ST1CC40 datasheet(24/37 Pages) STMICROELECTRONICS

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Application information

ST1CC40

24/37

DocID18279 Rev 5

To increase the design noise immunity, different signal and power ground should be

implemented in the layout (see Section 7.5: Application circuit). The signal ground serves

the small signal components, the device analog ground pin, the exposed pad and a small

filtering capacitor connected to the VINA pin. The power ground serves the device ground

pin and the input filter. The different grounds are connected underneath the output capacitor.

Neglecting the current ripple contribution, the current flowing through this component is

constant during the switching activity and so this is the cleanest ground point of the buck

application circuit.

Figure 13. Layout example

7.3

Thermal considerations

The dissipated power of the device is tied to three different sources:



Conduction losses due to the RDS(on), which are equal to:

Equation 28

where D is the duty cycle of the application. Note that the duty cycle is theoretically given by

the ratio between VOUT (nLED VLED + 100 mV) and VIN, but in practice it is substantially

higher than this value to compensate for the losses in the overall application. For this

reason, the conduction losses related to the RDS(on) increase compared to an ideal case.

PON

RRDSON_HS IOUT





2 D



POFF

RRDSON_LS IOUT





–





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