a5974ad STMicroelectronics, a5974ad Datasheet - Page 16

• Manufacturer Part Number: a5974ad
• Description: Up To 2 A Step-down Switching Regulator For Automotive Applications
• Manufacturer: STMicroelectronics

Functional description
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However, there is a limit introduced by the recovery time of the recirculation diode.
In fact, when the current of the power element is equal to the inductor current, the diode
turns off and the drain of the power is able to go high. But, during its recovery time, the diode
can be considered a high value capacitor and this produces a very high peak current,
responsible for numerous problems:
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The fall time of the current during turn-off is also critical, as it produces voltage spikes (due
to the parasitic 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 (the block
diagram is shown in
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
free-wheeling diode recovery time problem. The gate clamp is necessary to ensure that V
of the internal switch does not go higher than V
against any cross conduction between the supply line and ground.
Figure 8.
Spikes on the device supply voltage that cause oscillations (and therefore noise) due to
the board parasites.
Turn-on overcurrent leads to a decrease in the efficiency and system reliability.
Major EMI problems.
Shorter free-wheeling diode life.
Driving circuitry
Figure
8). The basic idea is to change the current levels used to turn
Doc ID 018762 Rev 1
GSmax
. The on/off control block protects
A5974AD
GS