AN2787 datasheet(17/37 Pages) STMICROELECTRONICS

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AN2787

Configuration

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7.4

JP5 1.5 V external/internal divider (VFB_1S5 pin)

The JP5 jumper allows selecting the internal divider or the external divider for the 1.5 V

switching regulator. When the VFB_1S5 pin is connected directly to the output capacitor, the

internal divider is enabled and this section provides 1.5 V output voltage. When the

multifunction pin VFB_1S5 is tied to the central tap of an external divider, the switching

regulator becomes adjustable, with the following output voltage:

Equation 2

Figure 12.

JP5 1.5 V divider selection

7.5

JP6 1.05 V external/internal divider (VFB_1S05 pin)

The JP6 jumper allows selecting the internal divider or the external divider for the 1.05 V

switching regulator. When the VFB_1S05 pin is connected directly to the output capacitor,

the internal divider is enabled and this section provides 1.05 V output voltage. When the

multifunction pin VFB_1S5 is tied to the central tap of an external divider, the switching

regulator becomes adjustable, with the following output voltage:

Equation 3

Figure 13.

JP6 1.05 V divider selection

Vout

⋅

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

External Divider Enabled

Internal Divider Enabled

Vout

⋅

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

Internal Divider Enabled

External Divider Enabled

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