AN557 datasheet(24/52 Pages) STMICROELECTRONICS

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AN557 APPLICATION NOTE

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with the value of the external components and with the relative pcb layout.

Output voltages higher than 5.1V are possible using an output resistive divider. For Vo > 24V, for safety

reasons it must be avoided the zero load condition. In the application with high current, connected to the

output divider are added two other resistances that permit the separation of sensing and forcing, in such

way as to compensate the fall of voltage on the connecting cables between the output and the load.

Connecting directly the output to the feedback pin a 5.1V ±2% is obtained. The following table can be help

for a rapid calculation of a resistor divider to obtain some of the most standard output voltage.

Figure 29. L4970A Typical Application Circuit.

Figure 30. Test and Evaluation Board Circuit

TYPICAL PERFORMANCES (using evaluation board) :

n = 83% (Vi = 35V ; Vo = VREF ; Io = 10A ; fSW = 200KHz)

Vo RIPPLE = 30mV (at 10A) with output filter capacitor ESR ≤ 60mΩ

Line regulation = 5mV (Vi = 15 to 50V)

Load regulation = 15mV (Io = 2 to 10A)

For component values, refer to test circuit part list.

AN557 Datasheet(PDF) 24 Page - STMicroelectronics