AN2559 datasheet(23/35 Pages) STMICROELECTRONICS

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AN2559

Measurements

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Measurements

The performance and properties of each part of the board is indicated in the measurements

below. These measurements were performed for the PM6680A and L5971AD blocks

independently.

6.1

PM6680A block - measurements

The performance measurements of the PM6680A part focus mainly on efficiency, light load

consumption, output ripple and transients.

6.1.1

Efficiency and light load consumption modes

Since the device consists of three power parts (two controllers and one LDO) it makes

sense to measure total efficiency. Figure 17 displays how efficiency depends on input

voltage level at full load output (VCORE 2.5 V / 4 A, VI/O 3.3 V / 2 A).

Figure 17.

Efficiency of the dual step-down converter at full load

The efficiency is in the range of 83 - 91%. It should be noted that the total efficiency strictly

depends on the performance of each component. The System Supply board was designed

to satisfy a wide input voltage range. Therefore, 60 V MOSFETS are used on the board. If

the input voltage of the end application is less (up to 30 V for instance), efficiency can be

improved by using lower RDSON 30 V MOSFETs in the same package. The expected

efficiency gain is about 3 - 4%.

The PM6680A can work in several modes with regard to light load. These options are mainly

used for battery applications where relatively high consumption at light load can drain the

battery even when no power is requested. The PM6680A allows three modes (see 3.0.2):

PWM, No Audible Noise and Skip. Figure 18 shows the consumption of the board for

different modes of the PM6680A. There is no load on the output and other parts of the

SMPS are disabled.

AI12696

Efficency (%)

100.0

90.0

80.0

70.0

60.0

50.0

40.0

30.0

20.0

10.0

0.0

Vin (V)

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