a5975d STMicroelectronics, a5975d Datasheet - Page 14

• Manufacturer Part Number: a5975d
• Description: Up To 3 A Step-down Switching Regulator For Automotive Applications
• Manufacturer: STMicroelectronics

Functional description
Figure 6.
5.4
14/50
Synchronization example
Current protection
The A5975D features two types of current limit protection; pulse-by-pulse and frequency
foldback.
The schematic of the current limitation circuitry for the pulse-by-pulse protection is shown in
Figure
The smallest one includes a resistor in series, R
R
switched off until the next falling edge of the internal clock pulse. Due to this reduction of the
ON time, the output voltage decreases. As the minimum switch-on time necessary to sense
the current, in order to avoid a false overcurrent signal, is too short to obtain a sufficiently
low duty cycle at 250 kHz (see
short-circuit conditions may not be properly limited. For this reason, the switching frequency
is also reduced, therefore keeping the inductor current under its maximum threshold. The
frequency shifter
voltage decreases (due to the reduced duty cycle), the switching frequency decreases also.
SENSE
7. The output power PDMOS transistor is split into two parallel PDMOS transistors.
and, if it reaches the threshold, the mirror becomes unbalanced and the PDMOS is
(Figure
5) functions based on the feedback voltage. As the feedback
Doc ID 018760 Rev 1
Section
8.5), the output current in strong overcurrent or
SENSE
. The current is sensed through
A5975D