AN2559 Datasheet, PDF (24/35 Pages) STMicroelectronics – System power supply board for digital solutions

Measurements
AN2559
Figure 18. PM6680A consumption at no load condition, in the different modes
lin (mA)
70.0
60.0
PWM
50.0
40.0
30.0
20.0
No Audible
10.0
SKIP
0.0
0
5
10 15
20 25
30
35 40
Vin (V)
AI12697
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: V_CORE 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
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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 V_CORE at the minimum input voltage (5 V), while Figure 21
displays the output voltage ripple of V_CORE at the maximum output voltage (36 V). Figure 22
shows the output voltage ripple of V_I/O at the minimum input voltage (5 V), and Figure 20
displays the output voltage ripple of V_I/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 V_CORE, and 1 V and 3.3 V at 2 A for V_I/O).