R5973AD datasheet(11/38 Pages) STMICROELECTRONICS

Part #	R5973AD

Description	Up to 1.5 A step-down switching regulator for aerospace applications

PDF	38 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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R5973AD

Functional description

Figure 4. Oscillator circuit block diagram

Figure 5. Synchronization example

5.4

Current protection

The R5973AD device 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 6. The output power PDMOS transistor is split into two parallel PDMOS transistors.

The smallest one includes a resistor in series, RSENSE. The current is sensed through

RSENSE and if it reaches the threshold, the mirror becomes unbalanced and the PDMOS is

switched off until the next falling edge of the internal clock pulse. Due to this reduction of the

ON time, the output voltage decreases. Since 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 500 kHz (see Section 8.4 on page 26), the output current in

R5973AD Datasheet(PDF) 11 Page - STMicroelectronics