode can be considered a high value capacitor and this produces a very high peak current,
responsible for numerous problems:
● Spikes on the device supply voltage that cause oscillations (and thus noise) due to the
board parasites.
● Turn ON overcurrent leads to a decrease in the efficiency and system reliability.
● Major EMI problems.
● Shorter freewheeling diode life.
The fall time of the current during turn OFF is also critical, as it produces voltage spikes (due
to the parasites elements of the board) that increase the voltage drop across the PDMOS.
In order to minimize these problems, a new driving circuit topology has been used and the
block diagram is shown in Figure 6. The basic idea is to change the current levels used to
turn the power switch ON and OFF, based on the PDMOS and the gate clamp status.
This circuitry allows the power switch to be turned OFF and ON quickly and addresses the
freewheeling diode recovery time problem. The gate clamp is necessary to ensure that V
GS
of the internal switch does not go higher than V
GS
max. The ON/OFF Control block protects
against any cross conduction between the supply line and ground.
Figure 6. Driving circuitry
5.6 Thermal shutdown
The shutdown block generates a signal that turns OFF the power stage if the temperature of
the chip goes higher than a fixed internal threshold (150±10 °C). The sensing element of the
chip is very close to the PDMOS area, ensuring fast and accurate temperature detection. A
hysteresis of approximately 20 °C keeps the device from turning ON and OFF continuously.