AN1882 Datasheet, PDF(8/30 Page) STMicroelectronics – This application note details the main features

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AN1882 Datasheet, PDF (8/30 Pages) STMicroelectronics – This application note details the main features

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Functional description

Figure 5. Low consumption mode

AN1882

Figure 6. Low noise mode

Measurement conditions: VIN = 4.2 V; VOUT = 1.5 V; IOUT = 30 mA; L = 6.8 ÂµH; CIN = 10 ÂµF;

COUT = 22 ÂµF; RC = 40 kÎ©; CC = 330 pF

In Figure 19 is shown a comparison between the efficiency in low noise mode and the

efficiency in low consumption mode.

3.2

System stability

Since the device operates with constant frequency peak current mode architecture, the

voltage loop stability is usually not a big issue. For most of the applications a 220 pF

connected between the COMP pin and ground is enough to guarantee the stability. In case

very low ESR capacitors are used for the output filter, such as multilayer ceramic capacitors,

the zero introduced by the capacitor itself can be shifted at a frequency well above the

resonance frequency of the L-C filter and the loop stability could be affected.

Adding a series resistor to the 220 pF capacitor can solve this problem. The right value for

the resistor can be determined by checking the load transient response voltage waveforms.

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Doc ID 10209 Rev 4

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