R5973AD datasheet(25/38 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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25 / 38 page

DocID027027 Rev 1

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R5973AD

Application information

compensate for the losses in the overall application. For this reason, the switching losses

related to the RDSON increases compared to an ideal case.



Switching losses due to turning ON and OFF. These are derived using the following

equation:

Equation 23

Where TRISE and TFALL represent the switching times of the power element that cause the

switching losses when driving an inductive load (see Figure 14). TSW is the equivalent

switching time.

Figure 14. Switching losses



Quiescent current losses.

Equation 24

Where IQ is the quiescent current.

Example 2



VIN = 12 V



VOUT = 3.3 V



IOUT = 1.5 A

RDS(on) has a typical value of 0.25 at 25 °C and increases up to a maximum value of 0.5. at

150 °C. We can consider a value of 0.4

.

TSW is approximately 70 ns.

IQ has a typical value of 2.7 mA at VIN = 12 V.

The overall losses are:

PSW

VIN IOUT

TON TOFF



------------------------------------



FSW VIN



IOUT TSW



FSW



VIN IQ



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