AN2559 datasheet(29/35 Pages) STMICROELECTRONICS

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AN2559

Measurements

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6.2

L5970AD blocks - measurements

6.2.1

Efficiency

The L5970AD is a powerful converter with very good performance and efficiency. Because a

diode is used as a low side switch, however, the efficiency is a slightly less compared to a

synchronous converter such as the PM6680A. Theoretically, the efficiency declines when

output voltage is decreasing and input voltage is increasing. Figure 28 displays the

efficiency of Output 3, depending on the input voltage at full load (800 mA). Figure 29

displays the same measurement for the Analog output. The efficiency of the Analog output

is better thanks to the higher output voltage level. The efficiency of the Analog output

voltage was measured in a range of 7 - 35 V. It should be noted that the output voltage is

5 V, so the device does not work as a switching converter in cases where the input and

output voltage are similar or lower than the required output. In this case the L5973AD works

with 100% duty cycle.

Figure 28.

Efficiency of output 3, by input voltage level

AI12698

Efficency (%)

90.0

80.0

70.0

60.0

50.0

40.0

30.0

20.0

10.0

0.0

Vin (V)

AN2559 Datasheet(PDF) 29 Page - STMicroelectronics