AN2559 datasheet(24/35 Pages) STMICROELECTRONICS

24 / 35 page

Measurements

AN2559

24/35

Figure 18.

PM6680A consumption at no load condition, in the different modes

In analyzing the data in Figure 18, it should be noted that the consumption is slightly

increased by several passive components which generate inhibit of the L5970ADs. Total

consumption of these parts at 35 V on the input is about 1.5 mA. This is not compensated

for in the chart in Figure 18. It is possible to see the effect of the different operating modes of

the converter by observing the output ripple voltage waveforms in Figure 19. These

measurements are made under the following conditions: VCORE output set to 2.5 V, no load,

at 12 V on the input.

Figure 19.

Output voltage ripple in different modes of light load operation

6.1.2

Output voltage ripple

Output voltage ripple depends on the current ripple flowing through the choke. The current

ripple depends on the input and output voltage levels. Therefore, it is mandatory to measure

the output voltage ripple for different input and output voltage conditions. Figure 20 shows

the output voltage ripple of VCORE at the minimum input voltage (5 V), while Figure 21

displays the output voltage ripple of VCORE at the maximum output voltage (36 V). Figure 22

shows the output voltage ripple of VI/O at the minimum input voltage (5 V), and Figure 20

displays the output voltage ripple of VI/O at the maximum input voltage (36 V). All of the

figures represent the minimum and maximum output voltages at maximum load (0.9 V and

2.5 V at 4 A for VCORE, and 1 V and 3.3 V at 2 A for VI/O).

AI12697

lin (mA)

70.0

60.0

50.0

40.0

30.0

20.0

10.0

0.0

Vin (V)

PWM

No Audible

SKIP

AN2559 Datasheet(PDF) 24 Page - STMicroelectronics